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.

Precipitation Partitioning, Tropical Clouds, and Intraseasonal Variability in GFDL AM2

2013 ◽  
Vol 26 (15) ◽  
pp. 5453-5466 ◽  
Author(s):  
Yanluan Lin ◽  
Ming Zhao ◽  
Yi Ming ◽  
Jean-Christophe Golaz ◽  
Leo J. Donner ◽  
...  
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Precipitation Variability ◽  
Cloud Fraction ◽  
Cumulus Parameterization ◽  
Convective Precipitation ◽  
Climate Simulation ◽  
Geophysical Fluid Dynamics Laboratory ◽  
The Tropics

Abstract A set of Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model version 2 (AM2) sensitivity simulations by varying an entrainment threshold rate to control deep convection occurrence are used to investigate how cumulus parameterization impacts tropical cloud and precipitation characteristics. In the tropics, model convective precipitation (CP) is frequent and light, while large-scale precipitation (LSP) is intermittent and strong. With deep convection inhibited, CP decreases significantly over land and LSP increases prominently over ocean. This results in an overall redistribution of precipitation from land to ocean. A composite analysis reveals that cloud fraction (low and middle) and cloud condensate associated with LSP are substantially larger than those associated with CP. With about the same total precipitation and precipitation frequency distribution over the tropics, simulations having greater LSP fraction tend to have larger cloud condensate and low and middle cloud fraction. Simulations having a greater LSP fraction tend to be drier and colder in the upper troposphere. The induced unstable stratification supports strong transient wind perturbations and LSP. Greater LSP also contributes to greater intraseasonal (20–100 days) precipitation variability. Model LSP has a close connection to the low-level convergence via the resolved grid-scale dynamics and, thus, a close coupling with the surface heat flux. Such wind–evaporation feedback is essential to the development and maintenance of LSP and enhances model precipitation variability. LSP has stronger dependence and sensitivity on column moisture than CP. The moisture–convection feedback, critical to tropical intraseasonal variability, is enhanced in simulations with large LSP. Strong precipitation variability accompanied by a worse mean state implies that an optimal precipitation partitioning is critical to model tropical climate simulation.

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 Factors for the Simulation of Convectively Coupled Kelvin Waves

2012 ◽  
Vol 25 (10) ◽  
pp. 3495-3514 ◽  
Author(s):  
Kyong-Hwan Seo ◽  
Jin-Ho Choi ◽  
Sang-Dae Han
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Kelvin Waves ◽  
Cumulus Parameterization ◽  
Kelvin Wave ◽  
Shallow Convection ◽  
Cumulus Parameterization Schemes ◽  
Environmental Prediction ◽  
Major Factors ◽  
Heating Profile

Abstract This study investigates the major factors for the realistic simulation of convectively coupled Kelvin waves (CCKWs) using the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) models. CFS simulations employing relaxed Arakawa–Schubert (RAS; hereafter CTRL) and simplified Arakawa–Schubert (SAS) cumulus parameterization schemes show that the former generates the observed Kelvin wave signature more realistically than the latter does. For example, the space–time spectral signal, eastward propagation, and tilted (and second baroclinic mode) vertical structures in convection, temperature, moisture, and circulation anomalies associated with CCKWs in CTRL are more comparable to observations than in the SAS simulation. CTRL and observations demonstrate the characteristic evolution and vertical heating profile associated with CCKWs similar to those seen in mesoscale convective systems in the tropics: shallow convection, followed by deep convection and then stratiform cloudiness, and resulting in a top-heavy diabatic heating profile. Five additional experiments demonstrate that the effects of convective downdrafts, subgrid-scale convective rain evaporation, and large-scale rain evaporation on CCKWs are assessed to be insignificant in CTRL, possibly due to a more humid environment than observation. However, the Kelvin wave signals are reduced by ~40% when shallow convection is disabled. More importantly, the removal of convective detrainment at the cloud top results in the greatest reduction in Kelvin wave activity (by more than 70%). Therefore, the preconditioning of the atmosphere by shallow convection and detrainment of water vapor and condensate from convective updrafts to the environment and subsequent stratiform heating (grid-scale condensational heating)/precipitation processes are the two most crucial factors for the successful simulation of CCKWs.

scholarly journals Improved Madden–Julian Oscillations with Improved Physics: The Impact of Modified Convection Parameterizations

