International Journal of Climatology

Most of the commonly used convective indices that depend upon surface temperature and moisture reveal a positive trend regarding both the annual extreme values and the number of days above/below specific thresholds. A relationship was established between the indices and the annual number of hail damage days, yielding correlation coefficients between 0.65 and 0.80. In contrast to this, indices derived from temperature and moisture at higher levels exhibit either a negative or no significant trend. It is shown that the trend directions of the indices may be attributed to differential temperature and moisture stratification in the various atmospheric layers. The significant positive trends of both surface temperature and water vapour can be concisely expressed by an increase in wet-bulb potential temperature. This indicates the presence of warmer parcels throughout the whole troposphere during convection. Copyright © 2009 Royal Meteorological Society

In a statistical analysis of more than a century of data we find a strong connection between strong warm El Nino winter events and high spring precipitation in a band from Southern England eastwards into Asia. This relationship is an extension of the connection mentioned by Kiladis and Diaz (1989), and much stronger than the winter season teleconnection that has been the subject of other studies. Linear correlation coefficients between DJF NINO3 indices and MAM precipitation are higher than r=0.3 for individual stations, and as high as r=0.49 for an index of precipitation anomalies around 50N from 5W to 35E. The lagged correlation suggests that south-east Asian surface temperature anomalies may act as intermediate variables.

Objectively analysed climatological mean fields of temperature and salinity have been calculated on a 0.25° grid for the World Ocean for the annual, seasonal, and monthly compositing periods using data from the World Ocean Database 2001. The annual and seasonal fields are calculated at standard levels from the surface to 5500 m. The monthly fields are calculated at standard levels from the surface to 1500 m. In comparison with similarly computed climatologies calculated on a 1° grid, ocean circulation features, such as the Gulf of Mexico Loop Current, are more clearly represented. The new 0.25° climatologies preserve most of the spatial resolution of earlier 0.25° temperature and salinity climatologies, while reducing noise by additional smoothing in horizontal space (geographically at each depth), vertically (along depth at each grid), as well as in time (Fourier filtering). Copyright © 2005 Royal Meteorological Society

An automated procedure has been developed to detect and select mesoscale cyclones and describe their tracks by means of the numerical analysis model, the HIRLAM(INM)-0.5°, operational at the Spanish Institute of Meteorology (INM). This procedure gives us a description of features of these cyclones, such as their frequency of appearance, geographical distribution and horizontal dimensions, and it also enables us to study the movement and the evolution of the cyclone centres. This procedure was developed in order to obtain an automated database of Mediterranean cyclones. To check the performance of this method, the distribution of cyclones was compared with the distribution obtained from a manual catalogue of mesoscale cyclones, and selected cases were studied using both methods. Some results obtained for the western Mediterranean are presented. A large number of cyclones are detected and most of them are located in specific zones, such as the Gulf of Genoa, south of the Pyrenees, south of the Iberian Peninsula and the Alboran Sea. The cyclones follow preferred tracks, which are different depending on the season. Copyright © 2001 Royal Meteorological Society

This study documents the variability of spring snow cover over the western Canadian Prairies and Northern Boreal Forest and its relationship to sea surface temperature (SST) over the North Pacific and atmospheric circulation over the North Pacific–North America. The work is based on monthly snow cover extent (SCE) estimates derived from Advanced Very High Resolution Radiometer data during 1972–2008. Results show that the SCE along eastern parts of the Canadian Rocky Mountains has the largest variance during March and April. Two regional SCE indices are defined using area mean SCE anomalies over the region of 47–53°N, 104–111°W (SCE-A) and 55–60°N, 111–120°W (SCE-B) based on the leading empirical orthogonal function (EOF) patterns of SCE in March and April, respectively. These two SCE indices are not only significantly correlated with simultaneous and preceding winter 500 hPa heights over mid-latitude northwestern North America and central North Pacific but also with SST in mid-latitude eastern North Pacific in preceding autumn and winter. Furthermore, it is found that the SST anomalies in the mid-latitudes along the western coast of North America in the preceding autumn–winter influence the 500 hPa height over northwestern North America in April and cause the variations of SCE-B. Finally, it is shown that the SCE-B can be used as a climatic index to characterize the connection of SCE with the regional skin temperature in late spring and early summer. Copyright © 2010 Royal Meteorological Society

