A Comparison of the Water Budgets between Clouds from AMMA and TWP-ICE

2013 ◽  
Vol 70 (2) ◽  
pp. 487-503 ◽  
Author(s):  
Xiping Zeng ◽  
Wei-Kuo Tao ◽  
Scott W. Powell ◽  
Robert A. Houze ◽  
Paul Ciesielski ◽  
...  
Keyword(s):  
General Circulation ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
General Circulation Models ◽  
Warm Pool ◽  
Water Budgets ◽  
Convective Systems ◽  
Convective Clouds ◽  
Distinct Structure ◽  
Multidisciplinary Analysis

Abstract Two field campaigns, the African Monsoon Multidisciplinary Analysis (AMMA) and the Tropical Warm Pool–International Cloud Experiment (TWP-ICE), took place in 2006 near Niamey, Niger, and Darwin, Northern Territory, Australia, providing extensive observations of mesoscale convective systems (MCSs) near a desert and a tropical coast, respectively. Under the constraint of their observations, three-dimensional cloud-resolving model simulations are carried out and presented in this paper to replicate the basic characteristics of the observed MCSs. All of the modeled MCSs exhibit a distinct structure having deep convective clouds accompanied by stratiform and anvil clouds. In contrast to the approximately 100-km-scale MCSs observed in TWP-ICE, the MCSs in AMMA have been successfully simulated with a scale of about 400 km. These modeled AMMA and TWP-ICE MCSs offer an opportunity to understand the structure and mechanism of MCSs. Comparing the water budgets between AMMA and TWP-ICE MCSs suggests that TWP-ICE convective clouds have stronger ascent while the mesoscale ascent outside convective clouds in AMMA is stronger. A case comparison, with the aid of sensitivity experiments, also suggests that vertical wind shear and ice crystal (or dust aerosol) concentration can significantly impact stratiform and anvil clouds (e.g., their areas) in MCSs. In addition, the obtained water budgets quantitatively describe the transport of water between convective, stratiform, and anvil regions as well as water sources/sinks from microphysical processes, providing information that can be used to help determine parameters in the convective and cloud parameterizations in general circulation models (GCMs).

scholarly journals Toward unification of the multiscale modeling of the atmosphere

2011 ◽  
Vol 11 (8) ◽  
pp. 3731-3742 ◽  
Author(s):  
A. Arakawa ◽  
J.-H. Jung ◽  
C.-M. Wu
Keyword(s):  
General Circulation ◽  
Three Dimensional ◽  
General Circulation Models ◽  
Moist Convection ◽  
Modeling Framework ◽  
Continuous Transition ◽  
Convective Clouds ◽  
Multi Scale ◽  
Scale Modeling ◽  
Deep Moist Convection

Abstract. As far as the representation of deep moist convection is concerned, only two kinds of model physics are used at present: highly parameterized as in the conventional general circulation models (GCMs) and explicitly simulated as in the cloud-resolving models (CRMs). Ideally, these two kinds of model physics should be unified so that a continuous transition of model physics from one kind to the other takes place as the resolution changes. With such unification, the GCM can converge to a global CRM (GCRM) as the grid size is refined. This paper suggests two possible routes to achieve the unification. ROUTE I continues to follow the parameterization approach, but uses a unified parameterization that is applicable to any horizontal resolutions between those typically used by GCMs and CRMs. It is shown that a key to construct such a unified parameterization is to eliminate the assumption of small fractional area covered by convective clouds, which is commonly used in the conventional cumulus parameterizations either explicitly or implicitly. A preliminary design of the unified parameterization is presented, which demonstrates that such an assumption can be eliminated through a relatively minor modification of the existing mass-flux based parameterizations. Partial evaluations of the unified parameterization are also presented. ROUTE II follows the "multi-scale modeling framework (MMF)" approach, which takes advantage of explicit representation of deep moist convection and associated cloud-scale processes by CRMs. The Quasi-3-D (Q3-D) MMF is an attempt to broaden the applicability of MMF without necessarily using a fully three-dimensional CRM. This is accomplished using a network of cloud-resolving grids with large gaps. An outline of the Q3-D algorithm and highlights of preliminary results are reviewed.

