Modes of tropical convection and their roles in transporting moisture and moist static energy: contrast between deep and shallow convection

2021 ◽  
Author(s):  
Yi-Chien Chen ◽  
Jia-Yuh Yu
Keyword(s):  
Tropical Convection ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Static Energy

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 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.

A Mechanism of Tropical Convection Inferred from Observed Variability in the Moist Static Energy Budget

2014 ◽  
Vol 71 (10) ◽  
pp. 3747-3766 ◽  
Author(s):  
Hirohiko Masunaga ◽  
Tristan S. L’Ecuyer
Keyword(s):  
Energy Budget ◽  
Large Scale ◽  
Deep Convection ◽  
Vertical Motion ◽  
Tropical Convection ◽  
Radiative Heating ◽  
Moist Convection ◽  
Baroclinic Mode ◽  
Moist Static Energy ◽  
Static Energy

Abstract Temporal variability in the moist static energy (MSE) budget is studied with measurements from a combination of different satellites including the Tropical Rainfall Measuring Mission (TRMM) and A-Train platforms. A composite time series before and after the development of moist convection is obtained from the observations to delineate the evolution of MSE and moisture convergences and, in their combination, gross moist stability (GMS). A new algorithm is then applied to estimate large-scale vertical motion from energy budget constraints through vertical-mode decomposition into first and second baroclinic modes and a background shallow mode. The findings are indicative of a possible mechanism of tropical convection. A gradual destabilization is brought about by the MSE convergence intrinsic to the positive second baroclinic mode (congestus mode) that increasingly counteracts a weak MSE divergence in the background state. GMS is driven to nearly zero as the first baroclinic mode begins to intensify, accelerating the growth of vigorous large-scale updrafts and deep convection. As the convective burst peaks, the positive second mode switches to the negative mode (stratiform mode) and introduces an abrupt rise in MSE divergence that likely discourages further maintenance of deep convection. The first mode quickly dissipates and GMS increases away from zero, eventually returning to the background shallow-mode state. A notable caveat to this scenario is that GMS serves as a more reliable metric when defined with a radiative heating rate included to offset MSE convergence.

Easterly waves in the East Pacific during the OTREC 2019 field campaign

2021 ◽  
Author(s):  
Lidia Huaman ◽  
Eric D. Maloney ◽  
Courtney Schumacher ◽  
George N. Kiladis
Keyword(s):  
Deep Convection ◽  
Phase Speed ◽  
Sea Surface ◽  
Boreal Summer ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Field Campaign ◽  
Easterly Waves ◽  
East Pacific ◽  
Static Energy

AbstractEasterly waves (EWs) are off-equatorial tropical synoptic disturbances with a westward phase speed between 11-14 m s−1. Over the East Pacific in boreal summer, the combination of EWs and other synoptic disturbances, plus local mechanisms associated with sea surface temperature (SST) gradients, define the climatological structure of the Intertropical Convergence Zone (ITCZ). The East Pacific ITCZ has both deep and shallow convection that is linked to deep and shallow meridional circulations, respectively. The deep convection is located around 9°N over warm SSTs. The shallow convection is located around 6°N and is driven by the meridional SST gradient south of the ITCZ. This study aims to document the interaction between East Pacific EWs and the deep and shallow meridional circulations during the Organization of Tropical East Pacific Convection (OTREC) field campaign in 2019 using field campaign observations, ERA5 reanalysis, and satellite precipitation. We identified three EWs during the OTREC period using precipitation and dynamical fields. Composite analysis shows that the convectively active part of the EW enhances ITCZ deep convection and is associated with an export of column-integrated moist static energy (MSE) by vertical advection. The subsequent convectively suppressed, anticyclonic part of the EW produces an increase of moisture and column-integrated MSE by horizontal advection that likely enhances shallow convection and the shallow overturning flow at 850 hPa over the southern part of the ITCZ. Therefore, EWs appear to strongly modulate shallow and deep circulations in the East Pacific ITCZ.

scholarly journals Disentangling the mechanisms of wave-convection coupling using idealized simulations in a tropical channel: wave composites of the moist static energy budget

2021 ◽  
Author(s):  
Hyunju Jung ◽  
Peter Knippertz ◽  
Corinna Hoose ◽  
Yvonne Ruckstuhl ◽  
Robert Redl ◽  
...  
Keyword(s):  
General Circulation ◽  
Equatorial Waves ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Grid Spacing ◽  
Budget Analysis ◽  
Fourier Filtering ◽  
Static Energy ◽  
Channel Configuration ◽  
Horizontal Grid

<p>Recent studies found that the coupling of equatorial waves to convection is key to improving weather forecasts in the tropics on the synoptic to the subseasonal timescale but many models struggle to realistically represent this coupling. To study the underlying mechanisms of convectively coupled equatorial waves, we use aquaplanet simulations with the ICOsahedral Nonhydrostatic (ICON) model in a tropical channel configuration with a horizontal grid spacing of 13 km and with a prescribed zonally symmetric, latitudinally varying sea surface temperature. We compare simulations with parameterized and explicit deep/shallow convection. Using wave identification tools that are based on Fourier filtering in time and space and on projections of dynamical fields on theoretical wave patterns, we observe a predominance of equator-symmetric equatorial waves such as Kelvin waves and slow large-scale variability resembling the Madden-Julian Oscillation.</p><p>To diagnose interactions between the equatorial waves and convection, we use a moist static energy (MSE) framework. A budget analysis for column integrated MSE shows that spatial anomalies of the net shortwave and longwave radiation and the surface enthalpy flux increase the spatial variance of the column MSE, while advection dampens variability. For wave-convection coupling we employ a wave composite technique for the terms of the MSE budget. Results from this analysis will be presented at the conference. The same filtering tools and diagnostics are applied to a realistic ICON simulation with a 2.5 km horizontal grid spacing from the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) project.</p>

scholarly journals Tropical Precipitation Evolution in a Buoyancy-Budget Framework

