Virtual Field Campaigns on Deep Tropical Convection in Climate Models

2009 ◽  
Vol 22 (2) ◽  
pp. 244-257 ◽  
Author(s):  
Brian Mapes ◽  
Julio Bacmeister ◽  
Marat Khairoutdinov ◽  
Cecile Hannay ◽  
Ming Zhao
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Cloud Model ◽  
Convective Heating ◽  
Cloud Forcing ◽  
Community Atmosphere Model ◽  
Virtual Field ◽  
Atmosphere Model ◽  
Rain Events ◽  
Tropospheric Heating

Abstract High-resolution time–height data over warm tropical oceans are examined, from three global atmosphere models [GFDL’s Atmosphere Model 2 (AM2), NCAR’s Community Atmosphere Model, version 3 (CAM3), and a NASA Global Modeling and Assimilation Office (GMAO) model], field campaign observations, and observation-driven cloud model outputs. The character of rain events is shown in data samples and summarized in lagged regressions versus surface rain rate. The CAM3 humidity and cloud exhibit little vertical coherence among three distinct layers, and its rain events have a short characteristic time, reflecting the convection scheme’s penetrative nature and its closure’s concentrated sensitivity to a thin boundary layer source level. In contrast, AM2 rain variations have much longer time scales as convection scheme plumes whose entrainment gives them tops below 500 hPa interact with humidity variations in that layer. Plumes detraining at model levels above 500 hPa are restricted by cloud work function thresholds, and upper-tropospheric humidity and cloud layers fed by these are detached from the lower levels and are somewhat sporadic. With these discrete entrainment rates and instability thresholds, AM2 also produces some synthetic-looking noise (sharp features in height and time) on top of its slow rain variations. A distinctive feature of the NASA model is a separate anvil scheme, distinct from the main large-scale cloud scheme, fed by relaxed Arakawa–Schubert (RAS) plume ensemble convection (a different implementation than in AM2). Its variability is rich and vertically coherent, and involves a very strong vertical dipole component to its tropospheric heating variations, of both signs (limited-depth convective heating and top-heavy heating in strong deep events with significant nonconvective rain). Grid-scale saturation events occur in all three models, often without nonconvective surface rain, causing relatively rare episodes of large negative top-of-atmosphere cloud forcing. Overall, cloud forcing regressions show a mild net positive forcing by rain-correlated clouds in CAM3 and mild net cooling in the other models, as the residual of large canceling shortwave and longwave contributions.

scholarly journals A unified parameterization of clouds and turbulence using CLUBB and subcolumns in the Community Atmosphere Model

2015 ◽  
Vol 8 (6) ◽  
pp. 5041-5088 ◽  
Author(s):  
K. Thayer-Calder ◽  
A. Gettelman ◽  
C. Craig ◽  
S. Goldhaber ◽  
P. A. Bogenschutz ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Climate Models ◽  
Convective Cloud ◽  
Global Climate Models ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Cloud Forcing ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Cloud Parameterization

Abstract. Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in short-wave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation. Also presented are estimations of computational expense and investigation of sensitivity to number of subcolumns.

scholarly journals A unified parameterization of clouds and turbulence using CLUBB and subcolumns in the Community Atmosphere Model

2015 ◽  
Vol 8 (12) ◽  
pp. 3801-3821 ◽  
Author(s):  
K. Thayer-Calder ◽  
A. Gettelman ◽  
C. Craig ◽  
S. Goldhaber ◽  
P. A. Bogenschutz ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Climate Models ◽  
Convective Cloud ◽  
Global Climate Models ◽  
Liquid Water Path ◽  
Microphysics Scheme ◽  
Cloud Forcing ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Cloud Parameterization

Abstract. Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Model computational expense is estimated, and sensitivity to the number of subcolumns is investigated. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in shortwave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation.

scholarly journals Relationship between Shortwave Cloud Radiative Forcing and Local Meteorological Variables Compared in Observations and Several Global Climate Models

2006 ◽  
Vol 19 (17) ◽  
pp. 4344-4359 ◽  
Author(s):  
Markus Stowasser ◽  
Kevin Hamilton
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Grid Point ◽  
Global Climate Models ◽  
Coupled Models ◽  
Cloud Radiative Forcing ◽  
Cloud Forcing