Organized Convection Parameterization for the ITCZ*

2015 ◽  
Vol 72 (8) ◽  
pp. 3073-3096 ◽  
Author(s):  
Boualem Khouider ◽  
Mitchell W. Moncrieff
Keyword(s):  
General Circulation ◽  
Potential Temperature ◽  
Three Dimensional ◽  
General Circulation Models ◽  
Dimensional Structure ◽  
Convective System ◽  
Convective Systems ◽  
Equatorial Wave ◽  
Upper Level ◽  
Upper Level Jet

Abstract Mesoscale convective systems (MCSs) are of fundamental importance in the dynamics of the atmospheric circulation and the climate system. They are often observed to develop over significant terrain in ambient shear flows in midlatitudes and embedded within the Madden–Julian oscillation (MJO) and convectively coupled equatorial wave (CCEW) envelopes, as well as in the intertropical convergence zone (ITCZ). Yet general circulation models (GCMs) fail to resolve these systems, and their underlying convective parameterizations are not directed to represent organized circulations. Shear-parallel MCSs, which are common in the ITCZ, have a three-dimensional structure and, as such, present a serious modeling challenge. Here, a previously developed multicloud model (MCM) is modified to parameterize MCSs. One of the main modifications is the parameterization of stratiform condensation to capture extended stratiform outflows, which characterize MCSs, resulting from strong upper-level jets. Linear analysis shows that, under the influence of a typical double African and equatorial jet shear flow, this modification results in an additional new scale-selective instability peaking at the mesoalpha scale of roughly 400 km. Nonlinear simulations conducted with the modified MCM on a 400 km × 400 km doubly periodic domain, without rotation, resulted in the spontaneous transition from a quasi-two-dimensional shear-perpendicular convective system, consistent with linear theory, to a fully three-dimensional flow structure. The simulation is characterized by shear-parallel bands of convection, moving slowly eastward, embedded in stratiform systems that expand perpendicularly and propagate westward with the upper-level jet. The mean circulation and the implications for the domain-averaged vertical transport of momentum and potential temperature are discussed.

scholarly journals Toward unification of the multiscale modeling of the atmosphere

2011 ◽  
Vol 11 (1) ◽  
pp. 3181-3217 ◽  
Author(s):  
A. Arakawa ◽  
J.-H. Jung ◽  
C.-M. Wu
Keyword(s):  
General Circulation ◽  
Three Dimensional ◽  
General Circulation Models ◽  
Moist Convection ◽  
Modeling Framework ◽  
Continuous Transition ◽  
Convective Clouds ◽  
Multi Scale ◽  
Deep Moist Convection ◽  
Fine Resolution

Abstract. This paper suggests two possible routes to achieve the unification of model physics in coarse- and fine-resolution atmospheric models. As far as representation of deep moist convection is concerned, only two kinds of model physics are used at present: highly parameterized as in the conventional general circulation models (GCMs) and explicitly simulated as in the cloud-resolving models (CRMs). Ideally, these two kinds of model physics should be unified so that a continuous transition of model physics from one kind to the other takes place as the resolution changes. With such unification, the GCM can converge to a global CRM (GCRM) as the grid size is refined. ROUTE I for unification continues to follow the parameterization approach, but uses a unified parameterization that is applicable to any horizontal resolutions between those typically used by GCMs and CRMs. It is shown that a key to construct such a unified parameterization is to eliminate the assumption of small fractional area covered by convective clouds, which is commonly used in the conventional cumulus parameterizations either explicitly or implicitly. A preliminary design of the unified parameterization is presented, which demonstrates that such an assumption can be eliminated through a relatively minor modification of the existing mass-flux based parameterizations. Partial evaluations of the unified parameterization are also presented. ROUTE II for unification follows the "multi-scale modeling framework (MMF)" approach, which takes advantage of explicit representation of deep moist convection and associated cloud-scale processes by CRMs. The Quasi-3-D (Q3-D) MMF is an attempt to broaden the applicability of MMF without necessarily using a fully three-dimensional CRM. This is accomplished using a network of cloud-resolving grids with gaps. An outline of the Q3-D algorithm and highlights of preliminary results are reviewed.

