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1.
Decadal and centennial variability of the southern semiannual oscillation simulated in the GFDL coupled GCM 总被引:1,自引:0,他引:1
We investigate the behavior of the semiannual oscillation (SAO) in surface pressure and 500 hPa baroclinicity at high southern
latitudes in a 1000-year GFDL coupled ocean-atmosphere GCM run. The model represents this feature but is shown to underestimate
its amplitude and percentage of variance explained in the midlatitudes. South of 60 °S the simulation of the pressure oscillation,
although somewhat too weak, is considerably better. Our analysis reveals significant interannual, decadal and centennial variability
in the modeled SAO. While there is only a short historical record of observational data in the middle and high southern latitudes,
existing studies suggest that the strength of the SAO does show significant variability on at least the first two of these
time scales. Strong relationships between the semiannual cycles of surface pressure and baroclinicity are apparent in the
model output, reinforcing the findings in earlier studies that the differing annual march of temperature between the midlatitudes
and the Antarctic coast leads to a semiannual component in the baroclinicity and thence the surface pressure. We draw attention
to extended periods when the model SAO is weak and strong, and have investigated the nature of the circulation during each
period. The GFDL model results suggest that a significant proportion of the SAO variation was associated more with variations
in the strength of the winter pressure maximum rather than the springtime minimum. The extent to which this and other aspects
of the modeled longterm variability are related to actual atmospheric structure must await the availability of longer data
records.
Received: 11 November 1996 / Accepted: 28 July 1997 相似文献
2.
Raphael E. Okoola 《Meteorology and Atmospheric Physics》2000,73(3-4):177-187
Summary Climatological statistics of extreme temperature events over Kenya are established from the analysis of daily and monthly
maximum temperatures for a representative station (Nairobi Dagoretti Corner) over the period 1956–1997.
The months of June to August were shown to be the coldest with a mean monthly maximum temperature of less than 22 °C. Seasonal
(June to August) mean maximum temperature was 21.5 °C. Using this seasonal mean temperature for the period 1967–1997 delineated
1968 as the coldest year in this series and 1983 as the warmest year.
Spectral analysis of the seasonal data, for both the coldest and the warmest years, revealed that the major periods were the
quasi-biweekly (10 days) and the Intraseasonal Oscillations (23 days). Secondary peaks occurred at periods of 4–6 and 2.5–3.5
days.
A temperature threshold of 16.7 °C during July was used to define cold air outbreaks over Nairobi. This threshold temperature
of 16.7 °C was obtained from the mean July maximum temperature (20.9 °C) minus two standard deviations. Notable trends include
a decrease in the frequency of station-days, between 1956 and 1997, with temperatures less than 16.7 °C during July.
Surface pressure patterns indicate that the origin of the cold air is near latitude 25° S and to the east of mainland South
Africa. The cold air near 25° S is advected northwards ahead of the surface pressure ridge.
Received July 19, 1999 Revised January 11, 2000 相似文献
3.
Summary The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces
an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with
the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared
utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These
sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal
components (PCs).
A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E
Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to
PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts
associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the
lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC
IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features,
such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric
anticyclones to the south.
The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition,
synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner
by such PCA.
Received July 18, 1997 Revised April 30, 1999 相似文献
4.
Influence of vegetation changes during the Last Glacial Maximum using the BMRC atmospheric general circulation model 总被引:3,自引:0,他引:3
The influence of different vegetation distributions on the atmospheric circulation during the Last Glacial Maximum (LGM,
21 000 years before present) is investigated. The atmospheric general circulation model of the Bureau of Meteorology Research
Center was run using a modern vegetation and in a second experiment with a vegetation reconstruction for the LGM. It is found
that a change from conifer to desert and tundra causes an additional LGM cooling of 1–2 °C in Western Europe, up to −4 °C
in North America and −6 °C in Siberia. An expansion of dryland vegetation causes an additional annual cooling of 1–2 °C for
Australia and northern Africa. On the other hand, an increase of temperature (2 °C) is found in Alaska due to changes in circulation.
In the equatorial region the LGM vegetation leads to an increased modelled temperature of 0.5–1.5 °C and decreased precipitation
(30%) over land due to a reduction of the tropical rainforest, mainly in Indonesia, where the reduction of precipitation over
land is associated with an increase of precipitation of 30% over the western Pacific.
Received: 15 December 1999 / Accepted: 10 January 2001 相似文献
5.
