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1.
V. V. S. S. Sarma 《Journal of Earth System Science》2006,115(4):433-450
Data on ocean color chlorophylla (Chl a) obtained using Sea-viewing Wide Field of view Sensor (SeaWiFS), sea surface temperature (SST) by Advanced Very High
Resolution Radiometer (AVHRR), and sea surface height (SSH) by TOPEX/POSEIDON were analyzed to examine the influence of Indian
Ocean Dipole (IOD) on the physical and biogeochemical processes with special reference to phytoplankton primary production
and air-sea fluxes of carbon dioxide in the Arabian Sea. Positive SST anomalies (SSTA) were found in the Arabian Sea (0.4
to 1.8°C) with higher values in the southwestern Arabian Sea that decreased towards north. The SSH anomalies (SSHA) and turbulent
kinetic energy anomalies (TKEA) suggest decreased mixing during the IOD compared to the normal period. Chlorophylla displayed significant negative correlations with SSTA and SSHA in the Arabian Sea. Consistently, Chla showed negative anomalies (low Chl a) during the IOD period which could be due to reduced inputs of nutrients. The photic
zone integrated primary production decreased by 30% during the IOD period compared to the normal whereas pCO2 levels were higher (by 10–20μatm). However, sea to air fluxes were lower by 10% during the IOD period due to prevailing weaker
winds. Primary production seems to be the key process controlling the surface pCO2 levels in the Arabian Sea. In future, the influence of IOD on ecosystem structure, export production and bacterial respiration
rates are to be probed throughin situ time-series observations. 相似文献
2.
T. K. Manual Ateef Khan Y. Nazeer Ahammed R. S. Tanwar R. S. Parmar K. S. Zalpuri Prabhat K. Gupta S. L. Jain Risal Singh A. P. Mitra S. C. Garg A. Suryanarayana V. S. N. Murty M. Dileep Kumar Andrew J. Shepherd 《Journal of Earth System Science》2006,115(4):473-484
Characteristics of trace gases (O3, CO, CO2, CH4 and N2O) and aerosols (particle size of 2.5 micron) were studied over the Arabian Sea, equatorial Indian Ocean and southwest part
of the Bay of Bengal during the monsoon transition period (October–November, 2004). Flow of pollutants is expected from south
and southeast Asia during the monsoonal transition period due to the patterns of wind flow which are different from the monsoon
period. This is the first detailed report on aerosols and trace gases during the sampled period as the earlier Bay of Bengal
Experiment (BOBMEX), Arabian Sea Monsoon Experiment (ARMEX) and Indian Ocean Experiments (INDOEX) were during monsoon seasons.
The significant observations during the transition period include: (i) low ozone concentration of the order of 5 ppbv around
the equator, (ii) high concentrations of CO2, CH4 and N2O and (iii) variations in PM2.5 of 5–20μg/m3. 相似文献
3.
T. M. Balakrishnan Nair 《Journal of Earth System Science》2006,115(4):461-472
Particulate fluxes of aluminium, iron, magnesium and titanium were measured using six time-series sediment traps deployed
in the eastern, central and western Arabian Sea. Annual Al fluxes at shallow and deep trap depths were 0.47 and 0.46 g m-2 in the western Arabian Sea, and 0.33 and 0.47 g m-2 in the eastern Arabian Sea. There is a difference of about 0.9–1.8 g m-2y-1 in the lithogenic fluxes determined analytically (residue remaining after leaching out all biogenic particles) and estimated
from the Al fluxes in the western Arabian Sea. This arises due to higher fluxes of Mg (as dolomite) in the western Arabian
Sea (6–11 times higher than the eastern Arabian Sea). The estimated dolomite fluxes at the western Arabian Sea site range
from 0.9 to 1.35gm-2y-1. Fe fluxes in the Arabian Sea were less than that of the reported atmospheric fluxes without any evidence for the presence
of labile fraction/excess of Fe in the settling particles. More than 75% of Al, Fe, Ti and Mg fluxes occurred during the southwest
(SW) monsoon in the western Arabian Sea. In the eastern Arabian Sea, peak Al, Fe, Mg and Ti fluxes were recorded during both
the northeast (NE) and SW monsoons. During the SW monsoon, there exists a time lag of around one month between the increases
in lithogenic and dolomite fluxes. Total lithogenic fluxes increase when the southern branch of dust bearing northwesterlies
is dragged by the SW monsoon winds to the trap locations. However, the dolomite fluxes increase only when the northern branch
of the northwesterlies (which carries a huge amount of dolomite accounting 60% of the total dust load) is dragged, from further
north, by SW monsoon winds. The potential for the use of Mg/Fe ratio as a paleo-monsoonal proxy is examined. 相似文献
4.
