Wave activity (planetary, tidal) throughout the middle atmosphere (20-100km) over the CUJO network: Satellite (TOMS) and Medium Frequency (MF) radar observations

Abstract

Planetary and tidal wave activity in the tropopause-lower stratosphere and mesosphere-lower thermosphere (MLT) is studied using combinations of ground-based (GB) and satellite instruments (2000-2002). The relatively new MFR (medium frequency radar) at Platteville (40° N, 105° W) has provided the opportunity to create an operational network of middle-latitude MFRs, stretching from 81° W-142° E, which provides winds and tides 70-100km. CUJO (Canada U.S. Japan Opportunity) comprises systems at London (43° N, 81° W), Platteville (40° N, 105° W), Saskatoon (52° N, 107° W), Wakkanai (45° N, 142° E) and Yamagawa (31° N, 131° E). It offers a significant 7000-km longitudinal sector in the North American-Pacific region, and a useful range of latitudes (12-14°) at two longitudes. Satellite data mainly involve the daily values of the total ozone column measured by the Earth Probe (EP) TOMS (Total Ozone Mapping Spectrometer) and provide a measure of tropopause-lower stratospheric planetary wave activity, as well as ozone variability. Climatologies of ozone and winds/tides involving frequency versus time (wavelet) contour plots for periods from 2-d to 30-d and the interval from mid 2000 to 2002, show that the changes with altitude, longitude and latitude are very significant and distinctive. Geometric-mean wavelets for the region of the 40° N MFRs demonstrate occasions during the autumn, winter and spring months when there are similarities in the spectral features of the lower atmosphere and at mesopause (85km) heights. Both direct planetary wave (PW) propagation into the MLT, nonlinear PW-tide interactions, and disturbances in MLT tides associated with fluctuations in the ozone forcing are considered to be possible coupling processes. The complex horizontal wave numbers of the longer period oscillations are provided in frequency contour plots for the TOMS satellite data to demonstrate the differences between lower atmospheric and MLT wave motions and their directions of propagation.

Full text

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Annales Geophysicae (2005) 23: 305–323
SRef-ID: 1432-0576/ag/2005-23-305
© European Geosciences Union 2005
Annales
Geophysicae
Wave activity (planetary, tidal) throughout the middle atmosphere
(20–100km) over the CUJO network: Satellite (TOMS) and
Medium Frequency (MF) radar observations
A. H. Manson1, C. E. Meek1, T. Chshyolkova1, S. K. Avery2, D. Thorsen3, J. W. MacDougall4, W. Hocking4,
Y. Murayama5, and K. Igarashi5
1Institute of Space and Atmospheric Studies, University of Saskatchewan, 116 Science Place, Saskatoon, SK, S7N 5E2,
Canada
2CIRES, University of Colorado, Boulder, USA
3Department of Electrical and Computer Engineering, University of Alaska, Fairbanks, USA
4Department of Physics and Astronomy, University of Western Ontario, London, Canada
5National Institute of Information and Communications Technology, Tokyo, Japan
Received: 12 February 2004 – Revised: 12 November 2004 – Accepted: 6 December 2004 – Published: 28 February 2005
Abstract.
tropopause-lower stratosphere and mesosphere-lower ther-
mosphere (MLT) is studied using combinations of ground-
based (GB) and satellite instruments (2000–2002). The rel-
atively new MFR (medium frequency radar) at Platteville
(40◦N, 105◦W) has provided the opportunity to create an
operational network of middle-latitude MFRs, stretching
from 81◦W–142◦E, which provides winds and tides 70–
100km.CUJO (Canada U.S. Japan Opportunity) com-
prises systems at London (43◦N, 81◦W), Platteville (40◦N,
105◦W), Saskatoon (52◦N, 107◦W), Wakkanai (45◦N,
142◦E) and Yamagawa (31◦N, 131◦E). It offers a significant
7000-km longitudinal sector in the North American-Pacific
region, and a useful range of latitudes (12–14◦) at two lon-
gitudes. Satellite data mainly involve the daily values of the
total ozone column measured by the Earth Probe (EP) TOMS
(Total Ozone Mapping Spectrometer) and provide a measure
of tropopause-lower stratospheric planetary wave activity, as
well as ozone variability.
Climatologies of ozone and winds/tides involving fre-
quency versus time (wavelet) contour plots for periods from
2-d to 30-d and the interval from mid 2000 to 2002, show
that the changes with altitude, longitude and latitude are very
significant and distinctive. Geometric-mean wavelets for the
region of the 40◦N MFRs demonstrate occasions during the
autumn, winter and spring months when there are similar-
ities in the spectral features of the lower atmosphere and
at mesopause (85km) heights. Both direct planetary wave
(PW) propagation into the MLT, nonlinear PW-tide interac-
tions, and disturbances in MLT tides associated with fluc-
tuations in the ozone forcing are considered to be possible
coupling processes. The complex horizontal wave numbers
Planetary and tidal wave activity in the
Correspondence to: A. H. Manson
(alan.manson@usask.ca)
of the longer period oscillations are provided in frequency
contour plots for the TOMS satellite data to demonstrate the
differences between lower atmospheric and MLT wave mo-
tions and their directions of propagation.
Key words. Meteorology and atmospheric dynamics (Mid-
dle atmosphere dynamics;
Waves and tides)
Synoptic-scale meteorology;
1Introduction
Studies of the dynamics of the atmosphere involving the
lower and middle atmosphere are comparatively rare, at least
partly due to the limited range of sensitivity of many sound-
ing instruments, but also due to the interests of the authors.
Some of our early papers considered the winds MLT (60–
100km) and the association of their variability with strato-
spheric processes, e.g. Gregory and Manson (1975); and
much more recently, Hoffmann et al. (2002) and Manson et
al. (2002a) assessed the coupling between stratospheric win-
ter warming events (using radiosonde and satellite sensors)
and MLT winds, gravity waves (GW) and tides using MFR
radars. Variability of stratospheric temperatures with scales
of several days has also been associated with variability of
MLT tides and winds (Manson et al., 1982), but remarkably
little has been done since then.
A more recent study worthy of note is that by Lawrence
and Randel (1996), who used Nimbus 6 satellite data (PMR)
to demonstrate stratospheric-mesospheric coupling in three
distinctive ways: the variance of the geopotential height
around latitude circles (50–70◦N) showed strong correla-
tion throughout the atmosphere (35–83km); and episodic
wave-like events, in particular westward propagating “nor-
mal” PW modes (periods, 5 to 10-d band) having near global