基于1979—2000年的NCEP/NCAR海平面气压和位势高度场资料分析了南半球大气环流的准半年振荡 (半年波) 现象。结果表明:这一现象主要出现在南半球对流层低层的中高纬度和中高层的热带地区。对南半球热带外大气而言, 40°S和65°S是低层大气环流准半年振荡最为显著的两个纬度带, 半年波的贡献都超过了70%, 低层南半球中高纬度海平面气压场季节变化的反位相也主要体现为各自半年波分量变化的反位相。在此基础上, 检验了IAP 9L AGCM (大气物理研究所9层大气环流模式) 对这一现象模拟的能力, 模拟结果显示, 模式成功模拟了65°S处海平面气压场的准半年振荡现象, 其振幅略低于观测结果, 但模式对40°S处气压场准半年振荡的模拟效果较差。 相似文献
6.
Holocene hydrological cycle changes in the Southern Hemisphere documented in East Antarctic deuterium excess records 总被引:1,自引:0,他引:1
F. Vimeux V. Masson J. Jouzel J. R. Petit E. J. Steig M. Stievenard R. Vaikmae J. W. C. White 《Climate Dynamics》2001,17(7):503-513
Four Holocene-long East Antarctic deuterium excess records are used to study past changes of the hydrological cycle in the
Southern Hemisphere. We combine simple and complex isotopic models to quantify the relationships between Antarctic deuterium
excess fluctuations and the sea surface temperature (SST) integrated over the moisture source areas for Antarctic snow. The
common deuterium excess increasing trend during the first half of the Holocene is therefore interpreted in terms of a warming
of the average ocean moisture source regions over this time. Available Southern Hemisphere SST records exhibit opposite trends
at low latitudes (warming) and at high latitudes (cooling) during the Holocene. The agreement between the Antarctic deuterium
excess and low-latitude SST trends supports the idea that the tropics dominate in providing moisture for Antarctic precipitation.
The opposite trends in SSTs at low and high latitudes can potentially be explained by the decreasing obliquity during the
Holocene inducing opposite trends in the local mean annual insolation between low and high latitudes. It also implies an increased
latitudinal insolation gradient that in turn can maintain a stronger atmospheric circulation transporting more tropical moisture
to Antarctica. This mechanism is supported by results from a mid-Holocene climate simulation performed using a coupled ocean-atmosphere
model.
Received: 7 July 1999 / Accepted: 21 July 2000 相似文献
7.
Thomas J. Bracegirdle 《Climate Dynamics》2011,37(11-12):2323-2333
The semi-annual oscillation (SAO) in sea-level pressure at high southern latitudes is the consequence of a twice-yearly contraction (and strengthening) and expansion (and weakening) of the storm track between 50 and 65°S, with the contracted phases in spring and autumn. In this study the extent to which inter-annual variability of the SAO is correlated with inter-annual variability in mid- to lower-stratospheric circulation at 60°S was determined using NCEP/NCAR Reanalysis 1 data for the period 1979?C2009. The second harmonic of the annual cycle of an SAO index was used to assess SAO amplitude and phase (the date of the first peak of the second harmonic). Zonal mean zonal wind at 60°S was used as an index for atmospheric circulation. The results show that year-to-year variability in the SAO amplitude is significantly correlated with mid-stratospheric (10?hPa) circulation variability in late summer/early autumn (February?CMarch) and late winter/early spring (August?CSeptember). However, variability in the SAO phase is significantly correlated with mid-stratospheric circulation variability in spring (September?CNovember). These maxima in significant correlations at 10?hPa propagate down to the surface in approximately one month. The characteristics of upward planetary wave propagation alone do not explain the late summer/early autumn and spring maxima in correlations. Evidence is shown that internal reflection of stationary wave-number 1 is important for explaining the strong correlations in late summer/early autumn, but that large variability during polar vortex break-up dominates the spring correlations. The results may be important for understanding seasonal differences in how stratospheric ozone depletion influences tropospheric circulation. 相似文献
8.
B. Alijani 《Theoretical and Applied Climatology》2002,72(1-2):41-54
Summary In order to explore the spatial and temporal variations of 500 hPa flow patterns and their relationship with the climate
of Iran, monthly mean geopotential heights for the region 0° E to 70° E and 20° N to 50° N, at 5 degree resolution, were analysed.
