Arctic boundary layer stratus, which tends to be mixed-phase, is a commonly observed cloud type in the arctic region and it has an important role in the surface radiation budget. However, due to the harsh environment, it is hard to collect cloud in-situ observation data in this region. This lack of data limits our knowledge of microphysical properties of Arctic boundary layer stratus and makes it difficult to evaluate its impacts on the surface radiation budget. During fall 2004, Mixed-Phase Arctic Cloud Experiment (MPACE) was executed in the North Slope Alaska (NSA) region, providing both cloud in-situ measurement and surface irradiance observation simultaneously. This experiment makes further studies of Arctic boundary layer stratus possible.
First, cloud microphysical properties such as cloud phase, liquid water content, ice water content, cloud particle size distribution and cloud particle shape are derived using cloud in-situ data. Then, small cloud particle shape and phase are studied. Further, boundary level stratus with different vertical structures, single-layer or multi-layer, are compared and contrasted to determine whether the cloud microphysical properties of these two types are different.
By using the cloud vertical structure derived from the in-situ data along with other inputs to radiative transfer models, such as atmospheric sounding profile and surface albedo, it becomes possible to simulate the surface irradiance more realistically and to compare the simulated surface irradiance with the surface observation. Also, preliminary results reveal that single-layer status is more influenced by supercooled water droplets while multi-layer stratus is more influenced by ice crystals during MPACE. This variation of cloud phase with cloud vertical structure can be used to evaluate the radiative forcing introduced by the cloud phase variation in Arctic boundary layer stratus.
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