Convectively Coupled Equatorial Wave Simulations Using the ECMWF IFS and the NOAA GFS Cumulus Convection Schemes in the NOAA GFS Model

2019 ◽  
Vol 147 (11) ◽  
pp. 4005-4025 ◽  
Author(s):  
Lisa Bengtsson ◽  
Juliana Dias ◽  
Maria Gehne ◽  
Peter Bechtold ◽  
Jeffrey Whitaker ◽  
...  
Keyword(s):  
Large Scale ◽  
Cumulus Convection ◽  
Convection Scheme ◽  
Equatorial Wave ◽  
Gfs Model ◽  
Convection Schemes ◽  
Tropical Wave ◽  
Consistent Treatment ◽  
The Tropics ◽  
Moisture Profiles

Abstract There is a longstanding challenge in numerical weather and climate prediction to accurately model tropical wave variability, including convectively coupled equatorial waves (CCEWs) and the Madden–Julian oscillation. For subseasonal prediction, the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) has been shown to be superior to the NOAA Global Forecast System (GFS) in simulating tropical variability, suggesting that the ECMWF model is better at simulating the interaction between cumulus convection and the large-scale tropical circulation. In this study, we experiment with the cumulus convection scheme of the ECMWF IFS in a research version of the GFS to understand which aspects of the IFS cumulus convection scheme outperform those of the GFS convection scheme in the tropics. We show that the IFS cumulus convection scheme produces significantly different tropical moisture and temperature tendency profiles from those simulated by the GFS convection scheme when it is coupled with other physics schemes in the GFS physics package. We show that a consistent treatment of the interaction between parameterized convective plumes in the GFS planetary boundary layer (PBL) and the IFS convection scheme is required for the GFS to replicate the tropical temperature and moisture profiles simulated by the IFS model. The GFS model with the IFS convection scheme, and the consistent treatment between the convection and PBL schemes, produces much more organized convection in the tropics, and generates tropical waves that propagate more coherently than the GFS in its default configuration due to better simulated interaction between low-level convergence and precipitation.

The Dynamics of Idealized Convection Schemes and Their Effect on the Zonally Averaged Tropical Circulation

2007 ◽  
Vol 64 (6) ◽  
pp. 1959-1976 ◽  
Author(s):  
Dargan M. W. Frierson
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Hadley Circulation ◽  
Horizontal Resolution ◽  
Shallow Convection ◽  
Tropical Circulation ◽  
Convection Scheme ◽  
Convection Schemes ◽  
Gross Moist Stability ◽  
The Tropics

In this paper, the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist GCM to obtain broad classifications of the influence of convection on the Tropics. This is accomplished with a simplified convection scheme in the style of Betts and Miller. The scheme is utilized in a moist GCM with simplified physical parameterizations (gray radiation, with zonally symmetric, slab mixed layer ocean boundary conditions). Comparisons are made with simulations without a convection scheme [i.e., with large-scale condensation (LSC) only], with the moist convective adjustment (MCA) parameterization, and with various formulations and parameter sets with a simplified Betts–Miller (SBM) scheme. With the control run using the SBM scheme, the Tropics become quieter and less dependent on horizontal resolution as compared with the LSC or MCA simulations. The Hadley circulation mass transport is significantly reduced with the SBM scheme, as is the ITCZ precipitation. An important factor determining this behavior is the parameterization of shallow convection: without shallow convection, the convection scheme is largely ineffective at preventing convection from occurring at the grid scale. The sensitivities to convection scheme parameters are also examined. The simulations are remarkably insensitive to the convective relaxation time, and only mildly sensitive to the relative humidity of the reference profile, provided significant large-scale condensation is not allowed to occur. The changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere.

scholarly journals Evaluation of the atmospheric transport in a GCM using radon measurements: sensitivity to cumulus convection parameterization