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306 A. H. Manson et al.: Wave activity over the CUJO network
coherence, and eastward propagating PWs (4-d period) in
southern winters (hereafter SH, Southern Hemisphere) asso-
ciated with an instability process, were identified throughout
the atmosphere.
Most recently, and during the preparation of this paper,
there have been three papers published which have interested
the authors and inevitably led to some of the directions pur-
sued in our work here. Pogoreltsev et al. (2002) identified a
6.5-d PW of wave number one (m=1) in the MLT using the
Saskatoon (52◦N) and Sheffield (53◦N) MFR and Meteor
radars, and explained this wave in terms of nonlinear inter-
actions between the normal mode (m=2) of period 7-d and
the standing PW (SPW) with m=1. UKMO (United King-
dom Meteorological Office) assimilated stratospheric fields
and a 2-D numerical model were used for explanatory pur-
poses within the study. A more general study by Fedulina
et al. (2002) of the stratospheric PW at 1hPa using UKMO
“data” preceded this work: longer period PW (T>10-d) were
dominant during winter months in both hemispheres (SH,
NH), with eastward and westward propagating waves being
seen; in the SH at wavenumber one (m=1) eastward waves
had somewhat larger amplitudes, while westward wave ac-
tivity was seasonally more sustained or of larger amplitude
in the NH. Shorter period waves (4- to 5-d) were dominantly
westward propagating and while they were seen through-
out the year, they increased in amplitude during the seasonal
transitions.
Pancheva et al. (2003) assessed the variability of the
semidiurnal (12-h) tide (circa 92km altitude) due to fluctu-
ations in solar activity and total (column) ozone. The latter
is of interest to us here. They provided frequency spectra of
TOMS data (Total Ozone Mapping Spectrometer) and Me-
teor radar semidiurnal tidal amplitude data (Sheffield, 53◦N)
for the entire autumn to spring intervals of 4 years (1989–
1993), which then showed similarities in the bands of 8–
12, 15–18 and 25–28 day oscillations; the cross products of
the respective wavelet spectra showed strong features, espe-
cially near 16 and 27–28 days, which were linked in their
occurrences (1989–1993) to the QBO (Quasi Biennial Os-
cillation), stratospheric warmings, and solar variability. Fi-
nally, Lawrence and Jarvis (2003) assessed the austral winter
(1997–1999) PW activity in the stratosphere (the European
Centre for Medium range Weather Forecasting (ECMWF)
wind product at 30km), upper middle atmosphere (an HF
radar (interferometer) provided winds 75–95km) and ther-
mosphere (the HF radar operated as an ionosonde). The
radar is at Halley Bay, 76S. Their results were complex and
to some degree apparently inconsistent with the Northern
Hemisphere study: there were times when strong PW ac-
tivity occurred in either the stratosphere or middle-upper at-
mosphere, with no simultaneous activity in the other region;
perversely, evidence for PW activity in the mesosphere was
stronger when the stratospheric activity was more restricted
in latitudinal extent; and a quite consistent anti-correlation
existed between PW activity in the mesosphere and the E-
region. Processes suggested included re-generation of the
PW component at higher altitudes through gravity wave
(GW) filtering and breaking, and nonlinear interactions be-
tween PW and tides.
In this study we use the Earth probe (EP) TOMS data
(level-3 product) for the time interval mid-2000 to 2002,
and wind data from the 5 MFR radars of the CUJO network
(London, Platteville, Saskatoon, Wakkanai and Yamagawa).
Wavelet analysis (a swept frequency spectral analysis), as de-
scribed briefly below, is applied to TOMS and the MFR wind
data to assess PW activity and propagation throughout the
middle atmosphere. It is then also applied to TOMS and the
MFR tidal amplitude data (diurnal and semidiurnal) to assess
the variability of tidal forcing and/or propagation processes
at periods consistent with PW variability. It is appropriate at
this point to mention the very useful and insightful paper by
Schoeberl and Krueger (1983) that was brought to our atten-
tion by Randel (private communication, 2003). They demon-
strated, using SH data, that the variability of the total ozone
(column) parameter is a very useful diagnostic for wave-like
(PW) disturbances of medium zonal wave numbers. This is
based upon the slowness of photochemical processes in the
lower stratosphere and below, such that the ozone may be
considered a passive tracer. Their conclusion was that, be-
cause the meridional and vertical advection of ozone corre-
lates strongly, evanescent waves near the tropopause produce
the maximum ozone (column) signal. They studied examples
of these waves, including an m=5 eastward propagating PW
and also synoptic scale baroclinic waves (also eastward mov-
ing) which decay above the tropopause (Charney and Drazin,
1961). They noted that the winter ozone fluctuations of the
NH are a complex superposition of disturbances from meso-
to planetary scale, while the SH disturbances are more reg-
ular (hence their detailed study of the m=5PW); and also
that propagating winter waves (m=1, 2) will provide a more
complex signal in the total ozone, as the advection terms
will not act to strengthen the signal in the total ozone. It
will be shown here that wave number spectral analysis of the
TOMS data distinguish these eastward propagating PW very
clearly. We shall also use cross products of the wavelet spec-
tra (for individual locations and also regions) to emphasize
the similarities of variability at PW periods, and the cou-
pling, between the stratosphere and mesosphere. There is
also discussion of the present and future use of UKMO data-
assimilation products, which includes radiosonde and satel-
lite data, and allows for analysis to near 50km in the middle
atmosphere.
2Systems and data analysis
2.1 Radars
The Saskatoon, London and Platteville MFRs (2.2 MHz) are
of very similar design, and have been well described in the
first CUJO papers (Manson et al., 2003a, 2004a). The spaced
antenna “full correlation analysis” method is used (Meek,
1980). Vertical soundings provide wind sampling at 3km in-
tervals every 5min from near 60 to 100km. The MFRs are of