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
5.
The intra-seasonal variability observed in the salinity field of the upper layers at a few locations in the east central Arabian
Sea and the northern Bay of Bengal during the summer monsoon seasons of 1977 and 1979 is documented with the aid of short
time series (1–2 weeks) of salinity measurements made from USSR and Indian ships deployed during MONSOON-77 (1977) and MONEX-79
(1979) field experiments. In the Arabian Sea a typical subsurface maxima observed beneath the mixed layer base either disappeared
or considerably weakened due to strong vertical mixing caused by the monsoonal forcing. In the northern Bay of Bengal the
salinity variability in the top 30 m water column was rapid and appeared to be influenced by large amounts of fresh water
from rain and probably from the major adjoining rivers. Some simple diagnostic calculations are presented to assess the relative
importance of various processes which control the observed salinity variability. 相似文献
6.
Lina P. Mergulhao Rahul Mohan V. S. N. Murty M. V. S. Guptha D. K. Sinha 《Journal of Earth System Science》2006,115(4):415-428
Sediment trap samples collected from a depth of 1018 m in the Central Arabian Sea Trap (CAST) at 14°28.2′N, 64°35.8′E were
analyzed for temporal variation of coccolithophore fluxes from October 1993 to August 1994. Out of the twenty species of coccolithophores
encountered,Gephyrocapsa oceanica, Emiliania huxleyi, Umbilicosphaera sibogae andUmbellosphaera irregularis were the most abundant. The total coccolithophore fluxes ranged from 28.5 × 106m-2d-1 to 50.3 × 106m-2d-1 showing seasonality with higher fluxes during the northeast (NE) monsoon and lower fluxes during the spring intermonsoon.
The higher fluxes were attributed to the enhancement of primary production in the central Arabian Sea due to southward extent
of nutrients from the northeast Arabian Sea by the prevailing surface currents. Similarly, the occurrences of relatively lower
coccolithophore fluxes during the spring intermonsoon and southwest (SW) monsoon were attributed to the low nutrients in the
warm, shallow surface mixed layer and downwelling to the south of Findlater Jet respectively in the central Arabian Sea. Some
of the coccolithophore species such asE. huxleyi, G. oceanica, Calcidiscus leptoporus andUmbellosphaera tenuis showed signs of dissolution. 相似文献
7.
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
8.
S. S. C. Shenoi N. Nasnodkar G. Rajesh K. Jossia Joseph I. Suresh A. M. Almeida 《Journal of Earth System Science》2009,118(5):483-496
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
9.
Rebecca E. Green Thomas S. Bianchi Michael J. Dagg Nan D. Walker Greg A. Breed 《Estuaries and Coasts》2006,29(4):579-597
We investigated seasonal variability in organic carbon (OC) budgets using a physical-biological model for the Mississippi
River turbidity plume. Plume volume was calculated from mixed layer depth and area in each of four salinity subregions based
on an extensive set of cruise data and satellite-derived suspended sediment distributions. These physical measurements were
coupled with an existing food web model to determine seasonally dependent budgets for labile (reactive on time scales of days
to weeks) OC in each salinity subregion. Autochthonous gross primary production (GPP) equaled 1.3×1012 g C yr−1 and dominated labile OC inputs (88% of the budget) because riverine OC was assumed mostly refractory (nonreactive). For perspective,
riverine OC inputs amounted to 3.9×1012 g C yr−1, such that physical inputs were 3 times greater than biological inputs to the plume. Annually, microbial respiration (R)
accounted for 65% of labile OC losses and net metabolism (GPP—R) for the entire plume was, autotrophic, equaling 5.1×1011 g C yr−1. Smaller losses of labile OC occurred via sedimentation (20%), advection (10%), and export to higher trophic levels (5%).
In our present model, annual losses of labile OC are 10% higher than inputs, indicating future improvements are required.
Application of our model to estimate air-sea carbon dioxide (CO2) fluxes indicated the plume was a net sink of 2.0×109 mol CO2 yr−1, of which 90% of the total drawdown was from biotic factors. In all seasons, low salinity waters were a source of CO2 (pCO2=560–890 μatm), and intermediate to high salinity waters were a sink of CO2 (pCO2=200–370 μatm). Our model was also used to calculate O2 demand for the development, of regional hypoxia, and our spring and early summer budgets indicated that sedimentation of
autochthonous OC from the immediate plume contributed 23% of the O2 demand necessary for establishment of hypoxia in the region. 相似文献
10.
