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 The Madden–Julian Oscillation in CCSM4

2011 ◽  
Vol 24 (24) ◽  
pp. 6261-6282 ◽  
Author(s):  
Aneesh C. Subramanian ◽  
Markus Jochum ◽  
Arthur J. Miller ◽  
Raghu Murtugudde ◽  
Richard B. Neale ◽  
...  
Keyword(s):  
Large Scale ◽  
Intraseasonal Variability ◽  
Power Spectra ◽  
Longwave Radiation ◽  
Meridional Wind ◽  
Dominant Mode ◽  
Madden Julian Oscillation ◽  
Asian Monsoon Region ◽  
Climate System Model ◽  
Zonal Winds

Abstract This study assesses the ability of the Community Climate System Model, version 4 (CCSM4) to represent the Madden–Julian oscillation (MJO), the dominant mode of intraseasonal variability in the tropical atmosphere. The U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group’s prescribed diagnostic tests are used to evaluate the model’s mean state, variance, and wavenumber–frequency characteristics in a 20-yr simulation of the intraseasonal variability in zonal winds at 850 hPa (U850) and 200 hPa (U200), and outgoing longwave radiation (OLR). Unlike its predecessor, CCSM4 reproduces a number of aspects of MJO behavior more realistically. The CCSM4 produces coherent, broadbanded, and energetic patterns in eastward-propagating intraseasonal zonal winds and OLR in the tropical Indian and Pacific Oceans that are generally consistent with MJO characteristics. Strong peaks occur in power spectra and coherence spectra with periods between 20 and 100 days and zonal wavenumbers between 1 and 3. Model MJOs, however, tend to be more broadbanded in frequency than in observations. Broad-scale patterns, as revealed in combined EOFs of U850, U200, and OLR, are remarkably consistent with observations and indicate that large-scale convergence–convection coupling occurs in the simulated MJO. Relations between MJO in the model and its concurrence with other climate states are also explored. MJO activity (defined as the percentage of time the MJO index exceeds 1.5) is enhanced during El Niño events compared to La Niña events, both in the model and observations. MJO activity is increased during periods of anomalously strong negative meridional wind shear in the Asian monsoon region and also during strong negative Indian Ocean zonal mode states, in both the model and observations.

scholarly journals The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6

2021 ◽  
Author(s):  
Gwendal Rivière ◽  
Meryl Wimmer ◽  
Philippe Arbogast ◽  
Jean-Marcel Piriou ◽  
Julien Delanoë ◽  
...  
Keyword(s):  
Heating Rate ◽  
Large Scale ◽  
Deep Convection ◽  
Atmospheric Model ◽  
Conveyor Belt ◽  
The Other ◽  
Jet Stream ◽  
Field Campaign ◽  
Global Atmospheric Model ◽  
The Impact

Abstract. The effect of parameterized deep convection on warm conveyor belt (WCB) activity and jet stream is investigated by performing simulations of an explosively-developing large-scale cyclone that occurred during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign using the Météo-France global atmospheric model ARPEGE. Three simulations differing only from their deep convection representation are analysed. The first one was performed with the Bougeault et al. (1985) scheme (B85), the second one with the Prognostic Condensates Microphysics and Transport (PCMT) scheme of Piriou et al. (2007), and the third one without any parameterized deep convection. In the latter simulation, the release of convective instability at the resolved scales of the model generates localized cells marked by strong heating with few degrees extent in longitude and latitude along the fronts. In runs with active parameterized deep convection (B85, PCMT), the heating rate is more homogeneously distributed along fronts as the instability release happens at sub-grid scales. This difference leads to more rapid and abrupt ascents in the WCB without parameterized deep convection, and more moderate but more sustained ascents with parameterized deep convection. While the number of WCB trajectories does not differ much between the three simulations, the averaged heating rates over the WCB trajectories exhibits distinct behavior. After one day of simulations, the upper-level heating rate is in average larger with B85 scheme leading to stronger potential vorticity (PV) destruction. The difference comes from the large-scale heating and not the parameterized heating.A comparison with (re)analyses and a large variety of airborne observations from the NAWDEX field campaign (Doppler radar, Doppler lidar, dropsondes) made during the coordinated flights of two aircraft in the WCB outflow region shows that B85 performs better in the representation of the double jet structure at 1-day lead time than the other two simulations. That can be attributed to the more active WCB at upper levels. However this effect is too strong and that simulation becomes less realistic at longer forecast range (1.5 to 2 days) than the other ones. The simulation with PCMT scheme has an intermediate behavior between the one with B85 scheme and without parameterized deep convection but its impact on the jet stream is closer to the latter one. Finally, additional numerical experiments show that main differences in the impact on the jet between PCMT and B85 largely come from the chosen closure, the former being based on CAPE and the latter on moisture convergence.

