Radiative transfer

About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.

ATMOSPHERIC CIRCULATION OF ECCENTRIC HOT NEPTUNE GJ436b

Abstract: GJ436b is a unique member of the transiting extrasolar planet population being one of the smallest and least irradiated and possessing an eccentric orbit. Because of its size, mass, and density, GJ436b could plausibly have an atmospheric metallicity similar to Neptune (20-60 times solar abundances), which makes it an ideal target to study the effects of atmospheric metallicity on dynamics and radiative transfer in an extrasolar planetary atmosphere. We present three-dimensional atmospheric circulation models that include realistic non-gray radiative transfer for 1, 3, 10, 30, and 50 times solar atmospheric metallicity cases of GJ436b. Low metallicity models (1 and 3 times solar) show little day/night temperature variation and strong high-latitude jets. In contrast, higher metallicity models (30 and 50 times solar) exhibit day/night temperature variations and a strong equatorial jet. Spectra and light curves produced from these simulations show strong orbital phase dependencies in the 50 times solar case and negligible variations with orbital phase in the 1 times solar case. Comparisons between the predicted planet/star flux ratio from these models and current secondary eclipse measurements support a high metallicity atmosphere (30-50 times solar abundances) with disequilibrium carbon chemistry at play for GJ436b. Regardless of the actual atmospheric composition of GJ436b, our models serve to illuminate how metallicity influences the atmospheric circulation for a broad range of warm extrasolar planets.

The Middle Atmosphere In the Absence of Dynamical Heat Fluxes

Abstract: A new radiative transfer scheme, developed for use in a three-dimensional dynamical model of the stratosphere and mesosphere, is used to consider the hypothetical state of the middle atmosphere in the absence of dynamical heat fluxes. Most previous work in this area has considered radiative equilibrium temperatures using a fixed solar forcing. This equilibrium state is shown to be different from a state calculated using a seasonal cycle of solar forcing; in particular, the winter pole is found to be warmer and the latitudinal temperature gradient across the edge of the polar night is found to be smaller. This difference is due to two processes. Firstly, latitudes just polewards of the edge of the polar night at solstice are in darkness for only a short period. Secondly, radiative time scales lengthen greatly as temperatures decrease, so that equilibrium cannot be reached before the sun reappears. Recent ozone climatologies are used to impose a realistic annual cycle of ozone on the model. It is found that the simulation of the lower stratosphere is in considerably better agreement with observations than previous radiation-only calculations. the better simulation is shown to be, in most cases, due to the use of the new ozone climatology. It is also shown that a realistic ozone distribution is necessary for a good simulation of the polar stratopause at the summer solstice. A comparison of the observed and calculated annual cycle of temperature in the polar regions of the southern hemisphere lower stratosphere indicates that this region is under strong radiative control. This contrasts with an implied strong dynamical control for the same region in the northern hemisphere.

Revisiting the radiative impact of dust on Mars using the LMD Global Climate Model

Abstract: [1] Airborne dust is the main driver of Martian atmospheric temperature, and accurately accounting for its radiative effect in Global Climate Models (GCMs) is essential. This requires the modeling of the dust distribution and radiative properties, and when trying to simulate the true climate variability, the use of the observed dust column opacity to guide the model. A recurrent problem has been the inability of Mars GCMs to predict realistic temperatures while using both the observed dust radiative properties and column opacity. One would have to drive the model with a tuned opacity to reach an agreement with the observations, thereby losing its self-consistency. In this paper, we show that using the most recently derived dust radiative properties in the LMD (Laboratoire de Meteorologie Dynamique) GCM solves this problem, which was mainly due to the underestimation of the dust single scattering albedo in the solar domain. However, an overall warm temperature bias remains above the 1 hPa pressure level. We therefore refine the model by implementing a “semi-interactive” dust transport scheme which is coupled to the radiative transfer calculations. This scheme allows a better representation of the dust layer depth in the model and thereby removes the remaining warm bias. The LMD/GCM is now able to predict accurate temperatures without any tuning of the dust opacity used to guide the model. Remaining discrepancies are discussed, and seem to be primarily due to the neglect of the radiative effect of water-ice clouds, and secondarily to persisting uncertainties in the dust spatial distribution.

Estimation of SW Flux Absorbed at the Surface from TOA Reflected Flux

Abstract: Measurements of radiation budgets, both at the top of the atmosphere (TOA) and at the surface, are essential to understanding the earth's climate. The TOA budgets can, in principle, be measured directly from satellites, while on a global scale surface budgets need to be deduced from TOA measurements. Most methods of inferring surface solar-radiation budgets from satellite measurements are applicable to particular scene types or geographic locations, and none is valid over highly reflective surfaces such as ice or snow. In addition, the majority of models require inputs such as cloud-optical thickness that are usually not known. Extensive radiative transfer modeling for different surface, atmospheric, and cloud conditions suggests a linear relationship between the TOA-reflected flux and the flux absorbed at the surface for a fixed solar zenith angle (SZA). The linear relationship is independent of cloud-optical thickness and surface albedo. Sensitivity tests show that the relationship depends stro...