Interplanetary assessment of dust-emission processes using active remote sensing on Earth and Mars

Wind-blown dust is among the most common aerosol types in Earth´s atmosphere.

It impacts the radiative energy budget, atmospheric chemistry, and the distribution of micro-nutrients to terrestrial and aquatic ecosystems, thus modulating climate, air quality, and the carbon cycle.

Yet predicting the spatial and temporal variability of dust concentrations is impaired by large uncertainties in the description of wind-driven emission processes.

To address these uncertainties we propose a comparative, interplanetary analysis of remote sensing observations from Earth and Mars.This idea will serve two main purposes.

Since we investigate emission processes in different planetary environments, we will focus on fundamental physical processes that govern dust emissions.

Comparing these effects on Earth and Mars will help us in identifying the dominant physical mechanisms in wind-driven emission of dust particles.

This will be instrumental in devising more accurate parametrisations of wind-blown dust emissions that can be used in large-scale models. By starting our investigation with wind-blown dust on Mars, we will first consider a simple system.

Complicating effects that are typical for Earth, such as the presence of different types of aerosols, varying amounts of water vapour, clouds, or varying surface types and soil moisture are of minor importance on Mars.

Thus, Mars will serve as a laboratory for studying dust emissions, which will help us to better understand how to treat these processes in the much more complex terrestrial system.For Mars, we will analyse lidar observations together with meteorological data, both from the Phoenix lander. The retrieved aerosol size and concentration will be confronted with a physical-based dust-emission model.

For Earth, we will exploit lidar data from polar orbiting satellites, namely, CALIOP/CALIPSO and ATLID/EarthCARE, to evaluate the emission model for different geographic regions and seasons.

Our project idea involves two major methodical novelties.The linear depolarization ratio (LDR) product from CALIPSO has, so far, only been used to derive a rough qualitative classification of the aerosol types.

In this study we will develop an inverse model using a recently developed aerosol-optics model for dust (Kahnert et al., 2020), which is capable of reproducing the size-dependence of LDR.

Thus we will attempt to exploit LDR in a quantitative size-retrieval algorithm, making use of LDR measurements from both CALIPSO and EarthCARE.

This will be a major step toward building a capacity to better exploit polarisation measurements in Earth observation and Astronomy.The Phoenix lidar data are presently only available as vertically-resolved voltage readings. We will process these level-0 data to obtain level-1 products of the backscattering and extinction coefficients.

A retrieval algorithm will be developed to obtain aerosol size and number concentration. The resulting output will be made freely available.