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1.
The quality of the surface wind analysis at the National Centre for Medium Range Weather Forecasts (NCMRWF), New Delhi over
the tropical Indian Ocean and its improvement in 2001 are examined by comparing it within situ buoy measurements and satellite derived surface winds from NASA QuikSCAT satellite (QSCT) during 1999, 2000 and 2001. The
NCMRWF surface winds suffered from easterly bias of 1.0–1.5 ms-1 in the equatorial Indian Ocean (IO) and northerly bias of 2.0–3.0 ms-1 in the south equatorial IO during 1999 and 2000 compared to QSCT winds. The amplitude of daily variability was also underestimated
compared to that in QSCT. In particular, the amplitude of daily variability of NCMRWF winds in the eastern equatorial IO was
only about 60% of that of QSCT during 1999 and 2000. The NCMRWF surface winds during 2001 have significantly improved with
the bias of the mean analyzed winds considerably reduced everywhere bringing it to within 0.5 ms-1 of QSCT winds in the equatorial IO. The amplitude and phase of daily and intraseasonal variability are very close to that
in QSCT almost everywhere during 2001. It is shown that the weakness in the surface wind analysis during 1999 and 2000 and
its improvement in 2001 are related to the weakness in simulation of precipitation by the forecast model in the equatorial
IO and its improvement in 2001. 相似文献
2.
Bijoy Thompson C. Gnanaseelan Anant Parekh P. S. Salvekar 《Journal of Earth System Science》2008,117(2):169-178
The variability in the long-term temperature and sea level over the north Indian Ocean during the period 1958–2000 has been
investigated using an Ocean General Circulation Model, Modular Ocean Model version 4. The model simulated fields are compared
with the sea level observations from tide-gauges, Topex/Poseidon (T/P) satellite, in situ temperature profile observations from WHOI moored buoy and sea surface temperature (SST) observations from DS1, DS3 and DS4
moored buoys. It is seen that the long (6–8 years) warming episodes in the SST over the north Indian Ocean are followed by
short episodes (2–3 years) of cooling. The model temperature and sea level anomaly over the north Indian Ocean show an increasing
trend in the study period. The model thermocline heat content per unit area shows a linear increasing trend (from 1958–2000)
at the rate of 0.0018 × 1011 J/m2 per year for north Indian Ocean. North Indian Ocean sea level anomaly (thermosteric component) also shows a linear increasing
trend of 0.31 mm/year during 1958–2000. 相似文献
3.
Impact of sea breeze on wind-seas off Goa, west coast of India 总被引:1,自引:0,他引:1
After withdrawal of the Indian Summer Monsoon and until onset of the next monsoon, i.e., roughly during November–May, winds
in the coastal regions of India are dominated by sea breeze. It has an impact on the daily cycle of the sea state near the
coast. The impact is quite significant when large scale winds are weak. During one such event, 1–15 April 1997, a Datawell
directional waverider buoy was deployed in 23 m water depth off Goa, west coast of India. Twenty-minute averaged spectra,
collected once every three hours, show that the spectrum of sea-breeze-related ‘wind-seas’ peaked at 0.23 ±0.05 Hz. These
wind-seas were well separated from swells of frequencies less than 0.15 Hz. The TMA spectrum (Bouwset al 1985) matched the observed seas spectra very well when the sea-breeze was active and the fetch corresponding to equilibrium
spectrum was found to be 77±43 km during such occasions. We emphasize on the diurnal cycle of sea-breeze-related sea off the
coast of Goa and write an equation for the energy of the seas as a function of the local wind 相似文献
4.
