Theory and Application of an Observational Method to Estimate the Direct Radiative Effect of Mineral Dust in Southeastern California
Abstract
Mineral dust, the largest aerosol by mass, directly affects the Earth's Energy Budget by scattering and absorbing shortwave (SW) and longwave (LW) radiation. This effect is commonly estimated from radiative transfer models as the direct radiative effect. The dust direct radiative effect estimated from radiative transfer models is uncertain because of the many degrees of freedom in the relevant optical properties of dust, which change as a function of space and time. In order to avoid the uncertainty in estimating the dust direct radiative effect from radiative transfer models, some studies have observationally estimated the forcing efficiency of dust (the direct radiative effect normalized by the aerosol optical depth) from satellite and in-situ observations and retrievals. However, uncertainties in this observational method arise because of instrument and retrieval errors, errors due to the sample size, and assumptions made about the relationship between dust and other atmospheric constituents. In this study we describe a theory for estimating the surface and top of the atmosphere SW forcing efficiency of dust using a modified version of this observational method that accounts for the effect of water vapor on the surface and top of the atmosphere SW forcing efficiency of dust. We apply both methods to satellite and in-situ observations over a new research site in extreme southeastern California. We find that depending on the sign of the correlation coefficient between dust and water vapor, there is an underestimation and overestimation of the magnitude of the dust surface and top of the atmosphere SW forcing efficiency and depending on the magnitude of the correlation, significant biases in the dust surface and top of the atmosphere SW forcing efficiency arise. We also find that after applying the modified observational method, biases in this parameter drastically decrease.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA007.0007K
- Keywords:
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- 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