A 1000 year reconstruction of cool-season (November–April) precipitation was developed for each climate division in Arizona and New Mexico from a network of 19 tree-ring chronologies in the southwestern USA. Linear regression (LR) and artificial neural network (NN) models were used to identify the cool-season precipitation signal in tree rings. Using 1931–88 records, the stepwise LR model was cross-validated with a leave-one-out procedure and the NN was validated with a bootstrap technique. The final models were also independently validated using the 1896–1930 precipitation data. In most of the climate divisions, both techniques can successfully reconstruct dry and normal years, and the NN seems to capture large precipitation events and more variability better than the LR. In the 1000 year reconstructions the NN also produces more distinctive wet events and more variability, whereas the LR produces more distinctive dry events. The 1000 year reconstructed precipitation from the two models shows several sustained dry and wet periods comparable to the 1950s drought (e.g. 16th century mega drought) and to the post-1976 wet period (e.g. 1330s, 1610s). The impact of extreme periods on the environment may be stronger during sudden reversals from dry to wet, which were not uncommon throughout the millennium, such as the 1610s wet interval that followed the 16th century mega drought. The instrumental records suggest that strong dry to wet precipitation reversals in the past 1000 years might be linked to strong shifts from cold to warm El Niño-southern oscillation events and from a negative to positive Pacific decadal oscillation. Copyright © 2002 Royal Meteorological Society.

Stalagmites can contain annual luminescence laminae, and some samples provide long continuous chronologies from which climatic information can be extracted. One such site is Uamh an Tartair in Assynt, northwest Scotland, where most stalagmites contain continuous laminae sets for the last two to three millennia. At this site, the normal mode of deposition is for one luminescent lamina to be deposited in autumn, derived from luminescent organic matter that is flushed onto the sample from the overlying peat. However, in the stalagmite investigated here, 43 lamina doublets occur, where two laminae appear to be preserved in a winter. We argue, both from the timing of these events within the ‘Little Ice Age’, as well as from analogous situations in alpine streams, that the doublets occur due to the presence of a second, spring melt flush of organic matter. The interpretation of stalagmite double laminae, therefore, has considerable potential as a palaeoclimate proxy, and at our study site, we suggest one of severe winters over the last millennium. Copyright © 2002 Royal Meteorological Society.

The distribution of outliers is used as a tool for finding the extreme value distribution of meteorological parameters and to provide return values for large return periods from short records. Its potential is demonstrated for five cases. For extreme winds in the Northern Hemisphere (NH) the method shows that appropriately transformed annual maximum wind speeds can be described by a Gumbel distribution; for extreme waves it rejects the proposed adoption of an exponential distribution and points to a Gumbel distribution; for extreme daily European precipitation R it confirms the theoretically predicted value k = 2/3 in its Weibull distribution and it also justifies the application of the Gumbel distribution to R2/3 up to return periods of about 50 000 years; for seasonal precipitation in the Netherlands it highlights enhanced extreme precipitation in the coastal area in December-January-February (DJF) and failure of the k = 2/3 hypothesis outside June-July-August (JJA); for sea levels in the Southern North Sea it points to the Gumbel distribution and provides improved estimates for the 104-return value of the sea level at coastal stations, which is elaborated for the Dutch tidal station Scheveningen. Copyright © 2009 Royal Meteorological Society

The yearly, monthly and seasonal total precipitation of a 105-year precipitation time series of Uccle, Belgium, were analyzed. Statistically significant trends were found for the yearly total precipitation, for precipitation observed in the winter (DJF) and for the monthly total precipitation of March, using the Mann–Kendall trend test. The few statistically significant trends that were found are shown to be of no statistical significance when the length of the series is changed. Using the adaptive Kolmogorov–Zurbenko (KZA) filter, the droughts around 1920 and during the mid-1970s and drier-than-normal conditions at the beginning of the twentieth century could be detected. Wavelet analysis of the monthly precipitation revealed an expected statistically significant yearly cycle in the data, together with multi-annual components of 3 and 7 years, which were absent during the period 1935–1945. Copyright © 2006 Royal Meteorological Society