Ajoy Kumar Peter Minnett Guillermo Podestá Robert Evans Katherine Kilpatrick 《Journal of Earth System Science》2000,109(4):395-405
As part of the Pathfinder program developed jointly by National Aeronautics and Space Administration (NASA) and National Oceanic
and Atmospheric Administration (NOAA) a large database ofin situ sea surface temperature (SST) measurements coincident with satellite data is now available to the user community. The Pathfinder
Matchup Database (PMDB) is a multi-year, multi-satellite collection of coincident measurements from the Advanced Very High
Resolution Radiometer (AVHRR) and broadly distributed buoy data (matchups). This database allows the user community to test
and validate new SST algorithms to improve the present accuracy of surface temperature measurements from satellites. In this
paper we investigate the performance of a global Pathfinder algorithm to specific regional conditions. It is shown that for
zenith angles less than 45°, the best-expected statistical discrepancy between satellite and buoy data is about ∼ 0.5 K. In
general, the bias of the residuals (satellite — buoy) is negative in most regions, except in the North Atlantic and adjacent
seas, where the residuals are always positive. A seasonal signal in SST residuals is observed in all regions and is strongest
in the Indian Ocean. The channel-difference term used as a proxy for atmospheric water vapor correction is observed to be
unresponsive for columnar water vapor values greater than 45 mm and high zenith angles. This unresponsiveness of the channels
leads to underestimation of sea surface temperature from satellites in these conditions. 相似文献
5.
Auto-correlation analysis of wave heights in the Bay of Bengal 总被引:1,自引:0,他引:1
Time series observations of significant wave heights in the Bay of Bengal were subjected to auto-correlation analysis to determine
temporal variability scale. The analysis indicates an exponential fall of auto-correlation in the first few hours with a decorrelation
time scale of about six hours. A similar figure was found earlier for ocean surface winds. The nature of variation of auto-correlation
with time lags was also found to be similar for winds and wave heights 相似文献
6.
Indian Space Research Organization (ISRO) conducted the ‘Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB)’
for a two-month pre-monsoon period in 2006 with the ocean segment covering Bay of Bengal and Arabian Sea. During this campaign,
carbon monoxide (CO) was continuously monitored using a non-dispersive IR analyser. Quantifying CO in ambient air is vital
in determining the air quality of a region. Being toxic, CO is a criteria pollutant, but it is a weak green house gas. Globally,
very few measurements exist over marine atmospheres to study its temporal pattern; particularly in situ CO measurements are few over the Bay of Bengal and Arabian Sea for comparison. Present measurements indicate: (i) predominant
single peak in the diurnal pattern of CO over the marine atmosphere in contrast to the double peak over the continent, (ii)
the mean diurnal CO over the marine atmosphere showing an increasing trend towards evening hours, (iii) the amplitude of the
AN peaks over the marine atmosphere was ∼ 100 ppbv, while at a remote island site in the Indian Ocean it was ∼ 5 ppbv and
(iv) high CO values were observed close to continent and the long range transport by wind also caused CO highs. 相似文献
7.
The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the
Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric
Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between
30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the
spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances),
indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics
of the two modes and their interannual variability are studied in detail.
The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’)
or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of
Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation.
The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough).
The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The
vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with
the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with
fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20
day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere
in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl
anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs
in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay.
On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly
mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree
well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite
structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean
winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual
variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence
of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual
scales. 相似文献
8.
M S Narayanan P K Pal P C Joshi M Mali Baby Simon 《Journal of Earth System Science》1989,98(3):247-254
Water vapour tracers can provide useful information on winds at ≈ 500mb by observing the 6·7μ radiances. This fills the data
gap in the cloud motion winds provided by conventional meteorological geostationary satellites. There is no geostationary
satellite at present over the Indian Ocean with 6·7μ imaging capability to provide mid-tropospheric winds. The potentials
of 6·7μ radiances, available from polar orbiting satellites, for mid-tropospheric circulation features have been examined
in this study. Tiros-N satellite data of May 1979 and ECMWF level-IIIb wind data were analysed to relate the radiances with
the streamlines. We find that the radiances of 6·7μ from orbiting satellites agree well with the wind field. 相似文献
9.
S. S. C. Shenoi N. Nasnodkar G. Rajesh K. Jossia Joseph I. Suresh A. M. Almeida 《Journal of Earth System Science》2009,118(5):483-496
This paper describes the variability in the diurnal range of SST in the north Indian Ocean using in situ measurements and tests the suitability of simple regression models in estimating the diurnal range. SST measurements obtained
from 1556 drifting and 25 moored buoys were used to determine the diurnal range of SSTs. The magnitude of diurnal range of
SST was highest in spring and lowest in summer monsoon. Except in spring, nearly 75–80% of the observations reported diurnal
range below 0.5°C. The distributions of the magnitudes of diurnal warming across the three basins of north Indian Ocean (Arabian
Sea, Bay of Bengal and Equatorial Indian Ocean) were similar except for the differences between the Arabian Sea and the other
two basins during November–February (winter monsoon) and May. The magnitude of diurnal warming that depended on the location
of temperature sensor below the water level varied with seasons. In spring, the magnitude of diurnal warming diminished drastically
with the increase in the depth of temperature sensor. The diurnal range estimated using the drifting buoy data was higher
than the diurnal range estimated using moored buoys fitted with temperature sensors at greater depths.
