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1.
D. R. Pattanaik 《Natural Hazards》2007,40(3):635-646
Between 1941 and 2002 there has been a decreasing trend in the frequency of monsoon disturbances (MDs) during the summer monsoon
season (June–September). This downwards trend is significant at the 99.9% level for the main monsoon phase (July–August) and
the withdrawal phase (September); however, it is not significant during the onset phase (June). The variability in rainfall
over the homogeneous regions of India on the sub-seasonal scale also shows a significant decreasing trend with respect to
the amount of rainfall over Northwest India (NWI) and Central India (CEI) during all three phases of the monsoon. Meteorological
observations reveal that there has been an eastward shift of the rainfall belt with time over the Indian region on the seasonal
scale and that this shift is more prominent during the withdrawal phase. This decreasing trend in MDs together with its restricted
westerly movement seem to be directly related to the decreasing trend in rainfall over CEI during both the main monsoon and
withdrawal phases and over NWI during the withdrawal phase. The low-level circulation anomalies observed during two periods
(period-I: 1951–1976; period-ii: 1977–2002) are in accordance with the changes in rainfall distribution, with comparatively
more (less) rainfall falling over NWI, CEI and Southern Peninsular India (SPI) during period-I (period-ii), and are accompanied
by a stronger (weaker) monsoon circulation embedded with an anomalous cyclonic (anti-cyclonic) circulation over CEI during
the main monsoon and withdrawal phases. During the onset phase, completely opposite circulation anomalies are observed during
both periods, and these are associated with more (less) rainfall over NWI, CEI and SPI during period-ii (period-I). 相似文献
2.
Meteorological fields variability over the Indian seas in pre and summer monsoon months during extreme monsoon seasons 总被引:1,自引:0,他引:1
U. C. Mohanty R. Bhatla P. V. S. Raju O. P. Madan A. Sarkar 《Journal of Earth System Science》2002,111(3):365-378
In this study, the possible linkage between summer monsoon rainfall over India and surface meteorological fields (basic fields
and heat budget components) over monsoon region (30‡E-120‡E, 30‡S30‡N) during the pre-monsoon month of May and summer monsoon
season (June to September) are examined. For this purpose, monthly surface meteorological fields anomaly are analyzed for
42 years (1958-1999) using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for
Atmospheric Research). The statistical significance of the anomaly (difference) between the surplus and deficient monsoon
years in the surface meteorological fields are also examined by Student’s t-test at 95% confidence level.
Significant negative anomalies of mean sea level pressure are observed over India, Arabian Sea and Arabian Peninsular in the
pre-monsoon month of May and monsoon season. Significant positive anomalies in the zonal and meridional wind (at 2 m) in the
month of May are observed in the west Arabian Sea off Somali coast and for monsoon season it is in the central Arabian Sea
that extends up to Somalia. Significant positive anomalies of the surface temperature and air temperature (at 2 m) in the
month of May are observed over north India and adjoining Pakistan and Afghanistan region. During monsoon season this region
is replaced by significant negative anomalies. In the month of May, significant positive anomalies of cloud amount are observed
over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows
positive anomalies over NW India and north Arabian Sea.
There is overall reduction in the incoming shortwave radiation flux during surplus monsoon years. A higher magnitude of latent
heat flux is also found in surplus monsoon years for the month of May as well as the monsoon season. The significant positive
anomaly of latent heat flux in May, observed over southwest Arabian Sea, may be considered as an advance indicator of the
possible behavior of the subsequent monsoon season. The distribution of net heat flux is predominantly negative over eastern
Arabian Sea, Bay of Bengal and Indian Ocean. Anomaly between the two extreme monsoon years in post 1980 (i.e., 1988 and 1987)
shows that shortwave flux, latent heat flux and net heat flux indicate reversal in sign, particularly in south Indian Ocean.
Variations of the heat budget components over four smaller sectors of Indian seas, namely Arabian Sea, Bay of Bengal and west
Indian Ocean and east Indian Ocean show that a small sector of Arabian Sea is most dominant during May and other sectors showing
reversal in sign of latent heat flux during monsoon season. 相似文献
3.
