Cloud Observations and Atmospheric Processes
Clouds and Climate
Clouds play a very important role in the climate sciences. They modulate incoming solar radiation (visible and near infrared) by reflecting about 30% of the total amount of sunlight reaching Earth. NASA instruments that observe the solar spectrum include but are not limited to the Moderate Resolution Imaging Spectroradiometer (MODIS), the Multiangle Imaging SpectroRadiometer (MISR), and Clouds and the Earth’s Radiant Energy System (CERES), which provide vital information on how clouds affect incoming solar radiation and the Earth’s climate response to it.
Clouds also modulate the outgoing longwave (infrared) radiation emitted by Earth’s surface and atmosphere. NASA instruments that observe portions of the infrared spectrum are the Atmospheric Infrared Sounder (AIRS), MODIS, and CERES instruments among others. Unique and valuable information is obtained from active profiling instruments. In particular, vertical cloud profiles and precipitation detection are well characterized by the NASA Cloudsat radar, while thin cloud and aerosol properties, including optical thickness, particle size, cloud thermodynamic phase, and aerosol type, are provided by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar instrument.
What AIRS Provides
The hyper-spectral infrared observations of the AIRS instrument are exceedingly adept at detecting and characterizing cirrus clouds. These clouds create a positive feedback (warming effect) in Earth’s atmosphere since they radiate at lower temperatures and are not an effective barrier to incoming solar radiation.
A series of cloud products are provided by the AIRS Team and are available for download from the NASA Goddard Earth Science Data and Information Services Center (GES DISC). The image above shows global mean maps of the two-layer cloud top temperature and effective cloud fraction products. One can see the prevalence of more frequent and colder cloud cover in the tropics and mid-latitude storm tracks, with less frequent and warmer cloud cover in the subtropics.
The image above shows maps of ice, liquid, and unknown cloud frequency for the same time period. Ice clouds are most prevalent in the tropical Western Pacific and Inter-Tropical Convergence Zone (ITCZ), the mid-latitude storm tracks, and over and downwind of large mountain ranges (e.g., the Rockies, Andes, and Central Asian Mountains). Liquid clouds are most frequent in the major stratocumulus regimes off the western coasts of S. and N. America, Africa, and Australia, as well as in the storm tracks. Unknown phase confidently tracks cloud occurrence, but corresponds to small and shallow cumulus clouds (e.g., trade cumulus) that do not exert a phase signature in the high-spectral-resolution infrared observations.
Lastly, ice cloud properties are shown in the image above. Many coherent patterns related to thin, convective, and orographic cirrus are observed. These data are currently being investigated to yield additional insights on the role of ice clouds in Earth’s climate system.