Abstract The relations between local monthly mean shortwave cloud radiative forcing and aspects of the resolved-scale meteorological fields are investigated in hindcast simulations performed with 12 of the global coupled models included in the model intercomparison conducted as part of the preparation for Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). In particular, the connection of the cloud forcing over tropical and subtropical ocean areas with resolved midtropospheric vertical velocity and with lower-level relative humidity are investigated and compared among the models. The model results are also compared with observational determinations of the same relationships using satellite data for the cloud forcing and global reanalysis products for the vertical velocity and humidity fields. In the analysis the geographical variability in the long-term mean among all grid points and the interannual variability of the monthly mean at each grid point are considered separately. The shortwave cloud radiative feedback (SWCRF) plays a crucial role in determining the predicted response to large-scale climate forcing (such as from increased greenhouse gas concentrations), and it is thus important to test how the cloud representations in current climate models respond to unforced variability. Overall there is considerable variation among the results for the various models, and all models show some substantial differences from the comparable observed results. The most notable deficiency is a weak representation of the cloud radiative response to variations in vertical velocity in cases of strong ascending or strong descending motions. While the models generally perform better in regimes with only modest upward or downward motions, even in these regimes there is considerable variation among the models in the dependence of SWCRF on vertical velocity. The largest differences between models and observations when SWCRF values are stratified by relative humidity are found in either very moist or very dry regimes. Thus, the largest errors in the model simulations of cloud forcing are prone to be in the western Pacific warm pool area, which is characterized by very moist strong upward currents, and in the rather dry regions where the flow is dominated by descending mean motions.

scholarly journals An Explanation for the Sensitivity of the Mean State of the Community Atmosphere Model to Horizontal Resolution on Aquaplanets

2017 ◽  
Vol 30 (13) ◽  
pp. 4781-4797 ◽  
Author(s):  
Adam R. Herrington ◽  
Kevin A. Reed
Keyword(s):  
Moisture Transport ◽  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Hadley Cell ◽  
Community Atmosphere Model ◽  
The Mean ◽  
Atmosphere Model ◽  
Mean State

The sensitivity of the mean state of the Community Atmosphere Model to horizontal resolutions typical of present-day general circulation models is investigated in an aquaplanet configuration. Nonconvergence of the mean state is characterized by a progressive drying of the atmosphere and large reductions in cloud coverage with increasing resolution. Analyses of energy and moisture budgets indicate that these trends are balanced by variations in moisture transport by the resolved circulation, and a reduction in activity of the convection scheme. In contrast, the large-scale precipitation rate increases with resolution, which is approximately balanced by greater advection of dry static energy associated with more active resolved vertical motion in the ascent region of the Hadley cell. An explanation for the sensitivity of the mean state to horizontal resolution is proposed, based on linear Boussinesq theory. The authors hypothesize that an increase in horizontal resolution in the model leads to a reduction in horizontal scale of the diabatic forcing arising from the column physics, facilitating finescale flow and faster resolved convective updrafts within the dynamical core, and steering the coupled system toward a new mean state. This hypothesis attempts to explain the underlying mechanism driving the variations in moisture transport observed in the simulations.

scholarly journals Modeling dust as component minerals in the Community Atmosphere Model: development of framework and impact on radiative forcing

2014 ◽  
Vol 14 (12) ◽  
pp. 17749-17816 ◽  
Author(s):  
R. A. Scanza ◽  
N. Mahowald ◽  
S. Ghan ◽  
C. S. Zender ◽  
J. F. Kok ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Mineral Soil ◽  
Model Development ◽  
Spatial And Temporal Variability ◽  
Model Version ◽  
Mineral Aerosols ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Aerosol Module

Abstract. The mineralogy of desert dust is important due to its effect on radiation, clouds and biogeochemical cycling of trace nutrients. This study presents the simulation of dust radiative forcing as a function of both mineral composition and size at the global scale using mineral soil maps for estimating emissions. Externally mixed mineral aerosols in the bulk aerosol module in the Community Atmosphere Model version 4 (CAM4) and internally mixed mineral aerosols in the modal aerosol module in the Community Atmosphere Model version 5.1 (CAM5) embedded in the Community Earth System Model version 1.0.5 (CESM) are speciated into common mineral components in place of total dust. The simulations with mineralogy are compared to available observations of mineral atmospheric distribution and deposition along with observations of clear-sky radiative forcing efficiency. Based on these simulations, we estimate the all-sky direct radiative forcing at the top of the atmosphere as +0.05 W m−2 for both CAM4 and CAM5 simulations with mineralogy and compare this both with simulations of dust in release versions of CAM4 and CAM5 (+0.08 and +0.17 W m−2) and of dust with optimized optical properties, wet scavenging and particle size distribution in CAM4 and CAM5, −0.05 and −0.17 W m−2, respectively. The ability to correctly include the mineralogy of dust in climate models is hindered by its spatial and temporal variability as well as insufficient global in-situ observations, incomplete and uncertain source mineralogies and the uncertainties associated with data retrieved from remote sensing methods.