2008 ◽  
Vol 8 (10) ◽  
pp. 2811-2832 ◽  
Author(s):  
K. Zhang ◽  
H. Wan ◽  
M. Zhang ◽  
B. Wang
Keyword(s):  
Vertical Distribution ◽  
Radon Concentration ◽  
Large Scale ◽  
Atmospheric Transport ◽  
Surface Concentration ◽  
Transport Processes ◽  
Cumulus Convection ◽  
Models Comparison ◽  
Convection Schemes ◽  
Convection Parameterization

Abstract. The radioactive species radon (222Rn) has long been used as a test tracer for the numerical simulation of large scale transport processes. In this study, radon transport experiments are carried out using an atmospheric GCM with a finite-difference dynamical core, the van Leer type FFSL advection algorithm, and two state-of-the-art cumulus convection parameterization schemes. Measurements of surface concentration and vertical distribution of radon collected from the literature are used as references in model evaluation. The simulated radon concentrations using both convection schemes turn out to be consistent with earlier studies with many other models. Comparison with measurements indicates that at the locations where significant seasonal variations are observed in reality, the model can reproduce both the monthly mean surface radon concentration and the annual cycle quite well. At those sites where the seasonal variation is not large, the model is able to give a correct magnitude of the annual mean. In East Asia, where radon simulations are rarely reported in the literature, detailed analysis shows that our results compare reasonably well with the observations. The most evident changes caused by the use of a different convection scheme are found in the vertical distribution of the tracer. The scheme associated with weaker upward transport gives higher radon concentration up to about 6 km above the surface, and lower values in higher altitudes. In the lower part of the atmosphere results from this scheme does not agree as well with the measurements as the other scheme. Differences from 6 km to the model top are even larger, although we are not yet able to tell which simulation is better due to the lack of observations at such high altitudes.

Dynamic Radiative–Convective Equilibria Using GCM Column Physics

2007 ◽  
Vol 64 (1) ◽  
pp. 228-238 ◽  
Author(s):  
Isaac M. Held ◽  
Ming Zhao ◽  
Bruce Wyman
Keyword(s):  
Fluid Dynamics ◽  
Large Scale ◽  
Homogeneous Model ◽  
Horizontal Resolution ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Geophysical Fluid Dynamics ◽  
Convection Scheme ◽  
Cloud Feedbacks ◽  
The Tropics ◽  
Convective Organization

Abstract The behavior of a GCM column physics package in a nonrotating, doubly periodic, homogeneous setting with prescribed SSTs is examined. This radiative–convective framework is proposed as a useful tool for studying some of the interactions between convection and larger-scale dynamics and the effects of differing modeling assumptions on convective organization and cloud feedbacks. For the column physics utilized here, from the Geophysical Fluid Dynamics Laboratory (GFDL) AM2 model, many of the properties of the homogeneous, nonrotating model are closely tied to the fraction of precipitation that is large-scale, rather than convective. Significant large-scale precipitation appears above a critical temperature and then increases with further increases in temperature. The amount of large-scale precipitation is a function of horizontal resolution and can also be controlled by modifying the convection scheme, as is illustrated here by modifying assumptions concerning entrainment into convective plumes. Significant similarities are found between the behavior of the homogeneous model and that of the Tropics of the parent GCM when ocean temperatures are increased and when the convection scheme is modified.

scholarly journals Evaluation of the atmospheric transport in a GCM using radon measurements: sensitivity to cumulus convection parameterization

2008 ◽  
Vol 8 (1) ◽  
pp. 2085-2127
Author(s):  
K. Zhang ◽  
H. Wan ◽  
M. Zhang ◽  
B. Wang
Keyword(s):  
Vertical Distribution ◽  
Radon Concentration ◽  
Large Scale ◽  
Atmospheric Transport ◽  
Surface Concentration ◽  
Transport Processes ◽  
Cumulus Convection ◽  
Models Comparison ◽  
Convection Schemes ◽  
Convection Parameterization

