Atmospheric aerosols (sub-micron and micron-sized particles suspended in air) originate both from natural and man-made sources. Due to their short lifetime and strong tropospheric interactions, their global concentrations and properties are poorly known. Aerosol particles affect atmospheric radiation and cloud microphysics, and are considered a major uncertainty in climate forcing. Saharan dust generated over Africa and transported over the Atlantic Ocean to America is an example of a natural source. It is hypothesized that the dust has a major role in fertilization of the Amazon forest. Also, oceanic phytoplankton generates dimethyl-sulfide gas that is a precursor of the oceanic sulfate aerosol, which is also a natural gas. More...

Clouds play a critical role in the Earth's hydrologic cycle and in the energy balance of the climate system. They have a strong effect on solar heating by reflecting part of the incident solar radiation back to space. An increase in the average albedo of the Earth-atmosphere system by only 10 percent could decrease the surface temperature to that of the last ice age. Clouds affect the thermal cooling by intercepting part of the infrared radiation emitted by the Earth and atmosphere below the cloud, and re-emitting part of this radiation back to the surface. Global change in surface temperature is highly sensitive to cloud amount and type. Increasing low-level and middle-level clouds has a net cooling effect because they reflect more solar radiation and have a relatively small effect on infrared radiation. On the other hand, increased high clouds will have a warming effect by virtue of their low temperature and reduced cooling to space. High cirrus also act as a natural cloud seeder and strongly modulate the radiatively-important upper tropospheric water vapor budget. Given the sensitivity of the global climate to clouds, it is not surprising that the largest uncertainty in model estimates of global warming is due to clouds. More...

The movement of water in its solid, liquid, and vapor forms, and the changes in phase from one form to another, are responsible for a considerable fraction of the heating and cooling of the atmosphere, which in turn drives the winds and affects the climate at each location on the Earth. The movement and transformations of water substance around the Earth are referred to as the "water cycle." More...

The solar radiation input is the major energy source for the Earth's biosphere, and the direct driving force for atmospheric, and oceanic circulations. The Sun is a typical main sequence star with spectral class of G2, one of 100 billion stars in the galaxy system. The energy generated in the fusion processes in the inner core is transported though radiative processes in the radiation zone, and by convections in the convection zone to the photosphere, which is what we can see. The photosphere has a thickness equal to 500 km, a small fraction of the total solar radius that equals 6.6 x 10⁵ km, and is often called the 'surface' of the Sun, and is the region from which solar energy is emitted to interplanetary space. The photosphere has an effective temperature of 5780°K. More...

The bidirectional reflectance distribution function (BRDF) characterizes the angular distribution of reflected solar radiation as a function of viewing direction. Different surfaces reflect solar radiation in very different ways. Snow and sea ice surfaces, for example, reflect radiation in a nearly isotropic (Lambertian) manner; oceans are characterized by bright reflection in the forward (specular) direction, known as sunglint; many vegetation surfaces are characterized with enhanced reflection in the antisolar (backscattered) direction, known as the 'hot spot;' and water clouds are characterized by enhanced reflection in the forward scattering direction but with noticeable glory (backscatter) and rainbow reflectance patterns. More...

One of the problems that makes climate research both interesting and challenging is the blending of physical processes whose evolution in time can be predicted well into the future with others that cannot. Comparisons of observations about the Earth's climate with models of how the climate is evolving must take into account this inherent lack of predictability, sometimes referred to as climate noise. Much of climate data analysis involves the separation of climate signal from the noise. Branch scientists carry out climate diagnostic studies using a mix of historical climate data, remote sensing data, and outputs from general circulation models. Methods have been developed to filter out climate noise from signal using optimal weighting of observations and using simplified models of the coupled climate system, to compare climate change predictions with observed changes. More...

In the area of theory and modeling, branch research efforts are focused on two complementary streams: cloud-radiative processes and climate dynamics. Plane-parallel radiation codes are developed for use in calculating radiative effects of clouds, water vapor, and the liquid water drop-size distribution; for the estimation of surface energy balance; and for radiative-convective boundary layer equilibrium calculations. The radiation codes include effects of absorption, emission, and scattering of radiation due to water vapor, clouds, aerosols, CO2, O3, O2, and minor trace gases. Using multi-level energy-balance models derived from the radiation models, branch scientists have carried out a series of sensitivity experiments to study the effect of CO2, clouds, volcanic eruptions, and SO2 emission on global climate change. Work is underway to develop a versatile radiation modular code that separates spectral information from the radiative transfer computations so that it can be used readily in general circulation models to test out different climate feedback hypotheses. The full 3D radiative transfer problem through inhomogeneous clouds is being studied by both Monte Carlo and analytic methods, using a variety of cloud structure models with parameters determined by analysis of data from the DOE ARM and NASA FIRE field programs. Results of the 3D studies are parameterized in terms of "effective" cloud parameters for use in plane-parallel GCM codes, and also provide improved algorithms for the retreival of cloud parameters from remote sensing data. More...

Satellites can provide nearly global coverage of the Earth with spatial resolutions and repetition rates that vary from one platform to another. Remote sensing research in the branch includes the use of satellite-measured radiances for estimating geophysical quantities such as atmospheric water vapor, trace gases, aerosol particles, clouds, and precipitation. In addition, satellite data are used to study the radiative and dynamical processes that affect the climate of the Earth. More...