A simple regression model based on the peak solar radiation and average wind speed was good enough to estimate the diurnal
range of SST at ∼1.0 m in the north Indian Ocean during most of the seasons except under low wind-high solar radiation conditions
that occur mostly during spring. The additional information on the rate of precipitation is found to be redundant for the
estimation of the magnitude of diurnal warming at those depths. 相似文献
10.
Validating a Tsunami Vulnerability Assessment Model (the PTVA Model) Using Field Data from the 2004 Indian Ocean Tsunami 总被引:2,自引:1,他引:2
The “PTVAM” tsunami vulnerability assessment model [Papathoma and Dominey-Howes: 2003, Nat. Hazards Earth Syst. Sci. 3, 733–744; Papathoma et al.: 2003, Nat. Hazards Earth Syst. Sci. 3, 377–389], like all models, requires validation. We use the results from post-tsunami surveys in the Maldives following the
December 26, 2004 Indian Ocean tsunami to ‘evaluate’ the appropriateness of the PTVAM attributes to understanding spatial
and temporal vulnerability to tsunami damage and loss. We find that some of the PTVAM attributes are significantly important
and others moderately important to understanding and assessing vulnerability. Some attributes require further investigation.
Based upon the ground-truth data, we make several modifications to the model framework and propose a revised version of the
PTVAM (PTVAM 2). 相似文献
11.
The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity
of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We
have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets
of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold’s
SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold’s
and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial
resolution showed sharper gradient when compared to the Reynold’s SST. The use of TMI SST improved the WRF cyclone intensity
prediction when compared to that using Reynold’s SST for both the cases studied. The improvements in intensity were mainly
due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold’s SST improved
cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling
study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification
and movement of tropical cyclones over the Indian Ocean. 相似文献
12.
Applying the method of ‘statistical linear regression’, atomspheric water vapour over oceanic areas has been estimated from
the 19GHz and 22 GHz data of the satellite microwave radiometer (SAMIR) system onboard the Bhaskara II satellite. In the absence of any simultaneousin situ measurements on water vapour over ocean, theSAMIR-derived water vapour data have been compared with like data from theNOAA-7 satellite. It is suggested that a positive bias seen in theSAMIR data could be due to calibration errors in the basic data. In view of the observed bias, the original regression equation
is modified and then used to obtain water vapour distributions over ocean for winter and south-west monsoon seasons usingSAMIR data of several orbits. 相似文献
13.
Parameterization of sensible heat and momentum fluxes as inferred from an analysis of tower observations archived during MONTBLEX-90
at Jodhpur is proposed, both in terms of standard exchange coefficientsC
H
andC
D
respectively and also according to free convection scaling. Both coefficients increase rapidly at low winds (the latter more
strongly) and with increasing instability. All the sensible heat flux data at Jodhpur (wind speed at 10 m Ū10 < 8 ms−1) also obey free convection scaling, with the flux proportional to the ‘4/3’ power of an appropriate temperature difference
such as that between 1 and 30 m. Furthermore, for Ū10 < 4 ms−1 the momentum flux displays a linear dependence on wind speed. 相似文献
14.
The focus of the present study is the assessment of the impact of wind forcing on the spectral wave model MIKE 21 SW in the Indian Ocean region. Three different wind fields, namely the ECMWF analyzed winds, the ECMWF blended winds, and the NCEP blended winds have been used to drive the model. The wave model results have been compared with in-situ observations and satellite altimeter data. This study also evaluated the performance of the wind products during local phenomenon like sea breeze, since it has a significant impact on the wave prediction in the Indian coastal region. Hence we explored the possibility of studying the impact of diurnal variation of winds on coastal waves using different wind fields. An analysis of the model performance has also been made during high wind conditions with the inference that blended winds generate more realistic wave fields in the high wind conditions and are able to produce the growth and decay of waves more realistically. 相似文献
15.
