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1.
Some characteristics of very heavy rainfall over Orissa during summer monsoon season 总被引：1，自引：0，他引：1
Orissa is one of the most flood prone states of India. The floods in Orissa mostly occur during monsoon season due to very
heavy rainfall caused by synoptic scale monsoon disturbances. Hence a study is undertaken to find out the characteristic features
of very heavy rainfall (24 hours rainfall ≥125 mm) over Orissa during summer monsoon season (June–September) by analysing
20 years (1980–1999) daily rainfall data of different stations in Orissa. The principal objective of this study is to find
out the role of synoptic scale monsoon disturbances in spatial and temporal variability of very heavy rainfall over Orissa.
Most of the very heavy rainfall events occur in July and August. The region, extending from central part of coastal Orissa
in the southeast towards Sambalpur district in the northwest, experiences higher frequency and higher intensity of very heavy
rainfall with less interannual variability. It is due to the fact that most of the causative synoptic disturbances like low
pressure systems (LPS) develop over northwest (NW) Bay of Bengal with minimum interannual variation and the monsoon trough
extends in west-northwesterly direction from the centre of the system. The very heavy rainfall occurs more frequently with
less interannual variability on the western side of Eastern Ghat during all the months and the season except September. It
occurs more frequently with less interannual variability on the eastern side of Eastern Ghat during September. The NW Bay
followed by Gangetic West Bengal/Orissa is the most favourable region of LPS to cause very heavy rainfall over different parts
of Orissa except eastern side of Eastern Ghat. The NW Bay and west central (WC) Bay are equally favourable regions of LPS
to cause very heavy rainfall over eastern side of Eastern Ghat. The frequency of very heavy rainfall does not show any significant
trend in recent years over Orissa except some places in north-east Orissa which exhibit significant rising trend in all the
monsoon months and the season as a whole. 相似文献
2.
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
3.
Some statistical properties of the summer monsoon seasonal rainfall for India during the last 100 years (1881–1980) are presented.
The most recent decade of 1971–1980 shows the lowest value of standard-decadal average monsoon rainfall (86.40 cm) and is
also characterised by the second highest value of coefficient of variation in monsoon rainfall (12.4 %). The combined last
two standard-decadal period of 1961–1980 was the period of the largest coefficient of variation and the lowest average monsoon
rainfall for India.
The possible influence of global climatic variability on the performance of the monsoon is also examined. Analyses of correlation
coefficient show that a statistically significant positive relationship with a time-lag of about six months exists between
monsoon rainfall and northern hemispheric surface air temperature. A cooler northern hemisphere during January/February leads
to a poor monsoon.
All the major drought years during the last 3 decades had much cooler January/February periods over the northern hemisphere—1972
having the coldest January/February with a temperature departure of −0.94°C and the most disastrous monsoon failure. 相似文献
4.
5.
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
6.
Temporal distribution of southwest monsoon (June –September) rainfall is very useful for the country’s agriculture and food
grain production. It contributes more than 75% of India’s annual rainfall. In view of this, an attempt has been made here
to understand the performance of the monthly rainfall for June, July, August and September when the seasonal rainfall is reported
as excess, deficient or normal. To know the dependence of seasonal rainfall on monthly rainfall, the probabilities of occurrence
of excess, deficient and normal monsoon when June, July, August and also June + July and August + September rainfall is reported
to be excess or deficient, are worked out using the long homogenous series of 124 years (1871-–1994) data of monthly and seasonal
rainfall of 29 meteorological sub-divisions of the plain regions of India.
In excess monsoon years, the average percentage contribution of each monsoon month to the long term mean (1871–1994) seasonal
rainfall (June –September) is more than that of the normal while in the deficient years it is less than normal. This is noticed
in all 29 meteorological sub-divisions. From the probability analysis, it is seen that there is a rare possibility of occurrence
of seasonal rainfall to be excess/deficient when the monthly rainfall of any month is deficient/excess. 相似文献
7.
R. N. Iyengar 《Journal of Earth System Science》1991,100(2):105-126
The usefulness of principal component analysis for understanding the temporal variability of monsoon rainfall is studied.
