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1.
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
2.
In this study, we elucidate the temporal characteristics of the onset and withdrawal of the Indian southwest monsoon, making
use of the model integration and daily analyses of the National Centre for Medium Range Weather Forecasting, India. The onset
of the Indian southwest monsoon over the Bay of Bengal is discernable by a gradual increase in the adiabatic generation of
kinetic energy, while over the Arabian Sea it is first noticeable by a steep and abrupt increase of generation. The horizontal
transport of heat indicates a convergence regime over the Bay of Bengal prior to onset, while over the Arabian Sea a convergence
regime is indicated by a change from the divergence to the convergence regime. The withdrawal of the southwest monsoon is
characterized by the horizontal transport of heat and moisture that evince a transition from the convergence to divergence
regime; similarly, diabatic heating noticed during the active period changes to cooling. The withdrawal over the Arabian Sea
is characterized by the divergence regime of the horizontal transport of moisture. This change precedes even the circulation
changes over northwest India, which may be regarded as a precursor. The withdrawal is further supported by a monotonic decrease
in the net tropospheric moisture over the Arabian Sea, followed by a similar change at land locations. 相似文献
3.
In this article, the interannual variability of certain dynamic and thermodynamic characteristics of various sectors in the
Asian summer monsoon domain was examined during the onset phase over the south Indian peninsula (Kerala Coast). Daily average
(0000 and 1200 UTC) reanalysis data sets of the National Centre for Environmental Prediction/National Centre for Atmospheric
Research (NCEP/NCAR) for the period 1948–1999 were used. Based on 52 years onset date of the Indian summer monsoon, we categorized
the pre-onset, onset, and post-onset periods (each an average of 5 days) to investigate the interannual variability of significant
budget terms over the Arabian Sea, Bay of Bengal, and the Indian peninsula. A higher difference was noticed in low-level kinetic
energy (850 hPa) and the vertically integrated generation of kinetic energy over the Arabian Sea from the pre-onset, onset,
and post-onset periods. Also, significant changes were noticed in the net tropospheric moisture and diabatic heating over
the Arabian Sea and Indian peninsula from the pre-onset to the post-onset period. It appears that attaining the magnitude
of 40 m2 s−2 and then a sharp rise in kinetic energy at 850 hPa is an appropriate time to declare the onset of the summer monsoon over
India. In addition to a sufficient level of net tropospheric moisture (40 mm), a minimum strength of low-level flow is needed
to trigger convective activity over the Arabian Sea and the Bay of Bengal. An attempt was also made to develop a location-specific
prediction of onset dates of the summer monsoon over India based on energetics and basic meteorological parameters using multivariate
statistical techniques. The regression technique was developed with the data of May and June for 42 years (1948–1989) and
validated with 10 years NCEP reanalysis from 1990 to 1999. It was found that the predicted onset dates from the regression
model are fairly in agreement with the observed onset dates obtained from the Indian Meteorology Department. 相似文献
4.
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
5.
An analysis of the meteorological data collected by the research vessel ORV Sagarkanya for the mean latent and sensible heat
fluxes over the Arabian Sea has indicated appreciable changes between active and weak phases of the southwest monsoon of 1986.
We suggest that: (a) the presence of a core of low level winds associated with the Somali jet and its southward shift during
the season, along with (b) a ridge in surface pressure over the central Arabian Sea could be responsible for the deficit in
monsoon rainfall along the west coast of India in 1986. 相似文献
6.
Monthly mean anomaly fields of various parameters like sea surface temperature, air temperature, wind stress, effective radiation
at the surface, heat gain over the ocean and the total heat loss between a good and bad monsoon composite and the evaporation
rates over the Arabian Sea and southern hemisphere have been studied over the tropical Indian Ocean. The mean rates of evaporation
on a seasonal scale over the Arabian Sea during a good and bad monsoon composites were equal (about 2·48 × 1010 tons/day). The evaporation rates over the southern hemisphere were greater during all the months. The mean evaporation rates
over the southern hemisphere on a seasonal scale for the good and bad monsoon composites were 4·4 × 1010 and 4·6 × 1010 tons/day respectively. The maximum evaporation rates over the southern hemisphere were observed in August. The anomalies
of wind stress, effective radiation at the surface and the heat gain over the ocean also exhibit large variations in August,
as compared to other monsoon months. 相似文献
7.
The aim of this paper is to study the feasibility of deriving vertical wind profiles from current satellite observations.
