Abstract
Abstract. A tropical channel version of the Weather Research and Forecasting (WRF) model is used to investigate the radiative impacts of upper tropospheric clouds on water vapor in the tropical tropopause layer (TTL). The WRF simulations of cloud radiative effects and water vapor in the upper troposphere and lower stratosphere show reasonable agreement with observations, including approximate reproduction of the water vapor "tape recorder" signal. By turning on and off the upper tropospheric cloud radiative effect (UTCRE) above 200 hPa, we find that UTCRE induces a warming of 0.76 K and a moistening of 9% in the upper troposphere at 215 hPa. However, UTCRE cools and dehydrates the TTL, with a cooling of 0.82 K and a dehydration of 16% at 100 hPa. The enhanced vertical ascent due to UTCRE contributes substantially to mass transport and the dehydration in the TTL. The hydration due to the enhanced vertical transport is counteracted by the dehydration from adiabatic cooling associated with the enhanced vertical motion. UTCRE also substantially changes the horizontal winds in the TTL, resulting in shifts of the strongest dehydration away from the lowest temperature anomalies in the TTL. UTCRE increases in-situ cloud formation in the TTL. A seasonal variation is shown in the simulated UTCRE, with stronger impact in the moist phase from June to November than in the dry phase from December to May.
Highlights
Water vapor in the stratosphere plays an important role in the stratospheric radiative budget and chemistry (e.g. Fueglistaler et al, 2009, and references therein)
It is widely accepted that the entry of water vapor into the stratosphere is primarily regulated by the interaction of mass transport and dehydration in the tropics
The Weather Research and Forecasting (WRF) CTRL simulation (Fig. 1b) captures seasonal variations of water vapor in the tropical tropopause layer (TTL), albeit with a smaller magnitude of the anomalies compared to the Microwave Limb Sounder (MLS) data
Summary
Water vapor in the stratosphere plays an important role in the stratospheric radiative budget and chemistry (e.g. Fueglistaler et al, 2009, and references therein). The radiative effect of cirrus clouds is proposed to be a likely mechanism to accelerate the mass transport from the troposphere to the stratosphere (Corti et al, 2005; 2006; Huang and Su, 2008; Tzella and Legras, 2011) Another debate exists because the entry of stratospheric water vapor is drier than the expected water vapor saturation mixing ratio with respect to zonal-mean temperature in the TTL (Newell and Gould-Stewart, 1981). Dinh et al (2010) suggested that radiative heating of subvisible cirrus has a potential to dehydrate the TTL by conversion of water vapor into ice through convergence of dry air, without involving adiabatic cooling associated with external large-scale uplift. A 3-D tropical channel model is used in this study to investigate the radiative impacts of upper tropospheric (above 200 hPa) clouds on the TTL water vapor.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