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A. H. Manson et al.: Wave activity over the CUJO network307
Fig. 1. Time sequences of daily mean zonal (east-west, EW) winds from the MF radar at Saskatoon (52◦N) for heights from 76- 94km:
the distance between the 3km samples represents 50m/s. The dashed lines are for TOMS values (median DU value in a 5*5 grid point cell
centred on Saskatoon): these are arbitrarily scaled according to the maximum variation during the year. The TOMS sequences are repeated
at each MFR height.
basically similar configuration, and any differences will not
lead to differences in the measured winds; e.g. the MFRs in
Japan are Australian ATRAD systems (Igarashi et al., 1996;
Murayama et al., 2000), which although physically very sim-
ilar to the Canadian systems, use a more classical method of
analysis which is closer to that described by Briggs (1984).
Comparisons have shown that no significant differences ex-
ist between these methods (Thayaparan et al., 1995a). The
Japanese radars provide samples of wind every 2 rather than
3km, and 2 rather than 5min, on a continuous basis. Our ear-
lier detailed studies of PW (Luo et al., 2000, 2002a, 2002b)
demonstrated that amplitudes of >3m/s from spectral analy-
ses provided a geophysically realistic signal.
All wind measurement systems have biases or selectivity
issues, so comments upon these for the radar winds are use-
ful. Examples of significant published comparisons include
an MFR and Meteor Wind Radar (MWR) at 43◦N (Thaya-
paran and Hocking, 2002); MFRs and Fabry-Perot Interfer-
ometers (“green line” and hydroxyl) at two 52◦N locations
(Manson et al., 1996; Meek et al., 1997); and rockets and
radars (MFR, VHF and EISCAT) near 70◦N (Manson et
al., 1992). Most recently, there has also been an extensive
comparison (Manson et al., 2004b) for the year 2000 involv-
ing two MFRs and an MWR, which comprise the so-called
Scandinavian-Triangle (68–70◦N, radar spacings of 125–
270km). In these studies the directions of the winds or their

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308 A. H. Manson et al.: Wave activity over the CUJO network
perturbations (tidal phases) have been satisfactorily consis-
tent e.g. means within standard errors. However, while the
Saskatoon optical-radar comparisons showed no speed bi-
ases, a limited “SKiYMET” MWR-MFR campaign at Saska-
toon (spring-summer, 1998) showed modest differences, e.g.
MFR/MWR ratios of about 0.75 near 88km (Meek, Hock-
ing and Manson, private communication, 2002); at 70◦N,
Tromsø, the speeds from the MFR were 0.65 of those from
the other types of radar and rocket systems for heights from
82–97km; and the Scandinavian-Triangle provided median
MFR/MWR ratios of 0.91/0.63 at 85/97km. Finally, sys-
tematic differences between “satellite-winds” from HRDI-
UARS (Doppler Imager) and radars have also been noted,
e.g. Saskatoon MFR speeds are 0.75–0.8 of HRDI speeds
(Meek et al., 1997). For our purposes here, and especially
as we are using only MFR radars for the upper middle at-
mosphere, we will simply bear in mind the potential speed
biases when any later comments are made on wave ampli-
tudes.
2.2Analysis techniques
To provide information on atmospheric oscillations from 2-
d to 30-d at particular heights (Sect. 3), a wavelet analysis
has been applied to the years of daily mean winds, tides (har-
monic analyses described below) or TOMS data, with addi-
tional data at the ends being used to cover the full sliding
window for all wave periods used (Figs. 2–6). A Gaussian
window of length 6 times the period (truncated at 0.05 of
peak value) is used to approximate a Morlet wavelet analy-
sis (Kumar and Foufoula-Georgiou, 1997), but one in which
gaps do not have to be filled. A Fourier transform (not an
FFT) is therefore used and applied to existing data points
only. Data selection criteria require that 80% of the phase
values in two different periods are available. Breaks in the
heavy data-existence lines at the bottoms of the frames in-
dicate that there were no data for those days, and provide a
warning that spectral data near the edges of and during these
intervals may be inaccurate. The period-scale uses 600 pix-
els and is linear in log (period) from 2 to 31 days. Each pixel
represents one spectral value, and there is no smoothing.
Amplitudes are increased appropriately during the calcu-
lations to correct for attenuation by the window, but on the
assumption that there are no significant gaps. In the plots
the value in dB (decibels) is equal to 20 log10(wave ampli-
tude in m/s for the MFR). This scale is used because of the
large range of amplitudes that exist for the various types of
waves (tides to PW) in the MLT region. Color renditions
are optimized by this scaling. There is discussion of signif-
icance levels for the more complex figures later, near their
presentation, but for the basic wavelet figures significances
have been taken to be as in Luo et al. (2002a). There they
were determined by comparison with “Lomb-Scargle” peri-
odograms (Lomb, 1976; Scargle, 1982; Luo et al., 2002a),
for which significance levels are available. Based upon these,
dB circa 17.5 (7m/s, yellow) can be considered significant at
the 99% level.
Tidal amplitudes are produced by analyzing 2-day se-
quences shifted by 12h. Data must be available for 12h
on each of the 2 days, following which a Fourier transform
is done. Amplitudes at periods of 48, 24, 12, 8h are used
to order these components, which are then fitted separately
by least-squares fit and subtracted in order of size, weith the
largest first. For the wavelet analysis, time sequences of am-
plitudes are used (with samples every 12h), but the periods
displayed start at 2-d (rather than the Nyquist period of 1-d)
to match the other analyses.
The daily background wind parameter comes from a least-
squares fit of mean, 24-h and 12-h oscillations to single days.
There must be data in at least 16h of each day for the fit-
ting to proceed. These background or mean winds are used
in Fig. 1 and in the wavelet analyses. (The combination of
different analyses and wavelet selection criteria lead to ap-
parent, but unimportant, differences in data gap locations be-
tween background winds and tidal amplitudes in the figures.)
Geometric means have been used as a type of “cross-
wavelet” analysis (Figs. 5 and 6). These are the means of
wavelet amplitudes and do not involve the wavelet phases.
The geometric mean wavelets are useful in that all parame-
ters must be relatively large for a large output, but there is
no certainty that a high value refers to a coherent oscillation.
However, there is discussion of the phases of the wavelets in
later sections. The motivation for forming these “regional”
means (for the CUJO network of North American-Japanese
40◦N locations) is due to the intermittency, both spatial and
temporal, found in our earlier studies of PW (Luo et al.,
2002a; Manson et al., 2004a).
Wave number analysis of TOMS data (Figs. 7 and 8) is
as follows: a 60-day time sequence is selected and then de-
trended. This latter is done by fitting a mean plus an annual
sine wave to 365 days of longitudinally averaged values, and
then subtracting these from each longitude value (the “bins”
are spaced by 1.25◦). Then frequency spectra (80% exis-
tence criterion is required) are calculated for each 60-day
detrended sequence and coherently averaged over a band of
5 TOMS latitudes (this is then a 5◦average). In this spec-
tral analysis the sampling times are pre-adjusted to refer to
the same absolute time at different longitudes. This then pro-
vides, for any chosen 60-day interval, complex amplitudes at
each frequency for each longitude bin. The sequence of com-
plexamplitudesversuslongitudeisthenFouriertransformed,
resulting in amplitudes at positive and negative spatial wave
numbers. We use the convention that a positive wave num-
ber indicates westward propagation, as is frequently done for
tidal analysis, e.g. Manson et al., 2004c. A log scale is con-
venient for showing a large range of amplitudes, and even
though dB (20 log10rms DU (Dobson Units)) is a power unit
and not normally applicable to total ozone, it is a well under-
stood unit.

