Verifying an Observational Method to Estimate the Direct Radiative Effect of Mineral Dust in the Sahara Desert
Abstract
Mineral dust directly affects the climate system by reflecting and absorbing incoming shortwave (SW) radiation and absorbing and emitting longwave (LW) radiation. Typically, the magnitude of this effect, the direct radiative effect (DRE) of dust, is quantified from radiative transfer models. This modeling method, however, contains large uncertainties due to its large number of spatial and temporal dependent degrees of freedom: dust size distribution, shape, single scatter albedo, asymmetry parameter, extinction coefficient, and, for LW radiation, vertical distribution. In order to avoid the pitfalls associated with estimating the DRE of dust from this modeling method, other studies used an observational (OBS) method that incorporated both in-situ and satellite observations to estimate the forcing efficiency (FE) of dust (the normalization of the DRE with aerosol optical depth); however, the OBS method still has large uncertainties. Our goal for this study is to verify the OBS method and to estimate the uncertainty of the SW FE by applying the OBS method to satellite observations and the outputs of a hierarchy of radiative transfer models. We find that the dust SW FE estimated from the OBS method is biased due to the presence and variability of other atmospheric constituents. Further, we find that the uncertainty of the dust SW FE varies with the presence and variability of these constituents and the number of observations used in the estimation. We describe an updated method to estimate the dust SW FE that corrects for biases caused by these other constituents and show preliminary results found when applying this updated methodology to satellite observations and recently acquired in-situ observations from a new research field site in Southern California.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A33C..04K
- Keywords:
-
- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 1622 Earth system modeling;
- GLOBAL CHANGE