Reduce the uncertainty in dust aerosol IN effect on cloud top temperature

Abstract:

Certain atmospheric aerosols, such as mineral dust, can act as effective ice nuclei (IN) to initiate ice formation at relatively warm temperatures. Evidences have been reported from satellite observations that dust-laden ice clouds tend to have warmer cloud top temperature (CTT) comparing to their dust-free counterparts. However, large uncertainties exist due to concerns that if the observed clouds really interacted with dust and how to untangle the dynamic related variations of CTT. Here we present an example to reduce such uncertainties by combining passive, active satellite observations and WRF model simulations of a typical event of dust invading mesoscale cyclone system on April 25^th 2008 in China. We first clearly identified the cloud-dust interactions based on 3-D satellite measurements and modeled wind field. Two heavy dust-laden areas (HD) and two light dust-laden areas (LD) were selected for comparison study. Satellite retrievals shown the probability distribution function (PDF) of CTT in HD shifted ~14^oC to the warmer end comparing to that in LD. Meanwhile, the dynamic-only effect was quantified with model simulation: without accounting any dust aerosol effect, the CTT in HD still shifted ~8^oC to the warmer end comparing to that in LD, most probably due to effects of warm and dry air mass accompanied with dust. We therefore concluded, in this case, the IN effect contributes about 42.8% to the total satellite observed warming of cloud CTT. This study suggested a new method to reduce the uncertainties in satellite observational study of aerosol indirect effect.