Reduced Near-Surface Thermal Inversions in 2005–06 in the Southeastern Arabian Sea (Lakshadweep Sea)*

2009 ◽  
Vol 39 (5) ◽  
pp. 1184-1199 ◽  
Author(s):  
K. Nisha ◽  
Suryachandra A. Rao ◽  
V. V. Gopalakrishna ◽  
R. R. Rao ◽  
M. S. Girishkumar ◽  
...  
Keyword(s):  
Bay Of Bengal ◽  
Arabian Sea ◽  
Surface Wind ◽  
Surface Heat ◽  
The Other ◽  
Near Surface ◽  
Low Salinity ◽  
Southeastern Arabian Sea ◽  
Surface Wind Field ◽  
Lakshadweep Sea

Abstract Repeat XBT transects made at near-fortnightly intervals in the Lakshadweep Sea (southeastern Arabian Sea) and ocean data assimilation products are examined to describe the year-to-year variability in the observed near-surface thermal inversions during the winter seasons of 2002–06. Despite the existence of a large low-salinity water intrusion into the Lakshadweep Sea, there was an unusually lower number of near-surface thermal inversions during the winter 2005/06 compared to the other winters. The possible causative mechanisms are examined. During the summer monsoon of 2005 and the following winter season, unusually heavy rainfall occurred over the southwestern Bay of Bengal and the Lakshadweep Sea compared to other years in the study. Furthermore, during the winter of 2005, both the East India Coastal Current and the Winter Monsoon Current were stronger compared to the other years, transporting larger quantities of low salinity waters from the Bay of Bengal into the Lakshadweep Sea where a relatively cooler near-surface thermal regime persisted owing to prolonged upwelling until November 2005. In addition, the observed local surface wind field was relatively stronger, and the net surface heat gain to the ocean was weaker over the Lakshadweep Sea during the postmonsoon season of 2005. Thus, in winter 2005/06, the combination of prolonged upwelling and stronger surface wind field resulting in anomalous net surface heat loss caused weaker secondary warming of the near-surface waters in the Lakshadweep Sea. This led to a weaker horizontal sea surface temperature (SST) gradient between the Lakshadweep Sea and the intruding Bay of Bengal waters and, hence, a reduced number of thermal inversions compared to other winters despite the presence of stronger vertical haline stratification.

scholarly journals Process-Oriented Diagnosis of Tropical Cyclones in High-Resolution GCMs

2018 ◽  
Vol 31 (5) ◽  
pp. 1685-1702 ◽  
Author(s):  
Daehyun Kim ◽  
Yumin Moon ◽  
Suzana J. Camargo ◽  
Allison A. Wing ◽  
Adam H. Sobel ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Resolution ◽  
Tropical Cyclones ◽  
Surface Heat Flux ◽  
Surface Wind ◽  
Atmospheric Model ◽  
Surface Heat ◽  
The Other ◽  
Near Surface ◽  
Surface Latent Heat Flux

This study proposes a set of process-oriented diagnostics with the aim of understanding how model physics and numerics control the representation of tropical cyclones (TCs), especially their intensity distribution, in GCMs. Three simulations are made using two 50-km GCMs developed at NOAA’s Geophysical Fluid Dynamics Laboratory. The two models are forced with the observed sea surface temperature [Atmospheric Model version 2.5 (AM2.5) and High Resolution Atmospheric Model (HiRAM)], and in the third simulation, the AM2.5 model is coupled to an ocean GCM [Forecast-Oriented Low Ocean Resolution (FLOR)]. The frequency distributions of maximum near-surface wind near TC centers show that HiRAM tends to develop stronger TCs than the other models do. Large-scale environmental parameters, such as potential intensity, do not explain the differences between HiRAM and the other models. It is found that HiRAM produces a greater amount of precipitation near the TC center, suggesting that associated greater diabatic heating enables TCs to become stronger in HiRAM. HiRAM also shows a greater contrast in relative humidity and surface latent heat flux between the inner and outer regions of TCs. Various fields are composited on precipitation percentiles to reveal the essential character of the interaction among convection, moisture, and surface heat flux. Results show that the moisture sensitivity of convection is higher in HiRAM than in the other model simulations. HiRAM also exhibits a stronger feedback from surface latent heat flux to convection via near-surface wind speed in heavy rain-rate regimes. The results emphasize that the moisture–convection coupling and the surface heat flux feedback are critical processes that affect the intensity of TCs in GCMs.

