scholarly journals Is the Tropical Atmosphere in Convective Quasi-Equilibrium?

2015 ◽  
Vol 28 (11) ◽  
pp. 4357-4372 ◽  
Author(s):  
Jia-Lin Lin ◽  
Taotao Qian ◽  
Toshiaki Shinoda ◽  
Shuanglin Li
Keyword(s):  
Boundary Layer ◽  
Global Climate Models ◽  
Quasi Equilibrium ◽  
Tropical Atmosphere ◽  
Tropospheric Temperature ◽  
Moist Convection ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Upper Troposphere ◽  
Static Energy

Abstract The hypothesis of convective quasi-equilibrium (CQE) has dominated thinking about the interaction between deep moist convection and the environment for at least two decades. In this view, deep convection develops or decays almost instantly to remove any changes of convective instability, making the tropospheric temperature always tied to the boundary layer moist static energy. The present study examines the validity of the CQE hypothesis at different vertical levels using long-term sounding data from tropical convection centers. The results show that the tropical atmosphere is far from the CQE with much weaker warming in the middle and upper troposphere associated with the increase of boundary layer moist static energy. This is true for all the time scales resolved by the observational data, ranging from hourly to interannual and decadal variability. It is possibly caused by the ubiquitous existence of shallow convection and stratiform precipitation, both leading to sign reversal of heating from lower to upper troposphere. The simulations by 42 global climate models from phases 3 and 5 of the Coupled Model Intercomparsion Project (CMIP3 and CMIP5) are also analyzed and compared with the observations.

scholarly journals Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

2013 ◽  
Vol 26 (8) ◽  
pp. 2417-2431 ◽  
Author(s):  
Qiongqiong Cai ◽  
Guang J. Zhang ◽  
Tianjun Zhou
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Reanalysis Data ◽  
Specific Humidity ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Budget Analysis ◽  
Static Energy

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

scholarly journals An Analysis of Convectively Coupled Kelvin Waves in 20 WCRP CMIP3 Global Coupled Climate Models

2010 ◽  
Vol 23 (11) ◽  
pp. 3031-3056 ◽  
Author(s):  
Katherine H. Straub ◽  
Patrick T. Haertel ◽  
George N. Kiladis
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Three Dimensional ◽  
Kelvin Waves ◽  
Global Climate Models ◽  
Specific Humidity ◽  
Tropospheric Temperature ◽  
Wave Band ◽  
Kelvin Wave ◽  
Shallow Convection

Abstract Output from 20 coupled global climate models is analyzed to determine whether convectively coupled Kelvin waves exist in the models, and, if so, how their horizontal and vertical structures compare to observations. Model data are obtained from the World Climate Research Program’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset. Ten of the 20 models contain spectral peaks in precipitation in the Kelvin wave band, and, of these 10, only 5 contain wave activity distributions and three-dimensional wave structures that resemble the observations. Thus, the majority (75%) of the global climate models surveyed do not accurately represent convectively coupled Kelvin waves, one of the primary sources of submonthly zonally propagating variability in the tropics. The primary feature common to the five successful models is the convective parameterization. Three of the five models use the Tiedtke–Nordeng convective scheme, while the other two utilize the Pan and Randall scheme. The 15 models with less success at generating Kelvin waves predominantly contain convective schemes that are based on the concept of convective adjustment, although it appears that those schemes can be improved by the addition of convective “trigger” functions. Three-dimensional Kelvin wave structures in the five successful models resemble observations to a large degree, with vertically tilted temperature, specific humidity, and zonal wind anomalies. However, no model completely captures the observed signal, with most of the models being deficient in lower-tropospheric temperature and humidity signals near the location of maximum precipitation. These results suggest the need for improvements in the representations of shallow convection and convective downdrafts in global models.