Nityanand Singh 《Journal of Earth System Science》1995,104(1):1-36
Large-scale interannual variability of the northern summer southwest monsoon over India is studied by examining its variation
in the dry area during the period 1871–1984. On the mean summer monsoon rainfall (June to September total) chart the 800 mm
isohyet divides the country into two nearly equal halves, named as dry area (monsoon rainfall less than 800 mm) and wet area
(monsoon rainfall greater than 800 mm). The dry area/wet area shows large variations from one year to another, and is considered
as an index for assessing the large-scale performance of the Indian summer monsoon. Statistical and fluctuation characteristics
of the summer monsoon dry area (SMDA) are reported.
To identify possible causes of variation in the Indian summer monsoon, the correlation between the summer monsoon dry area
and eleven regional/global circulation parameters is examined. The northern hemisphere surface air temperature, zonal/hemispheric/global
surface air and upper air temperatures, Southern Oscillation, Quasi-biennial oscillation of the equatorial lower stratosphere,
April 500-mb ridge along 75°E over India, the Indian surface air temperature and the Bombay sea level pressure showed significant
correlation.
A new predictor parameter that is preceding year mean monsoon rainfall of a few selected stations over India has been suggested
in the present study. The stations have been selected by applying the objective technique ‘selecting a subset of few gauges
whose mean monsoon rainfall of the preceding year has shown the highest correlation coefficient (CC) with the SMDA’. Bankura
(Gangetic West Bengal), Cuddalore (Tamil Nadu) and Anupgarh (West Rajasthan) entered the selection showing a CC of 0.724.
Using a dependent sample of 1951–1980 a predictive model (multiple CC = 0.745) has also been developed for the SMDA with preceding
year mean monsoon rainfall of the three selected stations and the sea level pressure tendency at Darwin from Jan–Feb to Mar–May
as independent parameters. 相似文献
4.
Analysis of fifty four (1951–2004) years of daily energetics of zonal waves derived from NCEP/NCAR wind (u and υ) data and daily rainfall received over the Indian landmass (real time data) during southwest monsoon season (1 June–30 September)
indicate that energetics (momentum transport and kinetic energy) of lower tropospheric ultra-long waves (waves 1 and 2) of
low latitudes hold a key to intra-seasonal variability of monsoon rainfall over India.
Correlation coefficient between climatology of daily (122 days) energetics of ultra-long waves and climatology of daily rainfall
over Indian landmass is 0.9. The relation is not only significant but also has a predictive potential. The normalised plot
of both the series clearly indicates that the response period of rainfall to the energetics is of 5–10 days during the onset
phase and 4–7 days during the withdrawal phase of monsoon over India. During the established phase of monsoon, both the series
move hand-in-hand. Normalised plot of energetics of ultra-long waves and rainfall for individual year do not show marked deviation
with respect to climatology. These results are first of its kind and are useful for the short range forecast of rainfall over
India. 相似文献
5.
S. R. Kalsi 《Journal of Earth System Science》2000,109(2):211-220
BOBMEX-Pilot was organised from 23rd October–11th November, 1998 when the seasonal trough had already shifted to south Bay
of Bengal. The activity during this period was marked by the development of a monsoon depression from 26th–29th October that
weakened over the sea; onset of northeast monsoon along the east coast of India on 29th October; a low pressure area that
formed on 2nd November over southwest Bay off Sri Lanka — southTamilnadu coast; and another cyclonic circulation that formed
towards the end of the BOBMEX-Pilot period. This paper describes the development of these synoptic systems through synoptic
charts and satellite data. 相似文献
6.
Homogeneous Indian Monsoon rainfall: Variability and prediction 总被引:1,自引:0,他引:1
The Indian summer monsoon rainfall is known to have considerable spatial variability, which imposes some limitations on the
all-India mean widely used at present. To prepare a spatially coherent monsoon rainfall series for the largest possible area,
fourteen subdivisions covering the northwestern and central parts of India (about 55% of the total area of the country), having
similar rainfall characteristics and associations with regional/global circulation parameters are merged and their area-weighted
means computed, to form monthly and seasonal Homogeneous Indian Monsoon (HIM) rainfall series for the period 1871–1990. This
paper includes a listing of monthly and seasonal rainfall of HIM region. HIM rainfall series has been statistically analysed
to understand its characteristics, variability and teleconnections for long-range prediction.