The study period covered the winter months October to March during the period 1961–90. The monthly height of the 500 hPa level
was averaged along each meridian from 25° N to 45° N. The height of the mean monthly pressure pattern was mapped against the
study years. The results showed that the characteristics of the 500 hPa flow pattern varied over monthly and annual time scales.
Principal Component Analysis, with S-mode and Varimax rotation, was also used to reduce the gridded data to 5 (6 in October)
significant factors. The factor scores for each month were then correlated with monthly Z-scores of precipitation and temperature
anomalies over Iran. The results showed that troughs and ridges located close to Iran had more influence on the climate of
Iran. Two troughs were identified and named the Caspian and Syrian troughs.
Received April 12, 2001 Revised July 24, 2001 相似文献
9.
Summary Degree-days as a measure of accumulated temperature deviations from a base temperature have many practical applications in
various human related activities such as home cooling, heating, plant growth in agriculture and power generation in addition
to energy requirement. Long temperature records are necessary for their reliable estimations at given stations. In this paper,
degree-day measure has been applied to monthly temperature records for systematically changed base temperature values from
− 25 °C to + 35 °C with 5 °C increments at 255 meteorology stations in Turkey. The results are represented in the form of
spatial degree-day distribution maps, which are then related to various climatic, meteorological and topographic features
of Turkey. For instance, free surface water bodies in forms of surrounding seas, lakes and rivers insert retardation in the
expansion of heating degree-days over large regions. On the other hand, cold air penetration from polar regions in the northeastern
Turkey originating from Siberia appears at moderate base temperature heating degree-days.
Received August 20, 1998 Revised June 21, 1999 相似文献
10.
G. Mastrantonio V. Malvestuto S. Argentini T. Georgiadis A. Viola 《Meteorology and Atmospheric Physics》1999,71(1-2):127-132
Summary The development of a convective boundary layer over the Antarctic Plateau is documented by a Doppler minisodar data-set recorded
during a 10 day campaign in January 1997. The vertical velocities associated with thermals do not exceed 1 m/s, while the
depth of the convective layer, usually less than 200 m, never surpasses 300 m. Measurements of momentum flux, sensible heat
flux, wind speed and radiation budget show characteristics that are typical of a convective boundary layer evolution. The
diurnal behaviour of absolute humidity, however, exhibits features that are not expected, e.g. anticorrelation with incoming
net radiation and air temperature.
Received October 30, 1998 Revised May 26, 1999 相似文献
11.
Impacts of shortwave radiation forcing on ENSO: a study with a coupled tropical ocean-atmosphere model 总被引:2,自引:0,他引:2
We describe a coupled tropical ocean-atmosphere model that represents a new class of models that fill the gap between anomaly
coupled models and fully coupled general circulation models. Both the atmosphere and ocean are described by two and half layer
primitive equation models, which emphasize the physical processes in the oceanic mixed layer and atmospheric boundary layer.
Ocean and atmosphere are coupled through both momentum and heat flux exchanges without explicit flux correction. The coupled
model, driven by solar radiation, reproduces a realistic annual cycle and El Nino-Southern Oscillation (ENSO). In the presence
of annual mean shortwave radiation forcing, the model exhibits an intrinsic mode of ENSO. The oscillation period depends on
the mean forcing that determines the coupled mean state. A perpetual April (October) mean forcing prolongs (shortens) the
oscillation period through weakening (enhancing) the mean upwelling and mean vertical temperature gradients. The annual cycle
of the solar forcing is shown to have fundamental impacts on the behavior of ENSO cycles through establishing a coupled annual
cycle that interacts with the ENSO mode. Due to the annual cycle solar forcing, the single spectral peak of the intrinsic
ENSO mode becomes a double peak with a quasi-biennial and a low-frequency (4–5 years) component; the evolution of ENSO becomes
phase-locked to the annual cycle; and the amplitude and frequency of ENSO become variable on an interdecadal time scale due
to interactions of the mean state and the two ENSO components. The western Pacific monsoon (the annual shortwave radiation
forcing in the western Pacific) is primarily responsible for the generation of the two ENSO components. The annual march of
the eastern Pacific ITCZ tends to lock ENSO phases to the annual cycle. The model's deficiencies, limitations, and future
work are also discussed.
Received: 15 June 1999 / Accepted: 11 December 1999 相似文献
12.
