L. Pan

National Center for Atmospheric Research, Boulder, Colorado, United States

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Publications (73)108.48 Total impact

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    ABSTRACT: explore the use of nonlinear empirical predictions of thin cirrus for diagnosing transport through the tropical tropopause layer (TTL). Thirty day back trajectories are calculated from the locations of CALIPSO cloud observations to obtain Lagrangian dry and cold points associated with each observation. These historical values are combined with "local" (at the location of the CALIPSO observation) temperature and specific humidity to predict cloud probability using multivariate polynomial regression. We demonstrate that our statistical sample (seven seasons) is sufficient to retrieve the full nonlinear relationship between cloud probability and its predictors and that substantial information is lost in a purely linear analysis. The best cloud prediction is obtained by the two-variable combination of local temperature and humidity, which reflects the close relationship between clouds and relative humidity. However, single-variable predictions involving air parcel histories are better than those based solely on the individual local fields, indicating the existence of reliable dynamical information content within parcel trajectories. Thermal fields are better cirrus predictors during boreal winter than summer primarily due to poor predictions over the Asian summer monsoon region, revealing that the functional relationship over southern Asia differs from the rest of the tropics; in short, TTL cirrus formation over regions of active maritime convection, such as the West Pacific, is thermally dominated, indicating an environment in which in situ cirrus are readily formed, while TTL cirrus of southern Asia is moisture dominated, indicating a more direct connection between convective injection of moisture and thin cirrus.
    02/2014; 119(6).
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    ABSTRACT: Simulations of observed convective systems with the Advanced Research Weather Research and Forecasting (ARW-WRF) model are used to test the influence of the large-scale lower stratosphere stability environment on the vertical extent of convective overshooting and transport above the extratropical tropopause. Three unique environments are identified (double tropopause, stratospheric intrusion, and single tropopause), and representative cases with comparable magnitudes of convective available potential energy are selected for simulation. Convective injection into the extratropical lower stratosphere is found to be deepest for the double-tropopause case (up to 4 km above the lapse-rate tropopause) and at comparable altitudes for the remaining cases (up to 2 km above the lapse-rate tropopause). All simulations show evidence of gravity wave breaking near the overshooting convective top, consistent with the identification of its role as a transport mechanism in previous studies. Simulations for the double-tropopause case, however, also show evidence of direct mixing of the overshooting top into the lower stratosphere, which is responsible for the highest levels of injection in that case. In addition, the choice of bulk microphysical parameterization for ARW-WRF simulations is found to have little impact on the transport characteristics for each case.
    02/2014; 119(5).
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    ABSTRACT: [1] We present a method of identifying the tropical tropopause transition layer (TTL) using chemical tracer-tracer relationships. Coincident ozone (O3) and water vapor (H2O) measurements over Alajuela, Costa Rica (~10°N) in July and August 2007 are used to demonstrate the concept. In the tracer-tracer space, the O3 and H2O relationship helps to separate the transition layer air mass from the background troposphere and stratosphere. This tracer-relationship-based transition layer is found to span an approximately 40 K potential temperature range between 340 and 380 K, and is largely confined between the level of minimum stability (LMS) and the cold point tropopause (CPT). This chemical composition based transition layer is, therefore, consistent with a definition of the TTL based on the thermal structure, for which the LMS and CPT are the lower and upper boundaries of TTL, respectively. We also examine the transition layer over the region of Asian summer monsoon (ASM) anticyclone using the measurements over Kunming, China (~25° N) and compare its behavior with the TTL structure in the deep tropics. The comparison shows that the transition layer over the ASM is similar to the TTL, although the data suggest the ASM transition layer lies at higher potential temperature levels and is potentially prone to the influence of extratropical processes.
