High-Resolution Image

In winter, snow is often lifted from the surface by strong winds at a height of several meters or more. In meteorology, it is called blowing snow and reported as ‘BLSN’ in observations. In a populated area, blowing snow can seriously affect people’s life by reducing visibility to a hazardous level. Panel 1 shows an example of blowing (or drifting) snow that makes driving difficult. For climate research, blowing snow has also a significant effect. Because of its high frequency of occurrence in winter in the polar regions, it is an important atmospheric phenomenon. For example, blowing snow redistributes snow thus affecting the mass balance of polar ice sheets, which is a critical component of the Earth's climate system. However, over the years, blowing snow observations over the ice sheets have been limited to ground-based observations and are rare in quantity because of harsh conditions.

Given the importance of blowing snow for understanding the Earth's climate system, observations on a global scale are crucial. This can only be achieved through satellite observations. Currently, scientists at the NASA/Goddard Space Flight Center Laboratory for Atmospheres are working on the development of algorithms to retrieve blowing snow properties using data from NASA’s satellites, such as the Ice, Cloud and land Elevation Satellite (ICESat), the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and the Aqua satellite. Panels 2a, 2b and 2c illustrate a blowing snow event observed from space. Panel 2a is the lidar backscatter image from CALIPSO for a pass over Antarctica showing the presence of blowing snow. The data at and below the ground has been blacked out, leaving the signal from the blowing snow apparent in the right third of the image. Lower panels (2b and 2c) are images for the same event but observed from the Moderate Resolution Imaging Spectroradiometer (MODIS), on board the Aqua satellite. These images show that even though blowing snow may not be well observed from the visible channel (Panel 2b), it can be detected by using the shortwave infrared channel at 2.1 µm. At this wavelength, blowing snow particles are much smaller than snow grains on the ground and hence absorb less solar radiation. As a result, areas affected by blowing snow will be brighter than the surrounding surface. Constructing a false color composite image using the 2.1 µm, 2.1 µm and 0.84 µm as red, green and blue, respectively, increases the contrast between the blowing snow and the surface even more (Panel 2c).

Submitted by Yuekui Yang (UMBC/GEST), Stephen Palm (SSAI) and Alexander Marshak (NASA/GSFC).

Panel 1 Image Credit: http://s218.photobucket.com/albums/cc278/KegRiver/Winter%20Images/?action=view¤t=DSCF2363.jpg