One of the most challenging research topics in atmospheric science is studying the climate of the polar regions. Understanding the cloud process is a key in understanding the polar climate system due to the complex interactions between cloud and other processes, e.g. radiation and snow/ice-covered surface. Correct simulation of such interactions requires accurate observations of cloud characteristics and their changes. However, observing the cloud in the polar regions faces serious challenges from both in-situ and passive satellite observations, which causes large uncertainties in the observed polar cloud characteristics. These uncertainties hamper our understanding of the mean state of the polar climate. Polar cloud is not well represented in either global or regional climate models, which contributes to the large uncertainties in projecting future climate change in the polar regions.

The recent availability of observations from CloudSat and Cloud-Aerosol lidar and Infrared Pathfinder Satellite Observations (CALIPSO) provide an unprecedented opportunity to paint a complete picture of cloud characteristics in the polar regions. As the first step, spatial, temporal, and vertical distributions of the Arctic cloud macrophyscial characteristics are presented based on four-year observations from combined CloudSat and CALIPSO level-2 product 2B-GEOPROF-Lidar. These macrophyscial characteristics include total, low-level, middle-level, high-level, single-layer, and multi-layer cloud frequencies, and histogram distributions of cloud top height, cloud bottom height, top cloud thickness, and bottom cloud thickness. The total Arctic cloud frequency from 2B-GEOPROF-Lidar is compared to the cloud amount from the Moderate Resolution Imaging Spectroradiometer (MODIS). Results show the differences of these two cloud amounts are a function of surface sea ice concentration.