May–June precipitation is the primary limiting factor in annual tree-ring growth of the oaks of northeastern Greece and northwestern Turkey (39–42°N, 22–37°E). In a regional tree-ring chronology of historic building and modern forest samples, the May–June precipitation explains at least 40% of the variance for 1900–1985, and is reconstructed here from A.D. 1089–1989. The reconstruction is compared to three other precipitation reconstructions for Turkey. The mean temperature of May and June is also a growth-limiting factor owing to its effect on the availability of precipitation to the trees, but is more difficult to calibrate and reconstruct accurately owing to the trees' indirect response and the low number of long-temperature records available for the interior of northwestern Turkey.An analysis of the various methods of manipulating oak tree-ring data for regional climate reconstruction shows that removing all but the high-frequency variability plus normalizing the oak data sets before combining them into a master chronology are optimal techniques for a reasonable precipitation reconstruction of the entire area over the instrumental period. However, these methods do remove the low-frequency signal and dampen some of the evidence of local extremes in May–June precipitation; these issues are discussed here and will be addressed in future research. Copyright © 2007 Royal Meteorological Society

Power spectrum analysis of 81 long and 202 short Chinese dryness-wetness indices yields evidence for two peaks with periods near 18.6 and 10.5 years, both of which are statistically significant at confidence levels of 99.9 per cent. They are identified as induced by the 18.6-year luni-solar, Mn, constituent tide and a 10–11-year solar cycle, Sc, variation in the Sun's luminosity of the order of 0.1 per cent. Amplitude and phase of Mn wavetrains are highly non-stationary with respect to both time and geography; in particular, abrupt 180° phase changes in wave polarity are often observed. Amplitude and phase of Sc waves are also highly non-stationary, with those in northern China out of phase with waves in the south since 1895 (they were in phase from 1815 to 1845). For the 202 short records variance contribution of the two signals to total variance in raw data varied from 6 per cent to 53 per cent, with a mean of 22 per cent, again demonstrating their extreme non-stationarity. Construction of a dry and very dry drought index (DVDI) shows that since 1470 by far the most prolonged, continuous, and serious drought (due to constructive interference and concomitant high amplitudes of the two waves) occurred from 1633 to 1643; the Ming Dynasty collapsed in 1644 and, in agreement with Hameed and Gong (1990), it is concluded that this climatic disaster was a causal factor in the fall of the Ming Empire.

The 115 year (1871–1985) long, summer monsoonal rainfall data of ten macroregions (m-r) of India have been subjected to maximum entropy spectral analysis (MESA). The results appear to indicate quasi-periodic fluctuations in rainfall in eight and six m-r, presumably corresponding to the 18.6–year luni-solar nodal and 10–11-year solar cycles respectively. The solar term in the remaining four m-r appears to be split up into two components, as a result of spectral analysis. The filtered data, evidencing either or both of the signals in MESA, were then subjected to two band-pass filters, centred at 19.0 and 10.5 years respectively. The derived rainfall waveforms are found to have some good phase relationships with the 18.6–year nodal and 10–11-year solar cycles, when relatively free from meteorological disturbances. The luni-solar rainfall waveforms in m-r 2, 3 and 7 exhibit the phenomenon of a sudden 180° phase change in the early parts of the data series.

Evidence for a narrow band-limited signal with period near 18.6-years is found in 126 out of 136 yearly total precipitation records, and in 1531 out of 1668 monthly records in the northeastern United States. From 1840 to near the end of the 19th century, rainfall minima in the wavetrain are highly correlated with tidal maxima of the 18.6-year luni-solar tide, the twelfth largest tidal constituent in Newton's theory; the wavetrain then switched phase by 180° and for most of the 20th century rainfall maxima are correlated with tidal maxima at 1917.5, 1936.1, 1954.7, and 1973.3. This bistable phenomenon of atmospheric science was discovered by Currie (1983) in a study of tree-rings from the Patagonian Andes, and O'Brien and Currie (1988) have suggested a dynamical explanation in terms of mathematical physics. In terms of yearly rainfall, the mean percentage amplitude modulation of the wave was near ±6% until 1940 after which it began to increase rapidly, reaching ±10% in the 1960s and 1970s. These results provide a rational explanation for the severe water shortage crisis that occurred at tidal minimum 1964.0 (Namias, 1966; 1967), and reoccurred 19 years later. In addition, a smaller band-limited term with period 10 to 11-years is found in a little more than half of the records.

