Convective Momentum Transport by Rainbands within a Madden–Julian Oscillation in a Global Nonhydrostatic Model with Explicit Deep Convective Processes. Part I: Methodology and General Results

2012 ◽  
Vol 69 (4) ◽  
pp. 1317-1338 ◽  
Author(s):  
Tomoki Miyakawa ◽  
Yukari N. Takayabu ◽  
Tomoe Nasuno ◽  
Hiroaki Miura ◽  
Masaki Satoh ◽  
...  
Keyword(s):  
Large Scale ◽  
Layer Structure ◽  
Propagation Speed ◽  
Momentum Transport ◽  
Madden Julian Oscillation ◽  
Convective Envelope ◽  
Upper Troposphere ◽  
Nonhydrostatic Model ◽  
The Mean ◽  
Convective Momentum Transport

Abstract The convective momentum transport (CMT) properties of 13 215 rainbands within a Madden–Julian oscillation (MJO) event simulated by a global nonhydrostatic model are examined. CMT vectors, which represent horizontal accelerations to the mean winds due to momentum flux convergences of deviation winds, are derived for each rainband. The CMT vectors are composited according to their locations relative to the MJO center. While a similar number of rainbands are detected in the eastern and western halves of the MJO convective envelope, CMT vectors with large zonal components are most plentiful between 0° and 20° to the west of the MJO center. The zonal components of the CMT vectors exhibit a coherent directionality and have a well-organized three-layer structure: positive near the surface, negative in the low to midtroposphere, and positive in the upper troposphere. In the low to midtroposphere, where the longitudinal difference in the mean zonal wind across the MJO is 10 m s−1 on average, the net acceleration due to CMT contributes about −16 m s−1. Possible roles of the CMT are proposed. First, the CMT delays the eastward progress of the low- to midtroposphere westerly wind, hence delaying the eastward migration of the convectively favorable region and reducing the propagation speed of the entire MJO. Second, the CMT tilts the MJO flow structure westward with height. Furthermore, the CMT counteracts the momentum transport due to large-scale flows that result from the tilted structure.

A Simple Dynamical Model with Features of Convective Momentum Transport

2009 ◽  
Vol 66 (2) ◽  
pp. 373-392 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Dynamic Model ◽  
Large Scale ◽  
Intraseasonal Oscillation ◽  
Momentum Transport ◽  
Linear Stability Theory ◽  
Westerly Wind ◽  
Mean Flow ◽  
Flow Interactions ◽  
The Mean ◽  
Convective Momentum Transport

Abstract Convective momentum transport (CMT) plays a central role in interactions across multiple space and time scales. However, because of the multiscale nature of CMT, quantifying and parameterizing its effects is often a challenge. Here a simple dynamic model with features of CMT is systematically derived and studied. The model includes interactions between a large-scale zonal mean flow and convectively coupled gravity waves, and convection is parameterized using a multicloud model. The moist convective wave–mean flow interactions shown here have several interesting features that distinguish them from other classical wave–mean flow settings. First an intraseasonal oscillation of the mean flow and convectively coupled waves (CCWs) is described. The mean flow oscillates due to both upscale and downscale CMT, and the CCWs weaken, change their propagation direction, and strengthen as the mean flow oscillates. The basic mechanisms of this oscillation are corroborated by linear stability theory with different mean flow background states. Another case is set up to imitate the westerly wind burst phase of the Madden–Julian oscillation (MJO) in the simplified dynamic model. In this case, CMT first accelerates the zonal jet with the strongest westerly wind aloft, and then there is deceleration of the winds due to CMT; this occurs on an intraseasonal time scale and is in qualitative agreement with actual observations of the MJO. Also, in this case, a multiscale envelope of convection propagates westward with smaller-scale convection propagating eastward within the envelope. The simplified dynamic model is able to produce this variety of behavior even though it has only a single horizontal direction and no Coriolis effect.

MJO-Induced Variability of the Diurnal Cycle of Precipitation over the Maritime Continent

2020 ◽  
Author(s):  
Ajda Savarin ◽  
Shuyi Chen
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Complex Nature ◽  
Madden Julian Oscillation ◽  
Maritime Continent ◽  
Convective Envelope ◽  
Modes Of Variability ◽  
Complex Interactions ◽  
The Indian Ocean ◽  
The Western Pacific

