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1.
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
2.
This paper reports the radiative transfer simulations for the passive microwave radiometer onboard the proposed Indian climate
research satellite Megha-Tropiques due to be launched in 2011. These simulations have been performed by employing an in-house
polarized radiative transfer code for raining systems ranging from depression and tropical cyclones to the Indian monsoon.
For the sake of validation and completeness, simulations have also been done for the Tropical Rainfall Measuring Mission (TRMM)’s
Microwave Imager (TMI) of the highly successful TRMM mission of NASA and JAXA. The paper is essentially divided into two parts:
(a) Radiometer response with specific focus on high frequency channels in both the radiometers is discussed in detail with
a parametric study of the effect of four hydrometeors (cloud liquid water, cloud ice, precipitating water and precipitating
ice) on the brightness temperatures. The results are compared with TMI measurements wherever possible. (b) Development of
a neural network-based fast radiative transfer model is elucidated here. The goal is to speed up the computational time involved
in the simulation of brightness temperatures, necessitated by the need for quick and online retrieval strategies. The neural
network model uses hydrometeor profiles as inputs and simulates spectral microwave brightness temperature at multiple frequencies
as output. A huge database is generated by executing the in-house radiative transfer code for seven different cyclones occurred
in North Indian Ocean region during the period 2001–2006. A part of the dataset is used to train the network while the remainder
is used for testing purposes. For the purpose of testing, a typical scene from the southwest monsoon rain is also considered.
The results obtained are very encouraging and show that the neural network is able to mimic the underlying physics of the
radiative transfer simulations with a correlation coefficient of over 99%. 相似文献
3.
C Balaji M Deiveegan S P Venkateshan R M Gairola A Sarkar V K Agarwal 《Journal of Earth System Science》2010,119(1):97-115
This paper reports the results of a Bayesian-based algorithm for the retrieval of hydrometeors from microwave satellite radiances.
The retrieval technique proposed makes use of an indigenously developed polarized radiative transfer (RT) model that drives
a data driven optimization engine (Bayesian) to perform retrievals of rain and other hydrometeors in a multi-layer, plane
parallel raining atmosphere. For the sake of completeness and for the purposes of comparison, retrievals with Artificial Neural
Networks (ANN) have also been done. Retrievals have been done first with a simplified two-layer atmosphere, where assumed
values of hydrometeors are given to the forward model and these are taken as ‘measured radiances’. The efficacy of the two
retrieval strategies is then tested for this case in order to establish accuracy and speed. The highlight of the work is however,
the case study wherein a tropical storm in the Bay of Bengal is taken up, to critically examine the performance of the retrieval
algorithm for an extreme event wherein a 14-layer realistic, raining atmosphere has been considered and retrievals are done
against Tropical Rainfall Measuring Mission (TRMM) measured radiances. The key novelties of the work are:
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inclusion of polarization from both hydrometeors and oceans in the RT model, and 相似文献
4.
Auto-correlation analysis of ocean surface wind vectors 总被引:1,自引:0,他引:1
Abhijit Sarkar Sujit Basu A. K. Varma Jignesh Kshatriya 《Journal of Earth System Science》2002,111(3):297-303
The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different
measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measuredin situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month
of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall of the autocorrelation
in the first few hours with a decorrelation time scale of about 6 hours. For a meaningful comparison between satellite derived
products andin situ data, satellite data acquired at different time intervals should be used with appropriate ‘weights’, rather than treating
the data as concurrent in time. This paper presents a scheme for temporal weighting using the auto-correlation analysis. These
temporal ‘weights’ can potentially improve the root mean square (rms) deviation between satellite andin situ measurements. A case study using the TRMM Microwave Imager (TMI) and Indian Ocean buoy wind speed data resulted in an improvement
of about 10%. 相似文献
5.