Observational Evaluation of a Convective Quasi-Equilibrium View of Monsoons

2010 ◽  
Vol 23 (16) ◽  
pp. 4416-4428 ◽  
Author(s):  
Ji Nie ◽  
William R. Boos ◽  
Zhiming Kuang
Keyword(s):  
Boundary Layer ◽  
South Asian ◽  
Asian Monsoon ◽  
Potential Temperature ◽  
South Asian Monsoon ◽  
Quasi Equilibrium ◽  
Tropospheric Temperature ◽  
The South ◽  
Layer Potential ◽  
The North

Abstract Idealized dynamical theories that employ a convective quasi-equilibrium (QE) treatment for the diabatic effects of moist convection have been used to explain the location, intensity, and intraseasonal evolution of monsoons. This paper examines whether observations of the earth’s regional monsoons are consistent with the assumption of QE. It is shown here that in local summer climatologies based on reanalysis data, maxima of free-tropospheric temperature are, indeed, nearly collocated with maxima of subcloud equivalent potential temperature, θeb, in all monsoon regions except the North and South American monsoons. Free-tropospheric temperatures over North Africa also exhibit a strong remote influence from the South Asian monsoon. Consistent with idealized dynamical theories, peak precipitation falls slightly equatorward of the maxima in θeb and free-tropospheric temperature in regions where QE seems to hold. Vertical structures of temperature and wind reveal two types of monsoon circulations. One is the deep, moist baroclinic circulation clearly seen in the South Asian monsoon. The other is of mixed type, with the deep moist circulation superimposed on a shallow dry circulation closely associated with boundary layer temperature gradients. While the existence of a shallow dry circulation has been documented extensively in the North African monsoon, here it is shown to also exist in Australia and southern Africa during the local summer. Analogous to moist QE theories for the deep circulation, the shallow circulation can be viewed in a dry QE framework in which shallow ascent occurs just equatorward of the peak boundary layer potential temperature, θb, providing a unified system where the poleward extents of deep and shallow circulations are bounded by maxima in θeb and θb, respectively.

scholarly journals A Vertically Resolved MSE Framework Highlights the Role of the Boundary Layer in Convective Self-Aggregation

2021 ◽  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Mathematical Formulation ◽  
Detailed Comparison ◽  
Moist Static Energy ◽  
Uniform Temperature ◽  
Static Energy ◽  
Global And Local ◽  
Self Aggregation

Abstract Convective self-aggregation refers to a phenomenon in which random convection can self-organize into large-scale clusters over an ocean surface with uniform temperature in cloud-resolving models. Previous literature studies convective aggregation primarily by analyzing vertically integrated (VI) moist static energy (MSE) variance. That is the global MSE variance, including both the local MSE variance at a given altitude and the covariance of MSE anomalies between different altitudes. Here we present a vertically resolved (VR) MSE framework that focuses on the local MSE variance to study convective self-aggregation. Using a cloud-resolving simulation, we show that the development of self-aggregation is associated with an increase of local MSE variance, and that the diabatic and adiabatic generation of the MSE variance is mainly dominated by the boundary layer (BL, the lowest 2 km). The results agree with recent numerical simulation results and the available potential energy analyses showing that the BL plays a key role in the development of self-aggregation. Additionally, we find that the lower free troposphere (2 - 4 km) also generates significant MSE variance in the first 15 days. We further present a detailed comparison between the global and local MSE variance frameworks in their mathematical formulation and diagnostic results, highlighting their differences.

scholarly journals A Moisture-Stratiform Instability for Convectively Coupled Waves

2008 ◽  
Vol 65 (3) ◽  
pp. 834-854 ◽  
Author(s):  
Zhiming Kuang
Keyword(s):  
Realistic Model ◽  
Model Parameters ◽  
Convective Heating ◽  
Quasi Equilibrium ◽  
Moist Static Energy ◽  
Instability Mechanism ◽  
Convectively Coupled Waves ◽  
The Difference ◽  
Static Energy ◽  
The Waves