<p>Large-scale convection associated with the Madden-Julian Oscillation (MJO) initiates over the Indian Ocean and propagates eastward across the Maritime Continent (MC) into the western Pacific. As an MJO enters the MC, it often weakens or completely dissipates due to complex interactions between the large-scale MJO and the MC landmass and its topography. This is referred to as the MC barrier effect, and it is responsible for the dissipation of 40-50% of observed MJO events. One of the main reasons for the MJO’s weakening and dissipation over the MC is the diurnal cycle (DC), one of the strongest modes of variability in the region. Due to the complex nature of the MJO and the MC’s complicated topography, the interaction between the DC and the MJO is not well understood.</p><p>In this study, we examine the MJO-induced variability of the DC of precipitation over the MC. We use gridded satellite precipitation products (TRMM 3B42 and GPM IMERG) to: (1) track the MJO convective envelope using the Large-scale Precipitation Tracking algorithm (LPT), (2) analyze the changes in the DC of precipitation over the MC relative to the passage of the MJO. We find that the presence of an MJO not only increases the amount of precipitation over the MC, but that the increase is more pronounced over water than over land. The results from observations are compared to those from two reanalysis datasets (ERA5, MERRA-2). The reanalysis datasets are then used to examine the dynamic and thermodynamic changes that drive the variability in the DC of precipitation relative to the MJO. In addition, we separate MJO events into two groups based on whether they cross the MC, and independently examine their influences on the evolution of the DC of precipitation.</p>

A Frictional Skeleton Model for the Madden–Julian Oscillation*

2012 ◽  
Vol 69 (9) ◽  
pp. 2749-2758 ◽  
Author(s):  
Fei Liu ◽  
Bin Wang
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Madden Julian Oscillation ◽  
Ekman Pumping ◽  
Convective Envelope ◽  
Skeleton Model ◽  
Planetary Scale ◽  
System A ◽  
Frictional Convergence

Abstract The Madden–Julian oscillation (MJO) is a multiscale system. A skeleton model, developed by Majda and Stechmann, can capture some of planetary-scale aspects of observed features such as slow eastward propagation, nondispersive behavior, and quadrupole-vortex structure. However, the Majda–Stechmann model cannot explain the source of instability and the preferred planetary scale of the MJO. Since the MJO major convection region is leaded by its planetary boundary layer (PBL) moisture convergence, here a frictional skeleton model is built by implementing a slab PBL into the neutral skeleton model. As a skeleton model allowing the scale interaction, this model is only valid for large-scale waves. This study shows that the PBL frictional convergence provides a strong instability source for the long eastward modes, although it also destabilizes very short westward modes. For the long waves (wavenumber less than 5), the PBL Ekman pumping moistens the low troposphere to the east of the MJO convective envelope, and sets up favorable moist conditions to destabilize the MJO and favor only eastward modes. Sensitivity experiments show that a weak PBL friction will enhance the instability slightly. The sea surface temperature (SST) with a maximum at the equator also prefers the long eastward modes. These theoretical analysis results encourage further observations on the PBL regulation of mesosynoptic-scale motions, and exploration of the interaction between PBL and multiscale motions, associated with the MJO to improve the MJO simulation in general circulation models (GCMs).

Simulation, Modeling, and Dynamically Based Parameterization of Organized Tropical Convection for Global Climate Models

2017 ◽  
Vol 74 (5) ◽  
pp. 1363-1380 ◽  
Author(s):  
Mitchell W. Moncrieff ◽  
Changhai Liu ◽  
Peter Bogenschutz
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Tropical Convection ◽  
Global Climate Models ◽  
Momentum Transport ◽  
Vertical Shear ◽  
Convergence Zone ◽  
Convective Momentum Transport ◽  
Organized Convection

Abstract A new approach for treating organized convection in global climate models (GCMs) referred to as multiscale coherent structure parameterization (MCSP) introduces physical and dynamical effects of organized convection that are missing from contemporary parameterizations. The effects of vertical shear are approximated by a nonlinear slantwise overturning model based on Lagrangian conservation principles. Simulation of the April 2009 Madden–Julian oscillation event during the Year of Tropical Convection (YOTC) over the Indian Ocean using the Weather Research and Forecasting (WRF) Model at 1.3-km grid spacing identifies self-similar properties for squall lines, MCSs, and superclusters embedded in equatorial waves. The slantwise overturning model approximates this observed self-similarity. The large-scale effects of MCSP are examined in two categories of GCM. First, large-scale convective systems simulated in an aquaplanet model are approximated by slantwise overturning with attention to convective momentum transport. Second, MCSP is utilized in the Community Atmosphere Model, version 5.5 (CAM5.5), as tendency equations for second-baroclinic heating and convective momentum transport. The difference between MCSP and CAM5.5 is a direct measure of the global effects of organized convection. Consistent with TRMM measurements, the MCSP generates large-scale precipitation patterns in the tropical warm pool and the adjoining locale; improves precipitation in the intertropical convergence zone (ITCZ), South Pacific convergence zone (SPCZ), and Maritime Continent regions; and affects tropical wave modes. In conclusion, the treatment of organized convection by MCSP is salient for the next generation of GCMs.

