Case study of longwave contribution to dust radiative effects over East Asia

Dust Radiative Effect Characteristics during a Typical Springtime Dust Storm with Persistent Floating Dust in the Tarim Basin, Northwest China

A special topography and ultra-high atmospheric boundary layer conditions in the Tarim Basin (TB) lead to the unique spatial–temporal distribution characteristics of dust aerosols. A typical dust storm with persistent floating dust over the TB from 27 April to 1 May 2015 was used to investigate the characteristics of the dust radiative effect using the Weather Research and Forecasting Model with Chemistry (WRF-Chem). Based on reasonable evaluations involving in situ sounding observations, as well as remotely sensed MODIS observations of meteorology, dust aerosols, and the ultra-high atmospheric boundary layer, the simulation characterized the complete characteristics of the dust direct radiative effect (DDRE) during the dust storm outbreak stage and persistent floating dust stage over the TB. During the daytime, the shortwave (SW) radiative effect heated the atmosphere and cooled the land surface (SUR), whereas the longwave (LW) radiative effect had the opposite effect on the TB. Regarding low-level dust, the LW radiative effect was greater than the SW DDRE in the atmosphere, while for high-level dust the situation was reversed. During the nighttime, the LW DDRE at the top of the atmosphere (TOA), at the SUR, and in the atmosphere was less than that during the daytime, when the DDRE at the SUR was the most significant. In contrast to the daytime, the near-surface dust aerosols exerted an LW warming effect in the atmosphere during the nighttime; however, the dust LW radiative effect had a cooling effect from above a 100 m altitude until the top of the dust layer. In contrast, the DDRE heating rate peaked at the top of the dust layer within the TB. The event-averaged net DDRE was 0.53, −5.90, and 6.43 W m−2 at the TOA, at the SUR, and in the atmosphere over the TB, respectively. The dust SW radiative effect was stronger than the dust L4W radiative effect over the TB at the SUR and in the atmosphere. Moreover, the DDRE at the TOA was weaker than that at the SUR. Overall, the study revealed noteworthy radiative effect features of dust aerosols during typical dust storms with persistent floating dust over the TB.