Séminaire
In the tropics, mesoscale convective systems (MCS) cause significant surface warming from their extensive anvils and heavy rainfall from their cores. But the adjustment of these radiative and hydrological impacts according to the phase of the El Nino Southern Oscillation remains unclear. To understand such changes, we construct tropical climatologies of MCS occurrence, lifetime, and extent between 1983 and 2008 using an ISCCP convective tracking database and differentiating for El Nino or La Nina months. System frequency, duration, and size overlap increase dramatically in regions of anomalously high sea surface temperature and convective available potential energy during El Nino. With an MCS "growth metric", we show that horizontal spreading of MCS relative to their vertical deepening is largest in these same regions. This thermodynamic story can be modulated by the dynamics in a particular region, illustrated by the shear profiles and convergence in different subdomains. Whether their explanation is thermodynamic or dynamic, MCS structural changes are reflected in outgoing longwave radiation anomalies (OLRa) and varying responses of precipitation accumulation and intensity (PA). In particular, we see that more extensive systems during El Nino induce more negative OLRa and larger PA.
bruno.deremble@ens.fr