scholarly journals 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)

2020 ◽  
Vol 20 (1) ◽  
pp. 55-81 ◽  
Author(s):  
Bing Pu ◽  
Paul Ginoux ◽  
Huan Guo ◽  
N. Christina Hsu ◽  
John Kimball ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Optical Depth ◽  
Wind Erosion ◽  
Surface Wind ◽  
Global Distribution ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Geophysical Fluid Dynamics ◽  
Erosion Threshold ◽  
Atmosphere Model ◽  
Dust Events

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 PM10 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.

scholarly journals Retrieving the global distribution of threshold of wind erosion from satellite data and implementing it into the GFDL AM4.0/LM4.0 model

2019 ◽  
Author(s):  
Bing Pu ◽  
Paul Ginoux ◽  
Huan Guo ◽  
N. Christine Hsu ◽  
John Kimball ◽  
...  
Keyword(s):  
Optical Depth ◽  
Seasonal Cycle ◽  
Wind Erosion ◽  
Surface Wind ◽  
Dust Emission ◽  
Global Distribution ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Threshold Velocity ◽  
Erosion Threshold ◽  
Dust Events

Abstract. Dust emission is initiated when surface wind velocities exceed the threshold of wind erosion. Most dust models used constant threshold values globally. Here we use satellite products to characterize the frequency of dust events and 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 wind erosion threshold (Vthreshold) over dry and sparsely-vegetated surface. 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 PM10 dust concentrations, and seasonal cycle of DOD are better captured over the dust belt (i.e. North 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 cycle as well as dust forecasting.

Dynamic Radiative–Convective Equilibria Using GCM Column Physics

2007 ◽  
Vol 64 (1) ◽  
pp. 228-238 ◽  
Author(s):  
Isaac M. Held ◽  
Ming Zhao ◽  
Bruce Wyman
Keyword(s):  
Fluid Dynamics ◽  
Large Scale ◽  
Homogeneous Model ◽  
Horizontal Resolution ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Geophysical Fluid Dynamics ◽  
Convection Scheme ◽  
Cloud Feedbacks ◽  
The Tropics ◽  
Convective Organization

Abstract The behavior of a GCM column physics package in a nonrotating, doubly periodic, homogeneous setting with prescribed SSTs is examined. This radiative–convective framework is proposed as a useful tool for studying some of the interactions between convection and larger-scale dynamics and the effects of differing modeling assumptions on convective organization and cloud feedbacks. For the column physics utilized here, from the Geophysical Fluid Dynamics Laboratory (GFDL) AM2 model, many of the properties of the homogeneous, nonrotating model are closely tied to the fraction of precipitation that is large-scale, rather than convective. Significant large-scale precipitation appears above a critical temperature and then increases with further increases in temperature. The amount of large-scale precipitation is a function of horizontal resolution and can also be controlled by modifying the convection scheme, as is illustrated here by modifying assumptions concerning entrainment into convective plumes. Significant similarities are found between the behavior of the homogeneous model and that of the Tropics of the parent GCM when ocean temperatures are increased and when the convection scheme is modified.

scholarly journals VOLUME AND HEAT TRANSPORTS ANALYSIS IN THE SOUTH ATLANTIC BASIN RELATED TO CLIMATE CHANGE SCENARIOS

2015 ◽  
Vol 33 (2) ◽  
Author(s):  
Lívia Maria Barbosa Sancho ◽  
Luiz Paulo De Freitas Assad ◽  
Luiz Landau
Keyword(s):  
Climate Change ◽  
Fluid Dynamics ◽  
Water Column ◽  
Heat Transport ◽  
South Atlantic ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Climate Change Scenarios ◽  
Geophysical Fluid Dynamics ◽  
Zonal Section ◽  
Advective Heat Transport