With this aim, we carried out complex empirical orthogonal function (CEOF) analysis of a large number of radiosonde observations
of wind profiles over the Indian Ocean during the monsoon months. It has been found that the first two CEOFs explain 67% of
the total variance in wind fields. While the first principal component is well correlated with the winds at 850 mb (r = 0:80), the second one is highly correlated with winds at 200 mb (r = 0:89). This analysis formed the basis of a retrieval
algorithm which ensures the retrieval of vertical profiles of winds using satellite tracked cloud motion vector winds. Under
the assumption that accurate measurements of wind are available at the above mentioned levels, the r.m.s. error of retrieval
of each component of wind is estimated to range between 2 ms-1 and 6 ms-1 at different levels, which is much less than the natural variance of winds at these levels. For a better visualization of
retrieval, we have provided retrieved and true wind profiles side by side for four typical synoptic conditions during the
monsoon season. 相似文献
8.
Terrigenous plant wax inputs to the Arabian Sea: Implications for the reconstruction of winds associated with the Indian Monsoon 总被引:1,自引:0,他引:1
Kristina A. Dahl Delia W. Oppo Konrad A. Hughen Frank Sirocko 《Geochimica et cosmochimica acta》2005,69(10):2547-2558
We have determined the accumulation rates and carbon isotopic compositions (δ13C) of long-chain (C24-C32) terrigenous plant wax fatty acids in 19 surface sediment samples geographically distributed throughout the Arabian Sea in order to assess the relationship between plant wax inputs and the surrounding monsoon wind systems. Both the accumulation rate data and the δ13C data show that there are three primary eolian sources of plant waxes to the Arabian Sea: Africa, Asia, and the Arabian Peninsula. These sources correspond to the three major wind systems in this region: the summer (Southwest) monsoon, the winter (Northeast) monsoon, and the summer northwesterlies that blow over the Arabian Peninsula. In addition, plant waxes are fluvially supplied to the Gulf of Oman and the Eastern African margin by nearby rivers. Plant wax δ13C values reflect the vegetation types of the continental source regions. Greater than 75% of the waxes from Africa and Asia are derived from C4 plants. Waxes delivered by northwesterly winds reflect a greater influence (25-40%) of C3 vegetation, likely derived from the Mesopotamian region. These data agree well with previously published studies of eolian dust deposition, particularly of dolomite derived from the Arabian Peninsula and the Mesopotamian region, in surface sediments of the Arabian Sea. The west-to-east gradient of plant wax δ13C and dolomite accumulation rates are separately useful indicators of the relationship between the northwesterly winds and the winds of the Southwest monsoon. Combined, however, these two proxies could provide a powerful tool for the reconstruction of both southwest monsoon strength as well as Mesopotamian aridity. 相似文献
9.
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
10.
南亚季风降水的双极振荡* 总被引:1,自引:2,他引:1
文章利用气象资料揭示在印度半岛南部和北部,南亚季风降水变化在10年尺度以上呈翘翘板变化形式;利用更长的季风降水资料,即300年的喜马拉雅山达索普冰芯降水记录和印度半岛南部石笋降水记录,发现印度南部和喜马拉雅山季风降水呈双极振荡行为。自1700年以来,喜马拉雅山,即印度北部(或印度半岛南部)季风降水经历了1700~1764年期间的减小(或增加)趋势,1764~1876年期间的增大(或减小)趋势,1876~2000年期间的减小(或增加)趋势。同时,发现印度半岛南部的季风降水同北半球温度变化具有相同的变化特征,而喜马拉雅山季风降水同北半球温度变化具有相反的变化特征。南亚季风降水的这种南北翘翘板变化形式,与跨赤道气流有密切的联系。 相似文献
11.
A coupled physical-biological-chemical model has been developed at C-MMACS. for studying the time-variation of primary productivity
and air-sea carbon-dioxide exchange in the Indian Ocean. The physical model is based on the Modular Ocean Model, Version 2
(MOM2) and the biological model describes the nonlinear dynamics of a 7-component marine ecosystem. The chemical model includes
dynamical equation for the evolution of dissolved inorganic carbon and total alkalinity. The interaction between the biological
and chemical model is through the Redfield ratio. The partial pressure of carbon dioxide (pCO2) of the surface layer is obtained from the chemical equilibrium equations of Penget al 1987. Transfer coefficients for air-sea exchange of CO2 are computed dynamically based on the wind speeds. The coupled model reproduces the high productivity observed in the Arabian
Sea off the Somali and Omani coasts during the Southwest (SW) monsoon. The entire Arabian Sea is an outgassing region for
CO2 in spite of high productivity with transfer rates as high as 80 m-mol C/m2 /day during SW monsoon near the Somali Coast on account of strong winds. 相似文献
12.