2020 ◽  
Author(s):  
Ángel F. Adames ◽  
Scott W. Powell ◽  
Fiaz Ahmed ◽  
Víctor C. Mayta ◽  
J. David Neelin
Keyword(s):  
Tropical Convection ◽  
Free Troposphere ◽  
Madden Julian Oscillation ◽  
Moist Static Energy ◽  
Convective Envelope ◽  
Tropical Precipitation ◽  
Moisture Advection ◽  
Approximation Analysis ◽  
Moist Static Energy Budget ◽  
Static Energy

AbstractObservations have shown that tropical convection is influenced by fluctuations in temperature and moisture in the lower free-troposphere (LFT, 600–850 hPa), as well as moist enthalpy (ME) fluctuations beneath the 850 hPa level, referred to as the deep boundary layer (DBL, 850–1000 hPa). A framework is developed that consolidates these three quantities within the context of the buoyancy of an entraining plume. A “plume buoyancy equation” is derived based on a relaxed version of the weak-temperature gradient (WTG) approximation. Analysis of this equation using quantities derived from the Dynamics of the Madden-Julian Oscillation (DYNAMO) sounding array data reveals that processes occurring within the DBL and the LFT contribute nearly equally to the evolution of plume buoyancy, indicating that processes that occur in both layers are critical to the evolution of tropical convection. Adiabatic motions play an important role in the evolution of buoyancy both at the daily and longer timescales and are comparable in magnitude to horizontal moisture advection and vertical moist static energy advection by convection. The plume buoyancy equation may explain convective coupling at short timescales in both temperature and moisture fluctuations and can be used to complement the commonly-used moist static energy budget, which emphasizes the slower evolution of the convective envelope in tropical motion systems.

Convective Coupling in Tropical-Depression-Type Waves. Part II: Moisture and Moist Static Energy Budgets

2020 ◽  
Vol 77 (10) ◽  
pp. 3423-3440 ◽  
Author(s):  
Tao Feng ◽  
Jia-Yuh Yu ◽  
Xiu-Qun Yang ◽  
Ronghui Huang
Keyword(s):  
Deep Convection ◽  
Critical Role ◽  
Precipitation Rate ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Convective Rainfall ◽  
Horizontal Advection ◽  
Tropical Depression ◽  
Moisture Advection ◽  
Static Energy

AbstractThe companion of this paper, Part I, discovered the characteristics of the rainfall progression in tropical-depression (TD)-type waves over the western North Pacific. In Part II, the large-scale controls on the convective rainfall progression have been investigated using the ERA-Interim data and the TRMM 3B42 precipitation-rate data during June–October from 1998 to 2013 through budgets of moist static energy (MSE) and moisture. A buildup of column-integrated MSE occurs in advance of deep convection, and an export of MSE occurs following deep convection, which is consistent with the MSE recharge–discharge paradigm. The MSE recharge–discharge is controlled by horizontal processes, whereby horizontal moisture advection causes net MSE import prior to deep convection. Such moistening by horizontal advection creates a moist midtroposphere, which helps destabilize the atmospheric column, leading to the development of deep convective rainfall. Following the heaviest rainfall, negative horizontal moisture advection dries the troposphere, inhibiting convection. Such moistening and drying processes explain why deep convection can develop without preceding shallow convection. The advection of moisture anomalies by the mean horizontal flow controls the tropospheric moistening and drying processes. As the TD-type waves propagate northwestward in coincidence with the northwestward environmental flow, the moisture, or convective rainfall, is phase locked to the waves. The critical role of the MSE import by horizontal advection in modulating the rainfall progression is supported by the anomalous gross moist stability (AGMS), where the lowest AGMS corresponds to the quickest increase in the precipitation rate prior to the rainfall maximum.

scholarly journals Impacts of Vertical Structure of Large-Scale Vertical Motion in Tropical Climate: Moist Static Energy Framework

2016 ◽  
Vol 73 (11) ◽  
pp. 4427-4437 ◽  
Author(s):  
Hien Xuan Bui ◽  
Jia-Yuh Yu ◽  
Chia Chou
Keyword(s):  
Large Scale ◽  
Vertical Structure ◽  
Model Simulation ◽  
Deep Convection ◽  
Vertical Motion ◽  
Tropical Climate ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Static Energy ◽  
Heavy Structure

Abstract Interactions between cumulus convection and its large-scale environment have been recognized as crucial to the understanding of tropical climate and its variability. In this study, the moist static energy (MSE) budget is employed to investigate the potential impact of the vertical structure of large-scale vertical motion in tropical climate based on results from both reanalysis data and model simulation. Two domains are selected over the western and eastern Pacific with vertical motion profiles that are dominated by top-heavy and bottom-heavy structures, respectively. The bottom-heavy structure is climatologically associated with more shallow convection, while the top-heavy structure is related to more deep convection. The column-integrated vertical MSE advection of top-heavy vertical motion is positive, while that of bottom-heavy vertical motion tends to be negative. Controlling factors responsible for the above vertical MSE advection contrast are discussed based on a simple decomposition of the MSE budget equation. It was found that the sign of vertical MSE advection is determined mainly by the vertical moisture transport, the magnitude of which is very sensitive to the structure of vertical motion. A top-heavy (bottom heavy) structure of vertical motion favors an export (import) of MSE and a positive (negative) value of the vertical MSE advection.

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