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A. H. Manson et al.: Wave activity over the CUJO network309
3 Comparisons of Tropopause-Stratospheric (TOMS)
and Mesospheric/MLT Data
3.1Variability of Total Ozone and Mesospheric Winds at
CUJO sites
Given the potential complexity of the linkages between the
different atmospheric regions, and indeed the different pa-
rameters being used, we will mention and show a variety of
comparisons which range from simple time sequences and
their correlations, to harmonic means (cross-products) of in-
dividual wavelets. Time sequences of the daily mean zonal
winds (eastward being positive) during the year 2001 are
plotted in Fig. 1 for the Saskatoon MFR; heights from 76–
94km are provided, along with the TOMS data (the units
being Dobson Units, 300DU is equivalent to a 3-mm col-
umn of ozone) for that location. The latter are medians in a
5*5 degree cell area centred on Saskatoon. This figure pro-
vides substantial information. At the lowest heights the sum-
mer winds are near −50m/s, which are consistent with the
stratospheric-mesospheric mid-latitude westward jet, while
in winter the circa 40m/s values are consistent with the win-
ter eastward jet.Frequently, planetary waves of the tro-
posphere and stratosphere will not propagate through this
strong summer westward jet due to critical levels (wave
phase speed matching the background wind speed) being
achieved; and indeed, a strong winter eastward jet will also
inhibit propagation of the larger (m>3 or 4) wave number
modes (Charney and Drazin, 1961; Luo et al., 2002a; Man-
son et al., 2003a, 2004a) due to their having small “critical
speeds” (this parameter varies as the inverse square of the
horizontal wave numbers). Thus, strong differences between
the oscillatory periods (and their amplitudes) of the winds,
associated with PW, in the MLT region are expected for the
two solstices.
Such is indeed the case, based upon visual inspection of
Fig. 1 and the wavelet spectra which follow. Wind oscilla-
tionsofnear20m/samplitudeandwithina10-to30-dperiod
are clearly evident from 76–94km during winter and autumn
months (exhibiting little phase shift with height), while the
amplitudes are smaller and the periods shorter (e.g. 2-d os-
cillations are evident) during the spring and summer. The
TOMS data share a rather similar morphology, although the
summer variability is comparatively less. There are also very
modestvisibleindicationsofcorrelationsbetweentheTOMS
and MFR winds data during the autumn and winter e.g. the
91kmwindsearlyin2001, and79kmwindsattheendofthat
year. Lagged cross correlations were calculated (not shown),
and although there were indications of similarity near zero
lag, the values were not high. It is evident from the fig-
ure that there are differences in spectral content, and that
has kept the calculated 60-day correlations rather modest.
Time sequences of the zonal winds from the other MFR loca-
tions of CUJO demonstrated quite similar behaviour to that
of Fig. 1. In contrast, the meridional winds (northward be-
ing positive) provided modest differences from Fig. 1, as the
amplitudes of the PW responsible for the longer period (>2
days) oscillations are smaller during the winter-like months,
while the amplitudes of the summer’s 2-d wave are larger
(Manson et al., 2003a, 2004a) and are at times dominant. Fi-
nally, the lags between oscillations in the lower atmosphere
and mesosphere were available from a modest number of se-
lected examples of the correlograms, and proved less noisy
than the phases from cross-spectral techniques; the lags were
highly variable but are typically a few days.
The wavelets for the daily mean winds from the MFR
radars and for TOMS (at the same locations) are shown in
Fig. 2. We have placed the highest and lowest latitudes at
the top and bottom of the figure, with the data from 40◦lat-
itudes in the middle for best comparisons. Spectra from the
MFR radars for the first third (2000–2001) of this observa-
tional interval were shown in our earlier paper (Manson et
al., 2004a). As in the earlier paper we show only 85-km
spectra, as the spectral changes from 79–88km (the height
range with best data for spectra) are usually quite modest.
We have used the same location for the TOMS data as for the
MFR for several reasons: we follow Pancheva et al. (2003) at
this stage for reasons of comparison; and the low frequency
(temporal and spatial) PW are expected to be present over
a significant range of latitudes and longitudes near the radar
sites (they are often described by global Hough modes). Un-
certainties about the latter expectation are the reason for the
formation of “regional” harmonic means for wavelets from
the 3 radar locations of the CUJO network (North American-
Japanese 40◦N locations); this was mentioned in the Analy-
sis Sect. 2.2 and is discussed in Sect. 3.3 below.
Despitetheinter-annualvariability, whichisexpectedwith
PWs whose forcings are variable in time and space, the sea-
sonal variability of the oscillations in the MLT winds and
TOMS data is consistent with expectations based upon the
time sequences of Fig. 1. Generally, and except for Yam-
agawa (31◦N), the wind oscillations at longer PW periods
(12- to 30-d) are stronger in winter-centred months (typically
November to March). For the MLT range of altitudes these
oscillations are usually associated with the classical west-
ward propagating Rossby “normal” PW modes (the so-called
5-, 10-, and 16-d waves), and the quasi-2-d Rossby-gravity
normalmode(Q2Dwave)(Luoetal., 2000). Thislatterwave
is at the Nyquist period (2 days) here, but there is spectral
energy evident near 2 days in the plots as the bandwidth of
this wave is quite broad and aliasing has further spread the
spectral peak near 2 days. However, the PW amplitudes at
2-d (summer, NS) and 16-d (winter, EW) are quite compa-
rable at, say Platteville, which is similar to the results of the
specific analysis of these two waves (Manson et al., 2004a).
The ranges of observed periods for these PWs are typically
2, 5–7, 8–10 and 12–22 days due to Doppler shifting by the
background winds (Luo et al., 2002a, b). There is also spec-
tral energy evident in Fig. 2 for those same winter months
at longer periods (circa 22- to 30-d) associated with “extra
long periods” that have correlations with the solar rotation
period (Luo et al., 2001). For the remaining months the MLT
wind activity is usually restricted to periods of less than 12
days. The color scale (range of dB with respect to color) was

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310A. H. Manson et al.: Wave activity over the CUJO network
Fig. 2. Wavelet spectral plots for the 85km daily mean winds (zonal EW, meridional NS) and the ozone (DU) values of TOMS for the radar
locations of the CUJO network.