HIM rainfall series isfound to be homogeneous, Gaussian distributed and free from persistence. The mean (R) rainfall is 757
mm (87% of annual) and standard deviation (S) 119 mm, with a Coefficient of Variation (CV) of 16%. There were 21 dry (K, -<R S) and 19 wet (R
i R + S) years during 1871–1990. There were clusters of frequent negative departures during 1899–1920 and 1965–1987 and positive
departures during 1942–1961. The recent three decades show very high rainfall variability with 10 dry and 6 wet years. The
decadal averages were alternatively positive and negative for three consecutive decades, viz., 1871–1900 (positive); 1901–1930
(negative); 1931–1960 (positive) and 1961–1990 (negative) respectively. Significant QBO and autocorrelation at 14th lag have
been found in HIM rainfall series.
To delineate the changes in the climatic regime of the Indian summer monsoon, sliding correlation coefficients (CCs) between
HIM rainfall series and (i) Bombay msl pressure, (ii) Darwin msl pressure and (iii) Northern Hemisphere surface air temperature
over the period 1871–1990 have been examined. The 31-year sliding CCs showed the systematic turning points of positive and
negative CCs around the years, 1900 and 1940. In the light of other corroborative evidences, these turning points seem to
delineate ‘meridional’ monsoon regime during 1871–1900 and 1940–1990 and ‘zonal’ monsoon regime during 1901–1940. The monsoon
signal is particularly dominant in many regional and global circulation parameters, during 1951–1990.
Using the teleconnections ofHIM series with 12 regional/global circulation parameters during the recent 36-year period 1951–86 regression models have been
developed for long-range prediction. In the regression equations 3 to 4 parameters were entered, explaining upto 80% of the
variance, depending upon the data period. The parameters that prominently enter the multiple regression equations are (i)
Bombay msl pressure, (ii) April 500 mb Ridge at 75°E, (iii) NH temperature, (iv) Nouvelle minus Agalega msl pressure and (v)
South American msl pressure. Eleven circulation parameters for the period 1951–80 were subjected to Principal Component Analysis
(PCA) and the PC’s were used in the regression model to estimate HIM rainfall. The multiple regression with three PCs explain
72% of variance in HIM rainfall. 相似文献
7.
Anomalous behaviour of the Indian summer monsoon 2009 总被引:1,自引:0,他引:1
The Indian subcontinent witnessed a severe monsoon drought in the year 2009. India as a whole received 77% of its long period
average during summer monsoon season (1 June to 30 September) of 2009, which is the third highest deficient all India monsoon
season rainfall year during the period 1901–2009. Therefore, an attempt is made in this paper to study the characteristic
features of summer monsoon rainfall of 2009 over the country and to investigate some of the possible causes behind the anomalous
behaviour of the monsoon. 相似文献
8.
Surya K. Dutta Someshwar Das S. C. Kar U. C. Mohanty P. C. Joshi 《Journal of Earth System Science》2009,118(5):413-440
The change in the type of vegetation fraction can induce major changes in the local effects such as local evaporation, surface
radiation, etc., that in turn induces changes in the model simulated outputs. The present study deals with the effects of
vegetation in climate modeling over the Indian region using the MM5 mesoscale model. The main objective of the present study
is to investigate the impact of vegetation dataset derived from SPOT satellite by ISRO (Indian Space Research Organization)
versus that of USGS (United States Geological Survey) vegetation dataset on the simulation of the Indian summer monsoon. The present
study has been conducted for five monsoon seasons (1998–2002), giving emphasis over the two contrasting southwest monsoon
seasons of 1998 (normal) and 2002 (deficient).