Donglian Sun Menas Kafatos Guido Cervone Zafer Boybeyi Ruixin Yang 《Natural Hazards》2007,43(2):273-284
Sea surface temperature (SST) from the remotely sensed infrared measurements, like the GOES, AVHRR, and MODIS, etc., show
missing values of SST over the cloudy regions associated with hurricanes. While satellite microwave measurements, like the
Tropical Rainfall Measuring Mission (TRMM) microwave imager (TMI), can provide SST even under cloudy conditions. Both satellite
microwave measurements and buoy observations show SST increase in advance of significant hurricane intensification. Moreover,
hurricane intensification may also be related to the location of high SST. Our results indicate pre-existing high SST anomaly
(SSTA) located at the right side of the storm track for Hurricane Katrina. Numerical simulations also confirm the important
impacts of SSTA location on hurricane intensification. Similar situations are also found for Hurricanes Rita and Wilma. In
contrast, if there is no high SSTA at the right location, hurricane may not undergo further intensification. This may explain
why not all tropical cyclones associated with warm waters can attain peak intensity (categories 4 and 5) during their life
cycle, and partially explains why hurricanes do not reach the maximum potential intensity as calculated only according to
the magnitude of SST. 相似文献
6.
C. Balaji M. Deiveegan S. P. Venkateshan R. M. Gairola A. Sarkar V. K. Agarwal 《Journal of Earth System Science》2009,118(4):331-343
In the present study, forward radiative transfer simulations are carried out for the tropical cyclone Fanoos that hit the coast off south India in December 2005. The in-house radiative transfer package used for this study employs
the doubling and adding method to calculate radiances leaving the top of the one dimensional precipitating atmosphere. The
particle drop size distribution is assumed to follow a modified gamma distribution in respect of the cloud liquid water and
cloud ice water content. For precipitation, the Marshall-Palmer particle size distribution is used. All the hydrometeor particles
are assumed to be spherical and Lorentz Mie theory is used to evaluate the interaction parameters like absorption, scattering
coefficients and polarized scattering matrix. In order to validate the drop size distributions and interaction parameter calculations,
the simulated brightness temperatures are compared with the TMI measured brightness temperatures for all the channels. For
carrying out this exercise, vertical hydrometeors retrieved by TMI are used as input. The differences between simulated and
measured brightness temperatures are found to be within ±10%. The maximum difference in the brightness temperatures between
the present work and the Eddington model which the TRMM algorithm employs is about 4.5K. This may become significant when
retrieval of precipitation is attempted by combining the forward model with a suitable retrieval strategy, under tropical
conditions. 相似文献
7.
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
8.
Dhiraj Kumar Singh Hemendra Singh Gusain Varunendra Mishra Neena Gupta Rajiv Kumar Das 《Arabian Journal of Geosciences》2018,11(6):136
In this paper, an automated method for retrieval of snow surface temperature (SST) in Beas River Basin, India, using Landsat-8 thermal data is proposed. Digital number (DN) values of thermal data were converted into Top of Atmospheric (TOA) radiance. Surface radiance has been estimated from TOA radiance using a single channel method. The estimated surface radiance was then converted into SST. Cloud free Landsat-8 data for January and February 2017 has been used to estimate SST. Snow and Avalanche Study Establishment (SASE) has established a wireless sensor network (WSN) in an avalanche prone slope in Beas River Basin, India. Landsat-8 retrieved SST has been compared and validated with recorded SST at WSN stations. The retrieved SST using proposed algorithm was in good agreement with SST recorded on ground by sensor network. The mean absolute error (MAE) and root-mean-square error (RMSE) between estimated and recorded SST has been observed as ~?1.1 K and ~?1.5 K for 23 January 2017 and ~?0.7 and ~?1.6 K for 24 February 2017. Algorithm has shown a potential for automated mapping of snow and ice surface temperature using Landsat-8 data for snow cover and glaciers in Himalaya. 相似文献
9.