Summary ?A calendar of the negative and positive phases of the North Sea – Caspian Pattern (NCP) for the period 1958–1998 was used to analyse the implication of the NCP upper level teleconnections on the regional climate of the eastern Mediterranean basin. Series of monthly mean air temperature
and monthly total rainfall from 33 stations across Greece, Turkey and Israel, for the same period, were used. For each month,
from October to April, averages of the monthly mean temperatures and the monthly rainfall totals as well as the standardized
values of both parameters were calculated separately for the negative (NCP (−)) and the positive (NCP (+)) phases of the NCP.
At all stations and in all months, temperature values were significantly higher during the NCP (−) as compared with the NCP (+). Furthermore, apart from very few exceptions, the absolute monthly mean maximum and monthly mean minimum values were
obtained during the NCP (−) and the NCP (+) phases, respectively. The maximum impact of the NCP on mean air temperature was detected in the continental Anatolian Plateau, where the mean seasonal differences are around 3.5 °C. This influence decreases westwards and southwards.
The influence on the rainfall regime is more complex. Regions exposed to the southern maritime trajectories, in Greece and
in Turkey, receive more rainfall during the NCP (−) phase, whereas in the regions exposed to the northern maritime trajectories, such as Crete in Greece, the Black Sea region in Turkey, and in all regions of Israel, there is more rainfall during the NCP (+) phase. The accumulated rainfall differences between the two phases are over 50% of the seasonal average for some stations.
A comparison of the capabilities of the NCP, the North Atlantic Oscillation (NAO) and the Southern Oscillation (SO) indices to differentiate between below and above normal temperatures was made. The results have placed the NCP, as the best by far of all three teleconnections in its ability to differentiate between below or above normal temperatures
and as the main teleconnection affecting the climate of the Balkans, the Anatolian Peninsula and the Middle East. These results may serve to downscale General Circulation Model (GCM) scenarios to a regional scale and provide forecasts
regarding eventual temperature and/or precipitation changes.
Received June 25, 2001; revised February 25, 2002; accepted March 3, 2002 相似文献
13.
Michelle Simões Reboita Rosmeri Porfírio da Rocha Tércio Ambrizzi Ernesto Caetano 《Climate Dynamics》2010,34(6):873-889
A Regional Climate Model (RegCM3) 10-year (1990–1999) simulation over southwestern South Atlantic Ocean (SAO) is evaluated
to assess the mean climatology and the simulation errors of turbulent fluxes over the sea. Moreover, the relationship between
these fluxes and the rainfall over some cyclogenetic areas is also analyzed. The RegCM3 results are validated using some reanalyses
datasets (ERA40, R2, GPCP and WHOI). The summer and winter spatial patterns of latent and sensible heat fluxes simulated by
the RegCM3 are in agreement with the reanalyses (WHOI, R2 and ERA40). They show large latent heat fluxes exchange in the subtropical
SAO and at higher latitudes in the warm waters of Brazil Current. In particular, the magnitude of RegCM3 latent heat fluxes
is similar to the WHOI, which is probably related to two factors: (a) small specific humidity bias, and (b) the RegCM3 flux
algorithm. In contrast, the RegCM3 presents large overestimation of sensible heat flux, though it simulates well their spatial
pattern. This simulation error is associated with the RegCM3 underestimation of the 2-m air temperature. In southwestern SAO,
in three known cyclogenetic areas, the reanalyses and the RegCM3 show the existence of different physical mechanisms that
control the annual cycles of latent/sensible heating and rainfall. It is shown that over the eastern coast of Uruguay (35°–43°S)
and the southeastern coast of Argentina (44°–52°S) the sea-air moisture and heat exchange play an important role to control
the annual cycle of precipitation. This does not happen on the south/southeastern coast of Brazil. 相似文献
14.
Monthly sea surface temperature anomalies (SSTA) at near-global scale (60 °N–40 °S) and May to October rainfall amounts in
West Africa (16 °N–5 °N; 16 °W–16 °E) are first used to investigate the seasonal and interannual evolutions of their relationship.
It is shown that West African rainfall variability is associated with two types of oceanic changes: (1) a large-scale evolution
involving the two largest SSTA leading eigenmodes (16% of the total variance with stronger loadings in the equatorial and
southern oceans) related to the long-term (multiannual) component of rainfall variability mainly expressed in the Sudan–Sahel
region; and (2) a regional and seasonally coupled evolution of the meridional thermal gradient in the tropical Atlantic due
to the linear combination of the two largest SSTA modes in the Atlantic (11% with strong inverse loadings over the northern
and southern tropics) which is associated with the interannual and quasi-decadal components of regional rainfall in West Africa.