The study reveals mixed results on the impact of vegetation datasets generated by ISRO and USGS on the simulations of the
monsoon. Results indicate that the ISRO data has a positive impact on the simulations of the monsoon over northeastern India
and along the western coast. The MM5-USGS has greater tendency of overestimation of rainfall. It has higher standard deviation
indicating that it induces a dispersive effect on the rainfall simulation. Among the five years of study, it is seen that
the RMSE of July and JJAS (June–July–August–September) for All India Rainfall is mostly lower for MM5-ISRO. Also, the bias
of July and JJAS rainfall is mostly closer to unity for MM5-ISRO. The wind fields at 850 hPa and 200 hPa are also better simulated
by MM5 using ISRO vegetation. The synoptic features like Somali jet and Tibetan anticyclone are simulated closer to the verification
analysis by ISRO vegetation. The 2 m air temperature is also better simulated by ISRO vegetation over the northeastern India,
showing greater spatial variability over the region. However, the JJAS total rainfall over north India and Deccan coast is
better simulated using the USGS vegetation. Sensible heat flux over north-west India is also better simulated by MM5-USGS. 相似文献
9.
The characteristic features of the marine boundary layer (MBL) over the Bay of Bengal during the southwest monsoon and the
factors influencing it are investigated. The Bay of Bengal and Monsoon Experiment (BOBMEX) carried out during July–August
1999 is the first observational experiment under the Indian Climate Research Programme (ICRP). A very high-resolution data
in the vertical was obtained during this experiment, which was used to study the MBL characteristics off the east coast of
India in the north and south Bay of Bengal. Spells of active and suppressed convection over the Bay were observed, of which,
three representative convective episodes were considered for the study. For this purpose a one-dimensional multi-level PBL
model with a TKE-ε closure scheme was used. The soundings, viz., the vertical profiles of temperature, humidity, zonal and
meridional component of wind, obtained onboard ORV Sagar Kanya and from coastal stations along the east coast are used for
the study. The temporal evolution of turbulent kinetic energy, marine boundary layer height (MBLH), sensible and latent heat
fluxes and drag coefficient of momentum are simulated for different epochs of monsoon and monsoon depressions during BOBMEX-99.The
model also generates the vertical profiles of potential temperature, specific humidity, zonal and meridional wind. These simulated
values compared reasonably well with the observations available from BOBMEX. 相似文献
10.
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
11.
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
12.
The summer monsoon rainfall over Orissa, a state on the eastern coast of India, is more significantly related than Indian
summer monsoon rainfall (ISMR) to the cyclonic disturbances developing over the Bay of Bengal. Orissa experiences floods and
droughts very often due to variation in the characteristics of these disturbances. Hence, an attempt was made to find out
the inter-annual variability in the rainfall over Orissa and the frequencies of different categories of cyclonic disturbances
affecting Orissa during monsoon season (June–September). For this purpose, different statistical characteristics, such as
mean, coefficient of variation, trends and periodicities in the rainfall and the frequencies of different categories of cyclonic
disturbances affecting Orissa, were analysed from 100 years (1901–2000) of data. The basic objective of the study was to find
out the contribution of inter-annual variability in the frequency of cyclonic disturbances to the inter-annual variability
of monsoon rainfall over Orissa.
The relationship between summer monsoon rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa shows
temporal variation. The correlation between them has significantly decreased since the 1950s. The variation in their relationship
is mainly due to the variation in the frequency of cyclonic disturbances affecting Orissa. The variability of both rainfall
and total cyclonic disturbances has been above normal since the 1960s, leading to more floods and droughts over Orissa during
recent years. The inter-annual variability of seasonal rainfall over Orissa and the frequency of cyclonic disturbances affecting
Orissa during monsoon season show a quasi-biennial oscillation period of 2–2.8 years. There is least impact of El Nino southern
oscillation (ENSO) on inter-annual variability of both the seasonal rainfall over Orissa and the frequencies of monsoon depressions/total
cyclonic disturbances affecting Orissa. 相似文献
13.
The predictability of Indian summer monsoon rainfall from pre-season circulation indices is explored from observations during
1939–91. The predictand is the all-India average of June–September precipitation NIR, and the precursors examined are the
latitude position of the 500 mb ridge along 75°E in April (L), the pressure tendency April minus January at Darwin (DPT),
March-April-May temperature at six stations in west central India (T6), the sea surface temperature (SST) anomaly in the northeastern
Arabian Sea in May (ASM), SST anomaly in the Arabian Sea in January (ANJ), northern hemisphere temperature anomaly in January–February
(NHT), and Eurasian snow cover in January (SNOW). Monsoon rainfall tends to be enhanced with a more northerly ridge position,
small Darwin pressure tendency, warmer pre-season conditions, and reduced winter snow cover. However, relationships have varied
considerably over the past half-century, with the strongest associations during 1950–80, and a drastic weakening in the 1980s.
