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1.
Utilizing data for the long period 1871–1990, variation in the relationships between Indian monsoon rainfall (IMR) and tendencies of the global factors. Southern Oscillation Index (SOI) and the sea surface temperature (SST) over eastern equatorial Pacific Ocean has been explored. The periods for which relationships exist have been identified. Tendencies from the season SON (Sept-Oct-Nov) to season DJF (Dec-Jan-Feb) and from DJF to MAM (Mar-Apr-May) before the Indian summer monsoon are indicated respectively by SOIT-2/SSTT-2 and SOIT-l/SSTT-1, current tendency from JJA (June-July-Aug) to SON, by SOIT0/SSTT0, tendencies from SON to DJF and DJF to MAM following monsoon, by SOIT1/SSTT1 and SOIT2/SSTT2 respectively. It is observed that while the relationships of IMR with SSTT-1, SSTT0 and SSTT2 exist almost throughout the whole period, that with SOIT-1 exists for 1942–1990, with SOIT0 for 1871–1921 and 1957–1990 and with SOIT2, for 1871–1921 only. The relationships that exist with SOIT-1, SOIT2, SSTT-1, SSTT2 and with SSTT0 (for period 1931–1990) are found to be very good and those that exist with SOIT0 for periods 1871–1921 and 1957–90 and for SSTT0 for the period 1871–1930 are good. It is thus seen that the relationships of SOIT-1, SOIT0 and SOIT2 with IMR do not correspond well with those of SSTT-1, SSTT0 and SSTT2 with IMR respectively, even though SOI and SST are closely related to each other for all the seasons. SOIT-1 and SSTT-1 can continue to be used as predictors for IMRDuring the whole period, IMR is found to play a passive, i.e. of being influenced or anticipated by SSTT-1 as well as an active role, i.e. of influencing or anticipating SSTT2. This implies a complex and perhaps non-linear interaction between IMR and SST tendency from DJF to MAM. Possibly, this is a part of the larger interaction between Asian monsoon rainfall and the tropical Pacific. A possible physical mechanism for the interaction is indicated.  相似文献   

2.
The impact of Southern Oscillation on thecyclogenesis over the Bay of Bengal duringthe summer monsoon has been investigated.The analysis of correlation coefficients(CCs) between the frequency of monsoondepressions and the Southern OscillationIndex (SOI) reveals that more depressionsform during July and August of El Niñoyears. Due to this, the seasonal frequencyof monsoon depressions remains little higherduring El Niño epochs even though thecorrelations for June and September are notsignificant. The CCs for July and August aresignificant at the 99% level.The El Niño-Southern Oscillation (ENSO)is known to affect Indian MonsoonRainfall (IMR) adversely. The enhancedcyclogenesis over the Bay of Bengal duringJuly and August is an impact of ENSO whichneeds to be examined closely. Increasedcyclogenesis over the Bay of Bengal may bereducing the deficiency in IMR duringEl Niño years by producing more rainfallover the eastern parts of India duringJuly and August. Thus there is a considerablespatial variation in the impact of ENSOon the monsoon rainfall over India and El Niñoneed not necessarily imply a monsoonfailure everywhere in India.The area of formation of monsoon depressionsshifts eastward during El Niño years.Warmer sea surface temperature (SST) anomaliesprevail over northwest and adjoiningwestcentral Bay of Bengal during premonsoon andmonsoon seasons of El Niño years.May minus March SOI can provide useful predictionsof monsoon depression frequencyduring July and August.  相似文献   

3.
Although previous literature have considered Southern Oscillation Index (SOI), Indian Dipole, and SST as the major teleconnection patterns to explain the variability of summer monsoon rainfall over India. South Asia low pressure and Indian Ocean high are the centers of action that dominates atmospheric circulations in Indian continent. This paper examines the possible impact of South Asian low pressure distribution on the variability of summer monsoon rainfall of India using centers of action approach. Our analysis demonstrates that the explanation of summer monsoon rainfall variability over Central India is improved significantly if the SOI is replaced by South Asian low heat. This contribution also explains the physical mechanisms to establish the relationships between the South Asian low heat and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR Reanalysis data.  相似文献   

