Abstract
Abstract. Fast convective transport in the tropics can efficiently redistribute water vapour and pollutants up to the upper troposphere. In this study we compare tropical convection characteristics for the year 2005 in a range of atmospheric models, including numerical weather prediction (NWP) models, chemistry transport models (CTMs), and chemistry-climate models (CCMs). The model runs have been performed within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The characteristics of tropical convection, such as seasonal cycle, land/sea contrast and vertical extent, are analysed using satellite observations as a benchmark for model simulations. The observational datasets used in this work comprise precipitation rates, outgoing longwave radiation, cloud-top pressure, and water vapour from a number of independent sources, including ERA-Interim analyses. Most models are generally able to reproduce the seasonal cycle and strength of precipitation for continental regions but show larger discrepancies with observations for the Maritime Continent region. The frequency distribution of high clouds from models and observations is calculated using highly temporally-resolved (up to 3-hourly) cloud top data. The percentage of clouds above 15 km varies significantly between the models. Vertical profiles of water vapour in the upper troposphere-lower stratosphere (UTLS) show large differences between the models which can only be partly attributed to temperature differences. If a convective plume reaches above the level of zero net radiative heating, which is estimated to be ~15 km in the tropics, the air detrained from it can be transported upwards by radiative heating into the lower stratosphere. In this context, we discuss the role of tropical convection as a precursor for the transport of short-lived species into the lower stratosphere.
Highlights
Tropical deep convection is recognised as an important atmospheric feature acting on the global water cycle and chemical composition of the atmosphere
We focus on surface precipitation rates and cloud top height to assess how well current models can represent tropical convection characteristics such as spatial patterns and vertical extent
The lack of a marked minimum in the seasonal cycle sive measurement campaigns aimed at understanding tropical convection, its interactions with aerosols and chemical species, and its impact on transport of pollutants and water vapour to the upper troposphere-lower stratosphere (UTLS) (Pommereau et al, 2007; Vaughan et al, 2008; Cairo et al, 2010)
Summary
Tropical deep convection is recognised as an important atmospheric feature acting on the global water cycle and chemical composition of the atmosphere. Because of differences in horizontal and vertical resolution, and in the treatment of advection and convection, models are likely to provide different locations, frequency and vertical extent of tropical convective events This can lead to differences in the convective transport of tracers, possibly affecting air composition in the free troposphere and the TTL at the global scale. CTMs use 3-D wind fields from an independent model, usually operational analyses and/or forecasts, to perform large-scale transport ( known as advection) For these models the fast vertical transport by deep convection can be either diagnosed from the convective fluxes provided by the independent model or recalculated by the CTM’s own convection parameterisation scheme. We focus on surface precipitation rates and cloud top height to assess how well current models can represent tropical convection characteristics such as spatial patterns and vertical extent.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 call
