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.

A Moist Static Energy Budget Analysis of Quasi-2-Day Waves Using Satellite and Reanalysis Data

2016 ◽  
Vol 73 (2) ◽  
pp. 743-759 ◽  
Author(s):  
Yukari Sumi ◽  
Hirohiko Masunaga
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Reanalysis Data ◽  
Convective Heating ◽  
Moist Static Energy ◽  
Wave Dynamics ◽  
Vertical Advection ◽  
Budget Analysis ◽  
Static Energy ◽  
Thermodynamic Processes

Abstract A moist static energy (MSE) budget analysis is applied to quasi-2-day waves to examine the effects of thermodynamic processes on the wave propagation mechanism. The 2-day waves are defined as westward inertia–gravity (WIG) modes identified with filtered geostationary infrared measurements, and the thermodynamic parameters and MSE budget variables computed from reanalysis data are composited with respect to the WIG peaks. The composite horizontal and vertical MSE structures are overall as theoretically expected from WIG wave dynamics. A prominent horizontal MSE advection is found to exist, although the wave dynamics is mainly regulated by vertical advection. The vertical advection decreases MSE around the times of the convective peak, plausibly resulting from the first baroclinic mode associated with deep convection. Normalized gross moist stability (NGMS) is used to examine the thermodynamic processes involving the large-scale dynamics and convective heating. NGMS gradually decreases to zero before deep convection and reaches a maximum after the convection peak, where low (high) NGMS leads (lags) deep convection. The decrease in NGMS toward zero before the occurrence of active convection suggests an increasingly efficient conversion from convective heating to large-scale dynamics as the wave comes in, while the increase afterward signifies that this linkage swiftly dies out after the peak.

scholarly journals Relationships between Rain Characteristics and Environment. Part II: Atmospheric Disturbances Associated with Shallow Convection over the Eastern Tropical Pacific

2012 ◽  
Vol 140 (9) ◽  
pp. 2841-2859 ◽  
Author(s):  
Chie Yokoyama ◽  
Yukari N. Takayabu
Keyword(s):  
Deep Convection ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Precipitable Water ◽  
Composite Analysis ◽  
Shallow Convection ◽  
Wave Type ◽  
Northeastern Part ◽  
Budget Analysis ◽  
Spectral Peaks

Abstract Synoptic-scale westward-propagating disturbances over the eastern Pacific (EP) are analyzed in boreal autumn, utilizing spectral analysis, composite analysis, and energy budget analysis. The results are compared with those over the western Pacific (WP). Spectral peaks of total precipitable water (TPW) and vertical velocity at 850 hPa (ω850), and outgoing longwave radiation (OLR) are detected at periods of ~3–7 days over the EP. Meanwhile over the WP, a spectral peak of OLR is pronounced, but peaks of TPW and ω850 are not detected. Composite analysis reveals that disturbances that have a coupled structure, with a vortex at its center near ~9°N and a mixed Rossby–gravity (MRG) wave–type disturbance, frequently exist over the EP. At the same time, the disturbances have a double-deck structure associated with divergence both in the upper and in the middle to lower troposphere. These disturbances are associated with both deep convection and congestus, which generate kinetic energy of the disturbance in the upper and in the lower troposphere, respectively. Examining diabatic heating in relation to the coupled disturbances, deep heating with the peak at the height of ~7.5 km is greatest in the northeastern part of the vortex. The coupled MRG wave–type disturbance provides a relatively deep cross-equatorial southerly flow into the northeastern part of the vortex. It is suggested that deep rain is maintained with the existence of deep convergence produced by the coupled disturbances over the EP, where a very shallow convergence field exists on average.

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 Reexamining the MJO Moisture Mode Theories with Normalized Phase Evolutions

2020 ◽  
Vol 33 (19) ◽  
pp. 8523-8536
Author(s):  
Lu Wang ◽  
Tim Li
Keyword(s):  
Boundary Layer ◽  
Characteristic Length ◽  
Deep Convection ◽  
Phase Speed ◽  
Phase Evolution ◽  
Kelvin Wave ◽  
Mode Theory ◽  
Budget Analysis ◽  
Moisture Mode ◽  
Static Energy

