L. Pan

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

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Publications (45)53.09 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A significant source of ozone in the troposphere is transport from the stratosphere. The stratospheric contribution has been estimated mainly using global models that attribute the transport process largely to the global scale Brewer-Dobson circulation and synoptic scale dynamics associated with upper tropospheric jet streams. We report observations from research aircraft that reveal additional transport of ozone-rich stratospheric air downward into the upper troposphere by a leading-line-trailing-stratiform (LLTS) mesoscale convective system (MCS) with convection overshooting the tropopause altitude. The fine-scale transport demonstrated by these observations poses a significant challenge to global models that currently do not resolve storm scale dynamics. Thus the upper tropospheric ozone budget simulated by global chemistry-climate models where large-scale dynamics and photochemical production from lightning-produced NO are the controlling factors may require modification.
    Geophysical Research Letters. 11/2014;
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    ABSTRACT: Aircraft measurements, including non-methane hydrocarbons (NMHCs), long-lived halocarbons, carbon monoxide (CO), and ozone (O3) collected on board the NASA DC-8 during the DC3 field campaign (May – June 2012) were used to investigate interactions and mixing between stratospheric intrusions and polluted air masses. Stratospherically-influenced air masses were detected using a suite of long-lived halocarbons, including CFCs and HCFCs, as a tracer for stratospheric air. A large number of stratospherically-influenced samples were found to have reduced levels of O3 and elevated levels of CO (both relative to background stratospheric air); indicative of mixing with anthropogenically-influenced air. Using n-butane and propane as further tracers of anthropogenically-influenced air, we show that this type of mixing was present both at low altitudes and in the upper troposphere (UT). At low altitudes, this mixing resulted in O3 enhancements consistent with those reported at surface sites during deep stratospheric intrusions, while in the UT, two case studies were performed to identify the process by which this mixing occurs. In the first case study, stratospheric air was found to be mixed with aged outflow from a convective storm, while in the second case study, stratospheric air was found to have mixed with outflow from an active storm occurring in the vicinity of a stratospheric intrusion. From these analyses, we conclude that deep convective events may facilitate the mixing between stratospheric air and polluted boundary layer air in the UT. Throughout the entire DC3 study region, this mixing was found to be prevalent: 72% of all samples that involve stratosphere-troposphere mixing show influence of polluted air. Applying a simple chemical kinetics analysis to these data, we show that during DC3, the instantaneous production of OH in these mixed stratospheric-polluted air masses was 11 ± 8 times higher than that of stratospheric air, and 4.2 ± 1.8 times higher than that of background upper tropospheric air.
    Journal of Geophysical Research: Atmospheres. 09/2014;
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    ABSTRACT: We present in situ observations of convectively injected water vapor in the lower stratosphere from instruments aboard two aircraft operated during the Deep Convective Clouds and Chemistry (DC3) experiment. Water vapor mixing ratios in the injected air are observed to be 60-225 ppmv at altitudes 1-2 km above the tropopause (350-370 K potential temperature), well above observed background mixing ratios of 5-10 ppmv in the lower stratosphere. Radar observations of the responsible convective systems show deep overshooting at altitudes up to 4 km above the lapse-rate tropopause and above the flight ceilings of the aircraft. Backward trajectories from the in situ observations show that convectively injected water vapor is observed from three distinct types of systems: isolated convection, a convective line, and a leading line - trailing stratiform mesoscale convective system. Significant transport of additional tropospheric or boundary layer trace gases is observed only for the leading-line trailing stratiform case. In addition, all observations of convective injection are found to occur within large-scale double tropopause events from poleward Rossby wave breaking. Based on this relationship, we present a hypothesis on the role of the large-scale lower stratosphere during convective overshooting. In particular, the reduced lower stratosphere stability associated with double tropopause environments may facilitate deeper levels of overshooting and convective injection.
    Journal of Geophysical Research: Atmospheres. 08/2014;
  • Leigh A. Munchak, Laura L. Pan
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    ABSTRACT: Four years of temperature profiles from COSMIC GPS satellite retrievals are used to examine the difference between the WMO lapse rate definition and the cold point definition of the tropopause in the tropics. The separation between the cold point tropopause (CPT) and lapse rate tropopause (LRT) heights is quantified in seasonal averages and with the frequency of occurrence. In seasonal averages, small separations, <0.5 km, are found in the deep tropics, increasing to ~1 km towards higher latitudes, and maximizing at ~1.5 km near the jet streams. The seasonal average separations show significant longitudinal structures in DJF and JJA seasons. Case studies indicate that breaking Rossby waves and their effects extending into the equatorial region are responsible for the longitudinal structure in the DJF season. The seasonal average CPT-LRT separation therefore identifies the regions of the tropical UTLS that is controlled by extratropical forcing. Examination of individual profiles shows that a small yet significant fraction (~12%) of temperature profiles have CPT-LRT separations of 1 km or larger in the region of small seasonal average separation. These large separations are produced by wave perturbations of the upper tropospheric temperature structure. The impact of tropopause separation on the cloud top –tropopause relationship is examined using co-located CALIPSO cloud top data. We find that the frequency of clouds above the tropopause is reduced by approximately 50% if the CPT is used instead of LRT. The occurrence of clouds above the CPT is nevertheless significant, especially over the western Pacific in DJF season and over the Asian monsoon region in JJA season.