It has been pointed out previously that tree-ring series from Formosa show an 11-year periodicity related to the sunspot cycle. However, significance tests of this finding have not been made and therefore the statistical reliability has not been known. Spectra of tree-ring series from other sites reported before show no evidence that the 11-year sunspot cycle appears in tree-ring series. Spectral analyses have been made of published tree-ring data from Formosa and previous studies have been re-examined. Tree-ring series from two different sites in Formosa show an 11-year spectral peak at the level of confidence higher than 90%. Cross spectral analysis between the tree-ring series and the Zurich annual sunspot number shows that the 11-year fluctuations in the tree-ring series are related to the sunspot cycle with a time lag of 1/4 phase at the 99% confidence level. Using a band-pass filter technique, it is found that the 11-year fluctuations in tree-ring series correspond to almost each cycle of the sunspot number except for periods of low solar activity. Significant 11 -year fluctuations in the tree-ring series appear during most of the periods of an ‘active’ sun as estimated by carbon 14 abundance in tree-rings.

Spectrum analysis of 59 South African rain-gauge records yields evidence for two peaks with periods 18.2·1.4 years (57 out of 59 series covering virtually the entire country) and 10.3·0.5 years (in 37 series covering almost all except easternmost South Africa). They are identified as the luni-solar 18.6-year Mn and 10–11-year solar cycle Sc signals in climate; their phases and amplitudes are non-stationary with respect to both time and geography and, in particular, 180° phase changes in wave polarity are observed. These phase changes occurred in the early part of the century and by mid-epochs 1964.0 and 1982.6 (mid-epochs are dates of minimum in Mn tidal forcing) a unipolar cell of drought encompassed virtually the entire nation. Constructive interference by the Sc wave, which reached a minimum near 1981, exacerbated the droughts of mid-epoch 1982.6 which were more severe than even those of the 1960s. The results confirm and extend in many respects those found by P. D. Tyson and his co-workers in the 1970s.

Rainfall data available in the form of books published by the India Meteorological Department for 115 rain-gauge stations in north-west India, the Plains of Uttar Pradesh, and north-central India for the period 1901–1950 have been subjected to maximum entropy spectral analysis (MESA). The results of the analysis indicate that 91 out of 115 rain-gauge stations appear to respond to 18·6-year luni-solar nodal (MN) signal. The statistical average value of the signal periodicity (T̄L) in rainfall proves to be 18·3 + 1·6 years. Maximum entropy spectral analysis results also appear to indicate the existence of a 10–11-year solar cycle (Sc) in 77 rain-gauge stations out of 115. Application of MESA apparently splits the solar signal term, resulting in its absence from the spectral results of some stations and the presence of an 8–9-year component in almost every station result. The statistical average value of the solar signal periodicity (T̄S) in rainfall proves to be 10·9±0·7 years.

Spectrum analysis of 1197 USA air temperature records yields evidence for two peaks with periods 18.8 ± 1.7 and 10.4 ± 0.5 years. Tests by the t-statistic show that both are significant at confidence levels of 99.9 per cent, and both account for 23 per cent of total variance in the raw data. They are identified as the luni-solar 18.6-year Mn and solar cycle Sc 10–11-year signals in climate, induced by the twelfth largest constituent tide acting on the Earth and a variation of 10 to 11 years in the Sun's luminosity of the order of 0.1 per cent. Amplitude and phase of Mn wavetrains are highly non-stationary with respect to both time and geography; in particular, abrupt 180° phase changes in wave polarity are often observed. Amplitude and phase of the Sc waves are also highly non-stationary, with those east of the Rocky Mountains out of phase with waves to the west. These results consolidate and greatly extend and clarify earlier studies of Currie based on far less American data.