    Journal of Geophysical Research: Atmospheres. 11/2013;
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    AGU Fall Meeting; 01/2013
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    ABSTRACT: We discuss the use of potential vorticity (PV) based equivalent latitude (EqLat) and potential temperature (θ) coordinates in the upper troposphere and lower stratosphere (UTLS) for chemical transport studies. The main objective is to provide a cautionary note on using EqLat-θ coordinates for aggregating chemical tracers in the UTLS. Several examples are used to show 3-D distributions of EqLat together with chemical constituents for a range of θ. We show that the use of PV-θ coordinates may not be suitable for several reasons when tropospheric processes are an important part of a study. Due to the different static stability structures between the stratosphere and troposphere, the use of θ as a vertical coordinate does not provide equal representations of the UT and LS. Since the θ surfaces in the troposphere often intersect the surface of the Earth, the θ variable does not work well distinguishing the UT from the boundary layer when used globally as a vertical coordinate. We further discuss the duality of PV/EqLat as a tracer versus as a coordinate variable. Using an example, we show that while PV/EqLat serves well as a transport tracer in the UTLS region, it may conceal the chemical structure associated with wave breaking when used as a coordinate to average chemical tracers. Overall, when choosing these coordinates, considerations need to be made not only based on the time scale of PV being a conservative tracer, but also the specific research questions to be addressed.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 10/2012; 12(19):9187-9199. · 5.51 Impact Factor
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    ABSTRACT: The Asian summer monsoon (ASM) anticyclone circulation system is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. The observational evidence, however, is largely based on satellite retrievals. We report the first coincident in situ measurements of water vapor and ozone within the ASM anticyclone. The combined water vapor and ozonesondes were launched from Kunming, China in August 2009 and Lhasa, China in August 2010. In total, 11 and 12 sondes were launched in Kunming and Lhasa, respectively. We present the key characteristics of these measurements, and provide a comparison to similar measurements from an equatorial tropical location, during the Tropical Composition, Cloud and Climate Coupling (TC4) campaign in July and August of 2007. Results show that the ASM anticyclone region has higher water vapor and lower ozone concentrations in the upper troposphere and lower stratosphere than the TC4 observations. The results also show that the cold point tropopause in the ASM region has a higher average height and potential temperature. The in situ observations therefore support the satellite-based conclusion that the ASM is an effective transport pathway for water vapor to enter stratosphere.
    Geophysical Research Letters 10/2012; 39(19):19808-. · 3.98 Impact Factor
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    ABSTRACT: The HIAPER Pole to Pole Observations (HIPPO) experiment was designed to obtain seasonally resolved measurements of climatically relevant trace gases and aerosols in the remote atmosphere. The NCAR Gulfstream V has completed five missions (January, 2009; October/November, 2009; March/April, 2010; June/July, 2011; August/September, 2011) reaching from 65S to 85N and the surface up to 14 km. Whole air samples and in-situ instruments were used to measure an array of trace gases. The wide latitude and altitude extent of the measurements provides a unique opportunity for comparison of the observational data to chemistry climate models. Observational data from the whole air samples were compared to simulations from the Whole Atmosphere Community Climate Model (WACCM) for approximately fifteen compounds monitored including chlorofluorocarbons, hydrofluorochlorocarbons, halons, non-methane hydrocarbons and organic halogens as well as carbon monoxide and ozone from fast in-situ measurements. WACCM simulations use a horizontal resolution of 1.9° x 2.5° with 66 vertical layers and specified dynamics from GEOS-5. The compounds included in have a variety of different lifetimes, sources and sinks so that they each have different information to offer about the processes included in the model. The goals of such comparisons include evaluation of transport and mixing time scales, improvement of emission schemes and latitudinal structures. In this presentation, we show a comparison between the observational data and model simulations. Overall, the model simulations represent the general features seen reasonably well.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Ozone profile retrievals from backscattered ultraviolet radiances greatly depend on the climatological a priori information in the lower stratosphere and troposphere. The use of a tropopause-based (TB) ozone profile climatology has been shown to better preserve the sharp gradient across the tropopause and significantly reduce ozone variance due to tropopause variation. In this study, we improve the TB ozone profile climatology, originally developed for AIRS (Atmospheric Infrared Sounder) retrievals, for OMI (Ozone Monitoring Instrument) retrievals using the optimal estimation technique, and evaluate retrieval improvement with the TB climatology using meteorological data, ozonesonde and aircraft observations. The original TB ozone climatology (mean and standard deviations) was derived at 23 layers for each 10°-latitude bin and each month from ozonesonde profiles (1983-2003) extended with climatological