4.
An analysis of the mean monthly data of 124 years reveals that the relationship between the Southern Oscillation Index in September and the winter monsoon rainfall (WMR) over Coastal Andhra Pradesh (CAP) is variable and non-stationary. In the recent four decades, however, SOI (Sept) is negatively and significantly correlated with CAP WMR. A similar analysis is performed using 50 years of mean monthly SSTs over Nino-3.4 region in August and September and CAP WMR to detect a possible relationship and there is a striking positive relation between them. In both of the above cases, the September signal is more significant in the recent four decades than for the other months and seasons for probable prediction of CAP WMR. Finally, to examine the influence of SO on the winter monsoon rainfall, a non-parametric test “Mann-Whitney Rank Statistics” test has been applied to the rainfall associated with extreme positive and negative SOI events  相似文献   

5.
Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali and Arabian coasts are associated with good monsoon rainfall over India. The strong monsoonal cooling in these regions can be attributed to strong low level winds and intense upwelling. The reappearance of 27°C isotherm off Somali coast in May/June coincides with the onset of southwest monsoon over India. Further, the influence of zonal anomaly of SST off Somalia Coast (SCZASST) and Central Indian Ocean Zonal Anomaly of SST (CIOZASST) with monsoon rainfall over India is brought out. The former is negatively related to the monsoon rainfall over western and central parts of India, whilst CIOZASST is positively related.  相似文献   

6.
Xu  Xiang-Zhou  Guo  Wen-Zhao  Liu  Ya-Kun  Ma  Jian-Zhong  Wang  Wen-Long  Zhang  Hong-Wu  Gao  Hang 《Natural Hazards》2017,85(3):1393-1416
China has a serious wildfire problem with a large number of fires in the south of the country especially during the winter (DJF) and spring (MAM) seasons. This study focused on identifying the causes of variability in inter-annual fire seasons. The relationship between fires and climatic parameters (precipitation, evapotranspiration and potential evapotranspiration) was evaluated on annual and seasonal (winter, spring) time scales. Certain other parameters (moisture balance, surface moisture balance, coefficient of variability of daily precipitation and ratio between evapotranspiration and potential evapotranspiration) were also calculated and related to fire variability for both time scales. Inter-annual time scale was found not to be strong enough to explain fire activity in the region; however, inter-seasonal fire variability showed significant correlation with potential evapotranspiration and with the ratio between evapotranspiration and potential evapotranspiration. The relationship and relative variability between evapotranspiration and the potential evapotranspiration were found to have important effect on inter-seasonal fire variability as compared to the other parameters studied, and link fire activity in the region to large-scale climatic systems.  相似文献   

7.
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   

8.
With an objective to understand the influence of surface marine meteorological parameters in relation to the extreme monsoon activity over the Indian sub-continent leading to flood/drought, a detailed analysis of the sea level pressure over the Southern Hemisphere and various surface meteorological parameters over the Indian seas is carried out. The present study using the long term data sets (Southern Hemispheric Sea Level Pressure Analysis; Comprehensive Ocean Atmospheric Data Set over the Indian Seas; Surface Station Climatology Data) clearly indicates that the sea surface temperature changes over the south eastern Pacific (El Ninõ/La Niña) have only a moderate impact (not exceeding 50% reliability) on the Indian summer monsoon activity. On the other hand, the sea level pressure anomaly (SOI) over Australia and the south Pacific has a reasonably high degree of significance (more than 70%) with the monsoon activity over India. However, these two parameters (SLP and SST) do not show any significant variability over the Indian seas in relation to the summer monsoon activity. Over the Indian seas, the parameters which are mainly associated with the convective activity such as cloud cover, relative humidity and the surface wind were found to have a strong association with the extreme monsoon activity (flood/drought) and thus the net oceanic heat loss over the Indian seas provides a strong positive feed-back for the monsoon activity over India.  相似文献   

9.
《Atmósfera》2014,27(3):287-303
Given the growing interest of the general public in accessing commercial weather forecasts through various media outlets and the available impetuses for promoting tourism in Saudi Arabia (SA), a first attempt is made to present a forecast skill comparison for surface temperature in four cities (Wejh, Yenbo, Jeddah, and Gizan) along the west coast of SA, for the 61-day transitional period (from January 16 to March 16) between the December-January-February (DJF) and the March-April-May (MAM) seasons. A simple skill score comparison method is used to assess the next-day city forecasts for surface temperature from six commercial weather forecast providers based on the operational numerical weather prediction (NWP) model outputs. All the NWP model forecast providers performed better than the respective daily climatology (Clm) for each station. Depending upon the station and the provider, the absolute average maximum daily surface temperature difference between the forecasts and the observations was less than 2 °C. Daily surface temperature forecasts from two versions of an atmospheric-ocean general circulation model are also compared to assess their performance for these coastal locations.  相似文献   