Maximum entropy and Yule-Walker methods of spectrum analysis applied to Lamb's dust veil indices (dvi) for the Northern Hemisphere (1500–1968) show two strong peaks, with periods of 18.6±0.5 and 10.8±0.3 years. They are identified as the 18.6-year luni-solar Mn and 10–11-year solar cycle Sc signals, which have recently been reported in a wide variety of climate and economic time series. The signals were transformed into the time domain by band-pass filters, their wavetrains summed, and the sum superimposed on trend-like components of the dvi; it is found that they account for 48 per cent of variance in the index.

A statistical study of daily maximum sea-level height at one station (Grau de la Dent) in the Camargue (Rhône delta, French Mediterranean coast) and daily sea-level pressure (SLP) at 12 h UTC over the eastern North Atlantic is used to identify the meteorological conditions associated with sea-level variations in the Camargue for the winters 1974–1975 to 2000–2001. Mean SLP composites during and 5 days before major surge events (defined as those with a daily maximum sea-level height > 80 cm) suggest the dominant influence of storms, moving northwest to southeast across the North Atlantic and strengthening as they approach the Bay of Biscay. During such storms, strong onshore winds may persist for up to 4–5 days. These winds tend to strengthen from 3 days to 1 day before the surge events. The mean October–March correlation between daily maximum sea-level height in the Camargue and SLP averaged over the Bay of Biscay (10°W–0° , 40° –50°N) is strong (r = − 0.69). A methodology is developed for assessing the low frequency SLP variability impact on sea-level height in the Camargue. A cross-validated linear regression is used to hindcast the interannual and intraseasonal variability of the monthly 75th and 90th percentiles of the daily maximum sea-level height from the monthly mean SLP over the Bay of Biscay. The linear correlation between the cross-validated hindcast and observed time series is 0.83 (0.77) for the 75th (90th) percentile over the 1974–1975 to 2000–2001 period. The mean bias error, reflecting systematic errors in predicting the monthly percentiles, is close to zero. Copyright © 2006 Royal Meteorological Society.

Based upon sea-surface temperature (SST) data, recently corrected for bucket-intake observational change, the SST fluctuations since 1873 in the Mediterranean are studied and compared with air temperature (AT) fluctuations at some land stations of this area and for the Northern Hemisphere (ATNH). Instead of the actual temperature, we used the frequency difference (per cent) of the number of the warm minus cold months, (fw—fc) annually and seasonally, smoothed using 10-year moving averages. This frequency difference was found to be a linear function of the actual temperature. For the whole Mediterranean, the trend of the SST is simple enough, with a minimum in about 1910 and a double maximum in about 1940 and 1965. A secondary minimum follows in 1975–1980, very strong in the eastern Mediterranean, with a rise after that to the present. This trend when compared with ATNH presents some differences: in the ATNH a minimum appears earlier, in 1890, but this is shown only slightly in the Mediterranean SST. The second SST maximum, in 1965, is not shown in ATNH, and the general rise of recent years starts in the ATNH about 10 years earlier. When considering the AT of the Mediterranean stations, it can be seen that the rise, after the minimum of 1910, stops 15 years earlier than the SST and ATNH. Then, an anomalous and slow decrease follows until about 1975–1980, followed by a rise to the present, which is delayed in the eastern Mediterranean.

The vertical velocity observed using the mesosphere–stratosphere–troposphere (MST) radar at Gadanki (13.47°N, 79.18°E), India, shows that downward motion prevails in the troposphere and lower stratosphere during both winter and summer. Zonal and meridional components of winds over the Gadanki region are compared with the Hadley circulation over the peninsular Indian region obtained from National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysed data. An anomalous northerly wind is observed in the lower troposphere over the radar station during summer monsoon months instead of southerlies according to the reverse Hadley cell theory. NCEP/NCAR reanalysed data show that this anomaly covers a large area around peninsular India. Copyright © 2001 Royal Meteorological Society