Abstract. The radioactive species radon (222Rn) has long been used as a test tracer for the numerical simulation of large scale transport processes. In this study, radon transport experiments are carried out using an atmospheric GCM with a finite-difference dynamical core, the van Leer type FFSL advection algorithm and two state-of-the-art cumulus convection parameterization schemes. Measurements of surface concentration and vertical distribution of radon collected from literature are used as references in model evaluation. The simulated radon concentrations using both convection schemes turn out to be consistent with earlier studies with many other models. Comparison with measurements indicates that at the locations where significant seasonal variations are observed in reality, the model can reproduce both the monthly mean surface radon concentration and the annual cycle quite well. At those sites where the seasonal variation is not large, the model is able to give a correct magnitude of the annual mean. In East Asia, where radon simulations are rarely reported in literature, detailed analysis shows that our results compare reasonably well with the observations. The most evident changes caused by the use of a different convection scheme are found in the vertical distribution of the tracer. The scheme associated with a weaker upward transport gives higher radon concentration up to about 6 km above the surface, and lower values in higher altitudes. In the lower part of the atmosphere results from this scheme does not agree as well with the measurements as the other scheme. Differences from 6 km to the model top are even larger, although we are not yet able to tell which simulation is better due to the lack of observations at such high altitudes.

scholarly journals Scale Analysis for Large-Scale Tropical Atmospheric Dynamics

2009 ◽  
Vol 66 (1) ◽  
pp. 159-172 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Marine Bonazzola
Keyword(s):  
Asymptotic Expansion ◽  
Large Scale ◽  
Diabatic Heating ◽  
Scale Analysis ◽  
Leading Order ◽  
Wave Dynamics ◽  
Advection Term ◽  
Equatorial Wave ◽  
Balanced Dynamics ◽  
The Tropics

Abstract A systematic scale analysis is performed for large-scale dynamics over the tropics. It is identified that two regimes are competing: 1) a dynamics characterized by balance between the vertical advection term and diabatic heating in the thermodynamic equation, realized at horizontal scales less than L ∼ 103 km given a velocity scale U ∼ 10 m s−1, and 2) a linear equatorial wave dynamics modulated by convective diabatic heating, realized at scales larger than L ∼ 3 × 103 km given U ∼ 3 m s−1. Under the first dynamic regime (balanced), the system may be approximated as nondivergent to leading order in asymptotic expansion, as originally pointed out by Charney. Inherent subtleties of scale analysis at large scales for the tropical atmosphere are emphasized. The subtleties chiefly arise from a strong sensitivity of the nondimensional β parameter to the horizontal scale. This amounts to qualitatively different dynamic regimes for scales differing only by a factor of 3, as summarized above. Because any regime under asymptotic expansion may have a wider applicability than a formal scale analysis would suggest, the question of which one of the two identified regimes dominates can be answered only after extensive modeling and observational studies. Preliminary data analysis suggests that the balanced dynamics, originally proposed by Sobel, Nilsson, and Polvani, is relevant for a wider range than the strict scale analysis suggests. A rather surprising conclusion from the present analysis is a likely persistence of balanced dynamics toward scales as small as the mesoscale L ∼ 102 km. Leading-order nondivergence also becomes more likely the case for the smaller scales because otherwise the required diabatic heating rate becomes excessive compared to observations by increasing inversely proportionally with decreasing horizontal scales.

scholarly journals Convectively Coupled Kelvin Waves in an Idealized Moist General Circulation Model

2007 ◽  
Vol 64 (6) ◽  
pp. 2076-2090 ◽  
Author(s):  
Dargan M. W. Frierson
Keyword(s):  
Relaxation Time ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Kelvin Waves ◽  
Convection Scheme ◽  
Gross Moist Stability ◽  
The Tropics ◽  
The Waves

