Xiaoyan Ma

Reassessment of satellite‐based estimate of aerosol climate forcing

Large uncertainties exist in estimations of aerosol direct radiative forcing and indirect radiative forcing, and the values derived from global modeling differ substantially with satellite-based calculations. Following the approach of Quaas et al. (2008; hereafter named Quaas2008), we reassess satellite-based clear- and cloudy-sky radiative forcings and their seasonal variations by employing updated satellite products from 2004 to 2011 in combination with the anthropogenic aerosol optical depth (AOD) fraction obtained from model simulations using the Goddard Earth Observing System-Chemistry-Advanced Particle Microphysics (GEOS-Chem-APM). Our derived annual mean aerosol clear-sky forcing (−0.59 W m−2) is lower, while the cloudy-sky forcing (−0.34 W m−2) is higher than the corresponding results (−0.9 W m−2 and −0.2 W m−2, respectively) reported in Quaas2008. Our study indicates that the derived forcings are sensitive to the anthropogenic AOD fraction and its spatial distribution but insensitive to the temporal resolution used to obtain the regression coefficients, i.e., monthly or seasonal based. The forcing efficiency (i.e., the magnitude per anthropogenic AOD) for the clear-sky forcing based on this study is 19.9 W m−2, which is about 5% smaller than Quaas2008s value of 21.1 W m−2. In contrast, the efficiency for the cloudy-sky forcing of this study (11 W m−2) is more than a factor of 2 larger than Quaas2008s value of 4.7 W m−2. Uncertainties tests indicate that anthropogenic fraction of AOD strongly affects the computed forcings while using aerosol index instead of AOD from satellite data as aerosol proxy does not appear to cause any significant differences in regression slopes and derived forcings.

Opposite Aerosol Index‐Cloud Droplet Effective Radius Correlations Over Major Industrial Regions and Their Adjacent Oceans

Abstract The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3 and the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA‐Interim reanalysis data from 2003 to 2016 are employed to study aerosol‐cloud correlations over three industrial regions and their adjacent oceans, as well as explore the impact of meteorological conditions on the correlations. The analysis focusing on liquid and single‐layer clouds indicates an opposite aerosol‐cloud correlation between land and ocean; namely, cloud effective radius is positively correlated with aerosol index over industrial regions (positive slopes), but negatively correlated over their adjacent oceans (negative slopes), for a quasi‐constant liquid water path. The positive slopes are relatively large under low lower‐tropospheric stability (LTS; weakly stable condition), but much weaker or even become negative under high LTS (stable conditions) and high liquid water path. The occurrence frequency of cloud top height (CTH) and LTS suggests that positive correlations are more likely corresponding to relatively high CTH and low LTS, while negative to low CTH and high LTS.

The influence of IMF clock angle on the cross‐section of the tail bow shock

We study effects of the interplanetary magnetic field (IMF) orientation on the terrestrial tail bow shock location and shape by using global MHD magnetosphere model and empirical bow shock models. It is shown that the tail bow shock cross section is well approximated by an ellipse with the direction of the major axis roughly perpendicular to the IMF clock angle direction. With the increasing IMF clock angle, the eccentricity of the bow shock cross section increases for northward IMF but decreases for southward IMF.

Ion mediated nucleation and anthropogenic aerosol indirect radiative forcing

A clear understanding of particle formation mechanisms is critical for assessing aerosol indirect radiative forcing (IRF) and associated climate feedback processes. Recent studies reveal the importance of ion-mediated nucleation (IMN) in generating new particles and cloud condensation nuclei (CCN) in the atmosphere. The IMN scheme has been implemented in two widely used community models (CAM5/MAM3 and GEOS-Chem/APM). Here we employ the two models to assess the effect of anthropogenic emissions on the aerosol IRF. Our model simulations, with new particle formation rates calculated by the IMN scheme, show a significant impact of anthropogenic emissions on global CCN abundance, cloud properties, and cloud radiative forcing. The total aerosol indirect radiative forcing based on CAM5/MAM3 is-1.81 W m−2. The first aerosol IRF based on GEOS-Chem/APM is −0.69 W m−2.