AbstractA normalization method is applied to MJO-scale precipitation and column integrated moist static energy (MSE) anomalies to clearly illustrate the phase evolution of MJO. It is found that the MJO peak phases do not move smoothly, rather they jump from the original convective region to a new location to its east. Such a discontinuous phase evolution is related to the emerging and developing of new congestus convection to the east of the preexisting deep convection. While the characteristic length scale of the phase jump depends on a Kelvin wave response, the associated time scale represents the establishment of an unstable stratification in the front due to boundary layer moistening. The combined effect of the aforementioned characteristic length and time scales determines the observed slow eastward phase speed. Such a phase evolution characteristic seems to support the moisture mode theory of the second type that emphasizes the boundary layer moisture asymmetry, because the moisture mode theory of the first type, which emphasizes the moisture or MSE tendency asymmetry, might favor more “smooth” phase propagation. A longitudinal-location-dependent premoistening mechanism is found based on moisture budget analysis. For the MJO in the eastern Indian Ocean, the premoistening in front of the MJO convection arises from vertical advection, whereas for the MJO over the western Pacific Ocean, it is attributed to the surface evaporating process.

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.

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>

Variations of the Moist Static Energy Budget of the Tropical Indian Ocean Atmospheric Boundary Layer

2018 ◽  
Vol 75 (5) ◽  
pp. 1545-1551 ◽  
Author(s):  
Simon P. de Szoeke
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Deep Convection ◽  
Tropical Indian Ocean ◽  
Free Troposphere ◽  
Moist Static Energy ◽  
Convective Conditions ◽  
Convective Clouds ◽  
Moist Static Energy Budget ◽  
Static Energy

The atmospheric circulation depends on poorly understood interactions between the tropical atmospheric boundary layer (BL) and convection. The surface moist static energy (MSE) source (130 W m−2, of which 120 W m−2 is evaporation) to the tropical marine BL is balanced by upward MSE flux at the BL top that is the source for deep convection. Important for modeling tropical convection and circulation is whether MSE enters the free troposphere by dry turbulent processes originating within the boundary layer or by motions generated by moist deep convection in the free troposphere. Here, highly resolved observations of the BL quantify the MSE fluxes in approximate agreement with recent cloud-resolving models, but the fluxes depend on convective conditions. In convectively suppressed (weak precipitation) conditions, entrainment and downdraft fluxes export equal shares (60 W m−2) of MSE from the BL. Downdraft fluxes are found to increase 50%, and entrainment to decrease, under strongly convective conditions. Variable entrainment and downdraft MSE fluxes between the BL and convective clouds must both be considered for modeling the climate.

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.

Reexamining the Moisture Mode Theories of the Madden–Julian Oscillation Based on Observational Analyses

2021 ◽  
Vol 34 (2) ◽  
pp. 839-853
Author(s):  
Feng Hu ◽  
Tim Li ◽  
Jianyun Gao ◽  
Lisheng Hao
Keyword(s):  
Boundary Layer ◽  
Positive Column ◽  
The Other ◽  
Madden Julian Oscillation ◽  
Moist Static Energy ◽  
Maritime Continent ◽  
Budget Analysis ◽  
Moisture Mode ◽  
The Difference ◽  
Static Energy

AbstractTwo existing moisture mode theories of the MJO, one emphasizing boundary layer moisture asymmetry (MA) and the other emphasizing column-integrated moist static energy (MSE) tendency asymmetry (TA), were validated with the diagnosis of observational data during 1979–2012. A total of 2343 MJO days are selected. While all these days show a clear phase leading of the boundary layer moisture, 20% of these days do not show a positive column-integrated MSE tendency in front of MJO convection (non-TA). A further MSE budget analysis indicates that the difference between the non-TA composite and the TA composite lies in the zonal extent of anomalously vertical overturning circulation in front of the MJO convection. A background mean precipitation modulation mechanism is proposed to explain the distinctive circulation responses. Dependent on the MJO location, an anomalous Gill response to the heating is greatly modulated by the seasonal mean and ENSO induced precipitation fields. Despite the negative MSE tendency in front of MJO convection in the non-TA group, the system continues moving eastward due to the effect of the boundary layer moistening, which promotes a convectively unstable stratification ahead of MJO convection. The analysis result suggests that the first type of moisture mode theories, the moisture asymmetry mechanism, appears more robust, particularly over the eastern Maritime Continent and western Pacific.

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