Linear regression and discriminant analyses provide evidence that the main July–September rainfall anomalies in Sudan–Sahel
can be detected with rather good skills using the leading (April–June) or synchronous (July–September) values of the four
main oceanic modes. In particular, the driest conditions over Sahel, more marked since the beginning of the 1970s, are specifically
linked to the warm phases of the two global modes and to cold/warm anomalies in the northern/southern tropical Atlantic. Idealized
but realistic SSTA patterns, obtained from some basic linear combinations of the four main oceanic modes appear sufficient
to generate quickly (from mid-July to the end of August) significant West African rainfall anomalies in model experiments,
consistent with the statistical results. The recent negative impact on West African rainfall exerted by the global oceanic
forcing is primarily due to the generation of subsidence anomalies in the mid-troposphere over West Africa. When an idealized
north to south SSTA gradient is added in the tropical Atlantic, strong north to south height gradients in the middle levels
appear. These limit the northward excursion of the rainbelt in West Africa: the Sahelian area experiences drier conditions
due to the additive effect (subsidence anomalies+latitudinal blocking) while over the Guinea regions wet conditions do not
significantly increase, since the subsidence anomalies and the blocking effect act here in opposite ways.
Received: 26 June 1997 / Accepted: 3 October 1997 相似文献
15.
Annual methane emission from Finnish mires estimated from eddy covariance campaign measurements 总被引:4,自引:0,他引:4
K. J. Hargreaves D. Fowler C. E. R. Pitcairn M. Aurela 《Theoretical and Applied Climatology》2001,70(1-4):203-213
Summary Measurements of landscape-scale methane emission were made over an aapa mire near Kaamanen in Finnish Lapland (69° 8′ N,
27° 16′ E, 155 m ASL). Emissions were measured during the spring thaw, in summer and in autumn. No effect of water table position
on CH4 emission was found as the water table remained at or above the surface of the peat. Methane emission fluxes increased with
surface temperature from which an activation energy of −99 kJ mol−1 was obtained. Annual emission from the site, modelled from temperature regression and short-term flux measurements made in
three separate years, was calculated to be 5.5 ± 0.4 g CH4 m−2 y−1 of which 0.6 ± 0.1 g CH4 m−2 y−1 (11%) was released during the spring thaw which lasted 20 to 30 days.
The effect of global warming on the CH4 budget of the site was estimated using the central scenario of the SILMU (Finnish Research Programme on Climate Change) model
which predicts annual mean temperature increases of 1.2, 2.4 and 4.4 °C in 2020, 2050 and 2100, respectively. Maximum enhancements
in CH4 emission due to warming were calculated to be 18, 40 and 84% for 2020, 2050 and 2100, respectively. Actual increases may
be smaller because prediction of changes in water table are highly uncertain.
Received September 17, 1999 Revised October 16, 2000 相似文献
16.
Summary We have examined station data from around the world to study the separate effects of the latitude (between 60° N–40° S),
elevation and distance inland, on the annual-mean screen temperature. In the first 200–400 km from some west coasts, screen
temperatures (after adjustment for elevation) rise inland, reaching a maximum called the ‘thermal-ridge temperature’ Tr. The
rise of temperature within this littoral fringe (of width F) depends mainly on the difference between the sea-surface temperature
off the west coast and the zonal mean. Further inland than such a fringe, adjusted temperatures generally decline eastwards,
approximately linearly, at a rate C. The rate is related to hemisphere and latitude.
Empirical relationships between latitude and the observed coastal sea-surface temperature, the near-shore screen temperature,
Tr, C and F for each continent are used to estimate annual mean temperatures on land. Independent estimates of this kind for
48 places, using a look-up table, differ overall by only 0.7 K from the actual long-term average annual mean temperatures.
This is less than half the error resulting from an assumption of zonal-mean temperatures. Basing estimates on coastal sea-surface
temperatures, instead of the look-up table, results in an average error of 1.0 K for the 48 places. The errors are comparable
with the standard deviation of annual mean temperatures during 30 years or so.
Received March 6, 2001 Revised July 30, 2001 相似文献
17.
Summary The possibility of climate change in the Korean Peninsula has been examined in view of the general increase in greenhouse
gases. Analyses include changes in annual temperature and precipitation. These analyses are supplemented with our observations
regarding the apparent decrease of forest areas.