The dynamics of convectively coupled Kelvin waves and their dependence on convection scheme parameters are studied within a simplified moist general circulation model. The model consists of the primitive equations on the sphere over zonally symmetric aquaplanet, slab mixed layer ocean boundary conditions, and idealized physical parameterizations including gray radiative transfer and a simplified Betts–Miller convection scheme. This framework allows the authors to study the dependence of Kelvin waves on quantities such as the gross moist stability in a clean manner. A control simulation with the model produces convectively coupled Kelvin waves that are remarkably persistent and dominate the variability within the Tropics. These waves propagate with an equivalent depth of ≈40 m. Linear regression analysis with respect to a Kelvin-filtered time series shows that the waves are driven by evaporation–wind feedback and have structures broadly consistent with theoretical predictions for Kelvin waves. Next, the determination of the speed and structure of the Kelvin waves is studied by examining the response of the waves to changes in convection scheme parameters. When the convective relaxation time is lengthened, the waves are damped and eventually are completely eliminated. The propagation speed additionally increases with longer relaxation time. Then changes to a convection scheme parameter that essentially controls the fraction of convective versus large-scale precipitation are examined. When some large-scale precipitation occurs, the waves increase in strength, propagate more slowly, and move to larger scales. However, when mostly large-scale precipitation occurs, the Kelvin wave disappears, and the Tropics are dominated by tropical storm–like variability. The decrease in speed is related here to the gross moist stability of the atmosphere, which is reduced with increased large-scale precipitation.

scholarly journals A Parameterization of Convective Dust Storms for Models with Mass-Flux Convection Schemes

2015 ◽  
Vol 72 (6) ◽  
pp. 2545-2561 ◽  
Author(s):  
Florian Pantillon ◽  
Peter Knippertz ◽  
John H. Marsham ◽  
Cathryn E. Birch
Keyword(s):  
Conceptual Model ◽  
Mass Flux ◽  
Large Scale ◽  
Dust Storms ◽  
Cold Pool ◽  
Moist Convection ◽  
Convection Scheme ◽  
Scale Models ◽  
Strong Winds ◽  
Convection Schemes

Abstract Cold pool outflows, generated by downdrafts from moist convection, can generate strong winds and therefore uplift of mineral dust. These so-called haboob convective dust storms occur over all major dust source areas worldwide and contribute substantially to emissions in northern Africa, the world’s largest source. Most large-scale models lack convective dust storms because they do not resolve moist convection, relying instead on convection schemes. The authors suggest a parameterization of convective dust storms to account for their contribution in such large-scale models. The parameterization is based on a simple conceptual model, in which the downdraft mass flux from the convection scheme spreads out radially in a cylindrical cold pool. The parameterization is tested with a set of Met Office Unified Model runs for June and July 2006 over West Africa. It is calibrated with a convection-permitting run and applied to a convection-parameterized run. The parameterization successfully produces the extensive area of dust-generating winds from cold pool outflows over the southern Sahara. However, this area extends farther to the east and dust-generating winds occur earlier in the day than in the convection-permitting run. These biases are caused by biases in the convection scheme. It is found that the location and timing of dust-generating winds are weakly sensitive to the parameters of the conceptual model. The results demonstrate that a simple parameterization has the potential to correct a major and long-standing limitation in global dust models.

scholarly journals Evaluating the Performance of Cumulus Convection Parameterization Schemes in Regional Climate Modeling System

2021 ◽  
Author(s):  
Sridhara Nayak ◽  
Suman Maity
Keyword(s):  
Climate Modeling ◽  
Regional Climate ◽  
Regional Climate Modeling ◽  
Horizontal Resolution ◽  
Cumulus Convection ◽  
Convection Scheme ◽  
Parameterization Schemes ◽  
Global Precipitation Climatology Centre ◽  
Convection Schemes ◽  
Convection Parameterization

In this study, we explored the performance of the cumulus convection parameterization schemes of Regional Climate Modeling System (RegCM) towards the Indian summer monsoon (ISM) of a catastrophic year through various numerical experiments conducted with different convection schemes (Kuo, Grell amd MIT) in RegCM. The model is integrated at 60KM horizontal resolution over Indian region and forced with NCEP/NCAR reanalysis. The simulated temperature at 2m and the wind at 10m are validated against the forced data and the total precipitation is compared with the Global Precipitation Climatology Centre (GPCC) observations. We find that the simulation with MIT convection scheme is close to the GPCC data and NCEP/NCAR reanalysis. Our results with three convection schemes suggest that the RegCM with MIT convection scheme successfully simulated some characteristics of ISM of a catastrophic year and may be further examined with more number of convection schemes to customize which convection scheme is much better.

