The Experts below are selected from a list of 5115 Experts worldwide ranked by ideXlab platform
Carlos Pérez García-pando - One of the best experts on this subject based on the ideXlab platform.
-
Retrieving the global distribution of the threshold of wind erosion from satellite data and implementing it into the Geophysical Fluid Dynamics Laboratory land–atmosphere model (GFDL AM4.0/LM4.0)
Atmospheric Chemistry and Physics, 2020Co-Authors: Paul Ginoux, H. Guo, N. Christina Hsu, John S. Kimball, Béatrice Marticorena, Sergey Malyshev, Vaishali Naik, Norman T. O'neill, Carlos Pérez García-pandoAbstract:Abstract. Dust emission is initiated when surface wind velocities exceed the threshold of wind erosion. Many dust models used constant threshold values globally. Here we use satellite products to characterize the frequency of dust events and land surface properties. By matching this frequency derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products with surface winds, we are able to retrieve a climatological monthly global distribution of the wind erosion threshold ( Vthreshold ) over dry and sparsely vegetated surfaces. This monthly two-dimensional threshold velocity is then implemented into the Geophysical Fluid Dynamics Laboratory coupled land–atmosphere model (AM4.0/LM4.0). It is found that the climatology of dust optical depth (DOD) and total aerosol optical depth, surface PM 10 dust concentrations, and the seasonal cycle of DOD are better captured over the “dust belt” (i.e., northern Africa and the Middle East) by simulations with the new wind erosion threshold than those using the default globally constant threshold. The most significant improvement is the frequency distribution of dust events, which is generally ignored in model evaluation. By using monthly rather than annual mean Vthreshold , all comparisons with observations are further improved. The monthly global threshold of wind erosion can be retrieved under different spatial resolutions to match the resolution of dust models and thus can help improve the simulations of dust climatology and seasonal cycles as well as dust forecasting.
Noboru Nakamura - One of the best experts on this subject based on the ideXlab platform.
-
Dynamics of wintertime stratospheric transport in the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model
Journal of Geophysical Research, 1995Co-Authors: Janusz Eluszkiewicz, R. Alan Plumb, Noboru NakamuraAbstract:The kinematics of air motions in and around the polar vortices in the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model are investigated by means of a Lagrangian particle analysis. Particles initialized in the mesosphere and upper stratosphere rapidly descend to the middle stratosphere. This descent is unmixed in the sense that the isentropic mass transport into the vortex is less than 5% of the vortex mass per month. Transport out of the vortex is less than 10% of the vortex mass per month. The reversible component of the Lagrangian mean downward velocity (in isentropic coordinates) is approximated to better than 20% by the diabatic heating rate at the time mean location of the center of mass. The interplay between diabatic descent and horizontal mixing in causing the steepness of tracer contours (e.g., N2O) around the vortex edge is vividly illustrated in our trajectory experiments. These experiments also illustrate the limitations of the concept of “air parcel” within the midlatitude surf zone. The Dynamics of polar descent are investigated by diagnosing the forcing of the residual circulation. In the upper stratosphere, diabatic descent inside polar vortices is driven by Eliassen-Palm flux divergences associated with motions of period shorter than 2 days (presumably gravity waves) in the Antarctic, but of period greater than 3 days (presumably planetary waves) in the Arctic. In the lower stratosphere, long period processes, mainly from the 10 to 1 hPa region, produce descent near the vortex edge in both hemispheres.
Paul Ginoux - One of the best experts on this subject based on the ideXlab platform.
