scholarly journals Simulation of monsoon circulation and cyclones with different types of orography

MAUSAM ◽  
2021 ◽  
Vol 47 (3) ◽  
pp. 237-250
Author(s):  
K. ROY ABRAHAM ◽  
S. K. DASH ◽  
U. C. MOHANTY
Keyword(s):  
Numerical Experiments ◽  
General Circulation ◽  
Digital Filters ◽  
Large Scale ◽  
Circulation Model ◽  
Monsoon Circulation ◽  
Rainfall Distribution ◽  
Sensitivity Experiments ◽  
Different Types ◽  
Rate Of Movement

In this study a number of sensitivity experiments have been conducted with different types of orography in the ECMWF spectral General Circulation Model (GCM). The basic aim is to simulate the large scale features of the Indian summer monsoon and the movement of cyclones. Different types of digital filters have been used to represent the orography as close to the observed values as possible. A comparative study shows that the Lanczos filter gives the best results. Thus, the Lanczos filter has been used in subsequent sensitivity experiments. One cyclone over the Bay of Bengal during pre-monsoon month of May, and another during the must active month of August have been selected for numerical experiments. The large scale features of the monsoonal rainfall were found to be close to those observed, when  standard deviation envelope orography was used. After 3 days of model integration, the rainfall distribution improved compared to the initial stages of integration. Although the predicted cyclone followed the observed track, the rate of movement was very sluggish. There was slight deepening of the systems with an increase of orography The movement of the systems was also found to be slightly faster with the enhancement of orography.    

scholarly journals Global atmospheric response to specific linear combinations of the main SST modes. Part I: numerical experiments and preliminary results

1996 ◽  
Vol 14 (10) ◽  
pp. 1066-1077 ◽  
Author(s):  
S. Trzaska ◽  
V. Moron ◽  
B. Fontaine
Keyword(s):  
Numerical Experiments ◽  
General Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Regional Scale ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Equatorial Atlantic ◽  
Preliminary Results ◽  
The Impact

Abstract. This article investigates through numerical experiments the controversial question of the impact of El Niño-Southern Oscillation (ENSO) phenomena on climate according to large-scale and regional-scale interhemispheric thermal contrast. Eight experiments (two considering only inversed Atlantic thermal anomalies and six combining ENSO warm phase with large-scale interhemispheric contrast and Atlantic anomaly patterns) were performed with the Météo-France atmospheric general circulation model. The definition of boundary conditions from observed composites and principal components is presented and preliminary results concerning the month of August, especially over West Africa and the equatorial Atlantic are discussed. Results are coherent with observations and show that interhemispheric and regional scale sea-surface-temperature anomaly (SST) patterns could significantly modulate the impact of ENSO phenomena: the impact of warm-phase ENSO, relative to the atmospheric model intercomparison project (AMIP) climatology, seems stronger when embedded in global and regional SSTA patterns representative of the post-1970 conditions [i.e. with temperatures warmer (colder) than the long-term mean in the southern hemisphere (northern hemisphere)]. Atlantic SSTAs may also play a significant role.

scholarly journals Monsoon Dynamics with Interactive Forcing. Part II: Impact of Eddies and Asymmetric Geometries

2007 ◽  
Vol 64 (5) ◽  
pp. 1431-1442 ◽  
Author(s):  
Nikki C. Privé ◽  
R. Alan Plumb
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Three Dimensional ◽  
Circulation Model ◽  
Qualitative Behavior ◽  
Monsoon Circulation ◽  
Moist Static Energy ◽  
Momentum Budget ◽  
Moist Static Energy Budget ◽  
Static Energy

Abstract The roles of eddies and forcing asymmetry in the dynamics of the large-scale monsoon circulation are investigated with a general circulation model. The net impact of eddies is found to be a slight weakening of the zonal mean monsoon circulation. The eddies strongly impact the momentum budget of the circulation, but the qualitative behavior of the monsoon flow is not substantially altered. The introduction of asymmetric forcing reveals the limitations of axisymmetric studies in representing the fully three-dimensional monsoon. Advection of low subcloud moist static energy air from the midlatitude oceans is seen to strongly impact the subcloud moist static energy budget in the continental subtropics, limiting the poleward extent of the monsoon. The advection of low moist static energy air must be blocked by orography, or the source of low moist static energy air must be removed, in order to induce strong precipitation over the subtropical landmass. An equatorial SST gradient is needed to induce a cross-equatorial meridional monsoon circulation. The location of the maximum subcloud moist static energy remains a good indicator for the limit of the monsoon.

Monsoon Dynamics with Interactive Forcing. Part I: Axisymmetric Studies

2007 ◽  
Vol 64 (5) ◽  
pp. 1417-1430 ◽  
Author(s):  
Nikki C. Privé ◽  
R. Alan Plumb
Keyword(s):  
Boundary Layer ◽  
Angular Momentum ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Meridional Flow ◽  
Monsoon Circulation ◽  
Moist Static Energy ◽  
Summer Hemisphere ◽  
Static Energy

Abstract The applicability of axisymmetric theory of angular momentum conserving circulations to the large-scale steady monsoon is studied in a general circulation model with idealized representations of continental geometry and simple physics. Results from an aquaplanet setup with localized subtropical forcing are compared with a continental case. It is found that the meridional circulation that develops is close to angular momentum conserving for cross-equatorial circulation cells, both in the aquaplanet and in the continental cases. The equator proves to be a substantial barrier to boundary layer meridional flow; flow into the summer hemisphere from the winter hemisphere tends to occur in the free troposphere rather than in the boundary layer. A theory is proposed to explain the location of the monsoon; assuming quasiequilibrium, the poleward boundary of the monsoon circulation is collocated with the maximum in subcloud moist static energy, with the monsoon rains occurring near and slightly equatorward of this maximum. The model results support this theory of monsoon location, and it is found that the subcloud moist static energy distribution is determined by a balance between surface forcing and advection by the large-scale flow.

