scholarly journals Accounting for moist processes in a sub‐grid orographic drag scheme

2021 ◽  
Author(s):  
Samantha Smith
Keyword(s):  
Moist Processes ◽  
Orographic Drag

Why is the tropical sky white? Numerical investigations to elucidate the shape of mesoscale vertical velocity spectra.

2021 ◽  
Author(s):  
Yanmichel Morfa-Avalos
Keyword(s):  
Energy Distribution ◽  
Vertical Velocity ◽  
Temporal Variability ◽  
Spectral Response ◽  
Surface Fluxes ◽  
Energy Spectra ◽  
Tropical Atlantic ◽  
Numerical Studies ◽  
Moist Processes ◽  
Velocity Spectra

<p>Vertical motions are fundamental to atmospheric dynamics and our understanding of phenomena such as moist convection. A long-standing problem in atmospheric sciences is to understand the mesoscale energy spectra. Several numerical studies show that the vertical velocity spectrum has a homogeneous energy distribution across the mesoscales with a flat spectrum. Compared to the energy spectra of horizontal motion, the mechanisms that govern the spectrum of vertical velocity are less well known. In the troposphere, most of the horizontal mesoscale energy comes from divergent motions. At large scales O(100 km), vertical velocity relates, to a good approximation, to the vertically averaged divergence of horizontal motions by continuity in the incompressible limit. Recent measurements from NARVAL-2 (Next Generation Remote Sensing for Validation Studies) campaign conducted in the tropical Atlantic, unveiled that mesoscale horizontal mass divergence profiles possess a rich vertical structure and high spatio-temporal variability. Although the premise of a radiatively-balanced circulation holds on the long-term average, instantaneous deviations from this equilibrium occur in the form of wave-like oscillations. Numerical studies show that our state-of-the-art models can reproduce the observed variability in mesoscale divergence. We ask the following question in support of the previous arguments: What controls the spectrum of coherent mesoscale vertical motion? We aim to elucidate the mechanisms determining the homogeneous energy distribution across horizontal scales of vertical velocity spectra. This study designs numerical experiments, which include mechanisms-denial simulations employing the Icosahedral Nonhydrostatic (ICON) model. We conducted numerical simulations on a limited-area domain located in the western tropical Atlantic (4°S – 18°N, 64°W – 42°W). This domain has a horizontal resolution of 1.25 km and a lid at 30 km—the analysis period spans 48 hours. The experiments include the following: (i) a control run using DWD NWP physics configuration (ii) a dry atmosphere with all moist processes excluded along with the latent heat surface fluxes (iii) clouds invisible to radiation and, (iv) effects of saturation adjustment on temperature neglected while maintaining surface heat fluxes. Preliminary results show that the divergence profiles horizontally averaged over 200 km present a clear dominance of vertical wavelengths of 3 – 6 km. We found autocorrelation time-scales of around 4 – 6 hours increasing with altitude outside convective areas and consistent among all simulations. All experiments show a systematic decrease of about 50% in the temporal autocorrelation inside convective areas; therefore, moist convective processes modulate divergence's temporal variability. Moreover, we found that local moist processes contribute the most considerable fraction to the energy spectrum at scales < 200 km. The spectral response to moist processes is broad and extends into the free troposphere. The spectral response of surface fluxes instead is confined to the subcloud layer.</p>

Axisymmetric Hurricane in a Dry Atmosphere: Theoretical Framework and Numerical Experiments

2011 ◽  
Vol 68 (8) ◽  
pp. 1607-1619 ◽  
Author(s):  
Agnieszka A. Mrowiec ◽  
Stephen T. Garner ◽  
Olivier M. Pauluis
Keyword(s):  
Water Vapor ◽  
High Resolution ◽  
Numerical Model ◽  
Numerical Experiments ◽  
Momentum Flux ◽  
Theoretical Framework ◽  
Moist Processes ◽  
Energy And Momentum ◽  
The Relationship ◽  
Theoretical Insight

Abstract This paper discusses the possible existence of hurricanes in an atmosphere without water vapor and analyzes the dynamic and thermodynamic structures of simulated hurricane-like storms in moist and dry environments. It is first shown that the “potential intensity” theory for axisymmetric hurricanes is directly applicable to the maintenance of a balanced vortex sustained by a combination of surface energy and momentum flux, even in the absence of water vapor. This theoretical insight is confirmed by simulations with a high-resolution numerical model. The same model is then used to compare dry and moist hurricanes. While it is found that both types of storms exhibit many similarities and fit well within the theoretical framework, there are several differences, most notably in the storm inflow and in the relationship between hurricane size and intensity. Such differences indicate that while water vapor is not necessary for the maintenance of hurricane-like vortices, moist processes directly affect the structure of these storms.

scholarly journals Cloud and Precipitation Parameterizations in Modeling and Variational Data Assimilation: A Review