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A. H. Manson et al.: Wave activity over the CUJO network311
chosen to allow for a best comparison of the various MFR
wavelets. These do differ significantly between, say, London
and Wakkanai. We add, in revision, that the very detailed
assessment of the wind analysis used at London is revealing
that a factor of typically 30% (smaller winds) is involved.
This correction would change yellow contours in Fig. 2 to
orange (2dB) and bring the wavelets into closer agreement
with those for Platteville. The work is in progress and so no
changes are made to the figure.
The TOMS oscillations, while also maximizing in the win-
ter months, do have an additional temporal different charac-
ter; and here some care is required by the reader, as the color
scale differs a little from that of the MLT winds, and was
chosen to optimize the TOMS regional differences. How-
ever, the TOMS characteristics are unique: the interval of
enhanced broad-spectral activity (yellow-red) is longer in du-
ration and extends from November to April; and the activ-
ity in the remaining months is less at all periods/frequencies
(whereas for the MLT winds, although spectral changes oc-
cur, there are peaks of similar intensity in the summer and
winter months). It is interesting that the variation in intensity
of ozone oscillations between sites also often differs from
that of the MLT winds: although TOMS for the Wakkanai
location also has higher intensities, values at the London site
are not low (they are similar to those at Platteville), and ac-
tivity at the Yamagawa site is very low.
It is appropriate to comment further on the relationship
between spectral variability of the TOMS data (measured in
DU) and PW activity. The considerations of Schoeberl and
Krueger (1983) have already been mentioned in the Intro-
duction, where it was noted that they showed that evanes-
cent waves (including baroclinic waves) are most effective
in providing an ozone perturbation. More recently, Fusco
andSalby(1999)demonstratedthat“variationsofup-welling
wave activity” (as determined by the Eliassen-Palm flux) cor-
relate very highly (99% level) with the increases in total
ozone. The variations in PW activity “modulate ozone trans-
port and chemical production by the diabatic mean circula-
tion” and “account for much of the variability in measure-
ments of total ozone”. The PWs involved have the great-
est activity in the winter months, and include the baroclinic
waves of the tropospheric weather systems, which are largely
absorbed in the lower stratosphere (Charney and Drazin,
1961). The scale sizes of these waves are of small to medium
size (typically more than zonal wave number 4), leading to
small so-called “critical speeds” (which vary inversely as the
square of the wave numbers) in their formulation (see also
Andrews et al. (1987) for a very nice presentation, page
178); even if the phase velocities (c) are relatively mod-
est and westward relative to the eastward winter flows (u),
the (relative) intrinsic phase velocities (u–c, Doppler shifted)
will often easily exceed the “critical speed”, which is then
the condition for negative squared refractive index. This in
turn leads to wave dissipation and strong damping. Thus,
many of the smaller scale PWs effective in providing spectral
peaks in the TOMS wavelets are likely to be often different in
characteristic from those (westward propagating, large-scale
normal modes) dominating the MLT wavelets.
OurstudiesofPW,inparticularthe16-dwave, haveshown
that there is considerable intermittency in the wave activity,
and a lack of strong correlation in the occurrence of bursts
of activity between radar sites (Luo et al., 2002a, b). Thus,
only oscillations in that band (12- to 22-d) which are strongly
evident at several locations (simultaneous bursts of activity
involving several complete oscillations) provide phase differ-
encesconsistentwithcoherentwestwardpropagationandun-
ambiguous determination of wave number (m=1) (Luo et al.,
2002b). Examples of such bursts are the circa 12- to 16-d PW
(EW) during April 2001, and spectral activity near 16 days
in January–February of 2001 and 2002; there are also several
spectral peaks in the TOMS data at these times. Consistent
withthatnotionwewilllatershowtheharmonicmeansofthe
3 pairs of wavelets (London, Platteville and Wakkanai) for
the daily mean winds from Fig. 2, and also harmonic means
including the TOMS wavelets. This analysis was used by
Manson et al. (2004a). Those later figures will also include
the harmonic-mean wavelets for the tidal data, so that wind
variability (directly related to PW) and tidal variability (e.g.
due to changes in tidal forcing at PW periods, or PW-tide
interactions) can be compared. However, we will first show
the wavelets appropriate to the individual sites for the MLT
tides, accompanied by only modest comment.
3.2Variability of Total Ozone and Mesospheric Tides at
CUJO Sites
Time sequences of the daily mean tides (12-, 24-h), in com-
parison with the TOMS daily samples, were examined for
each location. It was clear from these and from correlations
over 60-day intervals that the linkages were not strong. Com-
plex spectral structures for the two types of data sequences
were evident. The wavelets for the NS and EW components
of the respective tides at 85km for the 5 MFR locations are
shown in Figs. 3 and 4, along with the same TOMS wavelets
as before (Fig. 2). Variations in the tidal amplitudes at PW
periods can be caused by at least two different processes: the
temporal variation in the ozone associated with PW activity
in the stratosphere can provide a temporal variation in the
forcing of the tides, which will lead to variations or oscil-
lations in the local MLT tidal amplitudes at those same PW
periods; or PWs, which have a signal within TOMS data,
may propagate into the MLT where they non-linearly interact
with the tides to produce a beating or oscillation of the tidal
amplitudes, again at the tidal period. Pancheva et al. (2003)
mention other mechanisms (e.g. non linear interactions in the
stratosphere), and suggest that longer time lags may be asso-
ciated with processes involving propagation of PWs into the
mesosphere. Planetary scale oscillations in the background
winds of the stratosphere and mesosphere will also cause
significant variations in the tidal amplitudes (Jacobi et al.,
2001). Such processes lead to longitudinal changes in tidal
characteristics, which may make it more difficult to discern
other nonlinear PW-tidal interactions e.g. lower signal-to-
noise levels when the tidal amplitudes are small locally.

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312 A. H. Manson et al.: Wave activity over the CUJO network
Fig. 3. Wavelet spectral plots for the 85km daily 12-h (semidiurnal) tidal amplitudes (zonal EW, meridional NS) and the ozone (DU) values
of TOMS for the radar locations of CUJO network.

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A. H. Manson et al.: Wave activity over the CUJO network313
Fig. 4. Wavelet spectral plots for the 85km daily 24-h (diurnal) tidal amplitudes (zonal EW, meridional NS) and the ozone (DU) values of
TOMS for the radar locations of CUJO network.

