Balloon‐borne observations of water vapor and ozone in the tropical upper troposphere and lower stratosphere

Abstract

Balloon‐borne observations of frost‐point temperature and ozone in the equatorial western, central and eastern Pacific as well as over equatorial eastern Brazil provide a highly accurate data set of water vapor across the tropical tropopause. Data were obtained at San Cristóbal, Galapagos, Ecuador (0.9°S, 89.6°W), during the late northern winter and the late northern summer in 1998 and 1999 and at Juazeiro do Norte, Brazil (7.2°S, 39.3°W), in February and November 1997. Earlier data in the western Pacific region in March 1993 were reanalyzed to extend the scope of the observations. The data show three different circumstances in which saturation or supersaturation occurs and imply different mechanisms for dehydration at the tropical tropopause: (1) convective dehydration, (2) slow‐ascent dehydration, and (3) large‐scale wave‐driven dehydration. Furthermore, air that crosses the tropical tropopause in the late northern summer may be dehydrated further during late northern fall, as the average tropical tropopause rises and cools. Not all soundings show dehydration, and there are clear differences in the frequency and depth of saturation in different regions and seasons. The tropopause transition region can be identified in accurate measurements of relative humidity, even under conditions where ozone observations are ambiguous. Deep convection plays an important role in setting up this transition region, which is then subject to large‐scale wave activity and wave breaking at the tropopause or midlatitude intrusions. High relative humidities over regions of strong subsidence show that descending motion in the troposphere is limited to levels below the transition region.

In situ observations of dehydrated air parcels advected horizontally in the Tropical Tropopause Layer of the western Pacific

“…SOWER has been using the NOAA/CMDL frostpoint hygrometer (FPH) between 1998 and 2002 (Vömel et al, 2002) and the University of Colorado Cryogenic Frostpoint Hygrometer (CFH) since 2003 . It has also been flying the Snow White (SW) hygrometers since the year 2000, and has flown nearly 100 sondes.…”

Modelling study of the impact of deep convection on the utls air composition - Part I: Analysis of ozone precursors

“…They showed that this maximum was related to the uplifting of surface emissions by convective processes. These studies and others (e.g., Vömel et al, 2002) show that the TTL is characterized by a specific air composition, in particular during the wet season.…”

“…The main airborne experiments were the TROPOZ II (Tropospheric Ozone) experiment that took place in January 1991 (Marenco et al, 1995) and the TRACE A (Transport and Atmospheric Chemistry Near the Equator-Atlantic) experiment that took place during the dry (September/October) and the wet (April) seasons in 1992 (Fishman et al, 1996). In parallel, balloon-borne instruments were flown in Central and Eastern Brazil mainly performing measurements of ozone (Kirchhoff et al, 1996;Logan, 1999;Pundt et al, 2002;Vömel et al, 2002;Thompson et al, 2003). One of the most outstanding results from these observational studies was, that there is a large increase of the ozone mixing ratio with altitude starting in the UT well below the tropopause (Logan, 1999;Pundt et al, 2002;Thompson et al, 2003).…”

Ozonesonde Observations in the Equatorial Eastern Pacific. The Shoyo-Maru Survey.

“…Since 1998 the Soundings of Ozone and Water in the Equatorial Region (SOWER)/Pacific mission has been conducted on a campaign basis at San Cristóbal, Galá pagos, Ecuador (0.9 S, 89.6 W) and Christmas Island, Kiribati (2.0 N, 157.5 W) supplementing the on-going program at Watukosek, Indonesia (7.5 S, 112.6 E). Results from these campaigns have been contributing to the understanding of stratospheretroposphere exchange (e.g., Fujiwara et al 2001;Vömel et al 2002) and to the equatorial tropospheric ozone distribution which will be described in this paper.…”