Track prediction of very severe cyclone ‘Nargis’ using high resolution weather research forecasting (WRF) model 总被引:1,自引:0,他引:1
The recent very severe cyclonic storm (VSCS) ‘Nargis’ over the Bay of Bengal caused widespread destruction over Myanmar after
hitting the coast on 2 May 2008. The real time forecasting of the VSCS ‘Nargis’ was a very difficult task as it did not follow
the normal westerly/northwesterly track. In the present study, a detailed diagnostic analysis of the system ‘Nargis’ is carried
out initially to investigate the features associated with this unusual movement and subsequently the real time forecast of
VSCS ‘Nargis’ using high resolution advanced version weather research forecasting (WRF) model is presented. The advanced research
WRF model was run for 72 h at 27 km and 20 km resolutions with 28, 29, 30 April and 1 May as the initial conditions. The diagnostic
study indicates that the recurvature of the system ‘Nargis’ was mainly associated with:
The real time track forecast using the WRF model run at 27 km and 20 km resolution based on the initial conditions of 28 April
(when the system was only 550 km away from the Indian coast) indicated that the system had a northeasterly forecast track
and was not expected to cross the Indian coast. Similarly, based on 29 April initial condition the system showed east/east-northeasterly
movement towards the Myanmar coast. The east/east-northeasterly movement of the ‘Nargis’ was persisting in the forecast based
on 30 April and 1 May initial conditions with respective landfall errors of 85 km and 50 km with 27 km resolution, which reduces
to 30 km and 40 km respectively with 20 km resolution, however, with a landfall time delay of about 10 h. Improvement of mean
forecast errors at different forecast hours is noticed in WRF model run at higher resolution compared to that run at lower
resolution. Thus, it is very clear that the advanced version WRF model had captured movement of the system reasonably well
almost 3 days in advance. Consistence with the diagnostic analysis the WRF model forecast also indicates southerly/southwesterly
strong steering wind at 200 hPa level and maximum pressure fall to the east of the system. 相似文献
• | upper level southerly/southwesterly steering wind at 200 hPa level associated with anticyclonic circulation over southeastern sector of the centre of the system |
• | higher SST (29°C or more) with higher positive anomalies over the region to the northeast of the cyclone centre, and |
• | large negative 24 h pressure changes and large vorticity maximum to the east of the system. |
16.
Mesoscale modeling study of the oceanographic conditions off the southwest coast of India 总被引:1,自引:0,他引:1
Vibeke E. Haugen Ola M. Johannessen Geir Evensen 《Journal of Earth System Science》2002,111(3):321-337
A high resolution model, using the Miami Isopycnic Coordinate Ocean Model (MICOM), has been implemented for the first time
to study the seasonal circulation and coastal upwelling off the southwest Indian coast during 1974. This model is part of
a model and data assimilation system capable of describing the ocean circulation and variability in the Indian Ocean and its
predictability in response to the monsoon system.
Along the southwest coast of India the dominant coastal current is the reversing West Indian Coastal Current which is well
simulated and described, in addition to the weaker undercurrent of the opposite direction. Upwelling of cold water, 4‡C lower
than offshore temperatures appear in April. The upwelling intensifies with the southwest monsoon and is simulated in accordance
within situ observations. Upwelling appears to be strongest off Cochin and Quilon, and the upwelling of cold water is seen together with
a decrease in salinity in the model simulation. 相似文献
17.
The aim of this paper is to study the feasibility of deriving vertical wind profiles from current satellite observations.
With this aim, we carried out complex empirical orthogonal function (CEOF) analysis of a large number of radiosonde observations
of wind profiles over the Indian Ocean during the monsoon months. It has been found that the first two CEOFs explain 67% of
the total variance in wind fields. While the first principal component is well correlated with the winds at 850 mb (r = 0:80), the second one is highly correlated with winds at 200 mb (r = 0:89). This analysis formed the basis of a retrieval
algorithm which ensures the retrieval of vertical profiles of winds using satellite tracked cloud motion vector winds. Under
the assumption that accurate measurements of wind are available at the above mentioned levels, the r.m.s. error of retrieval
of each component of wind is estimated to range between 2 ms-1 and 6 ms-1 at different levels, which is much less than the natural variance of winds at these levels. For a better visualization of
retrieval, we have provided retrieved and true wind profiles side by side for four typical synoptic conditions during the
monsoon season. 相似文献
18.