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314 A. H. Manson et al.: Wave activity over the CUJO network
Considering the 12-h tide firstly (Fig. 3), the EW and NS
components are very similar for each location. This is con-
sistent with the circular nature of the tide and similarities in
the amplitudes of the two tidal components (Manson et al.,
2003a). Seasonalvariationsin thetidaloscillationsaresome-
what less clear than for the mean winds of Fig. 2, although
again the summer months are more likely to have less activ-
ity and shorter periods. Despite the intermittency, there are
temporal and spectral similarities between the three 40◦N
MFR sites e.g. an 8-d burst during December 2000, and a
12- to 16-d burst in early September 2001. There is signif-
icant spectral energy in the TOMS wavelets for the former
event, so coupling could be involved. Otherwise, there is
activity at periods near 16 days during the middle of both
winters. There is also an indication that the oscillations in
the tides are larger in the winter, and the autumn, when the
amplitudes of the 12-h tide are themselves largest (Manson
et al., 2003a). This may well favour the nonlinear PW-tidal
process, as larger tides will lead to larger oscillations.
Finally the wavelets for the 24-h tide (Fig. 4) are interest-
ing, in that the coupling of this tide with the stratospheric
ozone and its variability has not been considered before.
However, the forcing of this tide by stratospheric ozone is
significant (Hagan, 1996), although it has often been ig-
nored by some in discussions of this type. The differences
in wavelet intensities between the 40◦N locations, and be-
tween them and the 52◦N and 31◦N sites, is quite consider-
able, and reflects to some degree the decreasing amplitude of
this tide with increasing latitude. An example of a common
burst of MLT activity is at 16-d near March 2002, for both
the EW and NS components; there is again spectral energy
present in the TOMS spectra at this time, so that coupling
may exist. The variation in seasonal activity of the 24-h tide
is not strong. This suggests that much of the MLT variability
in summer-centred months is not related to local TOMS (PW
and ozone) variability.
3.3 PW activity and coupling over the CUJO region
As we discussed in Sect. 3.1 it is desirable to form geomet-
ric means of the three pairs of wavelets appropriate to the
40◦N locations for the mean daily winds and for both tides.
This process effectively locates in time and spectral space
the MLT events that are simultaneous and most likely to be
coherent in the Pacific-North American sector sampled by
CUJO. We show in Fig. 5 the mean MFR wavelets (specifi-
cally geometric means of the MFR wavelet amplitudes from
the three 40◦N locations are used), and in Fig. 6 we in-
clude the TOMS amplitudes in the mean wavelets. The latter
should locate the bursts or events that are common between
the lower atmosphere (circa 100mb) and mesosphere (or
MLT) over this large region of the planet, and which should
involve coupling of some type. Common dB values and col-
ors are used to allow for comparisons of components and of
wave type. For comparison with previous studies, the paper
by Pancheva et al. (2003) involved the 12-h tide for Sheffield
(52◦N) and a presentation similar to that of the MLT tidal-
TOMSdataofFig.6; whilethepaperbyLawrenceandJarvis
(2003) provided information on the winds and could be com-
pared with the appropriate (lower) sections of Figs. 5 and 6.
We consider firstly the mean winds of Fig. 5. The wavelets
forthemeanorbackgroundwindsprovideaclearersummary
of the seasonal variations discussed in Sect. 3.1. The activ-
ity is dominant in the EW component, for periods longer than
about 8 days, which is consistent with the polarizations of the
“normal” waves at mid-latitudes; and winter-centred activity
is dominant with the longest periods occurring in mid-winter.
Although the spring activity is limited spectrally, the intensi-
ties remain large. There is considerable activity in the 16-d
range (12–22 days), the 10-d and even in the Q2D ranges
throughout the winter-centred interval.
orange-red in color (above 14dB) have significance levels in
the individual wavelets (Figs. 1–3) in the 95–99% range (see
Sect. 2.2 for discussion of significances). Interannual vari-
ability is evident and expected with such oscillations, which
are responding to geophysical “noise” and variability in the
system for their sources.
The products of the wavelets for TOMS ozone and the
MLT winds (Fig. 6) provide indications of coupling: the
summer-winter differences are enhanced due to the minimal
summer PW activity in the TOMS wavelets; and substan-
tial bursts of activity are in common between the two atmo-
sphericregions, especiallyfromDecembertoMay. Although
some of the PW-related variability in the TOMS data has not
impacted the mesosphere (there was discussion in Sect. 3.1
on the PW of the lower atmosphere), it appears that much of
the PW flux detected by the TOMS systems has propagated
directly into the mesosphere. Careful inspection also demon-
strates that it is for the bursts of activity greater than 10 days
in period that the similarities between the mean wavelets of
the MLT winds (Fig. 5) and MLT winds-TOMS products
(Figs. 6) are the greatest. Features which were noted earlier
from perusal of Fig. 2 are very clear in both Figs. 5 and 6;
in particular the aforementioned 12- to 16-d (EW) event to-
ward the end of April 2001, and the 16-d events in January–
February of 2001 and 2002. (These features are clearly ev-
ident in the harmonic-mean TOMS wavelet (not shown).)
For the winters of 2000/2001 and 2001/2002 there were also
stratospheric warming (SSW) events (U.S. National Weather
Service, NCEP (National Centres for Environmental Predic-
tion) data) which in both cases involved December pulses
at high and polar latitudes followed by events in February.
There was substantial MLT and stratospheric PW activity in
both years near these times (Figs. 5, 6) but specific causal-
ity is difficult to establish. Jacobi et al. (2003), meanwhile,
noted the presence of an intensifying PW of a 10 day pe-
riod at the time of the SSW of 2000/2001 in the western-
European and Scandinavian sector. Returning to the individ-
ualMFRwaveletsofFig.2, thereisactivitynear12daysdur-
ing February at Saskatoon, the most northern location; and
there is also a feature in the regional CUJO wavelet (Fig. 5)
at this time. This result is encouraging, but a special inde-
pendent study would be needed to verify the details, and this
is an activity for the future.
Bursts which are

