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Bian J.,CAS Institute of Atmospheric Physics | Pan L.L.,U.S. National Center for Atmospheric Research | Paulik L.,U.S. National Center for Atmospheric Research | Vmel H.,Lead Center | And 2 more authors.
Geophysical Research Letters | Year: 2012

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. © 2012. American Geophysical Union. All Rights Reserved. Source

Hasebe F.,Hokkaido University | Inai Y.,Tohoku University | Shiotani M.,Kyoto University | Fujiwara M.,Hokkaido University | And 8 more authors.
Atmospheric Chemistry and Physics | Year: 2013

A network of balloon-borne radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since the late 1990s in the Tropical Pacific to capture the evolution of dehydration of air parcels advected quasihorizontally in the Tropical Tropopause Layer (TTL). The analysis of this dataset is made on isentropes taking advantage of the conservative properties of tracers moving adiabatically. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Although further observational evidence is needed to confirm the credibility of such high values of RHice, the evolution of TTL dehydration is evident from the data in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. Supersaturation exceeding the critical value of homogeneous ice nucleation (OMR > 1.6×SMR min) is frequently observed on the 360 and 365K surfaces indicating that cold trap dehydration is in progress in the TTL. The near correspondence between the two (OMR ∼ SMRmin) at 380K on the other hand implies that this surface is not sufficiently cold for the advected air parcels to be dehydrated. Above 380 K, cold trap dehydration would scarcely function while some moistening occurs before the air parcels reach the lowermost stratosphere at around 400K where OMR is generally smaller than SMRmin. © Author(s). Source

Inai Y.,Tohoku University | Inai Y.,Kyoto University | Hasebe F.,Hokkaido University | Fujiwara M.,Hokkaido University | And 7 more authors.
Atmospheric Chemistry and Physics | Year: 2013

We apply the match technique, whereby the same air mass is observed more than once and such cases are termed a "match", to study the dehydration process associated with horizontal advection in the tropical tropopause layer (TTL) over the western Pacific. The matches are obtained from profile data taken by the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaign network observations using isentropic trajectories calculated from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. For the matches identified, extensive screening procedures are performed to verify the representativeness of the air parcel and the validity of the isentropic treatment, and to check for possible water injection by deep convection, consistency between the sonde data and analysis field referring to the ozone conservation. Among the matches that passed the screening tests, we identified some cases corresponding to the first quantitative value of dehydration associated with horizontal advection in the TTL. The statistical features of dehydration for the air parcels advected in the lower TTL are derived from the matches. The threshold of nucleation is estimated to be 146 ± 1% (1σ) in relative humidity with respect to ice (RHice), while dehydration seems to continue until RHice reaches about 75 ± 23% (1σ) in the altitude region from 350 to 360 K. The efficiency of dehydration expressed by the relaxation time required for the supersaturated air parcel to approach saturation is empirically determined from the matches. A relaxation time of approximately one hour reproduces the second water vapor observation reasonably well, given the first observed water vapor amount and the history of the saturation mixing ratio during advection in the lower TTL. © 2013 Author(s). Source

Thompson A.M.,Pennsylvania State University | MacFarlane A.M.,Pennsylvania State University | MacFarlane A.M.,College of the Atlantic | Morris G.A.,Valparaiso University | And 16 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010

During the TC4 (Tropical Composition, Clouds, and Climate Coupling) campaign in July-August 2007, daily ozonesondes were launched over coastal Las Tablas, Panamá (7.8°N, 80°W) and several times per week at Alajuela, Costa Rica (10°N, 84°W). Wave activity, detected most prominently in 100-300 m thick ozone laminae in the tropical tropopause layer, occurred in 50% (Las Tablas) and 40% (Alajuela) of the soundings. These layers, associated with vertical displacements and classified as gravity waves (GW, possibly Kelvin waves) by laminar identification, occur with similar structure and frequency over the Paramaribo (5.8°N, 55°W) and San Cristóbal (0.92°S, 90°W) Southern Hemisphere Additional Ozonesondes (SHADOZ) sites. GW-labeled laminae in individual soundings correspond to cloud outflow as indicated by DC-8 tracers and other aircraft data, confirming convective initiation of equatorial waves. Layers representing quasihorizontal displacements, referred to as Rossby waves by the laminar technique, are robust features in soundings from 23 July to 5 August. The features associated with Rossby waves correspond to extratropical influence, possibly stratospheric, and sometimes to pollution transport. Comparison of Las Tablas and Alajuela ozone budgets with 1999- 2007 Paramaribo and San Cristóbal soundings shows that TC4 is typical of climatology for the equatorial Americas. Overall during TC4, convection and associated waves appear to dominate ozone transport in the tropical tropopause layer; intrusions from the extratropics occur throughout the free troposphere. Copyright © 2010 by the American Geophysical Union. Source

Pan L.L.,U.S. National Center for Atmospheric Research | Paulik L.C.,U.S. National Center for Atmospheric Research | Paulik L.C.,Science Systems And Applications Inc. | Honomichl S.B.,U.S. National Center for Atmospheric Research | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2014

We present a method of identifying the tropical tropopause transition layer (TTL) using chemical tracer-tracer relationships. Coincident ozone (O 3) 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. © 2013. American Geophysical Union. All Rights Reserved. Source

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