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

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.

The tropical tropopause inversion layer: variability and modulation by equatorial waves

“…Deep convection that is not coupled with any equatorial wave can also lead to tropopause cooling (by hydrostatic adjustment) and TIL enhancement, as discussed in Sect. 3.2 (Holloway and Neelin, 2007;Paulik and Birner, 2012). Given that deep convection near the equator is more frequent in winter, this would explain the occurrence of stronger TIL in Fig.…”

“…7) but part of it remains, and we point to non-wavecoupled deep convection (tropopause cooling by hydrostatic adjustment; Holloway and Neelin, 2007;Paulik and Birner, 2012) and radiative effects from clouds or humidity gradients as other possible mechanisms that could enhance the tropical TIL.…”

“…The pressure gradients extend above the heating, and the ascent and adiabatic cooling act to diminish these pressure gradients with height, cooling the tropopause region above the deep convective tower. Paulik and Birner (2012) showed that this negative temperature signal near the tropical tropopause can be found even a few thousand kilometers away from the convective region. In Fig.…”

The signature of the stratospheric Brewer‒Dobson circulation in tropospheric clouds

“…[18] Upper tropospheric cloud incidence is also strongly linked to tropical tropopause temperatures. Cloud incidence between 12 and 17 km decreases by 4% K -1 with increasing tropopause temperature between 189 K and 198 K. The linkages between tropopause temperatures and cloud incidences are consistent with those derived from in situ observations of tropical stratospheric waves [Boehm and Verlinde, 2000], the seasonal cycle of TTL cirrus derived from CALIPSO observations and the deep convective TTL temperature signal based on collocated CloudSat and COSMIC data [Paulik and Birner, 2012].…”

Role of deep convection on the tropical tropopause characteristics at sub-daily scales over the South India monsoon region

“…Among these, convective detrainment and the effect of overshooting convection on the heat balance of the TTL (Danielsen, 1993;Sherwood and Dessler, 2003;Randel and Jensen, 2013) remain rather unexplored. Several attempts have been made earlier to delineate the effects of tropical deep convection in modulating the TTL and the tropopause on day-to-day, monthly, seasonal, annual and inter-annual scales (Reid and Gage, 1996;Krishna Murthy et al, 1986;Kim and Dessler, 2004;Venkat Ratnam et al, 2005;Chae et al, 2010;Mehta et al, 2010;Paulik and Birner, 2012;Kumar et al, 2014;Parameswaran et al, 2003). However, the studies on tropopause at short time scales (day and less than a day) in relation to convection over land are sparse.…”