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A. H. Manson et al.: Wave activity over the CUJO network315
Fig. 5. Wavelet spectral plots for the 85km daily winds, 12-h (semidiurnal) and 24-h (diurnal) tidal amplitudes (zonal EW, meridional NS).
These plots are geometric means of the individual wavelets for the three 40–45◦N MF radars (London, Platteville, and Wakkanai) of the
CUJO network. A gap is shown if an amplitude value is unavailable for one or more sites.
Pancheva et al. (2003) noted several regular features dur-
ing the four years 1989–1993: 16-d PW bursts were im-
plicated (the oscillations were in the 12-h tide) in the au-
tumn (September–October) for each of the two years hav-
ing easterly phases of the QBO (negative westward strato-
spheric flow), and stronger 27-d oscillations were noted dur-
ing winter for the other westerly QBO phases. In Figs. 5
and 6 there is a much less clear morphology for the 16-d
oscillation, based upon the National Weather Service (Cli-
mate Prediction Service) analysis, whose QBO 30hPa in-
dex indicated that easterly flow dominated the tropical lati-
tude circles for the last 6 months of 2000, and all of 2001.
The flow was westerly during 2002.
(Fig. 5) the 16-d PW winds have a modest autumn burst and a
stronger long period (circa 24-d) burst during the 2000/2001
months (September–April) of easterly QBO phase (these fea-
tures are less evident in the TOMS/winds products of Fig. 6).
In the mesosphere
However, there was no 16-d burst for the autumn of 2001
when the flow was still easterly (the QBO was in the midst of
aphasetransitionfromtheshort-livedbiennialoscillation). It
is not surprising to see this difference for the 16-d PW during
these two different intervals (1989–1993 and 2000–2002).
Luo et al. (2000) assessed the 16-d PW activity at Saska-
toon for 1980–1996 in comparison with the QBO phases, and
found complex and often weak correlations. Some months
exhibited weak correlations with the westerly phase, and oth-
ers the easterly phase.
The phase differences or lags between stratospheric and
mesospheric PW activity are best assessed through 60-d cor-
relograms previously mentioned in Sect. 3.1. However, the
phase differences vary from site to site, and with the interval
chosen, as well as with the period dominating the correlo-
grams. A broad generalization, based upon these correlations
and also phase differences from the complex wavelets, is that

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316A. H. Manson et al.: Wave activity over the CUJO network
Fig. 6. Wavelet spectral plots: geometric means of the wavelets for the 85km daily winds, 12-h (semidiurnal) and 24-h (diurnal) tidal
amplitudes (zonal EW, meridional NS) shown in Fig. 5 and the wavelets for the ozone (DU) values of TOMS for the same locations. The log
is of the value of the term in the heading of the figure.
the MFR-derived phases for the longest periods often differ
from the TOMS phases by only a few (+/−2) days. It is in
fact not obvious what phases are to be expected. As noted
by Schoeberl and Krueger (1983) the phase differences be-
tween the vertical and horizontal perturbation velocities and
the maxima of ozone in the stratospheric-tropospheric PW
depend on the period of the wave; in addition, the propaga-
tion conditions and the vertical wavelength of the PW will
affect the final phase difference between the TOMS oscilla-
tion of interest and the mesospheric PW.
The patterns of activity at PW periods for the tidal ampli-
tudes in Fig. 5 are quite different from the mean winds. The
general levels (in dB) are lower, with the 12-h tide showing
modest bursts (orange and red; >14dB) that are also more
limited temporally in the autumn and winter, and the 24-h
having winter and spring bursts. The processes involved in
tidal variability are potentially more complex and numerous
than those for the background wind, so that identical activ-
ity in all wavelets of Figs. 5 (and 6) are not to be expected.
For the 12-h tide there are several 16-d bursts (in particu-
lar the previously noted event of early September 2001, as
well as mid-winter events during both winters, in Fig. 3), 8-d
bursts (that of December 2000 was seen in Fig. 3), and fre-
quent 4- to 6-d activity. The cross-product with the three
TOMS wavelets (Fig. 6) again provides a stronger seasonal
trend, and accentuates some different bursts e.g. the Septem-
ber 2001 burst is missing. However, the 8- and 16-d bursts
of December–January 2000–2001, as well as the 16-d event
in the mid-winter of 2002, are again evident. There is excel-
lent agreement between the NS and EW wavelets, which is
encouraging; the tidal components are not completely inde-
pendent in the analysis, but the strong similarities provides

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A. H. Manson et al.: Wave activity over the CUJO network317
a robust indication of PW activity in common between the
lower atmosphere and mesosphere. As discussed previously
(Sect. 3.2) the physical processes providing modulation of
the tides do differ, at least in detail, from the PW signal
in the winds; however, some of the features in the MLT
tidal-TOMS wavelets coincide with features in the MLT
(EW) wind-TOMS wavelet e.g. the 16-d features of January-
February of 2001 and 2002, indicating the involvement of a
common PW in both.
Finally, the 24-h tidal wavelets demonstrate coupling be-
tween the lower and middle atmosphere (Fig. 6), and some-
what greater inter-annual variability than for the 12-h tide
(Fig. 5).The bursts of activity in the MLT tide-TOMS
wavelets (Fig. 6) often occur at similar temporal-spectral lo-
cations to that for the 12-h tide e.g. the 16-d burst of January–
March 2002; but there are also striking differences e.g. the
24-h tidal activity during 2002 is clearly stronger than in
2001. Again, given that the 24-h tide’s mean wavelets for the
mesosphere over London-Platteville-Wakkanai have winter-
spring maxima, closer in morphology to the TOMS variabil-
ity, the MLT tide-TOMS products of Fig. 6 are very simi-
lar in temporal–spectral features to those for the mesosphere
(Fig. 5).
The presence of the apparent coupling between the 24-h
tide of the MLT and the TOMS parameter, which has both
PWandozonevariabilityassociatedwithit, isinterestingand
perhaps not expected as much as for the 12-h tide. This may
suggest that the MLT spectral variability involves the interac-
tions of PW and tides (in stratosphere or mesosphere) rather
than the simple radiational forcing of the tide by variable
ozone concentrations, given that processes involving water
vapour are normally considered to dominate the forcing of
the 24-h tide in the lower atmosphere. However, as noted
from the modelling experiments of Hagan (1996), the role
of stratospheric ozone in the 24-h tide’s MLT amplitudes is
substantial. The lags between stratospheric and mesospheric
activity are again available, in principle, from the correlo-
grams or complex wavelets. However, the assessments are
again not simple, with phase differences varying with time
interval, year and dominant period. Lags of several days are
typical.
4Wave numbers of PW in the stratosphere and meso-
sphere and discussion of coupling processes
There has been considerable discussion of the character
of PW in the lower atmosphere/stratosphere and meso-
sphere/MLT already in this paper. We noted in the Intro-
duction that Fedulina et al. (2002) had shown that at 1hPa
in the NH there was considerable spectral intensity for both
the eastward and westward propagating PW, with the west-
ward PW of largest scale (m=1) dominating; and that Schoe-
berl and Krueger (1983) identified evanescent PW of synop-
tic scale (including the baroclinic waves), which are mainly
eastward propagating, as being most effective in producing
the maximum ozone signal in the column values. Some
earlier studies include the seminal paper by Venne and Stan-
ford (1982); they noted spectral energy for eastward and
westward propagating waves of long period (above 5 days)
in both hemispheres; however, the analysis of NH data was
hinderedbypoorerNimbus4data(Nimbus5existed), signif-
icances were low, and unlike the SH, no clear predominance
of eastward motions was evident. Their results are, however,
qualitatively similar to Fedulina et al. (2002).
In contrast, the PW of the MLT most frequently studied,
and discussed here in Sect. 3.1, have been the Rossby or
“normal” modes. Relatively well-behaved westward prop-
agation has been demonstrated by the 16-d PW (e.g. Luo
et al., 2002b), for large simultaneous bursts of activity, and
by the quasi 2-d Rossby-gravity normal mode (e.g. Thaya-
paran et al., 1997). We have also argued in Sect. 3.1 that
the smaller scale (typically wave number m greater than 4)
synoptic waves of the troposphere and lower stratosphere
will be largely absorbed (due to their relatively small “crit-
ical speeds”, or eastward motion relative to the background
wind).
Nevertheless, the products of the wavelets for the TOMS
ozone and MLT winds in Fig. 6 showed considerable com-
mon activity in winter-centred months (temporally and spec-
trally), suggesting that significant portions of the PW flux
detected by the TOMS systems has propagated directly into
the mesosphere. It is the bursts of TOMS activity with pe-
riods greater than 5 days that have the greatest similarity to
the MLT activity in the daily mean winds (Fig. 5). It is worth
noting that the largest PW (m=1, 2), some of which may have
eastward phase speeds (c) at the TOMS-data heights, and
which may also be moving westward relative to the compar-
atively strong winter eastward flows (u) of the stratosphere
and mesosphere, appear to meet the conditions for propa-
gation into the middle atmosphere. These conditions are
that the intrinsic (relative-zonal) phase velocities (u–c) are
positive, and also smaller than the relatively large “critical
speeds” for these large-scale waves (Charney and Drazin,
1961; Andrews et al., 1987). We discussed this formula-
tion briefly in Sect. 3.1. Such waves could be associated
with jet stream movement and vortex variability, and have
not been recently considered as major contributors to MLT
dynamics. They appear to be worthy of renewed study with
models (Pogoreltsev, private communication, 2003). These
waves should propagate into the middle atmosphere more
easily than the stationary PW and certainly more easily than
the westward moving (relative to the ground) Rossby PW of
similar scale, since their intrinsic speeds are smaller. It is
possible, as suggested by a reviewer, that these waves may
propagate only to the stratopause; however they may become
evanescent above there and reach into the mesosphere and
therefore be detected with the MLT radars. (The Charney
and Drazin (1961) formulation for propagation works quali-
tatively well for Rossby PW such as the 16-d wave: despite
the intrinsic phase speeds being larger than for the station-
ary and largest scale eastward propagating PW, they are still
usually smaller than the “critical speeds” in the NH winter
months. This is consistent with the climatologies shown in