scholarly journals Linearization of a Simple Moist Convection Scheme for Large-Scale NWP Models

2005 ◽  
Vol 133 (6) ◽  
pp. 1655-1670 ◽  
Author(s):  
Jean-François Mahfouf
Keyword(s):  
Large Scale ◽  
Temporal Integration ◽  
Preliminary Evaluation ◽  
Moist Convection ◽  
Convection Scheme ◽  
Surface Precipitation ◽  
Cloud Properties ◽  
Convection Schemes ◽  
Linearized Scheme ◽  
Linearization Errors

Abstract A simple Kuo-type convection scheme with an improved closure based on moist enthalpy accession (Kuo symmetric) has been linearized for the tangent-linear (TL) and adjoint (AD) versions of the Global Environmental Multiscale (GEM) model. The nonlinear scheme exhibits a reasonable behavior in terms of heating and moistening rates when evaluated in stand-alone mode over a set of deep convective profiles. A preliminary evaluation of a straightforward linearization in the global TL model has revealed the existence of noise that leads to an unacceptable solution after 12 h of integration. By neglecting several terms in the linearization (detrainment rate and cloud properties), the temporal evolution of humidity analysis increments is improved by including this simplified linearized convection scheme in the TL model. The behavior of the linearized scheme has also been compared favorably to the linearized version of the European Centre for Medium-Range Weather Forecasts (ECMWF) mass-flux convection scheme. When examining the validity of the TL approximation for surface precipitation, it appears that linearization errors are large for both stratiform and convective rainfall (rms errors are about twice the mean absolute perturbed precipitation). These errors are not reduced when considering accumulated rain rates instead of instantaneous quantities. However, the occurrence of “on–off” processes is reduced by a temporal integration of rain. This could make the variational assimilation of accumulated precipitation rates easier. Finally, errors coming from internal nonlinearities are slightly larger than those produced by discontinuities. This confirms the interest for improving the linearity of nonlinear convection schemes for applications in variational contexts.

scholarly journals Updates in the NCEP GFS Cumulus Convection Schemes with Scale and Aerosol Awareness

2017 ◽  
Vol 32 (5) ◽  
pp. 2005-2017 ◽  
Author(s):  
Jongil Han ◽  
Weiguo Wang ◽  
Young C. Kwon ◽  
Song-You Hong ◽  
Vijay Tallapragada ◽  
...  
Keyword(s):  
Mass Flux ◽  
Deep Convection ◽  
Threshold Value ◽  
Turnover Time ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Quasi Equilibrium ◽  
Convection Scheme ◽  
Freezing Level ◽  
Convection Schemes

Abstract The current operational NCEP Global Forecast System (GFS) cumulus convection schemes are updated with a scale-aware parameterization where the cloud mass flux decreases with increasing grid resolution. The ratio of advective time to convective turnover time is also taken into account for the scale-aware parameterization. In addition, the present deep cumulus convection closure using the quasi-equilibrium assumption is no longer used for grid sizes smaller than a threshold value. For the shallow cumulus convection scheme, the cloud-base mass flux is modified to be given by a function of mean updraft velocity. A simple aerosol-aware parameterization where rain conversion in the convective updraft is modified by aerosol number concentration is also included in the update. Along with the scale- and aerosol-aware parameterizations, more changes are made to the schemes. The cloud-base mass-flux computation in the deep convection scheme is modified to use convective turnover time as the convective adjustment time scale. The rain conversion rate is modified to decrease with decreasing air temperature above the freezing level. Convective inhibition in the subcloud layer is used as an additional trigger condition. Convective cloudiness is enhanced by considering suspended cloud condensate in the updraft. The lateral entrainment in the deep convection scheme is also enhanced to more strongly suppress convection in a drier environment. The updated NCEP GFS cumulus convection schemes display significant improvements especially in the summertime continental U.S. precipitation forecasts.

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