ozone profiles above sonde burst altitude. Because ozone profiles in TB coordinates show reduced variances 3~5 km above/below the tropopause at middle and high-latitudes compared to the altitude-based (AB) climatology, we derive the TB climatology by applying tropopause-based transformation within 5 km around the tropopause using ozonesonde profiles when the tropopause height is less than 14 km (mostly at middle and high latitudes). The TB climatology is derived for every 1 km from -20 km to 60 km (0 means the tropopause). An AB climatology is also derived from 0 to 60 km at every 1 km. It will be used when the tropopause is greater than 14 km (e.g., tropics). Both climatologies are merged with the McPeters climatology between 5-10 km above the tropopause and are replaced by the latter 10 km above the tropopause. We evaluate OMI retrieval improvement with the TB climatology over the use of AB climatology using NCEP FNL (final operational global analysis) data, ozonesonde observations at Hohenpeissenberg and Sodankylä, and aircraft measurements during the START08 (Stratosphere-Troposphere Analyses of Regional Transport 2008) experiment. The FNL tropopause is used in the retrievals. The use of TB climatology significantly improves the spatial consistency in the upper troposphere and lower stratosphere (UT/LS) between ozone gradient and the potential vorticity gradient, and reduces the retrieval vertical smoothing across the UT/LS. Comparisons with ozonesonde observations (both mean biases and standard deviations) show substantial improvement in the lower stratosphere and troposphere especially during the winter. The use of the TB climatology also provides better comparisons with aircraft measurements in the UT/LS. The various comparisons support that the TB climatology provides better constraints to ozone retrievals in the troposphere and lower stratosphere from BUV measurements.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Stratospheric intrusions (tropopause folds) are known to be major contributors to stratosphere-troposphere exchange. The specific mixing processes that lead to irreversible exchange between stratospheric intrusions and the surrounding troposphere, however, are not entirely understood. This study presents direct observations of moist convection penetrating into stratospheric intrusions. The characteristics of convective injection are shown by using in situ aircraft measurements, radar reflectivities, and model analyses. Convective injection is observed at altitudes up to 5 km above the bottom of a stratospheric intrusion. Aircraft measurements from the Stratosphere-Troposphere Analyses of Regional Transport 2008 (START08) experiment show that convective injection in stratospheric intrusions can be uniquely identified by coincident observations of water vapor greater than about 100 ppmv and ozone greater than about 125 ppbv. Trajectory analyses show that convective injection can impact transport in both directions: from troposphere to stratosphere and from stratosphere to troposphere. We present a conceptual model of the synoptic meteorological conditions conducive to convective injection in stratospheric intrusions. In particular, convective injection is found to be associated with a "split front" where the upper-level frontal boundary outruns the surface cold front.
    Journal of Geophysical Research 12/2011; · 3.17 Impact Factor
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    ABSTRACT: In situ trace gas measurements on research aircraft have played critical roles in climate relevant processes studies. Despite the increased abundance of data, integrating the measurements with the chemistry-climate models is still a significant challenge. We present a set of studies using the measurements onboard the US NSF research aircraft Gulfstream V. A large suite of chemical tracer measurements during both the Stratosphere-Troposphere Analyses of Regional Transport 2008 (START08) and the HIAPER Pole-to-Pole Observations (HIPPO) missions are used to examine the NCAR Chemistry-Climate model WACCM. The main focus of the work is to contrast data-model comparisons in geophysical space and tracer space to show how the two types of comparisons complement each other in providing key diagnostic information. Using tracer-tracer correlation technique, the performance of the model in representing the chemical source/sink and transport is characterized. Examination of the model and data in tracer-tracer space also provides a perspective on the representativeness of aircraft sampling on a regional scale.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Cirrus clouds are one of the largest sources of uncertainties in predicting future climate. Ice nucleation and ice crystal growth inside cirrus clouds require ice supersaturation (ISS). However, the dynamical processes and conditions that control ISS are not well understood in the upper troposphere. In this work we present an analysis of ISS (T <= -40 °C) using the water vapor measurement by the Vertical Cavity Surface Emitting Laser (VCSEL) Hygrometer (Zondlo et al., 2010) on the NSF Gulf-stream V research airplane during the Stratosphere Troposphere Analyses of Regional Transport (START08) Campaign. START08 campaign sampled chemical and microphysical variables under various dynamical conditions near the extratropical tropopause and upper level jets. The data allow us to contrast ISS and ice crystals generated from the region of convective clouds versus those generated from the mixing of stratospheric and tropospheric air near the frontal zone during a stratospheric intrusion. We also compared the dynamical conditions of two different schemes for ISS: suppressed nucleation and suppressed growth schemes. To understand how mixing processes play a role in the formation of ISS and ice crystals, we analyzed how ISS and ice crystals are distributed relative to the jets streams and the extratropical tropopause transition layer based on O3-CO tracer-tracer correlations. The mixing lines represented by the tracer correlations help identify the dynamical processes that dominated the formation of the ISS parcels. Case studies identifying the specific dynamical conditions of observed ISS and ice particles will be presented.