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318 A. H. Manson et al.: Wave activity over the CUJO network
Fig. 7. TOMS wave number spectra for two latitude bands during the days 1–60 of 2001. The full set of available longitudes is used for these
spectra.
Figs. 2, 5 and 6. However, as discussed by Luo et al. (2002a),
using modelling results in the SH, the winter eastward MLT
winds are stronger, the intrinsic phase speeds larger, and
propagationisdiscouragedastheappropriate“criticalspeed”
is exceeded.)
As a further diagnostic of the PW activity, wave-number
analysis has been described in Sect. 2 and applied to the
TOMS data. This will provide insights into the scales and di-
rection of propagation of the PW at the 100mb (circa 20km)
level, and hence the processes for coupling with the MLT.
This follows our most recent work (Manson et al., 2004a),
where the analysis of multiple-site radar data to obtain wave
numbers for PW-scale oscillations in the wind field was pro-
vided for the year 2000/2001. While for periods greater than
7 days the preferred wave number was one (m=1, westward),
consistent with the frequently observed 16- and 10-d PW,
there was considerable spectral energy at m=3, 4 and −2
from October to April. Due to the limited number and lo-
cation of the radar sites, aliasing was possible, and it was
argued there that statistical coupling of mode-pairs whose
wave numbers differed by +/−3 may have affected the pro-
cess. Thus numbers m=4 and −2 could have been appro-
priate to an actual m=1. However, the originally calculated
values could well be correct descriptors of the PW. The data
in this recent study were of the highest quality available, and
indeed are for the year 2000/2001 which is also used here for
the wave number analysis.
Wave number analysis of the TOMS data is now shown in
Figs. 7 and 8. Days 1–60, and 61–120 from each of the years
2001 and 2002 have been chosen, with latitude ranges of 39–
44◦N to cover the CUJO network of three 40◦N MFRs, and
49–54◦N to include the Saskatoon MFR but also to provide
a range of latitudes for assessment of spatial variability. As
described in Sect. 2, the spectra are coherently averaged over

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A. H. Manson et al.: Wave activity over the CUJO network319
Fig. 8. TOMS wave number spectra for two latitude bands during the days 61–120 of 2001. The full set of available longitudes is used for
these spectra.
these latitude bands before wave number analysis is applied,
so that the intensity contours in these figures represent co-
herent averages. Based upon the analysis of global HRDI
data (UARS, Upper Atmosphere Research Satellite) for the
MLT winds, the results of which are contained within Luo
et al. (2002a), strong variations of PW activity with latitude
(even those oscillations having coherence at all longitudes)
are a common occurrence. Hence, variations in spectral fea-
tures between 39–44◦N and 49–54◦N in our figures are ex-
pected, and are indeed evident.
The general trends in these plots of the winter and spring
PW activity are for dominant eastward propagation of spec-
tral components m=−1 to −5 for periods of typically 5 to
30 days (there is also spectral energy at the lowest frequency
appropriate to periods near 60 days that would be associ-
ated with seasonal transitions). The westward components
are more restricted to periods of 12 days and more, although
the intensities of those are comparable to the eastward com-
ponents. It has just been argued above, that eastward PW
of large scale and long period (>10-d or so) should be able
to propagate into the stratosphere and perhaps mesosphere,
along with the westward PW, providing that their intrinsic
phase velocities are less than the “critical speed” (Charney
and Drazin, 1961; Luo et al., 2002a). Indeed, there are high
spectral intensities (red contours) in Fig. 7 that often include
the PW wave numbers featured for the CUJO radar wind data
(1, 3, 4 and −2; Manson et al., 2004a) for this same winter
(2000/2001), although other wave numbers have comparable
intensities. Of course, all waves at 100mb are not expected
to reach the MLT; and the CUJO network is not global, while
the global data set was required for the TOMS wave number
analysis. Extended radar coverage is desirable. Finally, there
is variability of the wave number contours of Figs. 7 and 8
with latitude (consistent with the HRDI analysis of the MLT