Representation of tropical deep convection in atmospheric models – Part 1: Meteorology and comparison with satellite observations

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)Correspondence to: M. Russo (maria.russo@atm.ch.cam.ac.uk) 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.

Lightning NO<sub>x</sub>, a key chemistry–climate interaction: impacts of future climate change and consequences for tropospheric oxidising capacity

“…Distributions of convective cloudtop height (CTH) (not shown) indicate a shift towards greater CTH under future climate change. For example, in CC8.5, mean CTH increases by 23.6 % (Maritime Continent), 9.3 % (Africa) and 4.6 % (South America) relative to Base, where the regions are defined as in Russo et al (2011). These increases in the depth of convection are consistent with rising tropopause heights (Fig.…”

“…Russo et al (2011) showed that although a high vertical model resolution is needed to match the vertical distribution of clouds to observations, a low horizontal resolution is sufficient to capture the geographical distribution.…”

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

“…By definition, the tracer mixing ratio at any location in the stratosphere equals the fraction of air which has left the monsoon anticyclone during the previous monsoon season (see Orbe et al, 2013). Initializing the air mass origin tracer in the UTLS part of the Asian monsoon avoids our results being affected by smallscale transport processes in the troposphere (e.g., convection), whose representation in global reanalysis data is uncertain (e.g., Russo et al, 2011). This choice of method is suitable to study the transport of air from the anticyclone, irrespective of where it originated at the surface.…”

Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

“…In the first paper Russo et al (2011), (hereafter R 2011), we evaluated the models' convection by comparison of modelled meteorological parameters to satellite observations. The main findings of this analysis were as follows: the frequency and distribution of cloud top heights reaching above 15 km varied largely between different models; the models represented reasonably well the average values and observed seasonal cycle of precipitation rates (used as a proxy for convection) for continental regions, however larger discrepancies with observations were found for the Maritime Continent, an important region for convective transport.…”