On the Accuracy of the Simple Ocean Data Assimilation Analysis for Estimating Heat Budgets of the Near-Surface Arabian Sea and Bay of Bengal*

2005 ◽  
Vol 35 (3) ◽  
pp. 395-400 ◽  
Author(s):  
S S C. Shenoi ◽  
D. Shankar ◽  
S. R. Shetye
Keyword(s):  
Data Assimilation ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Heat Budget ◽  
Heat Content ◽  
Heat Fluxes ◽  
Simple Ocean Data Assimilation ◽  
Near Surface ◽  
Surface Heat Fluxes ◽  
Ocean Data Assimilation

Abstract The accuracy of data from the Simple Ocean Data Assimilation (SODA) model for estimating the heat budget of the upper ocean is tested in the Arabian Sea and the Bay of Bengal. SODA is able to reproduce the changes in heat content when they are forced more by the winds, as in wind-forced mixing, upwelling, and advection, but not when they are forced exclusively by surface heat fluxes, as in the warming before the summer monsoon.

The Effects of Vertical Stratification and Land Use Data on Numerical Simulation of Wind Energy Resources

2014 ◽  
Vol 535 ◽  
pp. 135-140
Author(s):  
Yuan Chang Deng ◽  
Zhen Cao Zou
Keyword(s):  
Numerical Simulation ◽  
Land Use ◽  
Wind Field ◽  
Wind Profile ◽  
Surface Wind ◽  
Wrf Model ◽  
Vertical Stratification ◽  
Near Surface ◽  
Wind Field Simulation ◽  
Surface Wind Field

By adjusting the distribution of vertical layers and increasing its number in WRF model, this paper mainly studies the effects of vertical stratification on the near surface wind field and vertical profile simulation. The test outcomes show that moderately increasing vertical layers can effectively improve the near surface wind field simulation results, while it has little influence on the numeral and changing trend of high vertical wind profile. Considering both accuracy and efficiency, it is recommended to set 10~15 layers below 300m. On the basis of this research, instead of USGS data by using the MODIS_30S data, the data underlying surface land in Shenzhen and HK area are updated. Comparative results between the two schemes, due to the roughness and drag coefficient of difference types of surface are not identical; the surface data has a significant impact on wind field and wind profile simulation. Using the MODIS land use data which is more consistent with the actual situation can improve the accuracy of numerical simulation.

A mixed finite element/control volume model of wind-driven circulation in lakes

2013 ◽  
Vol 5 (1) ◽  
Author(s):  
Victor Podsechin
Keyword(s):  
Control Volume ◽  
Mixed Finite Element ◽  
Surface Wind ◽  
Three Dimensional ◽  
Circulation Model ◽  
Hydrodynamic Equations ◽  
Governing Equations ◽  
Near Surface ◽  
Stream Functions ◽  
Surface Wind Field

AbstractA three-dimensional numerical circulation model is described. The model is based on non-linear hydrodynamic equations, modified according to hydrostatic and Boussinesq approximations. A space-splitting scheme is used for numerical approximations of governing equations. The simple hypothesis on elliptic stream functions shape is utilized to reconstruct the near-surface wind field. The calculated currents correspond reasonably well with observed velocities in different locations lake-wide.

scholarly journals An Assessment of NASA’s GMAO MERRA-2 Reanalysis Surface Winds

2019 ◽  
Vol 32 (23) ◽  
pp. 8261-8281 ◽  
Author(s):  
D. Carvalho
Keyword(s):  
Surface Wind ◽  
The Other ◽  
Surface Winds ◽  
Wind Fields ◽  
Near Surface ◽  
Wind Speeds ◽  
Wide Range ◽  
Ocean Surface Winds ◽  
The Tropics ◽  
Global Surface

Abstract The quality of MERRA-2 surface wind fields was assessed by comparing them with 10 years of measurements from a wide range of surface wind observing platforms. This assessment includes a comparison of MERRA-2 global surface wind fields with the ones from its predecessor, MERRA, to assess if GMAO’s latest reanalyses improved the representation of the global surface winds. At the same time, surface wind fields from other modern reanalyses—NCEP-CFSR, ERA-Interim, and JRA-55—were also included in the comparisons to evaluate MERRA-2 global surface wind fields in the context of its contemporary reanalyses. Results show that MERRA-2, CFSR, ERA-Interim, and JRA-55 show similar error metrics while MERRA consistently shows the highest errors. Thus, when compared with wind observations, the accuracy of MERRA-2 surface wind fields represents a clear improvement over its predecessor MERRA and is in line with the other contemporary reanalyses in terms of the representation of global near-surface wind fields. All reanalyses showed a tendency to underestimate ocean surface winds (particularly in the tropics) and, oppositely, to overestimate inland surface winds (except JRA-55, which showed a global tendency to underestimate the wind speeds); to represent the wind direction rotated clockwise in the Northern Hemisphere (positive bias) and anticlockwise in the Southern Hemisphere (negative bias), with the exception of JRA-55; and to show higher errors near the poles and in the ITCZ, particularly in the equatorial western coasts of Central America and Africa. However, MERRA-2 showed substantially lower wind errors in the poles when compared with the other reanalyses.

