Quantifying the deep convective temperature signal within the tropical tropopause layer (TTL)

L C Paulik,T Birner

doi:10.5194/acp-12-12183-2012

Abstract

Abstract. Dynamics on a vast range of spatial and temporal scales, from individual convective plumes to planetary-scale circulations, play a role in driving the temperature variability in the tropical tropopause layer (TTL). Here, we aim to better quantify the deep convective temperature signal within the TTL using multiple datasets. First, we investigate the link between ozone and temperature in the TTL using the Southern Hemisphere Additional Ozonesondes (SHADOZ) dataset. Low ozone concentrations in the TTL are indicative of deep convective transport from the boundary layer. We confirm the usefulness of ozone as an indicator of deep convection by identifying a typical temperature signal associated with reduced ozone events: an anomalously warm mid to upper troposphere and an anomalously cold upper TTL. We quantify these temperature signals using two diagnostics: (1) the "ozone minimum" diagnostic, which has been used in previous studies and identifies the upper tropospheric minimum ozone concentration as a proxy for the level of main convective outflow; and (2) the "ozone mixing height", which we introduce in order to identify the maximum altitude in a vertical ozone profile up to which reduced ozone concentrations, typical of transport from the boundary layer are observed. Results indicate that the ozone mixing height diagnostic better separates profiles with convective influence than the ozone minimum diagnostic. Next, we collocate deep convective clouds identified by CloudSat 2B-CLDCLASS with temperature profiles based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Global Position System (GPS) radio occultations. We find a robust large-scale deep convective TTL temperature signal, that is persistent in time. However, it is only the convective events that penetrate into the upper half of the TTL that have a significant impact on TTL temperature. A distinct seasonal difference in the spatial scale and the persistence of the temperature signal is identified. Deep-convective cloud top heights are on average found to be well described by the level of neutral buoyancy.

Highlights

The interface between the troposphere and the stratosphere is best described as a transition layer. This region is known as the tropical tropopause layer (TTL)
The notion of the Lagrangian cold point determining stratospheric water vapor, which takes into account both horizontal and vertical transport through the TTL is consistent with this picture (e.g. Holton and Gettelman, 2001; Fueglistaler et al, 2005)
Folkins et al (2008) and Mitovski et al (2010) successfully revealed similar local convective temperature signals associated with high rainfall rates from the Tropical Rainfall Measuring Mission (TRMM) at tropical radiosonde stations

Summary

Background

The interface between the troposphere and the stratosphere is best described as a transition layer. Sherwood and Wahrlich (1999) and Sherwood et al (2003) studied the deep convective temperature signal at tropical radiosonde stations associated with low satellite brightness temperatures Their constructed deep convective life cycle is marked by cooling in the lower to mid troposphere, warming in the mid to upper troposphere, and cooling at TTL altitudes. Folkins et al (2008) and Mitovski et al (2010) successfully revealed similar local convective temperature signals associated with high rainfall rates from the Tropical Rainfall Measuring Mission (TRMM) at tropical radiosonde stations These earlier studies were limited by (1) using proxies for deep convective clouds (brightness temperature, rain rate), (2) the limited spatial coverage given by the small number of radiosonde station locations.

Data and methods

Findings

Deep convective temperature signal based on SHADOZ ozone and temperature data