scholarly journals Using Radar Observations to Evaluate 3D Radar Echo Structure Simulated by a Global Model

2020 ◽  
Author(s):  
Jingyu Wang ◽  
Jiwen Fan ◽  
Robert A. Houze Jr. ◽  
Stella R. Brodzik ◽  
Kai Zhang ◽  
...  
Keyword(s):  
General Circulation ◽  
Water Cycle ◽  
Three Dimensional ◽  
General Circulation Models ◽  
Atmospheric Model ◽  
Radar Reflectivity ◽  
Department Of Energy ◽  
Radar Observations ◽  
Convective Systems ◽  
Central United States

Abstract. The Energy Exascale Earth System Model (E3SM) developed by the Department of Energy has a goal of addressing challenges in understanding the global water cycle. Success depends on correct simulation of cloud and precipitation elements. However, lack of appropriate evaluation metrics has hindered the accurate representation of these elements in general circulation models. We derive metrics from the three-dimensional data of the ground-based Next generation radar (NEXRAD) network over the U.S. to evaluate both horizontal and vertical structures of precipitation elements. We coarsened the resolution of the radar observations to be consistent with the model resolution and improved the coupling of the Cloud Feedback Model Intercomparison Project Observation Simulator Package (COSP) and E3SM Atmospheric Model Version 1 (EAMv1) to obtain the best possible model output for comparison with the observations. Three warm seasons (2014–2016) of EAMv1 simulations of 3D radar reflectivity features at an hourly scale are evaluated. A general agreement in domain-mean radar reflectivity intensity is found between EAMv1 and NEXRAD below 4 km altitude; however, the model underestimates reflectivity over the central United States, which suggests that the model does not capture the mesoscale convective systems that produce much of precipitation in that region. The shape of the model estimated histogram of subgrid scale reflectivity is improved by correcting the microphysical assumptions in COSP. The model severely underestimates radar reflectivity at upper levels – the simulated echo top height is about 4 km lower than in observations – and this result is not changed by tuning any single physics parameter.

scholarly journals The MJO in a Coarse-Resolution GCM with a Stochastic Multicloud Parameterization

2015 ◽  
Vol 72 (1) ◽  
pp. 55-74 ◽  
Author(s):  
Qiang Deng ◽  
Boualem Khouider ◽  
Andrew J. Majda
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Deterministic Model ◽  
Weather Prediction ◽  
General Circulation Models ◽  
Radar Data ◽  
Equation Model ◽  
Death Process ◽  
Relevant Parameter ◽  
Convective Systems

Abstract The representation of the Madden–Julian oscillation (MJO) is still a challenge for numerical weather prediction and general circulation models (GCMs) because of the inadequate treatment of convection and the associated interactions across scales by the underlying cumulus parameterizations. One new promising direction is the use of the stochastic multicloud model (SMCM) that has been designed specifically to capture the missing variability due to unresolved processes of convection and their impact on the large-scale flow. The SMCM specifically models the area fractions of the three cloud types (congestus, deep, and stratiform) that characterize organized convective systems on all scales. The SMCM captures the stochastic behavior of these three cloud types via a judiciously constructed Markov birth–death process using a particle interacting lattice model. The SMCM has been successfully applied for convectively coupled waves in a simplified primitive equation model and validated against radar data of tropical precipitation. In this work, the authors use for the first time the SMCM in a GCM. The authors build on previous work of coupling the High-Order Methods Modeling Environment (HOMME) NCAR GCM to a simple multicloud model. The authors tested the new SMCM-HOMME model in the parameter regime considered previously and found that the stochastic model drastically improves the results of the deterministic model. Clear MJO-like structures with many realistic features from nature are reproduced by SMCM-HOMME in the physically relevant parameter regime including wave trains of MJOs that organize intermittently in time. Also one of the caveats of the deterministic simulation of requiring a doubling of the moisture background is not required anymore.