10.
In the paper, influence of extratropical circulation features on Indian Summer Monsoon Rainfall (ISMR) is examined. Energetics of extratropics, north of Indian subcontinent for deficient and non-deficient ISMR years, during two periods 1951–1978 and 1979–2005, are calculated and critically analyzed. It is observed that for the period 1951–1978, only two out of the 10 energetics parameters, viz., the zonal available potential energy (high) and conversion of zonal kinetic energy to eddy kinetic energy (low) differed significantly in JJA months of the deficient years from that of the non-deficient years. However, during the 1979–2005 period, as many as six out of the 10 energetics parameters, viz., eddy available potential energy, zonal available potential energy, eddy kinetic energy, generation of zonal available potential energy, conversion of zonal available potential energy to zonal kinetic energy and conversion of zonal kinetic energy to eddy kinetic energy differed significantly in JJA months of the deficient years from that of the non-deficient years. These results confirm growing influence of the transient stationary waves in deficient years after the climate shift year, 1979. Analysis of energetics parameters of the pre-monsoon season of the two periods also reveals similar results. This suggests that forcings apparently responsible for energetics in JJA months of the deficient years of the later period were present even before the advent of Indian summer monsoon season.  相似文献   

11.
There is a close relationship between interannual variability of the Indian summer monsoon rainfall and the El Niño/Southern Oscillation (ENSO) (drought conditions over India accompany warm ENSO events and vice versa). However, recent observations suggest a weakening of this ENSO-monsoon relationship that may be linked to global warming. We report here an analysis of the ENSO-monsoon relationship within the framework of a 1000-year control simulation of the MRI-coupled general circulation model (GCM), MRI-CGCM2.2. An overall correlation between the June-July-August (JJA) Nino3.4 sea surface temperature and the JJA Indian monsoon rainfall is –0.39, with reasonable circulation characteristics associated with the modeled ENSO. The simulated ENSO-monsoon relationship reveals long-term variations, from –0.71 to +0.07, in moving 31-year windows. This modulation in the ENSO-monsoon relationship is associated with decadal variability of the climate system.  相似文献   

12.
INTERACTION BETWEEN THE ENSO AND ASIAN MONSOON RECORDED IN DASUOPU ICE CORE FROM HIMALAYAS  相似文献   

13.
近百年全球温度变化中的ENSO分量   总被引：7，自引：0，他引：7  
首先利用Nin~o C区海温、Nin~o 3区海温及两个不同的SOI序列,建立了1867年春到1998年春期间的ENSO指数序列。近百年来ENSO对热带、热带外地区年际尺度的温度变化有显著影响,热带地区温度变化滞后ENSO约1个季,热带外地区滞后约2～3个季。ENSO能解释同期全球年平均温度方差的14%～16%左右;如果考虑ENSO对温度影响的滞后特征,则能解释的部分提高到20.6%。ENSO对温度的影响主要是在年际时间尺度上,对近百年来全球温度变化的长期趋势和年代际变率贡献不大。  相似文献   

14.
Indian summer monsoon is a global scale phenomenon controlled by different land, ocean, and atmospheric parameters. Sea surface temperature (SST) and snow are two of the major parameters, which may alter the spatial and temporal patterns of circulation and rainfall during Indian summer monsoon. In the current paper, we study the monsoon variability using long integrations (20 years) of the Indian Institute of Technology Delhi (IITD) Spectral model at T80L18 resolution with observed and climatological SST and snow. Study shows response of IITD GCM in simulating the Indian summer monsoon rainfall and circulation relative to the snow and SST as boundary conditions. The model’s response to SST and snow is examined by conducting four types of experiments by varying observed and climatological values of snow and SST. This paper discusses the seasonal total rainfall for country as a whole and 850 and 200 hPa wind for the period of 20 years starting from 1985 to 2004. The model has been integrated in the ensemble mode with five different initial conditions from the last week of April and first week of May. The model is able to capture the climatological patterns of seasonal total rainfall and averaged wind at lower and upper levels. Observed snow in the presence of climatological SST as a boundary condition shows much impact on rainfall and circulation than observed SST in the presence of climatological snow. Model performance is good in simulating the normal and excess monsoon conditions; it shows poor skill in capturing deficit monsoon years.  相似文献   