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: 1] Using isentropic trace gas gradients of O 3 and CO, the discontinuity in the chemical composition of the upper troposphere (UT) and lower stratosphere (LS) is examined on middle world isentropes from 300 to 380 K. The analysis is a follow‐up study of the dynamical discontinuity as represented by the potential vorticity (PV) gradient‐based tropopause, which is based on the product of isentropic PV gradients and wind speed. Overall, there is fairly good consistency between the chemical discontinuity in trace gas distributions and the PV gradient‐based tropopause. Trace gas gradients at the PV gradient‐based tropopause are stronger in winter than in summer, revealing the seasonal cycle of the tropopause transport barrier. The analysis of the trace gas gradients also identifies atmospheric transport pathways in the upper troposphere–lower stratosphere (UTLS). Several regions where trace gas gradients are found to be decoupled from the dynamical field indicate preferred transport pathways between the UT and LS. In particular, anomalous CO and O 3 gradients above eastern Africa, eastern Asia, and the West Pacific are likely related to convective transport, and anomalous O 3 gradients over the North Atlantic and North Pacific are related to isentropic transport connected to frequent wave breaking. The results indicate that the PV gradient‐based tropopause definition provides a good identification of the dynamical and chemical discontinuity and is therefore effective in locating the physical boundary in the UTLS.
    Journal of Geophysical Research 01/2011; 116. · 3.17 Impact Factor
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    ABSTRACT: 1] Since its inception, the dynamical tropopause based on potential vorticity (PV) is identified by the PV gradient on isentropes. Conceptually, significant isentropic gradients shown on the middle world PV maps reflect the underlying transport barrier associated with the tropopause, formed by jet streams that separate tropospheric air masses at low latitudes and stratospheric air masses at high latitudes. Largely owing to the lack of a general method, the dynamical tropopause has often been represented by a PV value chosen ad hoc without any temporal or spatial differentiation. In this work, we present a method for determining the PV isoline of the dynamical tropopause based on the isentropic PV gradients. Using 1 year of data from the European Centre for Medium–Range Weather Forecasts, the spatial and temporal variability of this PV gradient‐based dynamical tropopause is examined. The results show that in general there is a broad distribution of PV values at the dynamical tropopause, ranging from 1.5 to 5 potential vorticity units. Therefore, a fixed PV surface for all isentropes and seasons does not accurately represent the location of the "tropopause barrier." The PV at the dynamical tropopause increases with increasing potential temperature. This increase is more pronounced in the Southern Hemisphere than in the Northern Hemisphere. The seasonal cycle shows higher PV values at the dynamical tropopause during summer than during winter. This seasonal cycle is larger on higher isentropes. The dispersion of the PV at the dynamical tropopause about its mean is twofold larger during summer and autumn than during winter and spring in both hemispheres.
    Journal of Geophysical Research 01/2011; 116. · 3.17 Impact Factor
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    ABSTRACT: Model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by wind fields of the National Center for Environmental Prediction (NCEP) were performed in the midlatitude tropopause region in April 2008 to study two research flights conducted during the START08 campaign. One flight targeted a deep tropospheric intrusion and another flight targeted a deep stratospheric intrusion event, both of them in the vicinity of the subtropical and polar jet. Air masses with strong signatures of mixing between stratospheric and tropospheric air masses were identified from measured CO-O3 correlations, and the characteristics were reproduced by CLaMS model simulations. CLaMS simulations in turn complement the observations and provide a broader view of the mixed region in physical space. Using artificial tracers of air mass origin within CLaMS yields unique information about the transport pathways and their contribution to the composition in the mixed region from different transport origins. Three different regions are examined to categorize dominant transport processes: (1) on the cyclonic side of the polar jet within tropopause folds where air from the lowermost stratosphere and the cyclonic side of the jet is transported downward into the troposphere, (2) on the anticyclonic side of the polar jet around the 2 PVU surface air masses, where signatures of mixing between the troposphere and lowermost stratosphere were found with large contributions of air masses from low latitudes, and (3) in the lower stratosphere associated with a deep tropospheric intrusion originating in the tropical tropopause layer (TTL). Moreover, the time scale of transport from the TTL into the lowermost stratosphere is in the range of weeks whereas the stratospheric intrusions occur on a time scale of days.