scholarly journals Towards a regional ocean forecasting system for the IBI (Iberia-Biscay-Ireland area): developments and improvements within the ECOOP project framework

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 143-159 ◽  
Author(s):  
S. Cailleau ◽  
J. Chanut ◽  
J.-M. Lellouche ◽  
B. Levier ◽  
C. Maraldi ◽  
...  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Vertical Mixing ◽  
Circulation Model ◽  
Storm Surges ◽  
Ocean General Circulation Model ◽  
Tidal Mixing ◽  
Basin Scale ◽  
Forecasting System ◽  
Ocean Forecasting

Abstract. The regional ocean operational system remains a key element in downscaling from large scale (global or basin scale) systems to coastal ones. It enables the transition between systems in which the resolution and the resolved physics are quite different. Indeed, coastal applications need a system to predict local high frequency events (inferior to the day) such as storm surges, while deep sea applications need a system to predict large scale lower frequency ocean features. In the framework of the ECOOP project, a regional system for the Iberia-Biscay-Ireland area has been upgraded from an existing V0 version to a V2. This paper focuses on the improvements from the V1 system, for which the physics are close to a large scale basin system, to the V2 for which the physics are more adapted to shelf and coastal issues. Strong developments such as higher regional physics resolution in the NEMO Ocean General Circulation Model for tides, non linear free surface and adapted vertical mixing schemes among others have been implemented in the V2 version. Thus, regional thermal fronts due to tidal mixing now appear in the latest version solution and are quite well positioned. Moreover, simulation of the stratification in shelf areas is also improved in the V2.

scholarly journals Links between Tropical Pacific SST and Cholera Incidence in Bangladesh: Role of the Eastern and Central Tropical Pacific

2008 ◽  
Vol 21 (18) ◽  
pp. 4647-4663 ◽  
Author(s):  
Benjamin A. Cash ◽  
Xavier Rodó ◽  
James L. Kinter
Keyword(s):  
El Niño ◽  
General Circulation ◽  
Physical Mechanism ◽  
El Nino ◽  
Southern Oscillation ◽  
Regional Climate ◽  
Circulation Model ◽  
Tropical Pacific ◽  
Bacterial Disease ◽  
Monsoon Circulation

Abstract Recent studies arising from both statistical analysis and dynamical disease models indicate that there is a link between incidence of cholera, a paradigmatic waterborne bacterial disease (WBD) endemic to Bangladesh, and the El Niño–Southern Oscillation (ENSO). However, a physical mechanism explaining this relationship has not yet been established. A regionally coupled, or “pacemaker,” configuration of the Center for Ocean–Land–Atmosphere Studies atmospheric general circulation model is used to investigate links between sea surface temperature in the central and eastern tropical Pacific and the regional climate of Bangladesh. It is found that enhanced precipitation tends to follow winter El Niño events in both the model and observations, providing a plausible physical mechanism by which ENSO could influence cholera in Bangladesh. The enhanced precipitation in the model arises from a modification of the summer monsoon circulation over India and Bangladesh. Westerly wind anomalies over land to the west of Bangladesh lead to increased convergence in the zonal wind field and hence increased moisture convergence and rainfall. This change in circulation results from the tropics-wide warming in the model following a winter El Niño event. These results suggest that improved forecasting of cholera incidence may be possible through the use of climate predictions.

scholarly journals Utility of daily vs. monthly large-scale climate data: an intercomparison of two statistical downscaling methods

2007 ◽  
Vol 4 (5) ◽  
pp. 3413-3440 ◽  
Author(s):  
E. P. Maurer ◽  
H. G. Hidalgo
Keyword(s):  
Statistical Downscaling ◽  
General Circulation ◽  
Large Scale ◽  
Impact Analysis ◽  
Climate Model ◽  
Daily Precipitation ◽  
Circulation Model ◽  
Reanalysis Data ◽  
Temperature Extremes ◽  
Daily Data

Abstract. Downscaling of climate model data is essential to most impact analysis. We compare two methods of statistical downscaling to produce continuous, gridded time series of precipitation and surface air temperature at a 1/8-degree (approximately 140 km² per grid cell) resolution over the western U.S. We use NCEP/NCAR Reanalysis data from 1950–1999 as a surrogate General Circulation Model (GCM). The two methods included are constructed analogues (CA) and a bias correction and spatial downscaling (BCSD), both of which have been shown to be skillful in different settings, and BCSD has been used extensively in hydrologic impact analysis. Both methods use the coarse scale Reanalysis fields of precipitation and temperature as predictors of the corresponding fine scale fields. CA downscales daily large-scale data directly and BCSD downscales monthly data, with a random resampling technique to generate daily values. The methods produce comparable skill in producing downscaled, gridded fields of precipitation and temperatures at a monthly and seasonal level. For daily precipitation, both methods exhibit some skill in reproducing both observed wet and dry extremes and the difference between the methods is not significant, reflecting the general low skill in daily precipitation variability in the reanalysis data. For low temperature extremes, the CA method produces greater downscaling skill than BCSD for fall and winter seasons. For high temperature extremes, CA demonstrates higher skill than BCSD in summer. We find that the choice of most appropriate downscaling technique depends on the variables, seasons, and regions of interest, on the availability of daily data, and whether the day to day correspondence of weather from the GCM needs to be reproduced for some applications. The ability to produce skillful downscaled daily data depends primarily on the ability of the climate model to show daily skill.

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