Four prediction models were constructed based on stepwise multiple regression, using as predictors combinations of L, DPT,
T6, ASM, and NHT, with 1939–68 as “dependent” dataset, or training period, and 1969–91 as “independent” dataset or verification
period. For the 1969–80 portion of the verification period calculated and observed NIR values agreed closely, with the models
explaining 74–79% of the variance. By contrast, after 1980 predictions deteriorated drastically, with the explained variance
for the 1969–89 time span dropping to 25–31%. The monsoon rainfall of 1990 and 1991 turned out to be again highly predictable
from models based on stepwise multiple regression and linear discriminant analysis and using as input L + DPT or L + DPT +
NHT, and with this encouragement an experimental real-time forecast was issued of the 1992 monsoon rainfall.
These results underline the need for investigations into decadal-scale changes in the general circulation setting and raise
concern for the continued success of seasonal forecasting. 相似文献
14.
A two-dimensional, nonlinear, vertically integrated model was used to simulate depth-mean wind-driven circulation in the upper
Ekman layers of the Bay of Bengal and Andaman Sea. The model resolution was one third of a degree in the latitude and longitude
directions. Monthly mean wind stress components used to drive the model were obtained from the climatic monthly mean wind
data compiled by Hastenrath and Lamb. A steady-state solution was obtained after numerical integration of the model for 15
days. The sensitivity of the model to two types of open boundary conditions, namely, a radiation type and clamped type, was
tested. A comparison of simulated results for January with available ship drift data showed that the application of the latter
along the open boundary could reproduce all the observed features near the boundary and the interior of the model domain.
The model was integrated for 365 days to study the circulation during the southwest and northeast monsoon seasons. The model
was successful in simulating the broad features of circulation including gyres and eddies observed during both the seasons,
the development of north equatorial current during the northeast monsoon period and eastward moving monsoon drift current
up to 90°E during the southwest monsoon season. During the latter season, two anticyclonic gyres were observed in the central
and the southern parts of the Bay. A cyclonic type of circulation was prevalent in the central and western parts of the Bay
of Bengal during the northeast monsoon months of November and December. The simulated western boundary current along the east
coast of India, flows northward and southward during the southwest and northeast monsoon seasons respectively. It is presumed
that this western boundary current, simulated during both the seasons, is locally wind-driven. 相似文献
15.
Re-analysis, using surface, upper-air, and satellite observations specially collected during the Arabian Sea Monsoon Experiment-I
(ARMEX-I), has been performed with a global data assimilation system at T-80/L18 resolution. Re-analysis was performed for
the entire ARMEX-I period (15th June–16th August 2002). In this paper we discuss the results based on re-analysis and subsequent
forecasts for two successive intensive observation periods associated with heavy rainfall along the west coast of India during
2–12 August, 2002. Results indicate that the re-analysed fields can bring out better synoptic features, for example troughs
along the west coast and mid tropospheric circulation over the Arabian Sea. Simulated rainfall distribution using re-analysis
as initial condition also matches observed rainfall better than data from the initial analysis. 相似文献
16.
District-wide drought climatology of the southwest monsoon season over India based on standardized precipitation index (SPI) 总被引:5,自引:1,他引:4
District-wide drought climatology over India for the southwest monsoon season (June–September) has been examined using two
simple drought indices; Percent of Normal Precipitation (PNP) and Standardized Precipitation Index (SPI). The season drought
indices were computed using long times series (1901–2003) of southwest monsoon season rainfall data of 458 districts over
the country. Identification of all India (nation-wide) drought incidences using both PNP and SPI yielded nearly similar results.