H S S Sinha S V Kasture V Satyan R M Pandya P A Solanki 《Journal of Earth System Science》1980,89(2):197-208
Using an airborne scanning IR-radiometer, measurements of sea surface temperature (SST) were made from nine different levels in the Sandheads region of the Bay of Bengal on 5 October 1978. To retrieve SST from the observed radiances a temperature correction scheme, which uses the radiosonde data in the vicinity of flight area, has been generated. Atmospheric effects which have been considered include absorption due to water vapour and carbon dioxide, and the re-emission from different atmospheric layers. The radiances observed at different altitudes when corrected by our scheme yield a fairly consistent value of SST. The special ship measurements of SST, at the same location, are found to have very good agreement with the SST retrieved from the observed radiances using our scheme. The temperature corrections turn out to be 0·3 and 3·3°C at 600 and 3000 meters respectively for the type of atmosphere which has been used in our study. 相似文献
10.
C. P. Simha G. Pavan Kumar P. Mahesh A. Navaneeth K. M. Rao B. K. Rastogi V. N. Sridhar A. K. Shukla 《Natural Hazards》2014,70(1):935-940
The present study purports the analysis of total electron content (TEC, which is one of the major ionosphere anomalies during the earthquake), sea surface temperature (SST) and outgoing long-wave radiation (OLR) during the earthquake event recorded on 10 March 2013 (M = 6.5). Global assimilative ionosphere modelled output TEC values have been used for this present study; the clear signature of TEC during the recorded earthquake has been noticed (i.e. increase in TEC 60–70 TECU during the event). The correlation between the magnitude and location of earthquake with TEC is around 0.9, and the least correlation between SST and OLR is due to concerned atmospheric effects; we tried to study the variations of SST and OLR prior during and after the event from Kalpana satellite image products archived by IMD. 相似文献
11.
Diurnal soil water dynamics in the shallow vadose zone (field site of China University of Geosciences,China) 总被引:3,自引:0,他引:3
Yijian Zeng Li Wan Zhongbo Su Hirotaka Saito Kangle Huang Xusheng Wang 《Environmental Geology》2009,58(1):11-23
Because of the relatively low soil moisture in arid or semi-arid regions, water vapour movement often predominates in the
vadose zone and affects the partitioning of energy among various land surface fluxes. In an outdoor sand bunker experiment,
the soil water content at 10 and 30 cm depth were measured at hourly intervals for 2.5 days during October 2004. It was found
that the soil moisture reached the daily maximum value (5.9–6.1% at 10 cm and 11.9–13.1% at 30 cm) and minimum value (4.4–4.5%
at 10 cm and 10.4–10.8% at 30 cm) at midday (0–1 p.m. for 10 cm and 2–3 p.m. for 30 cm) and before dawn (2–3 a.m. for 10 cm
and 4–5 a.m. for 30 cm), respectively. The modified HYDRUS-1D code, which refers to the coupled water, water vapour and heat
transport in soil, was used to simulate the moisture and water vapour flow in the soil. The numerical analyses provided insight
into the diurnal movement of liquid water and water vapour driven by the gradients of pressure heads and temperatures in the
subsurface zone. The simulated temperature and water content were in good agreement with the measured values. The spatial–temporal
distribution of liquid water flux, water vapour flux and soil temperature showed a detailed diurnal pattern of soil water
dynamics in relatively coarse sand.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
P Jindal P K Thapliyal M V Shukla A K Mishra D Mitra 《Journal of Earth System Science》2014,123(6):1265-1271
The present study examines the potential of infrared sounder observations from Indian geostationary satellite INSAT-3D for the estimation of total column integrated ozone over the tropical Indian region. A dataset with diverse profiles was used to create training and testing datasets using forward simulations from a radiative transfer model for infrared sounder channels. A study was carried out for the standard tropical atmospheric profile to examine the sensitivity of ozone band radiance corresponding to the atmospheric temperature, water vapour, and ozone mixing ratios at different atmospheric pressure levels. Further, statistical retrieval technique has been used for the total column ozone estimation using two different approaches: (i) ozone channel observation along with the a-priori estimate of temperature and water vapour profile and (ii) only sounder channels observations. The accuracy of the retrieval algorithms was examined for different errors in the atmospheric profiles for the method (i) and different sensor noise specification for the method (ii). This study has shown that accurate temperature information is very important for ozone estimation and lower instrument noise results in better ozone estimates. 相似文献
13.