    Journal of Geophysical Research 01/2011; 116. · 3.17 Impact Factor
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    ABSTRACT: The extratropical upper troposphere and lower stratosphere (Ex-UTLS) is a transition region between the stratosphere and the troposphere. The Ex-UTLS includes the tropopause, a strong static stability gradient and dynamic barrier to transport. The barrier is reflected in tracer profiles. This region exhibits complex dynamical, radiative, and chemical characteristics that place stringent spatial and temporal requirements on observing and modeling systems. The Ex-UTLS couples the stratosphere to the troposphere through chemical constituent transport (of, e.g., ozone), by dynamically linking the stratospheric circulation with tropospheric wave patterns, and via radiative processes tied to optically thick clouds and clear-sky gradients of radiatively active gases. A comprehensive picture of the Ex-UTLS is presented that brings together different definitions of the tropopause, focusing on observed dynamical and chemical structure and their coupling. This integral view recognizes that thermal gradients and dynamic barriers are necessarily linked, that these barriers inhibit mixing and give rise to specific trace gas distributions, and that there are radiative feedbacks that help maintain this structure. The impacts of 21st century anthropogenic changes to the atmosphere due to ozone recovery and climate change will be felt in the Ex-UTLS, and recent simulations of these effects are summarized and placed in context.
    Reviews of Geophysics 01/2011; 49(RG3003). · 13.91 Impact Factor
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    ABSTRACT: Intrusions of air from the tropical upper troposphere into the extratropical stratosphere above the subtropical jet potentially have a significant impact on the composition of the lowermost stratosphere (the stratospheric part of the “middle world”). We present an analysis of tropospheric intrusion events observed during the Stratosphere-Troposphere Analyses of Regional Transport 2008 (START08) experiment using kinematic and chemical diagnostics. The transport processes operating during each event are discussed using high-resolution model analyses and backward trajectory calculations. Each intrusion observed during START08 can be related to a Rossby wavebreaking event over the Pacific Ocean. Trajectory analysis shows that the intruding air masses can be traced back to the tropical upper troposphere and lower stratosphere. In situ chemical observations of the tropospheric intrusions are used to estimate the mixing time scales of the observed intrusions through use of a simple box model and trace species with different photochemical lifetimes. We estimate that the time scale for an intrusion to mix with the background stratospheric air is 5 to 6 days. Detailed analysis of small-scale features with tropospheric characteristics observed in the stratosphere suggests frequent irreversible transport associated with tropospheric intrusions. Trace gas distributions and correlations are consistent with the dynamics of the high-resolution NCEP GFS analyses, suggesting that these features are captured by the GFS assimilation and forecast system. A global analysis of intrusion events observed during the START08 time period (April–June 2008) is also given.
    Journal of Geophysical Research 01/2011; 116. · 3.17 Impact Factor
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    ABSTRACT: Data from the Stratosphere-Troposphere Analyses of Regional Transport (START08) field campaign conducted April- June 2008 are used to evaluate trace gas simulations by the Whole-Atmosphere Community Climate Model version 3 (WACCM3). START08 sampled a variety of meteorological conditions over North America. To allow direct comparison with the in situ observations, in this study WACCM dynamics are nudged toward the Goddard Earth Observing System model version 5.1 (GEOS-5.1) analyses. Results show good qualitative agreement overall, but quantitative differences exist, primarily during intrusion events and near the subtropical tropopause break. The temporal evolution of ozone and carbon monoxide on potential temperature surfaces during several tropospheric intrusion events suggest that isentropic transport into the stratosphere is resolved but is mixed too quickly due to model diffusion. Ozone-carbon monoxide and ozone-water vapor relationships are used to assess the ability of the model to reproduce the chemical transition observed in the upper troposphere/lower stratosphere (UT/LS). The simulated mixing branches are more linear than those observed, but the thickness of the transition relative to the thermal tropopause agrees well. This suggests that model diffusion may play a larger role in determining the chemical composition in the UT/LS, as opposed to vertical resolution. Mean vertical profiles of selected trace gases with various lifetimes are also presented. Longer-lived species show little variability in the model troposphere, but agree well in the lower stratosphere. Other species show differences that are specific to their respective source distributions and chemistry.