Ice cores from both the Arctic and Antarctic record a massive volcanic eruption in around AD 1258. The inter-hemispheric transport of ash and sulphate aerosol suggests a low-latitude explosive eruption, but the volcano responsible is not known. This is remarkable given estimates of the magnitude of the event, which range up to 5 × 1014–2 × 1015 kg (∼200–800 km3 of dense magma), which would make this the largest eruption of the historic period, and one of the very largest of the Holocene. The associated collapse caldera could have had a diameter up to 10–30 km. Palaeoclimate reconstructions indicate very cold austral and boreal summers in AD 1257–59, consistent with known patterns of continental summer cooling following tropical, sulphur-rich explosive eruptions. This suggests an eruption in AD 1257, producing a stronger climate forcing than hitherto recognized. Copyright © 2003 Royal Meteorological Society

The North Atlantic Oscillation (NAO) is considered to be the dominant mode of winter atmospheric variability in the Northern Hemisphere (Barnston AG, Livezey RE. 1987. Classification, seasonality and persistence of low frequency atmospheric circulation patterns. Monthly Weather Review115: 1083–1126), especially in the North Atlantic region. A better understanding of its recent variability in the context of pre-instrumental period variations is critical for prediction purposes. A 555-year (1429–1983) multi-proxy reconstruction of the cool season NAO, calibrated against the Lisbon–Iceland (LISJHI) NAO, is presented. Predictor variables include tree-ring chronologies from Morocco and Finland, GISP2 δ18O annual series, and a GISP2 snow accumulation record. Although the reconstructed values are generally lower than the instrumental values during the calibration period (1863–1983), the final reconstruction does capture the low frequency of the instrumental NAO. The reconstruction compares favourably with existing shorter NAO reconstructions and with the instrumental NAO. The variability in the reconstructed NAO is also discussed within the context of lengthy regional climate records. Results suggest that the occurrence and length of the recent persistently high phase of the NAO are not unusual over the 555-year period of time, but that the magnitude of some of the instrumental values may, in fact, be unique. Copyright © 2001 Royal Meteorological Society

Tree-ring widths have been used widely in studies of environmental changes and reconstructions of past climate. Eleven tree-ring chronologies of approximately 800–1500 years long were developed from Qilian junipers (Sabina przewalskii Kom.) for northeastern Qaidam Basin, along the margin of the Qinghai–Tibetan Plateau. Previous studies have revealed that water usage stress is the most limiting factor for tree growth in the study region. To evaluate the impact of the combined effects of temperature and precipitation changes over time, we performed water balance modelling using 1955–2002 meteorological data. We found that the tree-ring widths were strongly correlated with variables representing soil moisture conditions obtained from the water balance model. Specifically we considered actual evapotranspiration (AE) to represent the combined effect of water use demand and moisture availability, deficit as the difference between potential evapotranspiration (PE) and AE to represent the severity of water use stress, and relative soil moisture as the measure of moisture availability. For certain individual monthly and seasonal combinations, the tree-ring chronologies explained up to 80% of the variation in the soil moisture variables in regression analysis, indicating very good potential for reconstruction of regional soil moisture conditions in the past. These soil moisture variables outperformed precipitation and Palmer's drought severity index in most cases. We reconstructed the soil moisture conditions from 566 AD to 2001, which revealed major dry and wet periods and a general trend toward a wetter condition during the most recent 300 years. By comparing with other proxies in the region, we concluded that the moisture conditions reconstructed from tree-ring widths very well reflected the climate variability at the interannual and interdecadal scales. Copyright © 2007 Royal Meteorological Society

On the basis of Chinese government records, the number of tropical cyclones making landfall along the East China coast during the period 1450–1949 is examined. The annual number of typhoons making landfall in East China during this period is found to possess a positive and statistically significant trend, as well as oscillations on centennial to decadal timescales. By classifying the years using proxy records of the El Niño and Pacific Decadal Oscillation phenomena, the annual number of typhoon landfall is found to vary with the different phases of these two prominent oscillations, and such variations can be explained to a large extent physically based on modern-day atmospheric data. These results, together with those from previous studies, suggest that variations in the number of landfalling tropical cyclones are largely governed by those in the planetary-scale atmospheric circulations that go through oscillations on various timescales. Copyright © 2011 Royal Meteorological Society