scholarly journals The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6

2021 ◽  
Vol 2 (4) ◽  
pp. 1011-1031
Author(s):  
Gwendal Rivière ◽  
Meryl Wimmer ◽  
Philippe Arbogast ◽  
Jean-Marcel Piriou ◽  
Julien Delanoë ◽  
...  
Keyword(s):  
Heating Rate ◽  
Large Scale ◽  
Deep Convection ◽  
Atmospheric Model ◽  
Conveyor Belt ◽  
The Other ◽  
Jet Stream ◽  
Field Campaign ◽  
Global Atmospheric Model ◽  
The Impact

Abstract. The effect of parameterized deep convection on warm conveyor belt (WCB) activity and the jet stream is investigated by performing simulations of an explosively developing large-scale cyclone that occurred during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign using the Météo-France global atmospheric model ARPEGE. Three simulations differing only from their deep convection representation are analysed. The first one was performed with the Bougeault (1985) scheme (B85), the second one with the Prognostic Condensates Microphysics and Transport (PCMT) scheme of Piriou et al. (2007), and the third one without any parameterized deep convection. In the latter simulation, the release of convective instability at the resolved scales of the model generates localized cells marked by strong heating with few degrees extent in longitude and latitude along the fronts. In runs with active parameterized deep convection (B85, PCMT), the heating rate is more homogeneously distributed along fronts as the instability release happens at subgrid scales. This difference leads to more rapid and abrupt ascents in the WCB without parameterized deep convection and more moderate but more sustained ascents with parameterized deep convection. While the number of WCB trajectories does not differ much between the three simulations, the averaged heating rates over the WCB trajectories exhibits distinct behaviour. After 1 d of simulations, the upper-level heating rate is on average larger, with the B85 scheme leading to stronger potential vorticity (PV) destruction. The difference comes from the resolved sensible and latent heating and not the parameterized one. A comparison with (re)analyses and a large variety of airborne observations from the NAWDEX field campaign (Doppler radar, Doppler lidar, dropsondes) made during the coordinated flights of two aircraft in the WCB outflow region shows that B85 performs better in the representation of the double jet structure at 1 d lead time than the other two simulations. That can be attributed to the more active WCB at upper levels. However, this effect is too strong and that simulation becomes less realistic than the other ones at forecast ranges beyond 1.5 d. The simulation with the PCMT scheme has an intermediate behaviour between the one with the B85 scheme and without parameterized deep convection, but its impact on the jet stream is closer to the latter one. Finally, additional numerical experiments show that main differences in the impact on the jet between PCMT and B85 largely come from the chosen closure, with the former being based on CAPE and the latter on moisture convergence.

scholarly journals A CloudSat–CALIPSO View of Cloud and Precipitation Properties across Cold Fronts over the Global Oceans

2015 ◽  
Vol 28 (17) ◽  
pp. 6743-6762 ◽  
Author(s):  
Catherine M. Naud ◽  
Derek J. Posselt ◽  
Susan C. van den Heever
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Conveyor Belt ◽  
Low Level ◽  
Scale Parameters ◽  
Convective Clouds ◽  
Cold Fronts ◽  
Surface Front ◽  
High Level ◽  
The Impact