15.
Indian Monsoon Variability in a Global Warming Scenario   总被引：4，自引：0，他引：4  
The Intergovernmental Panel on Climate Change (IPCC) constituted by the World Meteorological Organisation provides expert guidance regarding scientific and technical aspects of the climate problem. Since 1990 IPCC has, at five-yearlyintervals, assessedand reported on the current state of knowledge and understanding of the climate issue. These reports have projected the behaviour of the Asian monsoon in the warming world. While the IPCC Second Assessment Report (IPCC, 1996) on climate model projections of Asian/Indian monsoon stated ``Most climate models produce more rainfall over South Asia in a warmer climate with increasing CO2', the recent IPCC (2001) Third Assessment Report states ``It is likely that the warming associated with increasing greenhouse gas concentrations will cause an increase in Asian summer monsoon variability and changes in monsoon strength.'Climate model projections(IPCC, 2001) also suggest more El Niño – like events in the tropical Pacific, increase in surface temperatures and decrease in the northern hemisphere snow cover. The Indian Monsoon is an important component of the Asian monsoon and its links with the El Niño Southern Oscillation (ENSO) phenomenon, northern hemisphere surface temperature and Eurasian snow are well documented.In the light of the IPCC globalwarming projections on the Asian monsoon, the interannual and decadal variability in summer monsoon rainfall over India and its teleconnections have been examined by using observed data for the 131-year (1871–2001) period. While the interannual variations showyear-to-year random fluctuations, thedecadal variations reveal distinct alternate epochs of above and below normal rainfall. The epochs tend to last for about three decades. There is no clear evidence to suggest that the strength and variability of the Indian Monsoon Rainfall (IMR) nor the epochal changes are affected by the global warming. Though the 1990s have been the warmest decade of the millennium(IPCC, 2001), the IMR variability has decreased drastically.Connections between the ENSO phenomenon, Northern Hemisphere surface temperature and the Eurasian snow with IMR reveal that the correlations are not only weak but have changed signs in the early 1990s suggesting that the IMR has delinked not only with the Pacific but with the Northern Hemisphere/Eurasian continent also. The fact that temperature/snow relationships with IMR are weak further suggests that global warming need not be a cause for the recent ENSO-Monsoon weakening.Observed snow depth over theEurasian continent has been increasing, which could be a result of enhanced precipitation due to the global warming.  相似文献   

16.
In this paper an attempt has been made to search a new parameter for the prediction of the Indian summer monsoon rainfall. For this purpose the relationship of the global surface-air temperature of four standard seasons viz., Winter (December-January-February), Spring (March-April-May), Summer (June-July-August), Autumn (September-October-November) with the Indian summer monsoon rainfall has been carried out. The same analysis is also carried out with surface-air temperature anomalies within the tropical belt (30°S to 30°N) and Indian summer monsoon rainfall. For the present study data for 30 years period from 1958 to 1988 have been used. The analysis reveals that there is a strong inverse relationship between the monsoon activity and the tropical belt temperature.  相似文献   

17.
Fluxes of momentum, latent heat and sensible heat at fixed stations in the east-central Arabian sea during MONEX were studied. Observations at the same locations at different periods as well as simultaneous observation at different locations were compared. During the advance of monsoon, momentum flux showed remarkable increase. Latent heat loss from sea also increased while sensible heat flux, in general, changed direction to become a gain by the sea. SST decreased by about 1.5°C and air temperature decreased by about 1°C during the advance phase. A north-south difference in SST in the study region seemed to be favourable for the genesis of onset vortex of monsoon. The possible differential effect of this storm at two different locations, depending upon the SST before the storm, is also discussed.  相似文献   