Changes in the abundance of selected planktic foraminiferal species and some sedimentological parameters at ODP site 728A
were examined to understand the fluctuations in the surface productivity and deep sea oxygenation in the NW Arabian Sea during
last ∼540 kyr. The increased relative abundances of high fertility taxa, i.e., Globigerinita glutinata and Globigerina bulloides mainly during interglacial intervals indicate intense upwelling. Strong SW summer monsoon probably increased the upwelling
in the western Arabian Sea during interglacial intervals and caused high surface productivities due to the lateral transport
of eutrophic waters. Most of the glacial periods (i.e., MIS 2, 4, 6, 8 and 12) are characterized by higher relative abundances
of Neogloboquadrina pachyderma and Neogloboquadrina dutertrei associated with Globigerinoides ruber. The more stratified condition and deep mixed layer due to increased NE winter monsoon are mainly responsible for the higher
relative abundances of N. pachyderma during glacial periods. Some of the glacial intervals (i.e., MIS 6 and 8) are also characterized by pteropod spikes reflecting
deepening of aragonite compensation depth (ACD) and relatively less intense oxygen minimum zone (OMZ) in this region due to
deep sea mixing and thermocline ventilation, and relatively less intense surface productivity during winter monsoon. The interglacial
periods are largely devoid of pteropod shells indicating more aragonite dissolution due to increased intensity of OMZ in the
northwestern Arabian Sea. 相似文献
11.
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
12.
M. K. Sharada P. S. Swathi K. S. Yajnik C. Kalyani Devasena 《Journal of Earth System Science》2008,117(4):429-447
A physical-biological-chemical model (PBCM) is used for investigating the seasonal cycle of air-sea carbon flux and for assessing
the effect of the biological processes on seasonal time scale in the Arabian Sea (AS) and Bay of Bengal (BoB), where the surface
waters are subjected to contrasting physical conditions. The formulation of PBCM is given in Swathi et al (2000), and evaluation of several ammonium-inhibited nitrate uptake models is given in Sharada et al (2005). The PBCM is here first evaluated against JGOFS data on surface pCO2 in AS, Bay of Bengal Process Studies (BoBPS) data on column integrated primary productivity in BoB, and WOCE Il data on dissolved
inorganic carbon (DIC) and alkalinity (ALK) in the upper 500 meters at 9°N in AS and at 10°N in BoB in September–October.
There is good qualitative agreement with local quantitative discrepancies.
The net effect of biological processes on air-sea carbon flux on seasonal time scale is determined with an auxiliary computational
experiment, called the abiotic run, in which the biological processes are turned off. The difference between the biotic run
and abiotic run is interpreted as the net effect of biological processes on the seasonal variability of chemical variables.
The net biological effect on air-sea carbon flux is found to be highest in southwest monsoon season in the northwest AS, where
strong upwelling drives intense new production. The biological effect is larger in AS than in BoB, as seasonal upwelling and
mixing are strong in AS, especially in the northeast, while coastal upwelling and mixing are weak in BoB. 相似文献
13.
A study of arsenic,iron and other dissolved ion variations in the groundwater of Bishnupur District,Manipur, India 总被引:1,自引:1,他引:0
Jayalakshmi Devi Oinam AL. Ramanathan Anurag Linda Gurmeet Singh 《Environmental Earth Sciences》2011,62(6):1183-1195
The presence of arsenic (As) in groundwater and its effect on human health has become an issue of serious concern in recent
years. The present study assessed the groundwater quality of the Bishnupur District, Manipur, with respect to drinking water
standards. Higher concentrations of pH, iron and phosphate were observed at several locations. Phosphate and iron levels were
highest in the pre-monsoon, followed by monsoon and post-monsoon seasons. The arsenic concentrations were highest during post-monsoon
(1–200 μg L−1) as compared to pre-monsoon (1–108 μg L−1) and monsoon (2–99 μg L−1). Kwakta and Ngakhalawai show higher levels of arsenic concentration as compared to the prescribed World Health Organization
(WHO) and Bureau of Indian Standards (BIS) norms. Arsenic showed a strong positive correlation with phosphate and negative
correlation with sulphate, suggesting a partial influence of anthropogenic sources. The study suggests that the Bishnupur
area has an arsenic contamination problem, which is expected to increase in the near future. 相似文献
14.
