Subseasonal variability of mesoscale convective systems over the tropical northeastern Pacific

Abstract

Mesoscale Convective Systems (MCS) properties during large‐scale easterly and westerly regimes of the low‐level winds over the tropical northeastern Pacific (TEP) are analysed during boreal summers of years 2012–2014. East of 120°W, two regions located north and south of 10°N present different sensitivity of the MCS properties to the zonal wind regime. Long‐lasting and large MCS are favoured during the westerly regime over the northern region, while more numerous MCS, but with a steady lifetime distribution, are triggered during the easterly regime over the southern part of the Intertropical Convergence Zone (ITCZ). For long‐lasting MCS (lifetime longer than 10 h), the moderate low‐level wind shear conditions during the westerly regime are associated with larger MCS covering longer distances. The MCS cold cloud cover and the MCS lifetime tend to locally increase with the moisture of the mid‐troposphere. Conversely, the TEP area west of 120°W becomes less favourable to MCS development during the low‐level westerly regime, in accordance with the diminution of rainfall observed locally.