The edge intensification of ITCZ convection

Abstract:

Tropical precipitation in the climatological map is most intense at the heart of ITCZ, but this is not always true in instantaneous snapshots. It is not rare that precipitation is amplified along the ITCZ edge, rather than at its center, as depicted in the figure attached, where satellite microwave measurements of surface precipitation (yellow to red, [mm/h]) and column water vapor (green to blue, [mm]) are plotted together. A similar edge intensification of convection is known for idealized RCE simulations (Windmiller and Hohenegger, 2019). Mapes et al. (2018) revealed a sinuous tropical margin sharply separating the moist and dry air masses, which implies dynamic processes resembling the convection intensification at the ITCZ boundaries. Despite the growing body of evidence, the physical mechanism behind the edge intensification has yet to be clarified.

In this study, a variety of satellite observations of CWV and precipitation (AMSR-E) and radiation (CERES) as well as the wind field from the ERA5 dataset are analyzed to investigate the behavior of moist convection and atmospheric dynamics at the ITCZ edges. The cases with edge intensification identified in an objective manner are contrasted against those without in light of the local atmospheric energy imbalance. Among possible hypotheses for the edge intensification is the interplay of the cloud radiative effects and congestus-mode dynamics that could give rise to a rapid moistening and hence invigorate convection (Masunaga and Bony, 2018).

References:

Mapes, B. E., E.-S. Chung, W. M. Hannah, H. Masunaga, A. J. Wimmers and C. S. Velden, 2018: The meandering margin of the meteorological moist Tropics, Geophys. Res. Lett., 45, 1177-1184. doi:10.1002/2017GL076440

Masunaga, H. and S. Bony, 2018: Radiative invigoration of tropical convection by preceding cirrus clouds, J. Atmos. Sci., 75, 1327-1342. doi:10.1175/JAS-D-17-0355.1

Windmiller, J. M., & Hohenegger, C. 2019: Convection on the edge. J. Adv. Model. Earth Syst., 11, 3959-3972, 10.1029/2019MS001820