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
14.
Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal 总被引:2,自引:0,他引:2
We use daily satellite estimates of sea surface temperature (SST) and rainfall during 1998–2005 to show that onset of convection
over the central Bay of Bengal (88–92°E, 14–18°N) during the core summer monsoon (mid-May to September) is linked to the meridional
gradient of SST in the bay. The SST gradient was computed between two boxes in the northern (88–92°E, 18–22°N) and southern
(82–88°E, 4–8°N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current. Convection
over central bay followed the SST difference between the northern and southern bay (ΔT) exceeding 0.75°C in 28 cases. There was no instance of ΔT exceeding this threshold without a burst in convection. There were, however, five instances of convection occurring without
this SST gradient. Long rainfall events (events lasting more than a week) were associated with an SST event (ΔT ≥ 0.75°C); rainfall events tended to be short when not associated with an SST event. The SST gradient was important for the
onset of convection, but not for its persistence: convection often persisted for several days even after the SST gradient
weakened. The lag between ΔT exceeding 0.75°C and the onset of convection was 0–18 days, but the lag histogram peaked at one week. In 75% of the 28 cases,
convection occurred within a week of ΔT exceeding the threshold of 0.75°C. The northern bay SST, T
N
, contributed more to ΔT, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding
threshold for T
N
was 29°C. We hypothesise that the excess heating (∼1°C above the threshold for deep convection) required in the northern
bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient. 相似文献
15.
The time evolution of atmospheric parameters on intraseasonal time scale in the eastern Arabian Sea (EAS) is studied during
the summer monsoon seasons of 1998–2003 using Tropical Rainfall Measuring Mission Microwave Imager (TMI) data. This is done
using the spectral and wavelet analysis. Analysis shows that over EAS, total precipitable water vapour (TWV) and sea surface
wind speed (SWS) have a periodicity of 8–15 days, 15–30 days and 30–60 days during the monsoon season. Significant power is
seen in the 8–15-day time scale in TWV during onset and retreat of the summer monsoon. Analysis indicates that the timings
of the intensification of 8–15, 15–30, and 30–60 days oscillations have a profound effect on the evolution of the daily rainfall
over west coast of India. The positive and negative phases of these oscillations are directly related to the active and dry
spells of rainfall along the west coast of India. The spectral analysis shows interannual variation of TWV and SWS. Heavy
rainfall events generally occur over the west coast of India when positive phases of both 30–60 days and 15–30 days modes
of TWV and SWS are simultaneously present. 相似文献
16.
In order to characterize the pressure-induced decomposition of ringwoodite (γ-Mg2SiO4), the topological analysis of the electron density ρ(r), based upon the theory of atoms in molecules (AIM) developed by Bader in the framework of the catastrophe theory, has been
performed. Calculations have been carried out by means of the ab initio CRYSTAL09 code at the HF/DFT level, using Hamiltonians
based on the Becke- LYP scheme containing hybrid Hartree–Fock/density functional exchange–correlation terms. The equation
of state at 0 K has been constructed for the three phases involved in the post-spinel phase transition (ringwoodite → Mg-perovskite + periclase)
occurring at the transition zone–lower mantel boundary. The topological results show that the decomposition of the ringwoodite
at high pressures is caused by a conflict catastrophe. Furthermore, topological evidences of the central role played by the
oxygen atoms to facilitate the pressure-induced ringwoodite decomposition and the subsequent phase transition have been noticed. 相似文献
17.