scholarly journals Exploring the Role of Eddy Momentum Fluxes in Determining the Characteristics of the Equinoctial Hadley Circulation: Fixed-SST Simulations

2016 ◽  
Vol 73 (6) ◽  
pp. 2427-2444 ◽  
Author(s):  
Martin S. Singh ◽  
Zhiming Kuang
Keyword(s):  
Large Scale ◽  
Hadley Circulation ◽  
Momentum Transport ◽  
Secondary Importance ◽  
Wide Domain ◽  
Domain Configuration ◽  
Momentum Fluxes ◽  
Convective Momentum Transport ◽  
Mean Circulation

Abstract The influence of eddy momentum fluxes on the equinoctial Hadley circulation is explored using idealized simulations on an equatorial beta plane in which the sea surface temperature (SST) distribution is fixed. By comparing simulations run in a wide-domain configuration, in which large-scale eddies are present, to simulations in which the model domain is too narrow to permit baroclinic instability, the role of large-scale eddies in determining the characteristics of the Hadley circulation is elucidated. The simulations also include an explicit representation of deep convection, allowing for an evaluation of the influence of convective momentum transport on the zonal-mean circulation. The simulated eddy momentum fluxes are much weaker in the narrow-domain configuration than in the wide-domain case, and convective momentum transport is found to be of secondary importance. As a result, many characteristics of the narrow-domain Hadley circulation are well described by axisymmetric theory and differ from those of the wide-domain case. Nevertheless, the strength of the Hadley circulation is similar irrespective of the domain width. The sensitivity of this result to the strength of the eddy forcing is investigated using narrow-domain simulations forced by artificial sinks of zonal momentum. As the magnitude of the momentum sink increases, the Hadley circulation strengthens, but the increase is relatively modest except at very strong forcing magnitudes. The results suggest that the fixed-SST boundary condition places a strong thermodynamic constraint on the Hadley circulation strength and that one should consider the energy budget as well as the angular momentum budget in order to fully understand the influence of large-scale eddies on the zonal-mean circulation in the tropics.

Convective Momentum Transport Associated with the Madden–Julian Oscillation Based on a Reanalysis Dataset

2015 ◽  
Vol 28 (14) ◽  
pp. 5763-5782 ◽  
Author(s):  
Ji-Hyun Oh ◽  
Xianan Jiang ◽  
Duane E. Waliser ◽  
Mitchell W. Moncrieff ◽  
Richard H. Johnson
Keyword(s):  
Vertical Structure ◽  
Vertical Motion ◽  
Momentum Transport ◽  
Minor Role ◽  
Wind Component ◽  
Madden Julian Oscillation ◽  
Subgrid Scale ◽  
Free Atmosphere ◽  
Reanalysis Dataset ◽  
Convective Momentum Transport

Abstract A better understanding of multiscale interactions within the Madden–Julian oscillation (MJO), including momentum exchanges, is critical for improved MJO prediction skill. In this study, convective momentum transport (CMT) associated with the MJO is analyzed based on the NOAA Climate Forecast System Reanalysis (CFSR). A three-layer vertical structure associated with the MJO, as previously suggested in the mesoscale momentum tendency profile based on global cloud-resolving model simulations, is evident in the subgrid-scale momentum tendency from the CFSR. Positive (negative) subgrid-scale momentum tendency anomalies are found near the surface, negative (positive) anomalies are found in the low to midtroposphere, and positive (negative) anomalies in the upper troposphere are found within and to the west (east) of the MJO convection. This tends to damp the MJO circulation in the free atmosphere, while enhancing MJO winds near the surface. In addition, it could also reduce the MJO eastward propagation speed and lead to the backward tilt with height in the observed MJO structure through a secondary circulation near the MJO center. Further analyses illustrate that this three-layer vertical structure in subgrid-scale momentum tendency largely balances the grid-scale momentum transport of the zonal wind component u, mainly through the transport of seasonal mean u by the MJO-scale vertical motion. Synoptic-scale systems, which were previously proposed to be essential for the u-momentum transport of the MJO, however, are found to play a minor role for the total grid-scale momentum tendency. The above momentum tendency structure is also confirmed with the ECMWF analysis for the Year of Tropical Convection (YOTC) that lends confidence to these above results based on the CFSR.

scholarly journals Stochastic models for convective momentum transport

2008 ◽  
Vol 105 (46) ◽  
pp. 17614-17619 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Stochastic Model ◽  
Stochastic Models ◽  
Large Scale ◽  
Computer Models ◽  
Momentum Transport ◽  
Mean Flow ◽  
Stochastic Effects ◽  
Squall Lines ◽  
Convective Momentum Transport ◽  
Coupled Wave

The improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long-range ensemble forecasting of weather and short-term climate change. Observations, theory, and detailed smaller-scale numerical simulations suggest that convective momentum transport (CMT) from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models. Here, a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of CMT on the large scales due to organized unresolved convection from squall lines. Properties of the stochastic model for CMT are developed below in a test column model environment for the large-scale variables. The effects of CMT from the stochastic model on a large-scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem. Here, the upscale transports from stochastic effects are significant and even generate a large-scale mean flow which can interact with the convectively coupled wave.

scholarly journals Convective Organization in Evolving Large-Scale Forcing Represented by a Highly Truncated Numerical Archetype

2018 ◽  
Vol 75 (8) ◽  
pp. 2827-2847 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Mitchell W. Moncrieff
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Momentum Transport ◽  
Phase Iii ◽  
Cold Pools ◽  
Time Period ◽  
Toga Coare ◽  
Data Source ◽  
Convective Momentum Transport ◽  
Convection Parameterization

Abstract Considered as a prognostic generalization of mass-flux-based convection parameterization, the highly truncated nonhydrostatic anelastic model with segmentally constant approximation (NAM–SCA) is tested with time-evolving large-scale forcing. The 20-day GATE Phase III period is taken as a major data source. The main advantage of the NAM–SCA parameterization is consistency with subgrid-scale dynamics as represented by the nonhydrostatic anelastic formulation. The approach explicitly generates important dynamical structures of convection (e.g., mesoscale circulations, cold pools) spontaneously without further tuning or treatment as additional subcomponents. As with other convection parameterizations, the numerical simulation of the precipitation rate, the apparent heat source, and the apparent moisture sink is straightforward and reasonably insensitive to the numerical procedures. However, convective momentum transport by organized convection turns out to be difficult even with NAM–SCA, especially for the inherently three-dimensional shear-parallel systems. Modifications of NAM–SCA regarding the large-scale forcing formulation improves the mesoscale momentum transport. Simulation of the full 120-day TOGA COARE period demonstrates the performance of NAM–SCA in different meteorological conditions and its capacity to operate over a longer time period.

scholarly journals Models for Multiscale Interactions. Part II: Madden–Julian Oscillation, Moisture, and Convective Momentum Transport

2016 ◽  
Vol 56 ◽  
pp. 10.1-10.5 ◽  
Author(s):  
Andrew J. Majda ◽  
Samuel N. Stechmann
Keyword(s):  
Tropical Cyclones ◽  
Momentum Transport ◽  
Mesoscale Convective Systems ◽  
Equatorial Waves ◽  
Madden Julian Oscillation ◽  
Synoptic Scale ◽  
Convective Systems ◽  
Convectively Coupled Equatorial Waves ◽  
Mesoscale Convective ◽  
Convective Momentum Transport

Abstract It is well known that the envelope of the Madden–Julian oscillation (MJO) consists of smaller-scale convective systems, including mesoscale convective systems (MCS), tropical cyclones, and synoptic-scale waves called “convectively coupled equatorial waves” (CCW). In fact, recent results suggest that the fundamental mechanisms of the MJO involve interactions between the synoptic-scale CCW and their larger-scale environment (Majda and Stechmann). In light of this, this chapter reviews recent and past work on two-way interactions between convective systems—both MCSs and CCW—and their larger-scale environment, with a particular focus given to recent work on MJO–CCW interactions.

Mass, momentum, sensible heat and latent heat budgets for the lower atmosphere

1983 ◽  
Vol 308 (1503) ◽  
pp. 275-290 ◽  
Keyword(s):  
Boundary Layer ◽  
Latent Heat ◽  
Layer Structure ◽  
Vertical Motion ◽  
Cloud Layer ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
The Mean ◽  
Convective Momentum Transport ◽  
Heat Budgets

Radiosonde data from the JA SIN meteorological triangle, of sides 200 km, have been used to construct mean budgets of mass, momentum and sensible and latent heat. Typically the atmospheric boundary layer (bl) consisted of a near-neutral subcloud layer and a conditionally unstable cloud layer beneath an inversion. Clouds were cumulus under a stratocumulus layer. W ind shears within the bl were small and the mean vertical motion at the bl top was less than 1 pbar s-1||. Acceleration terms were of similar order (10 -4 m s -2 ) to the geostrophic departure, and significant stress within the cloud layer implied convective momentum transport. The latent heat flux dominated the sub-grid-scale vertical heat transfer, being on average nearly constant from the surface to the cloud-layer top. The results emphasize the importance of cloud processes in determining boundary layer structure.

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