Datensatz

Zusammenfassung

Convective downdraft (CD) produced by vigorous deep cumulus convection not only disturbs the atmospheric boundary layer (BL) air around the existing convection to trigger new convection, but also cools the BL to make the atmosphere more stable. It is thus important to estimate the CD mass flux for quantitative understanding of the influence of the convection on large-scale conditions. In order to estimate the CD mass flux and understand its variability, we analyze in situ observation performed onboard Research Vessel Mirai during her 9 cruises over the tropical deep convective regime, including tropical Western North Pacific, Maritime Continent, and tropical Indian Ocean, with a total of nearly 250 days. We adopt a method proposed by Yokoi and Katsumata (2022, JAS, 781-792), which estimates the CD mass flux through the BL top from surface meteorology and upper-air soundings by considering BL heat and moisture budges. We then compare the estimated CD mass flux with measures of convective activity around the vessel obtained by a ship-borne C-band weather radar and onboard rain gauge. We find that the CD mass flux exhibits positive and significant correlations with radar-echo coverage and precipitation mass flux in day-to-day and intraseasonal time scales, and try to estimate a ratio of the CD mass flux to precipitation mass flux. We also estimate to what extent the CD consumes BL moist static energy supplied by surface heat flux, under the BL quasi equilibrium approximation.