Based on the records of local governments, the frequency of typhoon landfall over 22 cities/counties in the Guangdong Province of China during the period 1470–1931 is examined. The number of typhoons making landfall each year is used to form a time series. To reduce the level of uncertainty in the records, two other series are also formed, using 5- and 10-year totals. Application of various time series analysis techniques to the three series suggests that the frequency of typhoon landfall has a positive linear trend as well as centennial and decadal oscillations, the most significant being around 140–210 years and 30–60 years, respectively. Furthermore, the period of oscillation appears to change with time. Three sub-series can also be identified from this 462-year period: 1470–1667, 1668–1790 and 1791–1931. Each sub-series has its own characteristics, with a different autoregressive (AR) order. Copyright © 2000 Royal Meteorological Society

This paper presents an analysis of the flash floods that occurred in Catalonia (NE Iberian Peninsula) on 10 June 2000, in the context of the historical floods recorded since the 14th century. The study starts with pluviometric and meteorological analyses (essentially synoptic and thermodynamic) of the episode. There follows a comparison of this event with previous floods for which we have instrumental information, information from archives, or both types of information. In some cases this permitted us to make a meteorological comparison of episodes similar to that of June 2000, and the complete series was used to carry out a frequency analysis of floods that have occurred in the basin under study. The conclusions show that although catastrophic flooding in spring is not as typical a phenomenon as autumn flooding, such floods have been recorded at least once each century, and it can be stated that the synoptic meteorological situation, where recorded, showed similar characteristics in all cases. Copyright © 2003 Royal Meteorological Society

In this paper we reconstructed river runoff to the Baltic Sea since 1500 using temperature and atmospheric circulation indices, showing the important atmospheric processes for river runoff in different regions. Runoff appears to be strongly linked to temperature, wind and rotational circulation components in the northern region and Gulf of Finland, but more associated with rotational and deformation circulation components in the south. No significant long-term change has been detected in total river runoff to the Baltic Sea for 500 years, although decadal and regional variability is large. Analysis of runoff sensitivity to temperature shows that the south region may become drier with rising air temperatures. This is in contrast to the north region and Gulf of Finland where warmer temperatures are associated with more river runoff. Over the past 500 years the total river runoff to the Baltic Sea has decreased by 3% (450 m3/s) per degree Celsius increase. Copyright © 2010 Royal Meteorological Society

The annual and seasonal mean temperature of Finland was calculated for 162 years based on spatially interpolated monthly mean temperature records. The spatial interpolation method, known as kriging, was used with the following forcing parameters: the geographical coordinates, elevation of the terrain, and percentage share of lakes and sea. Homogenised data was used, and thus the most important factor affecting the accuracy of the interpolated data was the uneven distribution of the available observation stations both in time and space. The uncertainty due to the homogenisation adjustments made earlier was notably smaller. In the mid-1800s, the uncertainty in the annual and seasonal mean temperatures was large, with a maximum in winter of over ± 2.0 °C, but the accuracy improved quickly with time as the number of the observation stations increased. At the beginning of the 20th century, the uncertainty related to the limited station network was less than ± 0.2 °C, in winter less than ± 0.4 °C. According to the data, the rise in Finland's annual mean temperature has been statistically significant during the last 100, 50 and 30 years. During the last 100 years the increase in the mean temperature was largest during spring, but during the last 50 years winters have warmed up the most. The temperature time series obtained are compatible with grid point values picked from the global temperature data grids starting from the 1880s, though the global data sets tend to smooth the extremes. Copyright © 2009 Royal Meteorological Society

The possible climatic impact in North China of the AD 1600 Huaynaputina eruption (Peru) is investigated utilizing the Chinese historical sources. According to the records in the historical local chronicles, exceptionally disastrous frosts occurred in many areas in North China during the summer and autumn of AD 1601, which destroyed crops and caused great famines. There was even a snowfall in the summer of AD 1601 in Huai'an County. No historical records of cold weather in AD 1602–1603 in North China are found. It seems that the climatic cooling following the Huaynaputina eruption is short-lived in this region, perhaps less than 1 year. According to the river ice condition records in the Journals of Mathew Ricci, the AD 1600/1601 winter might be not abnormally mild in North China. Copyright