ABSTRACT. This study evaluates how climate change might affect advective heat and volume transports in the South Atlantic Basin based on Intergovernmental Panel on Climate Change (IPCC) A1FI and B1 climate change scenarios projections. Using the Climatic Model 2.1 (CM2.1) results that were developed by the Geophysical Fluid Dynamics Laboratory (GFDL), integrated on the water column, analyses were conducted through two meridional sections and one zonal section of the study area (between 25◦S-70◦S and 70◦W-20◦E). The annual mean time series were analyzed using historical 100-year climate change scenarios. The analyses of the climate change experiment parameters were compared with those of the H2 climate scenario. The volume transport (VT) through the water column weakened of about 5% in average and the advective heat transport (HT) increased of about 22% at the Drake and Africa-Antarctic (AF-AA) passages at the end of the experiments. For the zonal section at 25◦S, direction oscillations were observed in the integrated VT through the water column due to velocity intensity variations of the water masses and a decrease of about 22% in the HT was observed. Thus, it was observed a decrease in the water and heat supplies at 25◦S due to the Drake and AF-AA VT behavior, which may alter deep circulation patterns.Keywords: water column analysis, advective heat transport, flow direction, Drake Passage, Africa-Antarctic passage.RESUMO. Baseado nas projeções dos cenários de mudanças climáticas A1FI e B1 do Painel Intergovernamental de Mudanc¸as Climáticas (IPCC), esse estudo avalia como as mudanças climáticas podem impactar os transportes advectivos de calor e volume na bacia do Atlântico Sul. Através de resultados gerados pelo Modelo Climático 2.1 (CM2.1) desenvolvido pelo Geophysical Fluid Dynamics Laboratory (GFDL), foram feitas análises através de duas seções meridionais e uma seção zonal na área de estudo (entre 25◦S-70◦S e 70◦W-20◦E) integradas na coluna d’água. Foram analisados campos prognósticos médios anuais referentes a experimentos com 100 anos de duração. As análises dos parâmetros dos experimentos de mudanças climáticas foram realizadas em comparação com o experimento clima (H2). O transporte de volume (TV) integrado na coluna d’água enfraqueceu aproximadamente 5%, enquanto o transporte advectivo de calor (TC) aumentou em torno de 22% no Drake e na Passagem África-Antártida (AF-AA) ao final dos experimentos. Para a seção em 25◦S, foram observadas oscilações de direção do fluxo devido a variações na intensidade das velocidades das massas d’água com um enfraquecimento médio de 22% para o TC. Adicionalmente, foi observada uma diminuição no suprimento de água em 25◦S devido ao comportamento do TV das demais seções, o que pode alterar os padrões de circulação profunda.Palavras-chave: análise na coluna d’água, transporte advectivo de calor, direção do fluxo, Passagem de Drake, passagem África-Antártida.

scholarly journals Analysis of the Characteristics and Mechanisms of the Pacific Decadal Oscillation in a Suite of Coupled Models from the Geophysical Fluid Dynamics Laboratory

2015 ◽  
Vol 28 (19) ◽  
pp. 7678-7701 ◽  
Author(s):  
Liping Zhang ◽  
Thomas L. Delworth
Keyword(s):  
Fluid Dynamics ◽  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Time Scale ◽  
Spectral Peak ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Geophysical Fluid Dynamics ◽  
Atmospheric Variability ◽  
Decadal Scale ◽  
Ocean Atmosphere

Abstract North Pacific decadal oceanic and atmospheric variability is examined in a suite of coupled climate models developed at the Geophysical Fluid Dynamics Laboratory (GFDL). The models have ocean horizontal resolutions ranging from 1° to 0.1° and atmospheric horizontal resolutions ranging from 200 to 50 km. In all simulations the dominant pattern of decadal-scale sea surface temperature (SST) variability over the North Pacific is similar to the observed Pacific decadal oscillation (PDO). Simulated SST anomalies in the Kuroshio–Oyashio Extension (KOE) region exhibit a significant spectral peak at approximately 20 yr. Sensitivity experiments are used to show that (i) the simulated PDO mechanism involves extratropical air–sea interaction and oceanic Rossby wave propagation; (ii) the oscillation can exist independent of interactions with the tropics, but such interactions can enhance the PDO; and (iii) ocean–atmosphere feedback in the extratropics is critical for establishing the approximately 20-yr time scale of the PDO. The spatial pattern of the PDO can be generated from atmospheric variability that occurs independently of ocean–atmosphere feedback, but the existence of a spectral peak depends on active air–sea coupling. The specific interdecadal time scale is strongly influenced by the propagation speed of oceanic Rossby waves in the subtropical and subpolar gyres, as they provide a delayed feedback to the atmosphere. The simulated PDO has a realistic association with precipitation variations over North America, with a warm phase of the PDO generally associated with positive precipitation anomalies over regions of the western United States. The seasonal dependence of this relationship is also reproduced by the model.

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