Criticality in Tropical Rainfall: A Simple Water Budget Model

2020 ◽  
Author(s):  
Mikkel Svendsen
Keyword(s):  
Water Budget ◽  
Large Scale ◽  
Rain Rate ◽  
Climate Models ◽  
Spatial Information ◽  
Model Simulation ◽  
Atmospheric Precipitation ◽  
Power Laws ◽  
Tropical Rainfall ◽  
Rain Events

<p>Deep convective rain events in the tropics represent an essential ingredient of Earth's climate system, acting as a driver of large-scale circulation which distributes energy and moisture. Understanding how they organize remains a challenge. Observational studies indicate that tropical convection may be understood as an instance of self-organized criticality (SOC) [1]:<br>(i) Rain rate vs. column water vapor follows a clear "pickup curve": Essentially no rain is observed in dry areas, while at column moistures above a critical value the rain rate increases sharply.<br>(ii) Rain events and clusters, defined as groups of contiguous rainy points in space and/or time, have size distributions well described by power laws.<br>The first result indicates that the atmosphere undergoes a phase transition, separating a non-raining "inactive" phase from a rainy "active" one. The second result suggests that the system is found close to the critical transition point, where "scale-free" power law distributions are expected. Indeed, observations find typical moisture values to be close to the critical moisture value. </p><p>SOC theory would suggest that the observational results are an emergent phenomenon, caused by simple local interactions that carry over to larger scales. However, to our knowledge, no simple SOC model linking moisture and rainfall has been suggested that explains how criticality arises from convective processes while also predicting the observed rain cluster sizes. A more complete theory, especially on spatial aspects, is lacking.<br>We therefore present a simple spatiotemporal model of the atmospheric water budget, exploring whether a fuller picture including spatial information can be developed. Each site of the model represents an atmospheric column, where water can enter through surface evaporation, leave as surface rain, or get redistributed among neighboring sites due to convective in- and outflows. We analyse a cloud resolving model simulation in radiative-convective equilibrium, by grouping grid points into three categories: rainy points (convectively active), neighbors of rainy points and others (convectively passive). Tendencies, evolutions and transitions are examined to identify local "rules" to inform the interactions and parameters in our model.<br>Hence, in this project we use a simple model approach to find whether local convection mechanisms of water rearrangements can explain why tropical rainfall seems to show critical characteristics. In addition, this might aid development of convective parameterizations for climate models: Including a few key convective scale interactions, suggested by our model, might help to better capture important effects of subgrid correlations in a simple way.<br> <br>[1] Peters, O., and J. D. Neelin (2006), Critical phenomena in atmospheric precipitation, <em>Nat. Phys.</em>, <em>2(6)</em>, 393-396, doi:10.1038/nphys314.</p>

Giant Sea-Salt Aerosols and Warm Rain Formation in Marine Stratocumulus

2008 ◽  
Vol 65 (12) ◽  
pp. 3678-3694 ◽  
Author(s):  
Jørgen B. Jensen ◽  
Sunhee Lee
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Cloud Model ◽  
Sea Salt ◽  
Droplet Growth ◽  
Anthropogenic Factors ◽  
Marine Stratocumulus ◽  
Sea Salt Aerosols ◽  
Warm Rain ◽  
Rain Formation

Abstract The concentrations and sizes of smaller aerosols (radius smaller than 0.5 μm) in the marine atmosphere vary owing to natural and anthropogenic factors. The concentrations and sizes of giant and ultragiant aerosols vary primarily due to wind-speed-dependent wave breaking. In climate models the formation of warm rain from marine stratocumulus clouds is usually parameterized based on the drops that form on the smaller aerosols. The present process study, using a stochastic Monte Carlo cloud model, shows that the variability of giant sea-salt aerosols and the variability of smaller aerosol cloud condensation nuclei are equally important in determining precipitation flux in marine stratocumulus. This strongly suggests that the effects of giant sea-salt aerosols should be included in the parameterization of warm rain formation in climate and other large-scale models. The above results are based on highly detailed calculations of droplet growth in an idealized marine stratocumulus cloud; the authors believe that other marine stratus cloud conditions may change the calculated rain rates but that the conclusions regarding the relative importance of small and giant aerosols are robust.

Effects of Localized Grid Refinement on the General Circulation and Climatology in the Community Atmosphere Model

2015 ◽  
Vol 28 (7) ◽  
pp. 2777-2803 ◽  
Author(s):  
Colin M. Zarzycki ◽  
Christiane Jablonowski ◽  
Diana R. Thatcher ◽  
Mark A. Taylor
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Precipitable Water ◽  
Atmospheric Model ◽  
Spectral Element ◽  
Horizontal Resolution ◽  
Department Of Energy ◽  
Extreme Precipitation Events ◽  
Community Atmosphere Model ◽  
Atmosphere Model