It has been known for some time that the potential exists to construct a long daily series of surface pressure for the city of Paris because of the existence of various instrumental series that might be pieced together. The remarkable weather diary kept by the physician, Louis Morin, sets the start of the potential series to 1670, and various other series have now been digitized and corrected to allow the formation of a daily series of Mean Sea-Level Pressure (MSLP) that spans the greater part of 300 years. Unfortunately, a gap in the series still exists for the period 1726–1747, where it appears that no barometer observations have survived. This paper discusses the sources of the various pressure data used in the Paris daily MSLP series, and describes how these observations have been corrected and amalgamated to form a near-continuous, homogeneous series. The data are compared with a similar long daily series that has been independently constructed for the city of London (1692–2007). This comparison indicates that the two MSLP series are of a sufficient quality to provide useful information about the atmospheric circulation across western Europe over the last 300 years. Copyright © 2011 Royal Meteorological Society

A reconstruction of April–August precipitation (1689–1994) was developed for the region by using Pinus nigra tree rings. A linear regression was performed using the residual chronology, composed of at least nine trees (SSS>0.85). Within this reconstructed period, dry years were distributed generally as 1 year (23 times), rarely 2 years (four times) and very rarely 3 years (one time). According to the results, dry events of 3 years' duration were seen only once (1745–47) in the reconstruction period, and wet events were seen twice (1727–29 and 1900–02). Events of 2 years' duration occurred during all three centuries: 1725–26, 1796–97, 1819–20, 1862–63 and 1927–28 (dry years), and 1770–71, 1901–02 (wet years). In accordance with other studies, the years 1693, 1725, 1819, 1868, 1878, 1887 and 1893, which were below two standard deviations, were determined as the driest years in the eastern Mediterranean basin. The distribution of dry and wet periods over time was irregular, and the time between two dry periods was not less than 6 years. There was a significant negative correlation between concurrent April–August North Atlantic oscillation and instrumental precipitation, but it was lower with reconstructed April–August precipitation and nonsignificant. The present results could be useful in the planning and management of water resources and agricultural activities in the region. Copyright © 2005 Royal Meteorological Society.

This paper presents a new 300-year daily series of Mean Sea-Level Pressure (MSLP) for the city of London. Daily barometer readings recorded in the vicinity of London were digitised from several sources and by joining these data with previously available data, a near-continuous series was constructed to span the period 1692–2007. The data were quality controlled and then corrected to represent daily means of MSLP at standard modern-day conditions. This series was then subjected to a statistical homogenisation procedure. The Penalized Maximal t-test was used with several reference series to identify breakpoints in the series over the period 1780–2007. In the absence of suitable reference series, the homogeneity of the earlier 1692–1779 period was tested using the Penalized Maximal F-test. Both tests were implemented through the RHtestV2 software on the monthly and annual means derived from the daily data. The majority of the identified breakpoints could be supported by meta-data and most occur at the juncture of the component series. A major feature of the homogenised series is that the long-term mean is 1.2 hPa lower than that of the previous monthly series for London created under the EU ADVICE project for the period 1774–1999. The long-term mean of 1015.2 hPa for the new series is more consistent with other long MSLP series in the UK. Copyright © 2011 Royal Meteorological Society

A standardized tree-ring width chronology of the Scots pine (Pinus sylvestris L.) along with different types of documentary evidence (e.g. annals, chronicles, diaries, private correspondence, records of public administration, early newspapers) have been used to reconstruct air temperature in Poland. The ground surface temperature (GST) history has been reconstructed based on the continuous temperature logs from 13 wells, using a new method developed recently by Harris and Chapman (1998; Journal of Geophysical Research103: 7371–7383) which is compared with the functional space inversion (FSI) method applied to all available Polish temperature–depth profiles analysed before.