Monthly rainfall data of Karnataka, spread on 50 stations for a period of 82 years have been analysed for interseasonal and
interannual variabilities. A subset of the above data comprising 10 stations from the coherent west zone of Karnataka has
also been investigated to bring out statistically significant interannual signals in the southwest monsoon rainfall. Conditional
probabilities are proposed for a few above normal/below normal transitions. A sample prediction exercise for June–July using
such a transition probability has been found to be successful. 相似文献
8.
NACHIKETA ACHARYA S C KAR MAKARAND A KULKARNI U C MOHANTY L N SAHOO 《Journal of Earth System Science》2011,120(5):795-805
The northeast (NE) monsoon season (October, November and December) is the major period of rainfall activity over south peninsular
India. This study is mainly focused on the prediction of northeast monsoon rainfall using lead-1 products (forecasts for the
season issued in beginning of September) of seven general circulation models (GCMs). An examination of the performances of
these GCMs during hindcast runs (1982–2008) indicates that these models are not able to simulate the observed interannual
variability of rainfall. Inaccurate response of the models to sea surface temperatures may be one of the probable reasons
for the poor performance of these models to predict seasonal mean rainfall anomalies over the study domain. An attempt has
been made to improve the accuracy of predicted rainfall using three different multi-model ensemble (MME) schemes, viz., simple arithmetic mean of models (EM), principal component regression (PCR) and singular value decomposition based multiple
linear regressions (SVD). It is found out that among these three schemes, SVD based MME has more skill than other MME schemes
as well as member models. 相似文献
9.
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
10.
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
11.
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
12.
R K Giri Jagabandhu Panda Sudhansu S Rath Ravindra Kumar 《Journal of Earth System Science》2016,125(4):709-723
In order to issue an accurate warning for flood, a better or appropriate quantitative forecasting of precipitation is required. In view of this, the present study intends to validate the quantitative precipitation forecast (QPF) issued during southwest monsoon season for six river catchments (basin) under the flood meteorological office, Patna region. The forecast is analysed statistically by computing various skill scores of six different precipitation ranges during the years 2011–2014. The analysis of QPF validation indicates that the multi-model ensemble (MME) based forecasting is more reliable in the precipitation ranges of 1–10 and 11–25 mm. However, the reliability decreases for higher ranges of rainfall and also for the lowest range, i.e., below 1 mm. In order to testify synoptic analogue method based MME forecasting for QPF during an extreme weather event, a case study of tropical cyclone Phailin is performed. It is realized that in case of extreme events like cyclonic storms, the MME forecasting is qualitatively useful for issue of warning for the occurrence of floods, though it may not be reliable for the QPF. However, QPF may be improved using satellite and radar products. 相似文献
13.
The study assessed changes in the rainfall regime in Nigeria between 1961 and 2004 in terms of (a) absolute seasonality—the
length of dry and wet season; (b) relative seasonality—rainfall contrast during the year; (c) number of rainfall maxima and
minima; and (d) timing of rainfall maxima and minima. Trends in the mean monthly surface locations of the Inter-tropical Discontinuity
(ITD) were also examined as a prominent factor of the rainfall regime. Changes in the regime were examined over four time
slices: 1961–1971, 1972–1982, 1983–1993 and 1994–2004. The results show that, in the area of single rainfall maximum regime,
the length of the wet season has increased from 4 months (in 1961–1971) to 5 months (since 1972–1982). The rainfall relative
seasonality has consistently been ‘most rain in 3 months or less’. The rainfall maxima still indicate single rainfall maximum
but shift in the peak from August to July. Rainfall during the months of June to September appears to have witnessed declining
trends over the first three time slices. The last time slice however indicates trends towards a wetter condition. For the
area of double maxima rainfall regime, the length of the wet season has consistently been 8 months. The rainfall relative
seasonality has consistently been ‘rather seasonal with a short drier season’. The rainfall maxima and minima still indicate
double rainfall maxima with August as the month of the minimum but shift in the primary peak from July to September. The northward
latitudinal distance of the surface location of the ITD from the equator indicates significant upward trends during the months
of May to September only and for a period of 1983–2000. The trend results of the ITD appears to account for most of the observed
changes in the rainfall regime in Nigeria. 相似文献
14.
Sea-breeze-initiated rainfall over the east coast of India during the Indian southwest monsoon 总被引：1，自引：0，他引：1
Matthew Simpson Hari Warrior Sethu Raman P. A. Aswathanarayana U. C. Mohanty R. Suresh 《Natural Hazards》2007,42(2):401-413
Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest
monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August)
along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai.
Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season.
Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection
initiated by sea-breeze circulation. 相似文献
15.
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
16.
David Tai-Wai Hui Karen Kit-Ying Shum Ji Chen Shyh-Chin Chen Jack Ritchie John O. Roads 《Natural Hazards》2007,42(1):193-207
Seasonal climate forecasts are one of the most promising tools for providing early warnings for natural hazards such as floods
and droughts. Using two case studies, this paper documents the skill of a regional climate model in the seasonal forecasting
of below normal rainfall in southern China during the rainy seasons of July–August–September 2003 and April–May–June 2004.
The regional model is based on the Regional Spectral Model of the National Centers for Environmental Prediction of the United
States. It is the first time that the model has been applied to a region dominated by the East Asian Monsoon.
The article shows that the regional climate model, when being forced by reasonably good forecasts from a global model, can
generate useful seasonal rainfall forecasts for the region, where it is dominated by the East Asia monsoon. The spatial details
of the dry conditions obtained from the regional climate model forecast are also found to be comparable with the observed
distribution. 相似文献
17.
P Guhathakurta Preetha Menon P M Inkane Usha Krishnan S T Sable 《Journal of Earth System Science》2017,126(8):120
Meteorological drought during the southwest monsoon season and for the northeast monsoon season over five meteorological subdivisions of India for the period 1901–2015 has been examined using district and all India standardized precipitation index (SPI). Whenever all India southwest monsoon rainfall was less than ?10% or below normal, for those years all India SPI was found as ?1 or less. Composite analysis of SPI for the below normal years, viz., less than ?15% and ?20% of normal rainfall years indicate that during those years more than 30% of country’s area was under drought condition, whenever all India southwest monsoon rainfall was –15% or less than normal. Trend analysis of monthly SPI for the monsoon months identified the districts experiencing significant increase in drought occurrences. Significant positive correlation has been found with the meteorological drought over most of the districts of central, northern and peninsular India, while negative correlation was seen over the districts of eastern India with NINO 3.4 SST. For the first time, meteorological drought analysis over districts and its association with equatorial pacific SST and probability analysis has been done for the northeast monsoon over the affected regions of south peninsular India. Temporal correlation of all India southwest monsoon SPI and south peninsular India northeast monsoon SPI has been done with the global SST to identify the teleconnection of drought in India with global parameters. 相似文献
18.
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
19.
G. Nageswara Rao 《Journal of Earth System Science》1999,108(4):327-332
Rainfall variability over a river basin has greater impact on the water resource in that basin. With this in view, the variability
of the monsoon rainfall over the Godavari river basin has been studied on different time scales. As expected, the monsoon
rainfall in Godavari basin is more variable (17%) than the all-India monsoon rainfall (11%) during the period of study (1951–90).
Similarly, inter-annual variability of the monsoon rainfall on smaller time scales is found to be still higher and increases
while going on from seasonal to daily scales. An interesting observation is that the intra-seasonal variability of the monsoon
rainfall has a significant negative relationship (CC= −0.53) with the total seasonal rainfall in the basin. 相似文献
20.
Rainfall variability and indices of extreme rainfall-analysis and perception study for two stations over Central Himalaya,India 总被引：1，自引：1，他引：0
The analysis of rainfall pattern and indices of extreme rainfall events is performed for two meteorological stations located in the Central Himalayan Region which is highly vulnerable to rain-induced hazards. The records of these rain-induced disasters suggest that such events are generally observed in later part of monsoon season, when soil is saturated after monsoon rains. An attempt is made here to test trends of 19 different extreme rainfall indices that have been widely used in the literature, using daily rainfall data for two urban centres (Nainital and Almora) over the period 1992–2005. We have used statistical tools such as Sen’s method and Mann–Kendall test for detection of trend in annual rainfall, monsoon rainfall, number of rainy days and 1-day extreme rainfall. Principal component analysis gives the correlation between different extreme rainfall indices. Time series of principal components are representing the trends of extreme indices, their variation and interrelation between different indices. The perception study conducted in the same sites indicates that extreme rainfall events and change in rainfall amount and timing are well perceived by the local people. 相似文献