2012 ◽  
Vol 25 (4) ◽  
pp. 1116-1136 ◽  
Author(s):  
Lei Zhou ◽  
Richard B. Neale ◽  
Markus Jochum ◽  
Raghu Murtugudde
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Conveyor Belt ◽  
Convective Heating ◽  
Climate System Model ◽  
Zonal Winds ◽  
Convective Momentum Transport ◽  
The Impact

Abstract Two modifications are made to the deep convection parameterization in the NCAR Community Climate System Model, version 3 (CCSM3): a dilute plume approximation and an implementation of the convective momentum transport (CMT). These changes lead to significant improvement in the simulated Madden–Julian oscillations (MJOs). With the dilute plume approximation, temperature and convective heating perturbations become more positively correlated. Consequently, more available potential energy is generated and the intraseasonal variability (ISV) becomes stronger. The organization of ISV is also improved, which is manifest in coherent structures between different MJO phases and an improved simulation of the eastward propagation of MJOs with a reasonable eastward speed. The improved propagation can be attributed to a better simulation of the low-level zonal winds due to the inclusion of CMT. The authors posit that the large-scale zonal winds are akin to a selective conveyor belt that facilitates the organization of ISVs into highly coherent structures, which are important features of observed MJOs. The conclusions are supported by two supplementary experiments, which include the dilute plume approximation and CMT separately.

scholarly journals Effects of Cloud Microphysics on Tropical Atmospheric Hydrologic Processes and Intraseasonal Variability

2005 ◽  
Vol 18 (22) ◽  
pp. 4731-4751 ◽  
Author(s):  
K. M. Lau ◽  
H. T. Wu ◽  
Y. C. Sud ◽  
G. K. Walker
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Water Cycle ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Hydrologic Processes ◽  
Warm Rain

Abstract The sensitivity of tropical atmospheric hydrologic processes to cloud microphysics is investigated using the NASA Goddard Earth Observing System (GEOS) general circulation model (GCM). Results show that a faster autoconversion rate leads to (a) enhanced deep convection in the climatological convective zones anchored to tropical land regions; (b) more warm rain, but less cloud over oceanic regions; and (c) an increased convective-to-stratiform rain ratio over the entire Tropics. Fewer clouds enhance longwave cooling and reduce shortwave heating in the upper troposphere, while more warm rain produces more condensation heating in the lower troposphere. This vertical differential heating destabilizes the tropical atmosphere, producing a positive feedback resulting in more rain and an enhanced atmospheric water cycle over the Tropics. The feedback is maintained via secondary circulations between convective tower and anvil regions (cold rain), and adjacent middle-to-low cloud (warm rain) regions. The lower cell is capped by horizontal divergence and maximum cloud detrainment near the freezing–melting (0°C) level, with rising motion (relative to the vertical mean) in the warm rain region connected to sinking motion in the cold rain region. The upper cell is found above the 0°C level, with induced subsidence in the warm rain and dry regions, coupled to forced ascent in the deep convection region. It is that warm rain plays an important role in regulating the time scales of convective cycles, and in altering the tropical large-scale circulation through radiative–dynamic interactions. Reduced cloud–radiation feedback due to a faster autoconversion rate results in intermittent but more energetic eastward propagating Madden–Julian oscillations (MJOs). Conversely, a slower autoconversion rate, with increased cloud radiation produces MJOs with more realistic westward-propagating transients embedded in eastward-propagating supercloud clusters. The implications of the present results on climate change and water cycle dynamics research are discussed.

scholarly journals Constraints on Cumulus Parameterization from Simulations of Observed MJO Events

2015 ◽  
Vol 28 (16) ◽  
pp. 6419-6442 ◽  
Author(s):  
Anthony D. Del Genio ◽  
Jingbo Wu ◽  
Audrey B. Wolf ◽  
Yonghua Chen ◽  
Mao-Sung Yao ◽  
...  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Deep Convection ◽  
Circulation Model ◽  
Longwave Radiation ◽  
Tropical Rainfall Measuring Mission ◽  
Cumulus Parameterization ◽  
Cold Pools ◽  
Atmospheric Radiation Measurement ◽  
Goddard Institute