However, the district-wide climatology based on PNP was biased by the aridity of the region. Whereas district-wide drought
climatology based on SPI was not biased by aridity. This study shows that SPI is a better drought index than PNP for the district-wide
drought monitoring over the country. SPI is also suitable for examining break and active events in the southwest monsoon rainfall
over the country. The trend analysis of district-wide season (June–September) SPI series showed significant negative trends
over several districts from Chattisgarh, Bihar, Kerala, Jharkhand, Assam and Meghalaya, Uttaranchal, east Madhya Pradesh,
Vidarbha etc., Whereas significant positive trends in the SPI series were observed over several districts from west Uttar
Pradesh, west Madhya Pradesh, South & north Interior Karnataka, Konkan and Goa, Madhya Maharashtra, Tamil Nadu, East Uttar
Pradesh, Punjab, Gujarat etc. 相似文献
17.
Matthew Simpson Sethu Raman R. Suresh U. C. Mohanty 《Journal of Earth System Science》2008,117(6):897-909
Doppler radar derived wind speed and direction profiles showed a well developed sea breeze circulation over the Chennai, India
region on 28 June, 2003. Rainfall totals in excess of 100 mm resulted from convection along the sea breeze front. Inland propagation
of the sea breeze front was observed in radar reflectivity imagery. High-resolution MM5 simulations were used to investigate
the influence of Chennai urban land use on sea breeze initiated convection and precipitation. A comparison of observed and
simulated 10m wind speed and direction over Chennai showed that the model was able to simulate the timing and strength of
the sea breeze. Urban effects are shown to increase the near surface air temperature over Chennai by 3.0K during the early
morning hours. The larger surface temperature gradient along the coast due to urban effects increased onshore flow by 4.0m
s−1. Model sensitivity study revealed that precipitation totals were enhanced by 25mm over a large region 150 km west of Chennai
due to urban effects. Deficiency in model physics related to night-time forecasts are addressed. 相似文献
18.
On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall 总被引:3,自引:0,他引:3
The relative impacts of the ENSO and Indian Ocean dipole (IOD) events on Indian summer (June–September) monsoon rainfall at
sub-regional scales have been examined in this study. GISST datasets from 1958 to 1998, along with Willmott and Matsuura gridded
rainfall data, all India summer monsoon rainfall data, and homogeneous and sub-regional Indian rainfall datasets were used.
The spatial distribution of partial correlations between the IOD and summer rainfall over India indicates a significant impact
on rainfall along the monsoon trough regions, parts of the southwest coastal regions of India, and also over Pakistan, Afghanistan,
and Iran. ENSO events have a wider impact, although opposite in nature over the monsoon trough region to that of IOD events.
The ENSO (IOD) index is negatively (positively) correlated (significant at the 95% confidence level from a two-tailed Student
t-test) with summer monsoon rainfall over seven (four) of the eight homogeneous rainfall zones of India. During summer, ENSO
events also cause drought over northern Sri Lanka, whereas the IOD events cause surplus rainfall in its south. On monthly
scales, the ENSO and IOD events have significant impacts on many parts of India. In general, the magnitude of ENSO-related
correlations is greater than those related to the IOD. The monthly-stratified IOD variability during each of the months from
July to September has a significant impact on Indian summer monsoon rainfall variability over different parts of India, confirming
that strong IOD events indeed affect the Indian summer monsoon.
相似文献
Karumuri AshokEmail: |
19.
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
20.
The annual salt budget of the Zuari is examined. The characteristics of the estuary differ markedly from the low run off season
during November–May to the heavy run off period of the southwest monsoon from June to October. During November–May the estuary
is vertically mixed and the two processes controlling the transport of salt are run off induced advective transport out of
the estuary, and tidally induced diffusive transport into the estuary. The magnitude of the latter is about 20% larger, leading
to a salinity rise in the estuary. The diffusion coefficient has been estimated to be 233 ± 101 m2/sec. With the onset of the southwest monsoon, the run off increases dramatically, and the estuary loses about 75% of its
salt during the first two months of the season. About 2/3 of this loss is recovered in the next two months when the run off
decreases. Because the estuary is partially stratified during June–October, gravitational circulation is expected to play
a role in addition to tidal diffusion and run off. The magnitude of its contribution has, however, not yet been determined. 相似文献