    Journal of Geophysical Research: Atmospheres. 06/2014;
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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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    ABSTRACT: [1] The transport of air from the planetary boundary layer (PBL) into the Asian Summer Monsoon anticyclone is investigated using backward trajectories initiated within the anti-cyclone at 100 mb and 200 mb during August 2011. Transport occurs through a well-defined conduit centered over the southern Tibetan plateau, where convection lofts air parcels into the anticyclone. The conduit, as a dynamical feature, is distinct from the anticyclone. Thus, while the anticyclone influences transport through the upper troposphere and lower stratosphere, it does not by itself define a transport pipeline through that region. To quantify model sensitivities, parcel trajectories are calculated using wind fields from multiple analysis data sets (European Centre for Medium-Range Weather Forecasts, National Center for Environmental Prediction's Global Forecasting System, and NASA's Modern-Era Retrospective Analysis for Research and Applications [MERRA]) and from synthetically modified data sets that explore the roles of vertical motion and horizontal resolution for discrepancies among these calculations. All calculations agree on the relative contributions to PBL sources for the anticyclone from large-scale regions with Tibetan Plateau and India/SE Asia being the most important. However, they disagree on the total fraction of air within the anticyclone that was recently in the PBL. At 200 mbar, calculations using MERRA are clear outliers due to problematic vertical motion in those data. Large differences among the different data sets at 100 mbar are more closely related to horizontal resolution. It is speculated that this reflects the importance of deep, small-scale convective updrafts for transport to 100 mbar.
    Journal of Geophysical Research: Atmospheres. 03/2013; 118(6).
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    ABSTRACT: The trace gas composition of the upper troposphere/lower stratosphere (UT/LS) region depends on emission sources, transport pathways, mixing rates and photochemical processing time. Because surface emissions include gases with a range of chemical lifetimes, and because different source emissions (e.g. marine boundary layer, anthropogenic emissions, biomass burning) can have different chemical signatures, the composition of the organic trace gases that are found in the UT/LS and throughout the remote atmosphere have the potential to provide diagnostic information on air mass sources and transport time scales. For most reactive organic halogen compounds, such as bromoform, air-sea exchange is a major source to the atmosphere. Measurements of this flux provide the boundary conditions to evaluate the potential impact of reactive halogen on the chemistry of the UT/LS region. In fact, measurement of short-lived organic halogen gases in the UT/LS provides data to define the reactive halogen budget and the chemical boundary conditions for the stratospheric chemistry that affects ozone depletion rates. Recent airborne and ship-based research campaigns in the tropics, the extra-tropics, and in mid-ocean transects, from near surface to the lower stratosphere have included the measurement of a wide range of trace gases including halocarbons, hydrocarbons, and related species. This presentation will emphasize short-lived trace gases and will highlight different aspects of these measurements that deal with distributions, seasonality, transport pathways, transport rates, and halogen budgets.
    93rd American Meteorological Society Annual Meeting 2013; 01/2013
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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
  • Paul Konopka, Laura L. Pan
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    ABSTRACT: We present a case study on the formation and structure of the Extratropical Transition Layer (ExTL) using in situ observations and a Lagrangian chemical transport model. The results show that the model with mixing parameterized from the large-scale flow deformations well reconstructs the observed asymmetric structure of the ExTL with a deeper transition layer on the cyclonic side of the jet stream. Information from the model and observations are integrated using tracer-tracer correlations between ozone (O3) and carbon monoxide (CO). Transport of chemical tracers from the stratospheric or tropospheric background to the ExTL through mixing is identified by the change of the CO-O3correlation in the CO-O3 space. The ExTL formation process simulated by the model, therefore, provides a scenario to connect the mixed air parcels to the history of mixing. An estimate of timescales of ExTL formation is made using model experiments. The results show that the fastest formation of the ExTL occurs on the isentropic levels below the subtropical jet core, e.g. around 3 weeks for 310 K, whereas at 360 K level (jet core) the formation of the ExTL needs around 3 months. Overall, this result demonstrates the important role of mixing in transport of trace gases across the tropopause.
    Journal of Geophysical Research Atmospheres 09/2012; 117(D18):18301-. · 3.44 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: 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: 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 Atmospheres 12/2011; · 3.44 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 Atmospheres 01/2011; 116. · 3.44 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. 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 Atmospheres 12/2010; · 3.44 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;