Modulations of aerosol impacts on cloud microphysics induced by the warm Kuroshio Current under the East Asian winter monsoon

Abstract

In our previous aircraft observations, the possible influence of high sea surface temperature (SST) along the Kuroshio Current on aerosol‐cloud interactions over the western North Pacific was revealed. The cloud droplet number concentration (Nc) was found to increase with decreasing near‐surface static stability (NSS), which was evaluated locally as the difference between the SST and surface air temperature (SAT). To explore the spatial and temporal extent to which this warm SST influence can be operative, the present study analyzed Nc values estimated from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite measurements. The comparison of the local Nc values between the high and low SST − SAT days revealed a marked increase in Nc (up to a factor of 1.8) along the Kuroshio Current in the southern East China Sea, where particularly high SST − SAT values (up to 8 K) were observed in winter under monsoonal cold air outflows from the Asian Continent. This cold airflow destabilizes the atmospheric boundary layer, which leads to enhanced updraft velocities within the well‐developed mixed layer and thus greater Nc. The monsoonal northwesterlies also bring a large amount of anthropogenic aerosols from the Asian continent that increase Nc in the first place. These results suggest that the same modulations of cloud microphysics can occur over other warm western boundary currents, including the Gulf Stream, under polluted cool continental airflows. Possibilities of influencing the cloud liquid water path are also discussed.

Observing severe precipitation near complex topography during the Yilan Experiment of Severe Rainfall in 2020 (YESR2020)

“…Previous investigations of precipitation processes in marine stratocumulus have been mainly focused on the formation of drizzle and light rain associated with the changes in cloud microphysics and dynamics, predominantly for the persisting low cloud decks over the northeastern and southeastern Pacific (Wood, 2012). Over the northwestern Pacific, where the East Asian winter monsoon is active, transient marine stratocumulus clouds are formed in the regions where the near‐surface northeasterly monsoonal wind is enhanced by the synoptic systems (Koike et al ., 2012; Koike et al ., 2016; Liu et al ., 2016; Chang, Chen, and Chen, 2021; Wu and Chen, 2021), as shown in the example in Figure 1a. With the presence of the marine stratocumulus, the boundary layer is moistened through enhanced vertical mixing (Lilly, 1968).…”