2007 ◽  
Vol 64 (11) ◽  
pp. 3766-3784 ◽  
Author(s):  
Philippe Lopez
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Large Scale ◽  
Weather Prediction ◽  
General Circulation Models ◽  
Variational Data Assimilation ◽  
Current Status ◽  
General Question ◽  
Observation Error ◽  
Moist Processes

Abstract This paper first reviews the current status, issues, and limitations of the parameterizations of atmospheric large-scale and convective moist processes that are used in numerical weather prediction and climate general circulation models. Both large-scale (resolved) and convective (subgrid scale) moist processes are dealt with. Then, the general question of the inclusion of diabatic processes in variational data assimilation systems is addressed. The focus is put on linearity and resolution issues, the specification of model and observation error statistics, the formulation of the control vector, and the problems specific to the assimilation of observations directly affected by clouds and precipitation.

Evaluation of WRF Simulations With Different Selections of Subgrid Orographic Drag Over the Tibetan Plateau

2017 ◽  
Vol 122 (18) ◽  
pp. 9759-9772 ◽  
Author(s):  
X. Zhou ◽  
A. Beljaars ◽  
Y. Wang ◽  
B. Huang ◽  
C. Lin ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
The Tibetan Plateau ◽  
Orographic Drag

scholarly journals Atmospheric Dynamics Triggered by an Oceanic SST Front in a Moist Quasigeostrophic Model

2012 ◽  
Vol 69 (5) ◽  
pp. 1617-1632 ◽  
Author(s):  
Bruno Deremble ◽  
Guillaume Lapeyre ◽  
Michael Ghil
Keyword(s):  
Heat Flux ◽  
Heat Release ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Latent Heat Release ◽  
Sst Front ◽  
Moist Processes ◽  
Surface Sensible Heat Flux ◽  
Sst Fronts

Abstract To understand the atmospheric response to a midlatitude oceanic front, this paper uses a quasigeostrophic (QG) model with moist processes. A well-known, three-level QG model on the sphere has been modified to include such processes in an aquaplanet setting. Its response is analyzed in terms of the upper-level atmospheric jet for sea surface temperature (SST) fronts of different profiles and located at different latitudes. When the SST front is sufficiently strong, it tends to anchor the mean atmospheric jet, suggesting that the jet’s spatial location and pattern are mainly affected by the latitude of the SST front. Changes in the jet’s pattern are studied, focusing on surface sensible heat flux and on moisture effects through latent heat release. It is found that latent heat release due to moist processes is modified when the SST front is changed, and this is responsible for the meridional displacement of the jet. Moreover, both latent heat release and surface sensible heat flux contribute to the jet’s strengthening. These results highlight the role of SST fronts and moist processes in affecting the characteristics of the midlatitude jet stream and of its associated storm track, particularly their positions.

scholarly journals COnstraining ORographic Drag Effects (COORDE): A Model Comparison of Resolved and Parametrized Orographic Drag

2020 ◽  
Vol 12 (11) ◽  
Author(s):  
Annelize Niekerk ◽  
Irina Sandu ◽  
Ayrton Zadra ◽  
Eric Bazile ◽  
Takafumi Kanehama ◽  
...  
Keyword(s):  
Model Comparison ◽  
Orographic Drag

scholarly journals Simulations of Monsoon Intraseasonal Oscillation Using Climate Forecast System Version 2: Insight for Horizontal Resolution and Moist Processes Parameterization

Atmosphere ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 429 ◽  
Author(s):  
Snehlata Tirkey ◽  
P. Mukhopadhyay ◽  
R. Phani Murali Krishna ◽  
Ashish Dhakate ◽  
Kiran Salunke
Keyword(s):  
Deep Convection ◽  
Intraseasonal Oscillation ◽  
Horizontal Resolution ◽  
Specific Humidity ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
The North ◽  
Northward Propagation ◽  
Moist Processes

In the present study, we analyze the Climate Forecast System version 2 (CFSv2) model in three resolutions, T62, T126, and T382. We evaluated the performance of all three resolutions of CFSv2 in simulating the Monsoon Intraseasonal Oscillation (MISO) of the Indian summer monsoon (ISM) by analyzing a suite of dynamic and thermodynamic parameters. Results reveal a slower northward propagation of MISO in all models with the characteristic northwest–southeast tilted rain band missing over India. The anomalous moisture convergence and vorticity were collocated with the convection center instead of being northwards. This affected the northward propagation of MISO. The easterly shear to the north of the equator was better simulated by the coarser resolution models than CFS T382. The low level specific humidity showed improvement only in CFS T382 until ~15° N. The analyses of the vertical profiles of moisture and its relation to rainfall revealed that all CFSv2 resolutions had a lower level of moisture in the lower level (< 850 hPa) and a drier level above. This eventually hampered the growth of deep convection in the model. These model shortcomings indicate a possible need of improvement in moist process parameterization in the model in tune with the increase in resolution.

Sign in / Sign up

Export Citation Format

Share Document