Abstract The distribution of cloud and precipitation properties across oceanic extratropical cyclone cold fronts is examined using four years of combined CloudSat radar and CALIPSO lidar retrievals. The global annual mean cloud and precipitation distributions show that low-level clouds are ubiquitous in the postfrontal zone while higher-level cloud frequency and precipitation peak in the warm sector along the surface front. Increases in temperature and moisture within the cold front region are associated with larger high-level but lower mid-/low-level cloud frequencies and precipitation decreases in the cold sector. This behavior seems to be related to a shift from stratiform to convective clouds and precipitation. Stronger ascent in the warm conveyor belt tends to enhance cloudiness and precipitation across the cold front. A strong temperature contrast between the warm and cold sectors also encourages greater post-cold-frontal cloud occurrence. While the seasonal contrasts in environmental temperature, moisture, and ascent strength are enough to explain most of the variations in cloud and precipitation across cold fronts in both hemispheres, they do not fully explain the differences between Northern and Southern Hemisphere cold fronts. These differences are better explained when the impact of the contrast in temperature across the cold front is also considered. In addition, these large-scale parameters do not explain the relatively large frequency in springtime postfrontal precipitation.

scholarly journals Ensemble forecasting with a stochastic convective parametrization based on equilibrium statistics

2011 ◽  
Vol 11 (11) ◽  
pp. 30457-30485 ◽  
Author(s):  
P. Groenemeijer ◽  
G. C. Craig
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Ensemble Forecasting ◽  
Total Variance ◽  
Ensemble Prediction ◽  
Ensemble Prediction System ◽  
The Impact

Abstract. The stochastic Plant-Craig scheme for deep convection was implemented in the COSMO mesoscale model and used for ensemble forecasting. Ensembles consisting of 100 48 h forecasts at 7 km horizontal resolution were generated for a 2000 × 2000 km domain covering central Europe. Forecasts were made for seven case studies and characterized by different large-scale meteorological environments. Each 100 member ensemble consisted of 10 groups of 10 members, with each group driven by boundary and initial conditions from a selected member from the global ECMWF Ensemble Prediction System. The precipitation variability within and among these groups of members was computed, and it was found that the relative contribution to the ensemble variance introduced by the stochastic convection scheme was substantial, amounting to as much as 76% of the total variance in the ensemble in one of the studied cases. The impact of the scheme was not confined to the grid scale, and typically contributed 25–50% of the total variance even after the precipitation fields had been smoothed to a resolution of 35 km. The variability of precipitation introduced by the scheme was approximately proportional to the total amount of convection that occurred, while the variability due to large-scale conditions changed from case to case, being highest in cases exhibiting strong mid-tropospheric flow and pronounced meso- to synoptic scale vorticity extrema. The stochastic scheme was thus found to be an important source of variability in precipitation cases of weak large-scale flow lacking strong vorticity extrema, but high convective activity.

scholarly journals Can the Impact of Aerosols on Deep Convection be Isolated from Meteorological Effects in Atmospheric Observations?

2018 ◽  
Vol 75 (10) ◽  
pp. 3347-3363 ◽  
Author(s):  
Wojciech W. Grabowski
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Cloud Condensation Nuclei ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Phase Iii ◽  
Moist Convection ◽  
Atmospheric Measurements ◽  
The Impact ◽  
Meteorological Effects

