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.

The Dynamics of Idealized Convection Schemes and Their Effect on the Zonally Averaged Tropical Circulation

2007 ◽  
Vol 64 (6) ◽  
pp. 1959-1976 ◽  
Author(s):  
Dargan M. W. Frierson
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Hadley Circulation ◽  
Horizontal Resolution ◽  
Shallow Convection ◽  
Tropical Circulation ◽  
Convection Scheme ◽  
Convection Schemes ◽  
Gross Moist Stability ◽  
The Tropics

In this paper, the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist GCM to obtain broad classifications of the influence of convection on the Tropics. This is accomplished with a simplified convection scheme in the style of Betts and Miller. The scheme is utilized in a moist GCM with simplified physical parameterizations (gray radiation, with zonally symmetric, slab mixed layer ocean boundary conditions). Comparisons are made with simulations without a convection scheme [i.e., with large-scale condensation (LSC) only], with the moist convective adjustment (MCA) parameterization, and with various formulations and parameter sets with a simplified Betts–Miller (SBM) scheme. With the control run using the SBM scheme, the Tropics become quieter and less dependent on horizontal resolution as compared with the LSC or MCA simulations. The Hadley circulation mass transport is significantly reduced with the SBM scheme, as is the ITCZ precipitation. An important factor determining this behavior is the parameterization of shallow convection: without shallow convection, the convection scheme is largely ineffective at preventing convection from occurring at the grid scale. The sensitivities to convection scheme parameters are also examined. The simulations are remarkably insensitive to the convective relaxation time, and only mildly sensitive to the relative humidity of the reference profile, provided significant large-scale condensation is not allowed to occur. The changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere.

scholarly journals Tropical Intraseasonal Variability in Version 3 of the GFDL Atmosphere Model

2013 ◽  
Vol 26 (2) ◽  
pp. 426-449 ◽  
Author(s):  
James J. Benedict ◽  
Eric D. Maloney ◽  
Adam H. Sobel ◽  
Dargan M. Frierson ◽  
Leo J. Donner
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Cumulus Parameterization ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Convection Scheme ◽  
West Pacific Ocean ◽  
Atmosphere Model ◽  
Convective Organization ◽  
Heating Profile

Abstract Tropical intraseasonal variability is examined in version 3 of the Geophysical Fluid Dynamics Laboratory Atmosphere Model (AM3). In contrast to its predecessor AM2, AM3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds. The AM3 cumulus parameterization is a mass-flux-based scheme but also, unlike that in AM2, incorporates subgrid-scale vertical velocities; these play a key role in cumulus microphysical processes. The AM3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds, which strongly influence large-scale moisture and radiation fields. The authors examine four AM3 simulations using a control model and three versions with different modifications to the deep convection scheme. In the control AM3, using a convective closure based on CAPE relaxation, both MJO and Kelvin waves are weak relative to those in observations. By modifying the convective closure and trigger assumptions to inhibit deep cumuli, AM3 produces reasonable intraseasonal variability but a degraded mean state. MJO-like disturbances in the modified AM3 propagate eastward at roughly the observed speed in the Indian Ocean but up to 2 times the observed speed in the west Pacific Ocean. Distinct differences in intraseasonal convective organization and propagation exist among the modified AM3 versions. Differences in vertical diabatic heating profiles associated with the MJO are also found. The two AM3 versions with the strongest intraseasonal signals have a more prominent “bottom heavy” heating profile leading the disturbance center and “top heavy” heating profile following the disturbance. The more realistic heating structures are associated with an improved depiction of moisture convergence and intraseasonal convective organization in AM3.

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 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.

Laboratory studies of equatorially trapped waves using ferrofluid

1997 ◽  
Vol 338 ◽  
pp. 35-58 ◽  
Author(s):  
DANIEL R. OHLSEN ◽  
PETER B. RHINES
Keyword(s):  
Fluid Dynamics ◽  
Rotation Rate ◽  
Large Scale ◽  
Rossby Waves ◽  
Low Frequency ◽  
Laboratory Studies ◽  
Geophysical Fluid Dynamics ◽  
Vertical Projection ◽  
Planetary Rotation ◽  
Oceanic Flows

We introduce a new technique to model spherical geophysical fluid dynamics in the terrestrial laboratory. The local vertical projection of planetary vorticity, f, varies with latitude on a rotating spherical planet and allows an important class of waves in large-scale atmospheric and oceanic flows. These Rossby waves have been extensively studied in the laboratory for middle and polar latitudes. At the equator f changes sign where gravity is perpendicular to the planetary rotation. This geometry has made laboratory studies of geophysical fluid dynamics near the equator very limited. We use ferrofluid and static magnetic fields to generate nearly spherical geopotentials in a rotating laboratory experiment. This system is the laboratory analogue of those large-scale atmospheric and oceanic flows whose horizontal motions are governed by the Laplace tidal equations. As the rotation rate in such a system increases, waves are trapped to latitudes near the equator and the dynamics can be formulated on the equatorial β-plane. This transition from planetary modes to equatorially trapped modes as the rotation rate increases is observed in the experiments. The equatorial β-plane solutions of non-dispersive Kelvin waves propagating eastward and non-dispersive Rossby waves propagating westward at low frequency are observed in the limit of rotation fast compared to gravity wave speed.

scholarly journals 100 Years of the Ocean General Circulation

2018 ◽  
Vol 59 ◽  
pp. 7.1-7.32 ◽  
Author(s):  
Carl Wunsch ◽  
Raffaele Ferrari
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Large Scale ◽  
Time Dependent ◽  
Steady Flows ◽  
Oceanic Circulation ◽  
Boundary Current ◽  
Geophysical Fluid Dynamics ◽  
The Past ◽  
The Tropics

Abstract The central change in understanding of the ocean circulation during the past 100 years has been its emergence as an intensely time-dependent, effectively turbulent and wave-dominated, flow. Early technologies for making the difficult observations were adequate only to depict large-scale, quasi-steady flows. With the electronic revolution of the past 50+ years, the emergence of geophysical fluid dynamics, the strongly inhomogeneous time-dependent nature of oceanic circulation physics finally emerged. Mesoscale (balanced), submesoscale oceanic eddies at 100-km horizontal scales and shorter, and internal waves are now known to be central to much of the behavior of the system. Ocean circulation is now recognized to involve both eddies and larger-scale flows with dominant elements and their interactions varying among the classical gyres, the boundary current regions, the Southern Ocean, and the tropics.

scholarly journals Shape and size of large-scale vortices: A generic fluid pattern in geophysical fluid dynamics

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Louis-Alexandre Couston ◽  
Daniel Lecoanet ◽  
Benjamin Favier ◽  
Michael Le Bars
Keyword(s):  
Fluid Dynamics ◽  
Large Scale ◽  
Geophysical Fluid Dynamics ◽  
Shape And Size
Sign in / Sign up

Export Citation Format

Share Document