M. R. Ramesh Kumar S. Sathyendranath N. K. Viswambharan L. V. Gangadhara Rao 《Journal of Earth System Science》1986,95(3):435-446
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
13.
The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the
Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric
Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between
30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the
spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances),
indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics
of the two modes and their interannual variability are studied in detail.
The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’)
or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of
Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation.
The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough).
The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The
vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with
the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with
fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20
day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere
in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl
anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs
in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay.
On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly
mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree
well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite
structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean
winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual
variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence
of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual
scales. 相似文献
14.
15.
Yuvaraja Arumugm Anil K Gupta Mruganka K Panigrahi 《Journal of Earth System Science》2014,123(7):1671-1680
Deep-sea benthic foraminifera are an important and widely used marine proxy to understand paleoceanographic and paleoclimatic changes on regional and global scales, owing to their sensitivity to oceanic and climatic turnovers. Some species of benthic foraminifera are sensitive to changes in water mass properties whereas others are sensitive to organic fluxes and deep-sea oxygenation. Benthic faunal diversity has been found closely linked to food web, bottom water oxygen levels, and substrate and water mass stability. The present study is aimed at analyzing species diversity trends in benthic foraminifera and their linkages with Indian monsoon variability during the Neogene. Species diversity of benthic foraminifera is examined in terms of number of species (S), information function (H), equitability (E) and Sanders’ rarefied values, which were combined with relative abundances of high and low productivity benthic foraminifera at Ocean Drilling Program Hole 730A, Oman margin, western Arabian Sea. The Oman margin offers the best opportunity to understand monsoon-driven changes in benthic diversity since summer monsoon winds have greater impact on the study area. The species diversity was higher during the early Miocene Climatic Optimum (~17.2–16.4 Ma) followed by a decrease during 16.4–13 Ma coinciding with a major increase in Antarctic ice volume and increased formation of Antarctic Bottom Water. All the diversity parameters show an increase during 13–11.6 Ma, a gradual decrease during 11.6–9 Ma and then an increase with a maximum at 7 Ma. Thereafter the values show little change until 1.2 Ma when all the parameters abruptly decrease. The benthic foraminiferal populations and diversity at Hole 730A were mainly driven by the Indian monsoon, and polar waters might have played a minor or no role since early Neogene period as the Arabian Sea is an enclosed basin. 相似文献
16.
A brief summary of Dr. G. V. Rao's research interests is presented. Many of his earlier studies were in conjunction with the
summer Monsoon Experiment of 1979 (MONEX-79). These included: 1) the structure of the Somali jet based on aerial observations;
2) sea-level air trajectories over the equatorial Indian Ocean; 3) structural features of the east African low-level flow;
4) effects of Indian Ocean surface temperature anomaly patterns on the summer monsoon circulations; 5) structures of the monsoon
low-level flow over the Arabian Sea; 6) characteristics and momentum-flux budgets of the Arabian Sea convective bands; and
7) evaporation and precipitation over the Arabian Sea during the monsoon seasons. Dr. Rao's research efforts in recent years
had focused on case studies of mesocyclones spawned by tropical cyclones (TCs) in Florida using Doppler radar data and a mesoscale
numerical model. These included: 1) research on tornadic mesocyclones spawned by TC Earl in 1998; 2) documentation of subtle
differences between tornadic and non-tornadic mesocyclones in TC Floyd in 1999; and 3) numerical simulation of the tornadic
environment observed in peninsular Florida during TC Earl in 1998. Preliminary findings show that the supercells' cold pools
interacted with an existing boundary resulting in increased baroclinicity and horizontal vorticity, and a maximization of
the tornado production potential by the updrafts. The model successfully simulated the mesoscale features of the mesocyclones
and the tornadic environment observed during TC Earl. A 24 h simulation of accumulated rainfall within the inner domain agreed
well with the observed precipitation pattern over the region. 相似文献
17.
Kay-Christian Emeis David M. Anderson Heidi Doose Dick Kroon Detlef Schulz-Bull 《Quaternary Research》1995,43(3)
Arabian Sea sediments record changes in the upwelling system off Arabia, which is driven by the monsoon circulation system over the NW Indian Ocean. In accordance with climate models, and differing from other large upwelling areas of the tropical ocean, a 500,000-yr record of productivity at ODP Site 723 shows consistently stronger upwelling during interglaciations than during glaciations. Sea-surface temperatures (SSTs) reconstructed from the alkenone unsaturation index (UK′37) are high (up to 27°C) during interglaciations and low (22-24°C) during glaciations, indicating a glacial-interglacial temperature change of >3°C in spite of the dampening effect of enhanced or weakened upwelling. The increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times, whereas the difference in SSTs must be unrelated to upwelling and to the summer monsoon intensity. The winter (NE) monsoon was more effective in cooling the Arabian Sea during glaciations then it is now. 相似文献
18.