    AGU Fall Meeting Abstracts. 12/2010;
  • L. Pan, L. A. Munchak
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    ABSTRACT: Cloud top and tropopause relationships are examined using CALIPSO cloud data and high resolution NCEP Global Forecast System (GFS) tropopause data. Our goal is to characterize the constraint of the background thermal and dynamical structure on cloud occurrences. Statistical analyses of cloud top occurrence in tropopause/jet referenced relative altitude coordinates are performed on a global scale using 1-year (2007) of CALIPSO 5 km resolution cloud layer data. The results show that the thermal tropopause appears to be a significant constraint for the cloud top. Using the correlation between the change of the tropopause height and the jet location, the tropics and the extratropics are effectively separated. The analyses show that there is no statistically significant cloud top occurrence above the tropopause in the extratropics, and there is no statistically significant cloud top occurrence higher than one kilometer above the tropopause in the tropics. Our analyses also show that the tropopause determination is a significant component of this type of studies and that errors in the tropopause height may lead to significantly different conclusions. To investigate this issue, we examined the tropopause products from the GFS analyses and the GEOS5 model (given as auxiliary data in the CALIPSO cloud layer data) in comparison with high-resolution radiosonde data from the TC4 campaign. The results show that the GEOS5 tropopause product has significant uncertainty and will have an impact on the cloud top analyses. We further investigated the differences between the thermal and the cold point tropopause in the tropics using the radiosonde data and compared with the collocated CALIPSO data. Based on selected case analyses, we suggest that the differences of the thermal and the cold point tropopause may be largely responsible for the cloud tops that do occur above the thermal tropopause in the tropics.
    Journal of Geophysical Research 12/2010; · 3.17 Impact Factor
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    ABSTRACT: An analysis of the extratropical UT/LS region is presented using in-situ aircraft data sampled during the START08 campaign and modeled data based on WACCM output fields. The focus is on the investigation of this region relative to different types of tropopauses. These are the lapse rate tropopause and the dynamical tropopause (2\ PVU isoline), as well as the recently developed gradient based dynamical tropopause. This tropopause is defined by the isentropic PV isoline, that marks the strongest isentropic gradient in the dynamical fields of PV and horizontal wind. The gradient based tropopause identifies the discontinuity in the dynamical field. We expect to see chemical tracer discontinuities associated with the dynamical discontinuity, since it reflects the presence of a transport barrier. The relation of the dynamical and chemical discontinuity is studied with analyses of isentropic trace gas gradients in CO and {O3} from both the aircraft data and the model results. During the START08 campaign, stratospheric and tropospheric intrusion events near the jet streams were measured. We examine these intrusions using CO-{O3} tracer correlations and different coordinate systems, which are based on altitudes and isentropes versus geographical and equivalent latitudes. The results show that based on the combination of these coordinates, intrusions can be visible and are clearly separated from their original reservoirs, but they can also be covered. The coordinate systems used in the data analyses may have significant influences on the data interpretation.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: The deep monsoon anticyclones, particularly the Asian summer monsoon anticyclone, are persistent UTLS features that strongly regulate transport in the tropical tropopause layer (TTL). Particularly important are the meridional in-mixing on the outer flanks and the vertical transport deep into the stratosphere inside of such anticyclones. Satellite, in-situ observations and the multi-annual simulations (2001-2010) with the Chemical Model of the Stratosphere (CLaMS) are used to study how such persistent dynamical structures influence the pathways of transport into the stratospheric part of the TTL. In particular, the observed and simulated seasonal cycles of H2O, O3 and CO are discussed where the contribution of the tropical upwelling is compared with that of the meridional in-mixing. Both, CLaMS simulations and pure trajectory calculations show that the strongest meridional transport into the stratospheric part of the TTL is driven by the Asian monsoon anticyclone that extends in summer between 150 and 70 hPa pressure levels. Using CLaMS simulations, we show how this nearly stationary circulation effectively isolates the air masses of tropospheric origin inside from much older, mainly stratospheric air outside of this anticyclone. To study the sensitivity of our results with respect to the vertical velocities, kinematic and diabatic trajectories based on ERA-Interim data are used. To quantify the quality of transport within the Asian monsoon circulation, we compare the recent balloon observations of water vapor and ozone over Kunming (25N, 102E) with our simulations.
    AGU Fall Meeting Abstracts. 12/2010;