Central Asia is surrounded by arid and desert regions, for example the desiccating Aral Sea or the Taklamakan desert. Therefore, Tajikistan is affected regularly by dust events. It is essential to characterize the microphysical and optical properties, the spatial and temporal distribution, as well as origin of the dust over Tajikistan in order to assess its effect on the regional climate, since Central Asia is a place highly vulnerable to climate change (UNDP, 2011). A tragic example for that are the glaciers of Tajikistan, which have shrunk about a third in the last century (Kayumov, A.). These glaciers are an important water resource since they feed rivers like Syrdarya and Amudarya, which in turn are of high ecological and economical value for the whole Central Asian region. Furthermore, the Central Asian glaciers can not only be affected indirectly by temperature effects of aerosols, but also directly by dust deposits on the glacier surfaces altering the glacier’s albedo (Chen, 2006). The dust is transported from its sources to the deposition regions via the atmosphere. Almost no measurements of these transport processes are available, especially no measurements of the vertical distribution and the types of particles above Tajikistan. But this knowledge is a necessary prerequisite to address possible climate effects of the air-transported dust. This lack of knowledge motivated the CADEX project to perform measurements of altitude ranges, properties, and aging of atmospheric particles along their transport route, and the possible radiation impact of (dust) particles above Tajikistan.
The GFZ-Potsdam is running a ground-based dust monitoring program at the northern slopes of the Tien Shan at an altitude of 1740 m about 25 kilometres south of the city of Bishkek (Schettler et al., 2014). The monitoring program, which was started in summer 2010, primarily aims on a better understanding of the palaeo-climatic interpretation of aeolian components in Asian lake sediments.
Dust transport across the Eurasian continent is highly influenced by seasonal and inter-annual changes in the Northern hemispherical circulation and orographic settings determined by the Central Asian High Mountain Belt. The co-operation between the Institute for Tropospheric Research Leipzig (TROPOS) and the GeoForschungs Zentrum Potsdam (GFZ) in the framework of the CADEX project (Central Asian Dust Experiment) offers the opportunity to synthesize monitoring data from two measuring sites: The north-eastern part of the Central Asian High Mountain Belt, south of the Alai mountain range (station 1) and the northern margin of the Tien Shan (station 2), 900 kilometre northeast of station 1. We expect to achieve a better understanding of the dust transport by the zonal westerlies towards the Pacific Ocean.
For the first time, a joint Soviet-American research group did extensive dust research in Tajikistan in 1989 (Golitsyn and Gillette, 1993). They characterized the chemical and physical properties of mineral dust collected in dust storms as well as the vertical dust distribution by aircraft measurements. A dust storm during the campaign period caused very high aerosol optical depths, so that Dushanbe Airport even had to be closed due to low visibility for one day in September 1989 (Pachenko, 1993). Among other things, it was found that the iron content of Central Asian dust is lower than, for example, of Saharan dust (Gomes and Gillette 1993), which is reflected in a less absorbing refractive index (Sokolik, 1993). Since this early field campaign, there has been no further attempt to quantify the microphysical and optical properties of mineral dust over Tajikistan. As this information, however, is crucial for active remote sensing and the differences in the dust optical properties are important to be considered in climate predictions, the CADEX campaign is dedicated to continue the research on Central Asian dust in Tajikistan with up-to-date techniques.
- Vertically resolved measurements of mineral dust
- Investigation of the measured intensive particle properties; particle type characterization of the dust over Tajikistan
- Statistical analysis of the measured data according to the dust’s origin via analysis of trajectories
- What are the differences of the dust optical properties when coming from local or remote sources? Does the lidar ratio change depending on that?
- Closure studies to atmospheric mineral dust: vertical-resolved results versus columnar-integrated results
- Aerosol-cloud interactions: how does mineral dust affect clouds over Tajikistan?
- How can regional modelling of atmospheric transport of mineral dust in the Central Asia region provide a spatial and temporal context to the measurements?
- What is the impact of Central Asian dust aerosol on the radiation budget and how does it affect atmospheric dynamics?
- How can the measurements help to evaluate and improve the modelled estimates of radiative effects of dust?
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