Thibaut Caley Bruno Malaizé Franck Bassinot Steven C. Clemens Nicolas Caillon Rossignol Linda Karine Charlier Helene Rebaubier 《Quaternary Research》2011,76(2):285-293
Previous studies have suggested that Marine Isotope Stage (MIS) 13, recognized as atypical in many paleoclimate records, is marked by the development of anomalously strong summer monsoons in the northern tropical areas. To test this hypothesis, we performed a multi-proxy study on three marine records from the tropical Indian Ocean in order to reconstruct and analyse changes in the summer Indian monsoon winds and precipitations during MIS 13. Our data confirm the existence of a low-salinity event during MIS 13 in the equatorial Indian Ocean but we argue that this event should not be considered as “atypical”. Taking only into account a smaller precession does not make it possible to explain such precipitation episode. However, when considering also the larger obliquity in a more complete orbitally driven monsoon “model,” one can successfully explain this event. In addition, our data suggest that intense summer monsoon winds, although not atypical in strength, prevailed during MIS 13 in the western Arabian Sea. These strong monsoon winds, transporting important moisture, together with the effect of insolation and Eurasian ice sheet, are likely one of the factors responsible for the intense monsoon precipitation signal recorded in China loess, as suggested by model simulations. 相似文献
19.
In order to investigate how monsoons influence biogeochemical fluxes in the ocean, twelve time-series sediment traps were
deployed at six locations in the northern Indian Ocean. In this paper we present particle flux data collected during May 1986
to November 1991 and November 1987 to November 1992 in the Arabian Sea and Bay of Bengal respectively. Particle fluxes were
high during both the SW and NE monsoons in the Arabian Sea as well as in the Bay of Bengal. The mechanisms of particle production
and transport, however, differ in both the regions.
In the Arabian Sea, average annual fluxes are over 50gm-2y-1 in the western Arabian Sea and less than 27gm-2 y-1 in the central part. Biogenic matter is dominant at sites located near upwelling centers, and is less degraded during peak
flux periods. High particle fluxes in the offshore areas of the Arabian Sea are caused by injection of nutrients into the
euphotic zone due to wind-induced mixed layer deepening. In the Bay of Bengal, average annual fluxes are highest in the central
Bay of Bengal (over
50gm-2y-1) and are least in the southern part of the Bay (37gm-2y-1). Particle flux patterns coincide with freshwater discharge patterns of the Ganges-Brahmaputra river system. Opal/carbonate
and organic carbon/carbonate carbon ratios increase during the SW monsoon due to variations in salinity and productivity patterns
in the surface waters as a result of increased freshwater and nutrient input from rivers.
Comparison of S years data show that fluxes of biogenic and lithogenic particulate matter are higher in the Bay of Bengal
even though the Arabian Sea is considered to be more productive. Our results indicate that in the northern Indian Ocean interannual
variability in organic carbon flux is directly related to the strength and intensity of the SW monsoon while its transfer
from the upper layers to the deep sea is partly controlled by input of lithogenic matter from adjacent continents. 相似文献
20.
Hamza Varikoden Hilal Sulthan Ali Al-shukaili C. A. Babu A. A. Samah 《Arabian Journal of Geosciences》2016,9(8):520
The Sultanate of Oman is located in the south-eastern part of the Arabian Peninsula and covers the larger part of the southern coasts of the Arabian Peninsula in both arid and semi-arid environments except for the southern part which is swept by the monsoon affecting the Arabian Sea during the period from June to September. The summer rainfall over Oman shows year-to-year variability, and this is caused by oceanic and atmospheric influences. In the present study, we tried to explore the influence of El Niño on the rainfall over Oman using different data sets. The empirical orthogonal function (EOF) technique employed to the zonal wind at 850 hPa for the 30-year period shows that the second and third modes of EOF are showing high variability over the Oman regions. The corresponding PCs were subjected to FFT analysis, and it showed a peak about 5–6 years. In addition to this, the zonal wind over the Oman regions is correlated with the global zonal wind and found a significant correlation (1 % significant level). It has already been proved that the wind and rainfall during summer monsoon is in phase. Moreover, the spectral analysis of rainfall at Masirah station and the Niño3.4 index show the similar mode of variability indicating a direct relationship. The correlation between rainfall and the Niño3.4 index is also showing a positive significant value, and therefore, it can be concluded that the El Niño in the Pacific favours rainfall over the Oman region. 相似文献