NAVEEN R SHAHI NEERAJ AGARWAL ALOKE K MATHUR ABHIJIT SARKAR 《Journal of Earth System Science》2011,120(3):337-345
An atmospheric correction method has been applied on sea surface temperature (SST) retrieval algorithm using Very High Resolution
Radiometer (VHRR) single window channel radiance data onboard Kalpana satellite (K-SAT). The technique makes use of concurrent
water vapour fields available from Microwave Imager onboard Tropical Rainfall Measuring Mission (TRMM/TMI) satellite. Total
water vapour content and satellite zenith angle dependent SST retrieval algorithm has been developed using Radiative Transfer
Model [MODTRAN ver3.0] simulations for Kalpana 10.5–12.5 μm thermal window channel. Retrieval of Kalpana SST (K-SST) has been
carried out for every half-hourly acquisition of Kalpana data for the year 2008 to cover whole annual cycle of SST over Indian
Ocean (IO). Validation of the retrieved corrected SST has been carried out using near-simultaneous observations of ship and
buoys datasets covering Arabian Sea, Bay of Bengal and IO regions. A significant improvement in Root Mean Square Deviation
(RMSD) of K-SST with respect to buoy (1.50–1.02 K) and to ship datasets (1.41–1.19 K) is seen with the use of near real-time
water vapour fields of TMI. Furthermore, comparison of the retrieved SST has also been carried out using near simultaneous
observations of TRMM/TMI SST over IO regions. The analysis shows that K-SST has overall cold bias of 1.17 K and an RMSD of
1.09 K after bias correction. 相似文献
19.
Manoj K. Pandit Helga de Wall Narendra K. Chauhan 《Journal of Earth System Science》2008,117(3):201-209
A number of fine-grained sericite bearing pelitic, schistose lithologies occur along the Archean (Banded Gneiss Complex)-Proterozoic
(Aravalli Supergroup) contact (APC) in the Udaipur valley in NW Indian craton. These Al-rich lithologies (subsequently metamorphosed)
have been described as ‘paleosols’, developed over a 3.3 Ga old Archean gneissic basement and are overlain by Paleoproterozoic
Aravalli quartzite. The paleosol was developed between 2.5 and 2.1, coincident with the globally recognized Great Oxidation
Event (GOE). In previous studies these paleosol sections were interpreted to have developed under reducing environment, however,
the finding of a ‘ferricrete’ zone in the upper part of Tulsi Namla section (east of Udaipur) during the present study (in
addition to earlier reported lithologies) has led to an alternative suggestion of oxygen-rich conditions during paleosol development.
The Tulsi Namla paleosol section shows all the features characteristic of a complete paleosol section described from other
Archean cratons. The paleosol includes sericite schist with kyanite as the prevalent Al-silicate in the lower part of profile
while chloritoid and Fe-oxides typify the Fe-rich upper part. Alumina has remained immobile during the weathering process
while Fe and Mn show a decrease in the lower part of the section and an abrupt rise in the upper part, in the ferricrete zone.
The field and geochemical data indicate that the Tulsi Namla section is an in situ weathering profile and at least the upper part shows evidence of oxidizing conditions. 相似文献
20.
SMMR-derived sea ice concentrations for November 1978 – October 1984 in the Canada Basin are examined to determine temporal and spatial scales of variability in ice concentration and extent. Large regions of reduced-concentration ice are observed in late summer in four of the six years studied. Examination of the brightness temperature patterns and comparison of the SMMR-derived concentrations with visible-band imagery and drifting buoy temperatures support the interpretation of these features as true reductions in ice concentration. The observed areas of reduced concentration appears as a mixture of big floes andrazvodye, or open water areas of irregular shape and indefinite duration. Comparison with buoy-measured surface pressure and winds suggests that reduced ice concentrations are associated with regions of strong winds and divergence beneath low pressure systems. 相似文献