Abstract Using the spectral element (SE) dynamical core within the National Center for Atmospheric Research–Department of Energy Community Atmosphere Model (CAM), a regionally refined nest at 0.25° (~28 km) horizontal resolution located over the North Atlantic is embedded within a global 1° (~111 km) grid. A 23-yr simulation using Atmospheric Model Intercomparison Project (AMIP) protocols and default CAM, version 5, physics is compared to an identically forced run using the global 1° (~111 km) grid without refinement. The addition of a refined patch over the Atlantic basin does not noticeably affect the global circulation. In the area where the refinement is located, large-scale precipitation increases with the higher resolution. This increase is partly offset by a decrease in precipitation resulting from convective parameterizations, although total precipitation is also slightly higher at finer resolutions. Equatorial waves are not significantly impacted when traversing multiple grid spacings. Despite the grid transition region bisecting northern Africa, local zonal jets and African easterly wave activity are highly similar in both simulations. The frequency of extreme precipitation events increases with resolution, although this increase is restricted to the refined patch. Topography is better resolved in the nest as a result of finer grid spacing. The spatial patterns of variables with strong orographic forcing (such as precipitation, cloud, and precipitable water) are improved with local refinement. Additionally, dynamical features, such as wind patterns, associated with steep terrain are improved in the variable-resolution simulation when compared to the uniform coarser run.

scholarly journals Role of updraft velocity in temporal variability of global cloud hydrometeor number

2016 ◽  
Vol 113 (21) ◽  
pp. 5791-5796 ◽  
Author(s):  
Sylvia C. Sullivan ◽  
Dongmin Lee ◽  
Lazaros Oreopoulos ◽  
Athanasios Nenes
Keyword(s):  
Vertical Velocity ◽  
Temporal Variability ◽  
Climate Models ◽  
System Model ◽  
Ice Crystal ◽  
Cloud Forcing ◽  
Model Version ◽  
Earth Observing System ◽  
Community Atmosphere Model

Understanding how dynamical and aerosol inputs affect the temporal variability of hydrometeor formation in climate models will help to explain sources of model diversity in cloud forcing, to provide robust comparisons with data, and, ultimately, to reduce the uncertainty in estimates of the aerosol indirect effect. This variability attribution can be done at various spatial and temporal resolutions with metrics derived from online adjoint sensitivities of droplet and crystal number to relevant inputs. Such metrics are defined and calculated from simulations using the NASA Goddard Earth Observing System Model, Version 5 (GEOS-5) and the National Center for Atmospheric Research Community Atmosphere Model Version 5.1 (CAM5.1). Input updraft velocity fluctuations can explain as much as 48% of temporal variability in output ice crystal number and 61% in droplet number in GEOS-5 and up to 89% of temporal variability in output ice crystal number in CAM5.1. In both models, this vertical velocity attribution depends strongly on altitude. Despite its importance for hydrometeor formation, simulated vertical velocity distributions are rarely evaluated against observations due to the sparsity of relevant data. Coordinated effort by the atmospheric community to develop more consistent, observationally based updraft treatments will help to close this knowledge gap.

scholarly journals Downscale cascades in tracer transport test cases: an intercomparison of the dynamical cores in the Community Atmosphere Model CAM5

2012 ◽  
Vol 5 (3) ◽  
pp. 1781-1816 ◽  
Author(s):  
J. Kent ◽  
C. Jablonowski ◽  
J. P. Whitehead ◽  
R. B. Rood
Keyword(s):  
Climate Models ◽  
Western Hemisphere ◽  
Test Cases ◽  
Tracer Transport ◽  
Model Version ◽  
Eastern Hemisphere ◽  
Community Atmosphere Model ◽  
Advection Schemes ◽  
Spectral Transform ◽  
Atmosphere Model

Abstract. The accurate modelling of cascades to unresolved scales is an important part of the tracer transport component of dynamical cores of weather and climate models. This paper aims to investigate the ability of the advection schemes in the National Center for Atmospheric Research's Community Atmosphere Model version 5 (CAM5) to model this cascade. In order to quantify the effects of the different advection schemes in CAM5, four two-dimensional tracer transport test cases are presented. Three of the tests stretch the tracer below the scale of coarse resolution grids to ensure the downscale cascade of tracer variance. These results are compared with a high resolution reference solution, which is simulated on a resolution fine enough to resolve the tracer during the test. The fourth test has two separate flow cells, and is designed so that any tracer in the Western Hemisphere should not pass into the Eastern Hemisphere. This is to test whether the diffusion in transport schemes, often in the form of explicit hyper-diffusion terms or implicit through monotonic limiters, contains unphysical mixing. An intercomparison of three of the dynamical cores of the National Center for Atmospheric Research's Community Atmosphere Model version 5 is performed. The results show that the finite-volume (CAM-FV) and spectral element (CAM-SE) dynamical cores model the downscale cascade of tracer variance better than the semi-Lagrangian transport scheme of the Eulerian spectral transform core (CAM-EUL). Each scheme tested produces unphysical mass in the Eastern Hemisphere of the separate cells test.

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