Influence of pollution on dynamics of deep convection continues to be a controversial topic. Arguably, only carefully designed numerical simulations can clearly separate the impact of aerosols from the effects of meteorological factors that affect moist convection. This paper argues that such a separation is virtually impossible using observations because of the insufficient accuracy of atmospheric measurements and the fundamental nature of the interaction between deep convection and its environment. To support this conjecture, results from numerical simulations are presented that apply modeling methodology previously developed by the author. The simulations consider small modifications, difficult to detect in observations, of the initial sounding, surface fluxes, and large-scale forcing tendencies. All these represent variations of meteorological conditions that affect deep convective dynamics independently of aerosols. The setup follows the case of daytime convective development over land based on observations during the Large-Scale Biosphere–Atmosphere (LBA) field project in Amazonia. The simulated observable macroscopic changes of convection, such as the surface precipitation and upper-tropospheric cloudiness, are similar to or larger than those resulting from changes of cloud condensation nuclei from pristine to polluted conditions studied previously using the same modeling case. Observations from Phase III of the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) are also used to support the argument concerning the impact of the large-scale forcing. The simulations suggest that the aerosol impacts on dynamics of deep convection cannot be isolated from meteorological effects, at least for the daytime development of unorganized deep convection considered in this study.

Intraseasonal Transitions of the Wintertime Pacific Jet Stream

2020 ◽  
Author(s):  
Maria Madsen ◽  
Jonathan Martin
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Weather Prediction ◽  
Intraseasonal Variability ◽  
Extreme Weather Events ◽  
Jet Stream ◽  
The Pacific ◽  
Basin Scale ◽  
Jet Variability ◽  
The Impact

<p>The deficiency in predictability at subseasonal-to-seasonal timescales, as compared to prediction at conventional weather prediction timescales, is significant. Intraseasonal variability of atmospheric features like the jet stream, occurring within this gap, lead to extreme weather events that present considerable hazards to society. As jets are an important feature at the interface of the large-scale general circulation and the life cycle of individual weather systems, there is strong incentive to more comprehensively understand their variability.</p><p>The wintertime Pacific jet manifests its intraseasonal variability in two predominant modes: a zonal extension or retraction and a meridional shift by as much as 20° of the jet exit region. These two leading modes are associated with basin-scale anomalies in the Pacific that directly impact weather in Hawaii and continental North America. Although recent work has demonstrated the impact intramodal changes of the Pacific jet have on large-scale structure, sensible weather phenomena, and forecast skill in and around the vast North Pacific Basin, the transitions between the leading modes have hardly been considered and, therefore, are poorly understood. Consequently, this work examines the nature and predictability of transitions between modes of wintertime Pacific jet variability as well as their associated synoptic environments.</p><p>We apply two distinct but complementary statistical analyses to 70 cold seasons (NDJFM 1948/49-2017/18) of daily 250-hPa zonal winds from the NCEP/NCAR Reanalysis to investigate such transitions. Empirical orthogonal analysis (EOF)/principal component (PC) analysis is used to depict the state of the daily Pacific jet as a point in a two dimensional phase space defined by the two leading modes.  Supporting this technique is a self-organizing maps (SOMs) analysis that identifies non-orthogonal, synoptically recurring patterns of the Pacific jet. Together, these analyses show that there are, in fact, preferred transitions between these leading modes of variability. Composite and individual case analyses of preferred transition evolutions provides new insight into the synoptic-scale environments that drive Pacific jet variability.</p>

Intraseasonal Variability of the Zonal-Mean Tropical Tropopause Height

2007 ◽  
Vol 64 (7) ◽  
pp. 2695-2706 ◽  
Author(s):  
Seok-Woo Son ◽  
Sukyoung Lee
Keyword(s):  
Large Scale ◽  
Intraseasonal Variability ◽  
Warm Pool ◽  
Temperature Fields ◽  
Convective Heating ◽  
Tropopause Height ◽  
Tropical Tropopause ◽  
The Pacific ◽  
Pacific Warm Pool ◽  
Tropical Troposphere

Abstract Intraseasonal variability of the zonal-mean tropical tropopause height is shown to be modulated by localized tropical convection. Most of this convective activity is identified as being part of the Madden–Julian oscillation. While the convection is highly localized over the Pacific warm pool, a large-scale circulation response to the convective heating rapidly warms most of the tropical troposphere and cools most of the lowest few kilometers of the tropical stratosphere. These changes in temperature fields raise the tropical tropopause at most longitudes within 10 days of the convective heating maximum.

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 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.

Sign in / Sign up

Export Citation Format

Share Document