scholarly journals Pathways of PFOA to the Arctic: variabilities and contributions of oceanic currents and atmospheric transport and chemistry sources

2010 ◽  
Vol 10 (5) ◽  
pp. 11577-11614 ◽  
Author(s):  
I. Stemmler ◽  
G. Lammel
Keyword(s):  
General Circulation ◽  
Atmospheric Transport ◽  
Three Dimensional ◽  
General Circulation Models ◽  
The Arctic ◽  
Boreal Winter ◽  
Polar Regions ◽  
Industrial Chemicals ◽  
Spatially Resolved ◽  
Primary Emissions

Abstract. Perfluorooctanoic acid (PFOA) and other perfluorinated compounds are industrial chemicals in use since decades which resist degradation in the environment and seem to accumulate in polar regions. Transport of PFOA was modeled using a spatially resolved global multicompartment model including fully coupled three-dimensional ocean and atmosphere general circulation models, and two-dimensional top soil, vegetation surfaces, and sea ice compartments. In addition to primary emissions, the formation of PFOA in the atmosphere from degradation of 8:2 fluorotelomer alcohol was included as a PFOA source. Oceanic transport, delivered 14.8±5.0 (8–23) t a−1 to the Arctic, strongly influenced by changes in water transport, which determined its interannual variability. This pathway constituted the dominant source of PFOA to the Arctic. Formation of PFOA in the atmosphere lead to episodic transport events (timescale of days) into the Arctic with small spatial extent. Deposition in the polar region was found to be dominated by wet deposition over land, and shows maxima in boreal winter. The total atmospheric deposition of PFOA in the Arctic in the 1990s was ≈1 t a−1, much higher than previously estimated, and is dominated by primary emissions rather than secondarily formed.

scholarly journals Wet scavenging limits the detection of aerosol–cloud–precipitation interactions

2015 ◽  
Vol 15 (5) ◽  
pp. 6851-6886 ◽  
Author(s):  
E. Gryspeerdt ◽  
P. Stier ◽  
B. A. White ◽  
Z. Kipling
Keyword(s):  
Spatial Variability ◽  
General Circulation ◽  
Regional Scale ◽  
General Circulation Models ◽  
Satellite Observations ◽  
Scale Model ◽  
Convective Clouds ◽  
Aerosol Cloud ◽  
Wet Scavenging ◽  
Aerosol Properties

Abstract. Satellite studies of aerosol–cloud interactions usually make use of retrievals of both aerosol and cloud properties, but these retrievals are rarely spatially co-located. While it is possible to retrieve aerosol properties above clouds under certain circumstances, aerosol properties are usually only retrieved in cloud free scenes. Generally, the smaller spatial variability of aerosols compared to clouds reduces the importance of this sampling difference. However, as precipitation generates an increase in spatial variability, the imperfect co-location of aerosol and cloud property retrievals may lead to changes in observed aerosol–cloud–precipitation relationships in precipitating environments. In this work, we use a regional-scale model, satellite observations and reanalysis data to investigate how the non-coincidence of aerosol, cloud and precipitation retrievals affects correlations between them. We show that the difference in the aerosol optical depth (AOD)-precipitation relationship between general circulation models (GCMs) and satellite observations can be explained by the wet scavenging of aerosol. Using observations of the development of precipitation from cloud regimes, we show how the influence of wet scavenging can obscure possible aerosol influences on precipitation from convective clouds. This obscuring of aerosol–cloud–precipitation interactions by wet scavenging suggests that even if GCMs contained a perfect representation of aerosol influences on convective clouds, the difficulty of separating the "clear-sky" aerosol from the "all-sky" aerosol in GCMs may prevent them from reproducing the correlations seen in satellite data.