-
Retrieving the global distribution of the threshold of wind erosion from satellite data and implementing it into the Geophysical Fluid Dynamics Laboratory land–atmosphere model (GFDL AM4.0/LM4.0)
Atmospheric Chemistry and Physics, 2020Co-Authors: Paul Ginoux, H. Guo, N. Christina Hsu, John S. Kimball, Béatrice Marticorena, Sergey Malyshev, Vaishali Naik, Norman T. O'neill, Carlos Pérez García-pandoAbstract:Abstract. Dust emission is initiated when surface wind velocities exceed the threshold of wind erosion. Many dust models used constant threshold values globally. Here we use satellite products to characterize the frequency of dust events and land surface properties. By matching this frequency derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products with surface winds, we are able to retrieve a climatological monthly global distribution of the wind erosion threshold ( Vthreshold ) over dry and sparsely vegetated surfaces. This monthly two-dimensional threshold velocity is then implemented into the Geophysical Fluid Dynamics Laboratory coupled land–atmosphere model (AM4.0/LM4.0). It is found that the climatology of dust optical depth (DOD) and total aerosol optical depth, surface PM 10 dust concentrations, and the seasonal cycle of DOD are better captured over the “dust belt” (i.e., northern Africa and the Middle East) by simulations with the new wind erosion threshold than those using the default globally constant threshold. The most significant improvement is the frequency distribution of dust events, which is generally ignored in model evaluation. By using monthly rather than annual mean Vthreshold , all comparisons with observations are further improved. The monthly global threshold of wind erosion can be retrieved under different spatial resolutions to match the resolution of dust models and thus can help improve the simulations of dust climatology and seasonal cycles as well as dust forecasting.
Kenneth P Bowman - One of the best experts on this subject based on the ideXlab platform.
-
tropical mixing barriers in the lower stratosphere in the Geophysical Fluid Dynamics laboratory skyhi model
Journal of Geophysical Research, 1997Co-Authors: Kenneth P BowmanAbstract:Large-scale isentropic mixing in the tropical lower stratosphere is investigated by computing Lagrangian trajectories using winds from the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model. The use of model-simulated winds avoids some problems with analyzed winds in the tropics. During the solstitial seasons a weak-mixing zone is present in the tropics in the model simulations. The weak-mixing zone is relatively isolated from the midlatitude surf zones in the northern and southern hemispheres by two mixing barriers: a strong one on the summer hemisphere side and a weak one on the winter side. The mixing barriers vary seasonally in response to seasonal variations of the tropical zonal-mean zonal flow and wave spectrum. The roles of the zonal-mean flow and of different parts of the wave spectrum in meridional transport are tested using filter techniques. Effective meridional diffusion coefficients are calculated by using filtered and antifiltered winds (i.e., winds with selected spatial scales either attenuated or amplified). The results suggest that mixing in the tropical easterlies occurs near the critical layers for the large-scale (zonal wavenumber <10) westward moving waves, which is where the waves would be expected to break. Wave spectrum analysis indicates that during the solstitial seasons there is a zone in the tropics, exactly matching the weak-mixing zone, where there is relatively little power in westward moving waves. The tropical mixing barriers are a result of the relative lack of such waves.
A Weaver - One of the best experts on this subject based on the ideXlab platform.
-
evolution of the 1991 1992 arctic vortex and comparison with the Geophysical Fluid Dynamics laboratory skyhi general circulation model
Journal of Geophysical Research, 1994Co-Authors: S E Strahan, Joan E Rosenfield, M Loewenstein, J R Podolske, A WeaverAbstract:Nitrous oxide (N2O) measured on board the ER-2 aircraft during the Airborne Arctic Stratospheric Expedition 2 (AASE 2) has been used to monitor descent of air inside the Arctic vortex between October 1991 and March 1992. Monthly mean N2O fields are calculated from the flight data and then compared with mean fields calculated from the high-resolution Geophysical Fluid Dynamics Laboratory general circulation model SKYHI in order to evaluate the model's simulation of the polar vortex. From late fall through winter the model vortex evolves in much the same way as the 1991-1992 vortex, with N2O gradients at the edge becoming progressively steeper. The October to March trends in N2O profiles inside the vortex are used to verify daily net heating rates in the vortex that were computed from clear sky radiative heating rates and National Meteorological Center temperature observations. The computed heating rates successfully estimate the descent of vortex air from December through February but suggest that before December, air at high latitudes may not be isolated from the midlatitudes. SKYHI heating rates are in good agreement with the computed rates but tend to be slightly higher (i.e., less cooling) due to meteorological differences between SKYHI and the 1991-1992 winter. Three ER-2 flights measured N2O just north of the subtropical jet. These low-midlatitude profiles show only slight differences from the high-midlatitude profiles (45 deg - 60 deg N), indicating strong meridional mixing in the midlatitude 'surf zone.' Mean midwinter N2O profiles inside and outside the vortex calculated from AASE 2 data are shown to be nearly identical to 1989 AASE profiles, pointing to the N2O/potential temperature relationship as an excellent marker for vortex air.