Profiling of Saharan dust and biomass-burning smoke with multiwavelength polarization Raman lidar at Cape Verde

Published under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported LicenseExtensive lidar measurements of Saharan dust and biomass-burning smoke were performed with one airborne and three ground-based instruments in the framework of the second part of the SAharan Mineral dUst experiMent (SAMUM-2a) during January and February of 2008 at Cape Verde. Further lidar observations with one system only were conducted during May and June of 2008 (SAMUM-2b). The active measurements were supported by Sun photometer observations. During winter, layers of mineral dust from the Sahara and biomass-burning smoke from southern West Africa pass Cape Verde on their way to South America while pure dust layers cross the Atlantic on their way to the Caribbean during summer. The mean 500-nm aerosol optical thickness (AOT) observed during SAMUM-2a was 0.35 +/- 0.18. SAMUM-2a observations showed transport of pure dust within the lowermost 1.5 km of the atmospheric column. In the height range from 1.5 to 5.0 km, mixed dust/smoke layers with mean lidar ratios of 67 +/- 14 sr at 355 and 532 nm, respectively, prevailed. Within these layers, wavelength-independent linear particle depolarization ratios of 0.12-0.18 at 355, 532, and 710 nm indicate a large contribution (30-70%) of mineral dust to the measured optical properties. Angstrom exponents for backscatter and extinction of around 0.7 support this finding. Mean extinction coefficients in the height range between 2 and 4 km were 66 +/- 6 Mm(-1) at 355 nm and 48 +/- 5 Mm(-1) at 532 nm. Comparisons with airborne high-spectral-resolution lidar observations show good agreement within the elevated layers. 3-5 km deep dust layers where observed during SAMUM-2b. These layers showed optical properties similar to the ones of SAMUM-1 in Morocco with a mean 500-nm AOT of 0.4 +/- 0.2. Dust extinction coefficients were about 80 +/- 6 Mm(-1) at 355 and 532 nm. Dust lidar ratios were 53 +/- 10 sr at 355 and 532 nm, respectively. Dust depolarization ratios showed an increase with wavelength from 0.31 +/- 0.10 at 532 nm to 0.37 +/- 0.07 at 710 nm.Peer reviewe

Implementation of PLACE Land Surface Hydrology in MM5

This paper presents the implementation scheme for coupling the land surface hydrology component of PLACE (Parameterization for Land-AtmosphereCloud Exchange) model [Wetzel and Boone, 1995] with MM5 version 1. This land surface model is one of the participants of PILPS [Project for Intercomparison of Land-Surface Parameterization Schemes

Impact of Saharan Dust on Ocean Surface Wind Speed Derived by Microwave Satellite Sensors

In the present paper ground truth and remotely sensed datasets were used for the investigation and quantification of the impact of Saharan dust on microwave propagation, the verification of theoretical results, and the validation of wind speeds determined by satellite microwave sensors. The influence of atmospheric dust was verified in two different study areas by investigations of single dust storms, wind statistics, wind speed scatter plots divided by the strength of Saharan dust storms, and wind speed differences in dependence of microwave frequencies and dust component of aerosol optical depth. An increase of the deviations of satellite wind speeds to ground truth wind speeds with higher microwave frequencies, with stronger dust storms, and with higher amount of coarse dust aerosols in coastal regions was obtained. Strong Saharan dust storms in coastal areas caused mean relative errors in the determination of wind speed by satellite microwave sensors of 16.3% at 10.7 GHz and of 20.3% at 37 GHz. The mean relative errors were smaller in the open sea area with 3.7% at 10.7 GHz and with 11.9% at 37 GHz

Microlidar observations of biomass burning aerosol over Djougou (Benin) during African Monsoon Multidisciplinary Analysis Special Observation Period 0: Dust and Biomass-Burning Experiment

International audienceMicrolidar observations have been performed at the Djougou-Nangatchori site in northern Benin during the African Monsoon Multidisciplinary Analysis (AMMA) Special Observation Period 0 in the dry season, combined with the Dust and Biomass-Burning Experiment (DABEX) from mid-January to mid-February 2006. During the dry season, the Djougou area is a region where biomass burning aerosols are heavily produced from agriculture fires. The aerosol vertical distribution is also controlled by dynamics, and the penetration of the winter monsoon flux to the north and northern winds bringing mineral dust to the South leads to a frontal discontinuity location close to Djougou latitude. During the early dry season, the aerosol vertical distribution was observed to be structured in two layers, the lower being the boundary layer reaching altitudes up to 2 km and the upper one corresponding to the trade wind layer extending up to 5 km. Lidar data are used to retrieve the time evolution and vertical profile of extinction and discuss transport processes during the period analyzed. As the monsoon flux during the dry season is steadily progressing to the north but also moving back and forth according to shorter timescale forcings, biomass burning particles are transported from the boundary layer into the upper troposphere. This transport has a strong impact on the distribution of aerosol particles on the vertical, and extinction values larger than 0.3 km−1 have been retrieved at altitudes close to 3 km. A particular event of biomass burning air mass outbreak associated with a synoptic forcing is studied, where satellite observations are used to discuss observations of biomass burning particles over Djougou and at the regional scale

Introduction

Mineral dust is a key player in the Earth system with important impacts on the global energy and carbon cycles, acting on timescales of minutes to millennia. Megatons of dust are lifted each year into the atmosphere by strong near-surface winds over the world's arid regions. Such winds can be generated by short-lived small-scale dust devils, cold outflow from thunderstorms up to continental-scale dust storms. The tiny dust particles can be lifted to great heights and transported thousands of kilometres across the globe. Once airborne, dust affects radiation and clouds and thereby also precipitation. Dust also alters chemical processes in the atmosphere and deteriorates air quality and visibility for aviation. Dust is removed from the atmosphere by gravitational settling, turbulence or precipitation. Deposition on plants, snow and ice changes the amount of reflected solar radiation. Iron and other nutrients contained in dust fertilise both terrestrial and marine ecosystems. Dust deposits in glaciers, soils and ocean or lake sediments constitute an important archive of past environmental changes. For the first time, this book gives a detailed account of the state of the art in the fascinating, highly interdisciplinary and dynamically evolving area of dust research including results from field campaigns, laboratory, aircraft, satellite, modelling and theoretical studies. This chapter gives a short introduction into the topic, placing several recent developments in dust research into a historical context