Abstract A simple model of two vertical modes is constructed and analyzed to reveal the basic instability mechanisms of convectively coupled waves. The main novelty of this model is a convective parameterization based on the quasi-equilibrium concept and simplified for a model of two vertical modes. It hypothesizes 1) the approximate invariance of the difference between saturation moist static energy in the lower half of the troposphere and moist static energy in the subcloud layer, regardless of free troposphere humidity, and 2) that variations in the depth of convection are determined by moisture-deficit variations in the midtroposphere. Physical arguments for such a treatment are presented. For realistic model parameters chosen based on cloud system resolving model simulations (CSRMs) of an earlier study, the model produces unstable waves at wavelengths and with structures that compare well with the CSRM simulations and observations. A moisture–stratiform instability and a direct–stratiform instability are identified as the main instability mechanisms in the model. The former relies on the effect of midtroposphere humidity on the depth of convection. The latter relies on the climatological mean convective heating profile being top heavy, and it is identified to be the same as the stratiform instability mechanism proposed by B. E. Mapes. The moisture–stratiform instability appears to be the main instability mechanism for the convectively coupled wave development in the CSRM simulations. The finite response time of convection has a damping effect on the waves that is stronger at high wavenumbers. The net moistening effect of the second-mode convective heating also damps the waves, but more strongly at low wavenumbers. These effects help to shape the growth rate curve so that the most unstable waves are of a few thousand kilometers in scale.

A Satellite Study of the Atmospheric Forcing and Response to Moist Convection over Tropical and Subtropical Oceans

2012 ◽  
Vol 69 (1) ◽  
pp. 150-167 ◽  
Author(s):  
Hirohiko Masunaga
Keyword(s):  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Tropical Rainfall Measuring Mission ◽  
Quasi Equilibrium ◽  
Tropospheric Temperature ◽  
Moist Convection ◽  
Atmospheric Forcing ◽  
Test Bed ◽  
Convective Adjustment ◽  
Subtropical Oceans

Abstract Satellite data are analyzed to explore the thermodynamic evolution of tropical and subtropical atmospheres prior and subsequent to moist convection in order to offer an observational test bed for convective adjustment, which is central to the quasi-equilibrium hypothesis. Tropical Rainfall Measuring Mission (TRMM) and Aqua satellite measurements are projected onto a composite temporal sequence over an hourly to daily time scale by exploiting the temporal gap between the local satellite overpasses, which changes from one day to another. The atmospheric forcing and response to convection are investigated separately for deep convective and congestus clouds. In the deep tropics, systematic moisture transport from the atmospheric boundary layer (ABL) to the free troposphere is evident in association with deep convection. The quick ABL ventilation suggests a swift convective adjustment but is preceded by a steady buildup of ABL moisture, which does not imply continuous adjustment to equilibrium. The evolution of convective available potential energy (CAPE) is controlled not only by the ABL moisture but also largely by a coincident ABL cooling linked with a bipolar anomaly of tropospheric temperature. The ABL moisture and temperature effects together lead to a rapid drop of CAPE for 12 h preceding convection, followed by a restoring phase that emerges as the cool anomaly recovers for a day or two. When moist convection is brought by congestus clouds with no deep convection nearby, CAPE gently increases over a period of 1–2 days until congestus occurs and then declines as slowly, suggestive of no efficient convective adjustment. The subtropical atmosphere shows no sign of convective adjustment whether or not vigorous convection is present.

High-Resolution Simulation of Shallow-to-Deep Convection Transition over Land

2006 ◽  
Vol 63 (12) ◽  
pp. 3421-3436 ◽  
Author(s):  
Marat Khairoutdinov ◽  
David Randall
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
High Resolution ◽  
Deep Convection ◽  
Radiative Heating ◽  
Moist Static Energy ◽  
Cold Pools ◽  
Shallow Clouds ◽  
The Mean ◽  
Static Energy