H. Z. Abidin R. J. Davies M. A. Kusuma H. Andreas T. Deguchi 《Environmental Geology》2009,57(4):833-844
Global positioning system (GPS) and satellite-based InSAR (Interferometric Synthetic Aperture Radar) measurements of the subsidence
and uplift of a populated area of Sidoarjo, East Java are due to the eruption of the Lusi mud volcano (2006–present). These
data are the first direct quantitative measurements of deformation due to the growth of a mud volcano edifice. The GPS data
were recorded over periods of a few hours to several months and show that between June 2006 and September 2007, the earth’s
surface has been subsiding at rates of 0.1–4 cm/day. Maximum rates of subsidence occurred in an area 300–400 m to the northwest
of the main mud volcano vent. Horizontal displacements were 0.03–0.9 cm/day and were also towards this area. In general uplifts
of up to 0.09 cm/day were recorded in areas outside of the edifice. Changes in elevation measured using satellite imagery
(InSAR technique) provide regional datasets of subsidence and uplift. They confirm that during the first year a roughly circular
area was undergoing sag-like subsidence centered to the northwest of the main vent and that uplift was occurring 3–4 months
after the initiation of the eruption due to the movement Watukosek fault system. Subsidence occurred due to the weight of
mud and man-made dams and the collapse of the overburden due to removal of mud from the subsurface. Assuming constant rates
of subsidence of 4 cm/day, then in the centre of the edifice there would be up to 44 m of subsidence in 3 years, and up to
16 m in 10 years. The mud volcano is now in a self-organizing state with new fluid conduits forming as a result of the collapse.
An erratum to this article can be found at 相似文献
18.
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
19.
Western disturbances seen with AMSU-B and infrared sensors 总被引:2,自引:0,他引:2
Western disturbances (WD) of winter and pre-monsoon seasons are the important sources of rainfall in the Indo-Gangetic plains.
WDs are troughs or circulations in the westerly winds modified by the Himalayas. Operationally, WDs are monitored using infrared
(IR) and water vapour (WV) images. Advanced Microwave Sounding Unit-B (AMSU-B), flying onboard the NOAA satellites, also allows
WDs to be monitored in five microwave frequencies. Two are in water vapour window (89, 150 GHz) and three are absorption channels
(centred at 183.31 GHz). Unlike the top of cloud view in IR or WV, AMSU-B radiances show the effect of moisture and hydrometeors
in different layers.
Two cases of WD (17 April 2001 and 18–19 February 2003) are discussed using the microwave data from AMSU-B and the IR and
WV data from Meteosat-5. The aim here is to demonstrate the skill of AMSU-B in delineating structure of WDs. In particular,
the cold intrusion and the moist conveyor belts are examined. It was found that the multi-channel view of the AMSU-B permits
a better understanding of the moist structures seen in the conveyor belts.
The à trous wavelet transform is used to clearly bring out mesoscale features in WDs. AMSU-B brings out intense convection as a large
depression of BTs (>50K) at 150/176 GHz, cirrus and moist bands at 180/182 GHz. Mesoscale convection lines within WDs that
last short time are shown here for the first time only in the AMSU-B images. Large-scale cirrus features are separated using
the à trous wavelet transform.
Lastly, it is shown that there is a good likeness in the rain contours in the 3-h rain 3B42 (computed from TRMM and other
data) to AMSU-B depressions in BT. Overall, AMSU-B shows better skill in delineating the structure of clouds and rain in WDs. 相似文献
20.
Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible
spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the
spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to
retrieve vertical profiles of ozone (O3) and nitrogen dioxide (NO2) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured
and recalculated slant column densities (SCDs) and they are found to be well matching. O3 and NO2 vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡
SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and
they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities
(TCDs) of O3 and NO2 along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003.
The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer
and minimum in the winter season. Increasing trend is found in column density of NO2 in stratospheric, tropospheric and surface layers, but no trend is observed in O3 columns for above layers during the period 2000–2003 相似文献
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