Yongsik Sin Bonggil Hyun Quang-Dung Bach Sungryull Yang Chul Park 《Estuaries and Coasts》2012,35(3):839-852
Temporal and spatial variations in phytoplankton in Asan Bay, a temperate estuary under the influence of monsoon, were investigated
over an annual cycle (2004). Phytoplankton blooms started in February (>20 μg chl l−1) and continued until April (>13 μg chl l−1) during the dry season, especially in upstream regions. The percentage contribution of large phytoplankton (micro-sized)
was high (78–95%) during the blooms, and diatoms such as Skeletonema costatum and Thalassiosira spp. were dominant. The precipitation and freshwater discharge from embankments peaked and supplied nutrients into the bay
during the monsoon event, especially in July. Species that favor freshwater, such as Oscillatoria spp. (cyanobacteria), dominated during the monsoon period. The phytoplankton biomass was minimal in this season despite nutrient
concentrations that were relatively sufficient (enriched), and this pattern differed from that in tropical estuaries affected
by monsoon and in temperate estuaries where phytoplankton respond to nutrient inputs during wet seasons. The flushing time
estimated from the salinity was shorter than the doubling time in Asan Bay, which suggests that exports of phytoplankton maximized
by high discharge directly from embankments differentiate this bay from other estuaries in temperate and tropical regions.
This implies that the change in physical properties, especially in the freshwater discharge rates, has mainly been a regulator
of phytoplankton dynamics since the construction of embankments in Asan Bay. 相似文献
15.
K. V. S. R. Prasad S. V. V. Arun Kumar Ch. Venkata Ramu P. Sreenivas 《Natural Hazards》2009,49(2):347-360
The nearshore parameters, viz., wave runup, wave setup, and wave energy have been estimated during storm and normal conditions
of SW monsoon (June–September) and NE monsoon (November–February) by empirical parameterization along Visakhapatnam coast.
These results were compared with the field observations during three storms of SW monsoon season in the year 2007. The higher
nearshore wave energies were observed at R.K. Beach, Jodugullapalem beach, and Sagarnagar beach during both the seasons. During
storm events, the higher wave energies associated with higher wave runups cause severe erosion along the wave convergence
zones. The storm wave runups (SWRUs) were higher at R.K. Beach, Palm beach, Jodugullapalem beach, and Sagarnagar Beach. The
yearly low wave energy was observed at Lawson’s Bay with lowest wave runup, considered as safest zone. R.K. Beach, Palm beach,
and Jodugullapalem beach are identified as vulnerable zones of wave attack. It is noteworthy that in addition to wave energies,
wave runups and wave setups also play a vital role in endangering the coast. 相似文献
16.
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
17.
Hydrography of the Bay of Bengal is highly influenced by the river runoff and rainfall during the southwest monsoon. We have reconstructed δ18Osw, sea surface salinity and sea surface temperature (SST) changes in the Bay of Bengal by using paired measurements of δ18O and Mg/Ca in a planktonic foraminifera species Globigerinoides ruber from core SK218/1 in the western Bay of Bengal in order to understand the rainfall variability associated with southwest monsoon over the past 32 kyr. Our SST reconstructions reveal that Bay of Bengal was ~3.2 °C cooler during the LGM as compared to present day temperature and a ~3.5 °C rise in SST is documented from 17 to 10 ka. Both SST and δ18Osw exhibit greater amplitude fluctuations during MIS 2 which is attributable to the variability of NE monsoon rainfall and associated river discharge into the Bay of Bengal in association with strong seasonal temperature contrast. On set of strengthening phase of SW monsoon was started during Bølling/Allerød as evidenced by the low δ18Osw values ~14.7 ka. δ18Osw show consistently lower values during Holocene (with an exception around 5 ka), which suggests that the freshening of Bay of Bengal due to heavy precipitation and river discharge caused by strong SW monsoon. Results of this study signify that the maximum fluctuations of the NE monsoon rainfall during MIS 2 appear to be controlled by the strong seasonality and boundary conditions. 相似文献
18.
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
19.
Y. Sadhuram 《Journal of Earth System Science》1987,96(1):59-67
Variability in the standard deviation of surface wind direction (σθ), under different Pasquill stability regimes on diurnal, seasonal and interannual scales has been investigated making use
of a 10-year data set collected at Visakhapatnam (17°42′ N., 82° 18′ E) during January, April, August and October for winter,
pre-monsoon, monsoon and post-monsoon seasons respectively. The diurnal scale variability in σθ is more pronounced during day time than in night. The seasonal variability in σθ is only moderate around noon while relatively large fluctuations are noticed on inter-annual scale only during day time in
January and August. The seasonal dispersion in σθ decreased from most unstable regime to most stable regime. 相似文献
20.
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