Results are presented from a high-resolution three-dimensional simulation of shallow-to-deep convection transition based on idealization of observations made during the Large-Scale Biosphere–Atmosphere (LBA) experiment in Amazonia, Brazil, during the Tropical Rainfall Measuring Mission (TRMM)-LBA mission on 23 February. The doubly periodic grid has 1536 × 1536 × 256 grid cells with horizontal grid spacing of 100 m, thus covering an area of 154 × 154 km2. The vertical resolution varies from 50 m in the boundary layer to 100 m in the free troposphere and gradually coarsens to 250 m near the domain top at 25.4 km. The length of the simulation is 6 h, starting from an early morning sounding corresponding to 0730 local time. Convection is forced by prescribed surface latent and sensible heat fluxes and prescribed horizontally uniform radiative heating Despite a considerable amount of convective available potential energy (CAPE) in the range of 1600–2400 J kg−1, and despite virtually no convective inhibition (CIN) in the mean sounding throughout the simulation, the cumulus convection starts as shallow, gradually developing into congestus, and becomes deep only toward the end of simulation. Analysis shows that the reason is that the shallow clouds generated by the boundary layer turbulence are too small to penetrate deep into the troposphere, as they are quickly diluted by mixing with the environment. Precipitation and the associated cold pools are needed to generate thermals big enough to support the growth of deep clouds. This positive feedback involving precipitation is supported by a sensitivity experiment in which the cold pools are effectively eliminated by artificially switching off the evaporation of precipitation; in the experiment, the convection remains shallow throughout the entire simulation, with a few congestus but no deep clouds. The probability distribution function (PDF) of cloud size during the shallow, congestus, and deep phases is analyzed using a new method. During each of the three phases, the shallow clouds dominate the mode of the PDFs at about 1-km diameter. During the deep phase, the PDFs show cloud bases as wide as 4 km. Analysis of the joint PDFs of cloud size and in-cloud variables demonstrates that, as expected, the bigger clouds are far less diluted above their bases than their smaller counterparts. Also, thermodynamic properties at cloud bases are found to be nearly identical for all cloud sizes, with the moist static energy exceeding the mean value by as much as 4 kJ kg−1. The width of the moist static energy distribution in the boundary layer is mostly due to variability of water vapor; therefore, clouds appear to grow from the air with the highest water vapor content available. No undiluted cloudy parcels are found near the level of neutral buoyancy. It appears that a simple entraining-plume model explains the entrainment rates rather well. The least diluted plumes in the simulation correspond to an entrainment parameter of about 0.1 km−1.

scholarly journals A Potential Problem with the Application of Moist Static Energy in Tropical Cyclone Studies

2015 ◽  
Vol 72 (8) ◽  
pp. 3009-3019 ◽  
Author(s):  
Zhanhong Ma ◽  
Jianfang Fei ◽  
Xiaogang Huang ◽  
Xiaoping Cheng
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Energy Transport ◽  
Potential Temperature ◽  
Moist Static Energy ◽  
Horizontal Advection ◽  
Vertical Advection ◽  
Conservation Property ◽  
Static Energy

Abstract The moist static energy (MSE) is derived from the first law of thermodynamics and has been widely used in tropical cyclone (TC) studies because of its energetic and conventionally recognized conservation properties. This study investigates the validation of the MSE application in TC systems based on cloud-resolving numerical simulations. By examining the approximations made in deriving the MSE, neglecting the horizontal advection of pressure (namely, the generation of kinetic energy) relative to the vertical advection of pressure is found to be in error in the boundary layer of TCs with the horizontal advection of pressure even being several times larger than the vertical advection of pressure near the surface. Such a problematic approximation has broken down the conservation property of MSE in adiabatic conditions. An investigation of the energetic characteristics based on an MSE budget equation demonstrates that the MSE has created significant bias in evaluating the energy transport in the inner region of the TC boundary layer. Neglecting the kinetic energy conversion term in the boundary layer leads to a more strengthened cool-pool feature of MSE relative to the equivalent potential temperature; therefore, the interchangeable relationship between these two terms may also be inaccurate in the boundary layer. It is concluded that, although the MSE is an instrumental term for TC studies, caution should be taken when it is used in the boundary layer of TCs.