18.
The second campaign of the Arabian Sea Monsoon Experiment (ARMEX-II) was conducted in two phases viz., March–April and May–June 2003. In the present work, the buoy and ocean research vessel data collected during the second phase of ARMEX-II have been analysed to bring out the characteristic features of monsoon onset. The results have shown that the thermodynamical features such as build up of lower tropospheric instability and increased height of zero degree isotherm occurred about a week before the monsoon onset over Kerala and adjoining southeast Arabian Sea. There was a sharp fall in the temperature difference between 850 and 500 hPa, and the height of zero degree isotherm about 2–3 days before the monsoon onset. The flux of sensible heat was positive (sea to air) over south Arabian Sea during the onset phase. Over the Bay of Bengal higher negative (air to sea) values of sensible flux prevailed before the monsoon onset which became less negative with the advance of monsoon over that region. The pre-onset period was characterized by large sea surface temperature (SST) gradient over the Arabian Sea with rapid decrease towards north of the warm pool region. The buoy observations have shown that SST remained close to 30.5°C in the warm pool region during the pre-onset period in 2003 but only 2–3 degrees away (north of this region) SSTs were as low as 28.5–29°C. An interesting aspect of sea level pressure (SLP) variability over the Indian seas during the onset phase of summer monsoon 2003 was undoubtedly, the highest SLP in the warm pool region inspite of very high SSTs.  相似文献   

19.
It has been shown that large-scale weather patterns in both the tropical South Pacific (El Niño-Southern Oscillation, or ENSO, events) and the North Pacific (Pacific-North American, or PNA, patterns) have strong teleconnection effects on the air, ice, and ocean environments of the Bering Sea. This signal apparently comes via the atmosphere and not the ocean. The connection between variability of the Bering Sea and the ENSO and PNA appears to be the winter position of the Aleutian Low. Interannual variability in air temperatures, ice cover, and surface winds in the Bering Sea generally are in phase with each other, whereas sea-surface temperatures (SST) tend to lag these variables by 1–3 months. These Bering Sea time-series are significantly correlated with the Southern Oscillation Index (SOI) time-series (an indicator of ENSO events) when the Bering sea data are lagged behind the SOI for up to 18 months. The correlations suggest that warming in the Bering Sea follows negative anomalies in the SOI (i.e., El Niño events). Cooling in the Bering Sea tends to follow positive anomalies (i.e., precursors of El Niños) in the SOI. Maximal correlations for the PNA also lag the SOI by a mouth or two.Analyses of variance indicate that the SOI can explain 30–40% of the variability in the Bering Sea. Stepwise multiple regressions can explain up to 54% of the variation in air temperatures, up to 39% of the variation in sea ice cover, and up to 46% of the variation in SST in the Bering Sea. PNA and SOI were significant variables only in the equation for air temperatures, indicating a close relationship between them and the atmosphere in the Bering Sea and suggesting that energy is transmitted to the water and ice via the atmosphere. The three variables airtemps, ice, and SST were significant each time they were used as independent variables, indicating a rapid and strong feedback relationship among them.Three ENSO events have occurred since the mid-1970s, but none have been typical. There have been either two positive SOI anomalies preceding an El Niño or there have been none preceding an El Niño. When there has been a positive anomaly, ice cover has been above normal, but neither a positive anomaly nor above-normal ice has occurred in the past two ENSO events. An ice retreat has occurred any time there has been an ENSO event, except in the case of the great El Niño of 1982–1983; the anomalous position of the Aleutian Low at that time explains the lack of response of the ice. Finally, one ice retreat occurred that was unrelated to an ENSO event, but was related to a PNA event.  相似文献   

20.
In Japan the seasons are characterized by the progress of monsoons in summer and winter. Since ancient times Japanese life has closely been connected with the changes of the seasons, in other words, with the development of monsoons, especially with the winter monsoon, because it is more predominant and consistent than summer's, besides the difference of atmospheric stability brought by them. The relationship between Japanese life and monsoons has been remarkably variable all the more because the landforms of Japan are quite complicated. In the present paper some examples are introduced to make the relationship between them and, moreover, their changes in recent years clear, for instance, the distribution of windbreaks, the life in snowy regions and some traditional local industries, etc. On the whole the relationship mentioned above has been changing qualitatively or gradually been becoming more indistinct as urbanization or industrialization progresses. Despite these tendencies, however, Japanese life is still based on the progress of monsoons, as some examples, for instance climatic reliabilities caused by developments of monsoon, indicate clearly.  相似文献   

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