Abstract
During the Tropical Composition, Clouds and Climate Coupling (TC4) experiment that occurred in July and August of 2007, extensive sampling of active convection in the ITCZ region near Central America was performed from multiple aircraft and satellite sensors. As part of a sampling strategy designed to study cloud processes, the NASA ER‐2, WB‐57 and DC‐8 flew in stacked “racetrack patterns” in convective cells. On July 24, 2007, the ER‐2 and DC‐8 probed an actively developing storm and the DC‐8 was hit by lightning. Case studies of this flight, and of convective outflow on August 5, 2007 reveal a significant anti‐correlation between ozone and condensed cloud water content. With little variability in the boundary layer and a vertical gradient, low ozone in the upper troposphere indicates convective transport. Because of the large spatial and temporal variability in surface CO and other pollutants in this region, low ozone is a better convective indicator. Lower tropospheric tracers methyl hydrogen peroxide, total organic bromine and calcium substantiate the ozone results. OMI measurements of mean upper tropospheric ozone near convection show lower ozone in convective outflow. A mass balance estimation of the amount of convective turnover below the tropical tropopause transition layer (TTL) is 50%, with an altitude of maximum convective outflow located between 10 and 11 km, 4 km below the cirrus anvil tops. It appears that convective lofting in this region of the ITCZ is either a two‐stage or a rapid mixing process, because undiluted boundary layer air is never sampled in the convective outflow.
Highlights
[18] We evaluate mean tropospheric ozone volume mixing ratios calculated between the tropopause and sampling by the DC‐8 that are derived using the NASA Aura Ozone Monitoring Instrument (OMI) [Levelt et al, 2006], and the Microwave Limb Sounder (MLS)
We developed a special‐purpose program to combine the Cloud Physics Lidar (CPL) and CALIOP images and DC‐8 data, as well as their geo‐location and time stamp information, into geometry and scalar‐data files compatible with the COTS 3‐D Visualization software tool called “EnSight.” These data sets could be co‐located in space and time, with respect to a map of the Earth built from the GTOPO30 digital elevation model (DEM) and the NASA Blue Marble cloud‐free image
We look at ozone and carbon monoxide because neither gas is soluble in the cloudy tropical environment, and they both have similar chemical lifetimes of about 50–60 days, much longer than the vertical mixing time of less than 1 day
Summary
Processes that control ozone in the tropical upper troposphere (500–150 hPa) are expected to be predominantly convective outflow from the boundary layer, extra‐tropical advection, and in situ photochemical production. Morris et al (Observations of ozone production in a dissipating convective cell during TC4, submitted to Journal of Geophysical Research, 2010) measured even higher ozone production rates of 1.1–3.2 ppb/hour between 2 and 5 km in a convective cloud This suggests that in situ ozone production can sometimes occur vigorously during vertical transport in convection. Large‐ scale data analysis [Pfister et al, 2010] and dust collected from low altitude sampling shows that the lower level winds brought air from Africa and South America into the boundary layer in the main TC4 study region, while vector winds measured on the DC‐8 show winds coming from all 4 quadrants, and chemical tracers showed a mix of both polluted continentally influenced air and very clean maritime air, as discussed below. Periods of active convection were sampled by the airplanes, at the beginning and at the end of the mission
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