scholarly journals Reconstruction of Near-Surface Tornado Wind Fields from Forest Damage

2010 ◽  
Vol 49 (7) ◽  
pp. 1517-1537 ◽  
Author(s):  
Veronika Beck ◽  
Nikolai Dotzek
Keyword(s):  
Wind Field ◽  
Surface Wind ◽  
Forest Damage ◽  
Wind Fields ◽  
Tree Model ◽  
Translation Speed ◽  
Near Surface ◽  
Additional Information ◽  
Secondary Vortices ◽  
Surface Wind Field

Abstract Tornado intensity is usually inferred from the damage produced. To foster postevent tornado intensity assessments, the authors present a model to reconstruct near-surface wind fields from forest damage patterns. By comparing the structure of observed and simulated damage patterns, essential parameters to describe a tornado near-surface wind field are derived, such as the ratio Gmax between circular and translational velocity, and the deflection angle α between peak wind and pressure gradient. The model consists of a wind field module following the Letzmann analytical tornado model and a tree module based on the mechanistic HWIND tree model to assess tree breakage. Using this method, the velocity components of the near-surface wind field, the track of the tornado center, and the spatial distribution of the Fujita scale along and across the damage path can be assessed. Necessary requirements to apply the model are knowledge of the tornado translation speed (e.g., from radar observations) and a detailed analysis of the forest damage patterns. One of the key findings of this analysis is that the maximum intensity of the tornado is determinable with an uncertainty of only (Gmax + 1) times the variability of the usually well-known tornado translation speed. Further, if Letzmann’s model is applied and the translation speed of the tornado is known, the detailed tree model is unnecessary and could be replaced by an average critical velocity for stem breakage υcrit independent of the tree species. Under this framework, the F3 and F2 ratings of the tornadoes in Milosovice, Czech Republic, on 30 May 2001 and Castellcir, Spain, on 18 October 2006, respectively, could be verified. For the Milosovice event, the uncertainty in peak intensity was only ±6.0 m s−1. Additional information about the structure of the near-surface wind field in the tornado and several secondary vortices was also gained. Further, this model allows for distinguishing downburst damage patterns from those of tornadoes.

A New Technique for Forecasting Surface Wind Field From Scatterometer Observations: A Case Study for the Arabian Sea

2007 ◽  
Vol 45 (3) ◽  
pp. 613-620 ◽  
Author(s):  
Rashmi Sharma ◽  
Abhijit Sarkar ◽  
Neeraj Agarwal ◽  
Raj Kumar ◽  
Sujit Basu
Keyword(s):  
Wind Field ◽  
Arabian Sea ◽  
Surface Wind ◽  
New Technique ◽  
A New Technique ◽  
Surface Wind Field

scholarly journals Spatial Coherence of winds and waves over the Arabian Sea and Bay of Bengal and their evolution during SW Monsoon: a novel application of along-track Radar Altimeter measurements from Space

2014 ◽  
Vol XL-8 ◽  
pp. 1027-1033 ◽  
Author(s):  
S. M. Bhandari ◽  
K. Hareef Baba Shaeb
Keyword(s):  
Bay Of Bengal ◽  
Arabian Sea ◽  
Surface Wind ◽  
Spatial Coherence ◽  
Radar Altimeter ◽  
Ocean Surface Wind ◽  
Along Track ◽  
First Time ◽  
Coherence Lengths ◽  
Sw Monsoon

We have examined, for the first time, the spatial coherence of oceanic parameters, namely, the ocean surface wind and significant wave height (SWH), using near-instantaneous along-track sampling over vast oceanic tracks provided by Poseidon-2 Radar Altimeter onboard Jason-1. The spatial coherence length scales over the Arabian Sea and the Bay of Bengal regions, derived using Auto correlation analysis, display interesting characteristics in relation to onset and evolution of SW Monsoon over India. The estimated spatial coherence scales are found to be of the order of 100–500 km. Generally, SWH coherence lengths over Arabian Sea are observed to increase from June to July during good monsoon year (2012). This trend is not followed for the poor monsoon year (2002). Similar trend is observed for spatial coherence scales for wind speed. The temporal evolution of analyzed spatial coherence scales of winds and waves over Arabian Sea clearly brings out the distinction between a "good" (2012) and a "poor" (2002) monsoon year. The spatial coherence lengths of these parameters over the Bay of Bengal are found to be shorter and do not show any systematic relation to onset and evolution of SW monsoon. Anisotropy in coherence lengths is also analyzed by treating ascending and descending tracks separately. Generally, the descending tracks measurements show higher spatial coherence lengths than the ascending ones. Like the spatial coherence scales, the anisotropy of the coherence scales over the Arabian Sea also mimics the behaviour of the strength of SW Monsoon.

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