Using the Stochastic Multicloud Model to Improve Tropical Convective Parameterization: A Paradigm Example

2012 ◽  
Vol 69 (3) ◽  
pp. 1080-1105 ◽  
Author(s):  
Yevgeniy Frenkel ◽  
Andrew J. Majda ◽  
Boualem Khouider
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Tropical Convection ◽  
Convective Parameterization ◽  
Convective Systems ◽  
Squall Lines ◽  
Walker Cell ◽  
Single Column ◽  
Mesoscale Convective ◽  
Coarse Grids

Abstract Despite recent advances in supercomputing, current general circulation models (GCMs) poorly represent the variability associated with organized tropical convection. A stochastic multicloud convective parameterization based on three cloud types (congestus, deep, and stratiform), introduced recently by Khouider, Biello, and Majda in the context of a single column model, is used here to study flows above the equator without rotation effects. The stochastic model dramatically improves the variability of tropical convection compared to the conventional moderate- and coarse-resolution paradigm GCM parameterizations. This increase in variability comes from intermittent coherent structures such as synoptic and mesoscale convective systems, analogs of squall lines and convectively coupled waves seen in nature whose representation is improved by the stochastic parameterization. Furthermore, simulations with a sea surface temperature (SST) gradient yield realistic mean Walker cell circulation with plausible high variability. An additional feature of the present stochastic parameterization is a natural scaling of the model from moderate to coarse grids that preserves the variability and statistical structure of the coherent features. These results systematically illustrate, in a paradigm model, the benefits of using the stochastic multicloud framework to improve deterministic parameterizations with clear deficiencies.

scholarly journals An Anomalous Genesis Potential Index for MJO Modulation of Tropical Cyclones

2017 ◽  
Vol 30 (11) ◽  
pp. 4021-4035 ◽  
Author(s):  
Bin Wang ◽  
Ja-Yeon Moon
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
General Circulation Models ◽  
Intraseasonal Variation ◽  
Coriolis Parameter ◽  
Genesis Potential Index ◽  
Low Level ◽  
Potential Index

Abstract Modulation of tropical cyclone (TC) genesis by the Madden–Julian oscillation (MJO) has been quantitatively diagnosed by using a climatological genesis potential index (GPI). Analysis of TC genesis during November–April of 1979–2014 indicates the most effective factors controlling intraseasonal TC genesis are 850-hPa relative vorticity weighted by the Coriolis parameter fζr850 and 500-hPa vertical motion ω500. The total vertical wind shear and maximum potential intensity are unimportant, and the role of 600-hPa relative humidity is greatly represented by ω500. The MJO modulates TC genesis primarily through changing low-level vorticity induced by its Rossby wave gyres and meridional shears of equatorial zonal winds. A new intraseasonal GPI (ISGPI) is proposed to quantify the MJO’s modulation of TC genesis. The ISGPI significantly improves representation of intraseasonal variation of TC genesis in the tropics and in each subregion of the southern Indian Ocean, Australian monsoon, and South Pacific. In the hot spots of the Southern Hemisphere TC genesis zone, the probability of TC genesis can differ by a factor of 5–19 as a result of MJO modulation. The results suggest that the large-scale factors controlling TC genesis may vary with different time scales, and the climatological GPI may not be quite applicable for diagnoses of climate variability and future change of TC genesis potential. To simulate realistic impacts of the MJO on TC genesis, general circulation models must reproduce not only realistic eastward propagation but also the MJO low-level circulation structure. Application of the new ISGPI may have a large potential to improve dynamical subseasonal prediction of TC genesis.

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