It was found that there was a 0.96 °C (0.42 °C per decade) increase in annual mean temperature between 1974 and 1997. The
increase in large cities was 1.5 °C but only 0.58 °C at rural and marine stations. The difference in the mean temperature
between large cities and rural stations was small from 1974 to 1981. However, the difference increased from 1982 to 1997.
In particular, the warming appears most significant in winter. Prior to 1982, the lowest temperatures were often −18 °C in
central Korea, and since then the lowest temperatures have been only −12∼−14 °C. Recently, the minimum January temperature
has increased at a rate of 1.5 °C per decade. It is estimated that the increase of1 °C in annual mean temperature corresponds
to about a 250 km northward shift of the subtropical zone boundary.
The analysis of data from 1906 to 1997 indicates a trend of increasing annual precipitation, an increase of 182 mm during
the 92-year peirod, with large year-to-year variations. More than half of the annual mean amount, 1,274 mm, occurred from
June to September.
Meteorological data and satellite observations suggest that changes have occurred in the characteristics of the quasi-stationary
fronts that produce summer rain. In recent years scattered local heavy showers usually occur with an inactive showery front,
in comparison with the classical steady rain for more than three weeks. For instance, local heavy rainfall, on 6 August 1998
was in the range of 123–481 mm. The scattered convective storms resulted in flooding with a heavy toll of approx. 500 people.
The northward shift of the inactive showery front over Korea, and of a convergence zone in central China, correlate with the
increase in temperature. It has been suggested that the decrease in forest areas and the change in ground cover also contribute
to the warming of the Korean Peninsula.
Received March 16, 2000 相似文献
18.
We demonstrate that a hemispherically averaged upwelling-diffusion energy-balance climate model (UD/EBM) can emulate the
surface air temperature change and sea-level rise due to thermal expansion, predicted by the HadCM2 coupled atmosphere-ocean
general circulation model, for various scenarios of anthropogenic radiative forcing over 1860–2100. A climate sensitivity
of 2.6 °C is assumed, and a representation of the effect of sea-ice retreat on surface air temperature is required. In an
extended experiment, with CO2 concentration held constant at twice the control run value, the HadCM2 effective climate sensitivity is found to increase
from about 2.0 °C at the beginning of the integration to 3.85 °C after 900 years. The sea-level rise by this time is almost
1.0 m and the rate of rise fairly steady, implying that the final equilibrium value (the `commitment') is large. The base
UD/EBM can fit the 900-year simulation of surface temperature change and thermal expansion provided that the time-dependent
climate sensitivity is specified, but the vertical profile of warming in the ocean is not well reproduced. The main discrepancy
is the relatively large mid-depth warming in the HadCM2 ocean, that can be emulated by (1) diagnosing depth-dependent diffusivities
that increase through time; (2) diagnosing depth-dependent diffusivities for a pure-diffusion (zero upwelling) model; or (3)
diagnosing higher depth-dependent diffusivities that are applied to temperature perturbations only. The latter two models can be run to equilibrium, and with a climate sensitivity of 3.85 °C, they give sea-level rise
commitments of 1.7 m and 1.3 m, respectively.
Received: 27 April 1999 / Accepted: 13 September 2000 相似文献
19.
Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal)
were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up
over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies
were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared
to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have
resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and
Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would
have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea
(EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen
in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003.
The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods
of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm
over EAS during entire July and hence less rainfall.
The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen
that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation
in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence
less rainfall compared to July 2003. 相似文献
20.
Medha Khole 《Meteorology and Atmospheric Physics》2000,75(1-2):1-9
Summary The year 1997 witnessed one of the most severe El-Ni?o events of the century. However, the All-India Summer Monsoon Rainfall
(AISMR) was 102% of its long period average. In view of recent studies (Tourre and White, 1995, 1997) of detection of ENSO
signal over Indian Ocean, the Sea-Surface Temperature (SST) variation over Indian Ocean (20° N–10° S/50° E–100° E), concurrent
to El-Ni?o event of 1997 is examined. It is observed that during the developing, mature and decaying stages of El-Ni?o, the
North Indian Ocean was abnormally warm. This anomalous warming may be one of the factors responsible for anomalous precipitation
over India during October to December of 1997.
Received August 24, 1999/Revised February 15, 2000 相似文献