Abstract Two recent activities offer an opportunity to test general circulation model (GCM) convection and its interaction with large-scale dynamics for observed Madden–Julian oscillation (MJO) events. This study evaluates the sensitivity of the Goddard Institute for Space Studies (GISS) GCM to entrainment, rain evaporation, downdrafts, and cold pools. Single Column Model versions that restrict weakly entraining convection produce the most realistic dependence of convection depth on column water vapor (CWV) during the Atmospheric Radiation Measurement MJO Investigation Experiment at Gan Island. Differences among models are primarily at intermediate CWV where the transition from shallow to deeper convection occurs. GCM 20-day hindcasts during the Year of Tropical Convection that best capture the shallow–deep transition also produce strong MJOs, with significant predictability compared to Tropical Rainfall Measuring Mission data. The dry anomaly east of the disturbance on hindcast day 1 is a good predictor of MJO onset and evolution. Initial CWV there is near the shallow–deep transition point, implicating premature onset of deep convection as a predictor of a poor MJO simulation. Convection weakly moistens the dry region in good MJO simulations in the first week; weakening of large-scale subsidence over this time may also affect MJO onset. Longwave radiation anomalies are weakest in the worst model version, consistent with previous analyses of cloud/moisture greenhouse enhancement as the primary MJO energy source. The authors’ results suggest that both cloud-/moisture-radiative interactions and convection–moisture sensitivity are required to produce a successful MJO simulation.

scholarly journals Land-atmosphere coupling at the U.S. Southern Great Plains: A comparison on local convective regimes between ARM observations, reanalysis, and climate model simulations

2020 ◽  
Author(s):  
Cheng Tao ◽  
Yunyan Zhang ◽  
Qi Tang ◽  
Hsi-Yen Ma ◽  
Virendra P. Ghate ◽  
...  
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Deep Convection ◽  
Early Morning ◽  
Lower Atmosphere ◽  
Shortwave Radiation ◽  
Southern Great Plains ◽  
Model Version ◽  
Shallow Cumulus ◽  
Atmosphere Model

AbstractUsing the 9-yr warm-season observations at the Atmospheric Radiation Measurement Southern Great Plains site, we assess the land-atmosphere (L-A) coupling in North American Regional Reanalysis (NARR) and two climate models: hindcasts with the Community Atmosphere Model version 5.1 by Cloud-Associated Parameterizations Testbed (CAM5-CAPT) and nudged runs with the Energy Exascale Earth System Model Atmosphere Model version 1 Regionally Refined Model (EAMv1-RRM). We focus on three local convective regimes and diagnose model behaviors using the Local Coupling metrics (Santanello et al. 2018). NARR agrees well with observations except a slightly warmer and drier surface with higher downwelling shortwave radiation and lower evaporative fraction. On clear-sky days, it shows warmer and drier early-morning conditions in both models with significant underestimates in surface evaporation by EAMv1-RRM. On the majority of the ARM-observed shallow cumulus days, there is no or little low-level clouds in either model. When captured in models, the simulated shallow cumulus shows much less cloud fraction and lower cloud bases than observed. On the days with late-afternoon deep convection, models tend to present a stable early-morning lower atmosphere more frequently than the observations, suggesting that the deep convection is triggered more often by elevated instabilities. Generally, CAM5-CAPT can reproduce the local L-A coupling processes to some extent due to the constrained early-morning conditions and large-scale winds. EAMv1-RRM exhibits large precipitation deficits and warm and dry biases towards mid-to-late summers, which may be an amplification through a positive L-A feedback among initial atmosphere and land states, convection triggering and large-scale circulations.

Modulation of Tropical Cyclones over the Eastern Pacific by the Intraseasonal Variability Simulated in an AGCM

2012 ◽  
Vol 25 (19) ◽  
pp. 6524-6538 ◽  
Author(s):  
Xianan Jiang ◽  
Ming Zhao ◽  
Duane E. Waliser
Keyword(s):  
Relative Humidity ◽  
Wind Shear ◽  
Large Scale ◽  
Intraseasonal Variability ◽  
Vertical Wind Shear ◽  
Atmospheric Model ◽  
Horizontal Resolution ◽  
Vertical Wind ◽  
Eastern Pacific ◽  
Geophysical Fluid Dynamics Laboratory