scholarly journals Observational study on boundary-layer moist static energy budget over the tropical western Pacific and its variability associated with boreal summer intraseasonal oscillation

2021 ◽  
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Active Period ◽  
Convective Activity ◽  
Moist Static Energy ◽  
Tropical Western Pacific ◽  
Mass Fluxes ◽  
Static Energy

Abstract Moist static energy (MSE) in the atmospheric boundary layer (BL) is one of the essential parameters determining convective activity over tropical oceanic areas. It is thus important to quantitatively understand BL MSE budget processes and their variability. Among these processes, only few studies have evaluated contributions of entrainment across the BL top and convective downdraft. This study aims to estimate these contributions by analyzing upper-air and surface meteorological observations obtained using Research Vessel Mirai over the tropical western Pacific in June 2008. Daily-mean downward mass fluxes due to the two processes are calculated using BL dry static energy and moisture budget equations under the BL quasi-equilibrium approximation. Estimated mass fluxes are consistent with convective activity observed by a shipborne weather radar and a ceilometer. This study further examines how the mass fluxes and budget processes are modulated when a convectively active phase of boreal summer intraseasonal oscillation arrives at the observation area in the second half of the month. It is found that, while the contribution of the entrainment does not change significantly, the convective downdraft mass flux and the resultant BL MSE export increase 5 times and 3 times, respectively, in the convectively active period compared with those in the pre-active period. Furthermore, ~1/4 of the increase in the convective downdraft mass flux is attributable to the increase in MSE of convective downdraft air associated with mid-tropospheric moistening.

An Energy-Balance Analysis of Deep Convective Self-Aggregation above Uniform SST

2005 ◽  
Vol 62 (12) ◽  
pp. 4273-4292 ◽  
Author(s):  
Christopher S. Bretherton ◽  
Peter N. Blossey ◽  
Marat Khairoutdinov
Keyword(s):  
Radiative Forcing ◽  
Spatial Organization ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The Self ◽  
Radiative Cooling ◽  
Moist Convection ◽  
Moist Static Energy ◽  
Static Energy ◽  
Self Aggregation

Abstract The spatial organization of deep moist convection in radiative–convective equilibrium over a constant sea surface temperature is studied. A 100-day simulation is performed with a three-dimensional cloud-resolving model over a (576 km)2 domain with no ambient rotation and no mean wind. The convection self-aggregates within 10 days into quasi-stationary mesoscale patches of dry, subsiding and moist, rainy air columns. The patches ultimately merge into a single intensely convecting moist patch surrounded by a broad region of very dry subsiding air. The self-aggregation is analyzed as an instability of a horizontally homogeneous convecting atmosphere driven by convection–water vapor–radiation feedbacks that systematically dry the drier air columns and moisten the moister air columns. Column-integrated heat, water, and moist static energy budgets over (72 km)2 horizontal blocks show that this instability is primarily initiated by the reduced radiative cooling of air columns in which there is extensive anvil cirrus, augmented by enhanced surface latent and sensible heat fluxes under convectively active regions due to storm-induced gustiness. Mesoscale circulations intensify the later stages of self-aggregation by fluxing moist static energy from the dry to the moist regions. A simple mathematical model of the initial phase of self-aggregation is proposed based on the simulations. In accordance with this model, the self-aggregation can be suppressed by horizontally homogenizing the radiative cooling or surface fluxes. Lower-tropospheric wind shear leads to slightly slower and less pronounced self-aggregation into bands aligned along the shear vector. Self-aggregation is sensitive to the ice microphysical parameterization, which affects the location and extent of cirrus clouds and their radiative forcing. Self-aggregation is also sensitive to ambient Coriolis parameter f, and can induce spontaneous tropical cyclogenesis for large f. Inclusion of an interactive mixed-layer ocean slows but does not prevent self-aggregation.

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