Abstract This study illustrates that observed modulations of tropical cyclone (TC) genesis over the eastern Pacific (EPAC) by large-scale intraseasonal variability (ISV) are well represented in a recently developed high-resolution atmospheric model (HiRAM) at the NOAA/Geophysical Fluid Dynamics Laboratory (GFDL) with a horizontal resolution of about 50 km. Considering the intrinsic predictability of the ISV of 2–4 weeks, this analysis thus has significant implications for dynamically based TC predictions on intraseasonal time scales. Analysis indicates that the genesis potential index (GPI) anomalies associated with the ISV can generally well depict ISV modulations of EPAC TC genesis in both observations and HiRAM simulations. Further investigation is conducted to explore the key factors associated with ISV modulation of TC activity based on an analysis of budget terms of the observed GPI during the ISV life cycle. It is found that, while relative roles of GPI factors are dependent on ISV phase and location, lower-level cyclonic vorticity, enhanced midlevel relative humidity, and reduced vertical wind shear can all contribute to the observed active TC genesis over the EPAC during particular ISV phases. In general, the observed anomalous ISV patterns of these large-scale GPI factors are well represented in HiRAM. Model deficiencies are also noted particularly in the anomalous midlevel relative humidity patterns and amplitude of vertical wind shear associated with the EPAC ISV.

Large-scale state and evolution of the atmosphere and ocean during PISTON 2018

2021 ◽  
pp. 1-59
Author(s):  
Adam H. Sobel ◽  
Janet Sprintall ◽  
Eric D. Maloney ◽  
Zane K. Martin ◽  
Shuguang Wang ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Reanalysis Data ◽  
The Philippines ◽  
Heat Fluxes ◽  
Surface Heat Fluxes ◽  
Low Level ◽  
The North

AbstractThe Propagation of Intraseasonal Tropical Oscillations (PISTON) experiment conducted a field campaign inAugust-October 2018. The R/V Thomas G. Thompson made two cruises in thewestern North Pacific region north of Palau and east of the Philippines. Using select field observations and global observational and reanalysis data sets, this study describes the large-scale state and evolution of the atmosphere and ocean during these cruises. Intraseasonal variability was weak during the field program, except for a period of suppressed convection in October. Tropical cyclone activity, on the other hand, was strong. Variability at the ship location was characterized by periods of low-level easterly atmospheric flow with embedded westward propagating synoptic-scale atmospheric disturbances, punctuated by periods of strong low-level westerly winds that were both connected to the Asian monsoon westerlies and associated with tropical cyclones. In the most dramatic case, westerlies persisted for days during and after tropical cyclone Jebi had passed to the north of the ship. In these periods, the sea surface temperature was reduced by a couple of degrees by both wind mixing and net surface heat fluxes that were strongly (~200Wm−2) out of the ocean, due to both large latent heat flux and cloud shading associated with widespread deep convection. Underway conductivity-temperature transects showed dramatic cooling and deepening of the ocean mixed layer and erosion of the barrier layer after the passage of Typhoon Mangkhut due to entrainment of cooler water from below. Strong zonal currents observed over at least the upper 400 meters were likely related to the generation and propagation of near-inertial currents.

scholarly journals Effects of Coupling a Stochastic Convective Parameterization with Zhang-McFarlane Scheme on Precipitation Simulation in the DOE E3SMv1 Atmosphere Model

2020 ◽  
Author(s):  
Yong Wang ◽  
Guang J. Zhang ◽  
Shaocheng Xie ◽  
Wuyin Lin ◽  
George C. Craig ◽  
...  
Keyword(s):  
Large Scale ◽  
Rainfall Intensity ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Precipitation Amount ◽  
Convective Precipitation ◽  
Moderate Increase ◽  
Light Rain ◽  
Precipitation Simulation ◽  
Atmosphere Model

Abstract. A stochastic deep convection parameterization is implemented into the U.S. Department of Energy (DOE) Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1). This study evaluates its performance on the precipitation simulation. Compared to the default model, the probability distribution function (PDF) of rainfall intensity in the new simulation is greatly improved. Especially, the well-known problem of too much light rain and too little heavy rain is alleviated over the tropics. As a result, the contribution from different rain rates to the total precipitation amount is shifted toward heavier rain. The less frequent occurrence of convection contributes to the suppressed light rain, while both more intense large-scale and convective precipitation contribute to the enhanced heavy total rain. The synoptic and intraseasonal variabilities of precipitation are enhanced as well to be closer to observations. A sensitivity of the rainfall intensity PDF to the model vertical resolution is identified and explained in terms of the relationships between convective precipitation and convective available potential energy (CAPE) and between large-scale precipitation and resolved-scale upward moisture flux. The annual mean precipitation is largely unchanged with the use of the stochastic scheme except over the tropical western Pacific, where a moderate increase in precipitation represents a slight improvement. The responses of precipitation and its extremes to climate warming are similar with or without the stochastic deep convection scheme.

Sign in / Sign up

Export Citation Format

Share Document