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1.
The horizontal and vertical structure of the 3–5-day and 6–9-day easterly waves over West Africa and tropical Atlantic are
investigated. NCEP/NCAR reanalyses are used for the period 1979–1995 to produce a 17-year climatology of both 3–5-day and
6–9-day easterly waves. Composite patterns of convection, wind, temperature and vertical velocity are analysed with respect
to the following: the modulation by 3–5-day and 6–9-day wave regimes; the contrasts between the ITCZ (5°N–10°N) and the Sahelo-Saharan
band (15°N–20°N); the difference between land and ocean, and seasonal variations. Similarities and differences in the characteristics
of the two wave regimes are identified.
Received: 18 August 1999 / Accepted: 14 March 2001 相似文献
2.
S. H. Sajjad Babar Hussain M. Ahmed Khan Asif Raza B. Zaman Ijaz Ahmed 《Climatic change》2009,96(4):539-547
Karachi is the largest city of Pakistan. The temperature change in Karachi is studied in this research by analyzing the time
series data of mean maximum temperature (MMxT), mean minimum temperature (MMiT) and mean annual temperature (MAT) from 1947
to 2005 (59 years). Data is analyzed in three parts by running linear regression and by taking anomalies of all time periods:
(a) whole period from 1947–2005; (b) phase one 1947–1975 and (c) phase two 1976–2005. During 1947 to 2005 MMxT has increased
about 4.6°C, MMiT has no change and MAT has increased 2.25°C. During 1947–1975, MMxT increased 1.9°C, in this period there
is − 1.3°C decrease in MMiT and MAT has raised upto 0.3°C. During 1976–2005, the MMxT, MMiT and MAT increased 2.7°C, 1.2°C
and 1.95°C, respectively. The analysis shows significantly the role of extreme vulnerability of MMxT in rising the temperature
of Karachi than the MMiT. 相似文献
3.
C. V. Singh 《Theoretical and Applied Climatology》2006,84(4):207-211
Summary In this study, Principal Component Analysis (PCA) has been used to identify the major modes of the outgoing long-wave radiation
data for the period (1979–2002) during the Indian monsoon period (June–September), using seasonal mean values over the Indian
region covering 143 grid points (5° N–35° N and 70° E–95° E at 2.5° Longitude–Latitude intervals. The five principal components
explain up to 98.0% of the total variance. The first principal component explains 60% of the total variance with a pronounced
variation in the outgoing long-wave radiation over the region 10° N to 25° N. It appears that the major reason for the monsoon
variability is the intensity and associated fluctuations in the two major semi-permanent seasonal systems. This is largely
indicative of strong seasonal shift of the major area of cloudiness associated with convergence zone. The second principal
component explaining 20% of the total variance exhibits higher positive component loadings along 25° N and east of 80° E.
The possible reason for this could be the synoptic systems such as monsoon depression/lows over the north bay and trough/vortices
off the west-coast in the Arabian sea. 相似文献
4.
Summary By analyzing 12-year (1979–1990) 200 hPa wind data from National Centers for Environmental Prediction-National Center for
Atmospheric Research reanalysis, we demonstrate that the intraseasonal time scale (30–60 days) variability of the Tropical
Easterly Jet (TEJ) reported in individual case studies occurs during most years. In the entrance region (east of ∼70° E),
axis of the TEJ at 200 hPa is found along the near equatorial latitudes during monsoon onset/monsoon revivals and propagates
northward as the monsoon advances over India. This axis is found along ∼5° N and ∼15° N during active monsoon and break monsoon
conditions respectively. Examination of the European Centre for Medium Range Weather Forecasts reanalysis wind data also confirms
the northward propagation of the TEJ on intraseasonal time scales.
During the intraseasonal northward propagations, axis of the TEJ is found about 10°–15° latitudes south of the well-known
intraseasonally northward propagating monsoon convective belts. Because of this 10°–15° displacement, axis of the TEJ arrives
over a location about two weeks after the arrival of the monsoon convection. Systematic shifting of the locations by convection,
low level monsoon flow and TEJ in a collective way during different phases of the monsoon suggests that they all may be related. 相似文献
5.
Forecasting the equatorial Pacific sea surface temperatures by neural network models 总被引:2,自引:0,他引:2
We used neural network models to seasonally forecast the tropical Pacific sea surface temperature anomalies (SSTA) in the
Ni?o 3.4 region (6 °S–6 °N, 120 °W–170 °W). The inputs to the neural networks (i.e., the predictors) were the first seven wind stress empirical orthogonal function
(EOF) modes of the tropical Pacific (20 °S–20 °N, 120 °E–70 °W) for four seasons and the Ni?o 3.4 SSTA itself for the final season. The period of 1952–1981 was used for training the neural
network models, and the period 1982–1992 for forecast validation. At 6-month lead time, neural networks attained forecast
skills comparable to the other El Ni?o-Southern Oscillation (ENSO) models. Our results suggested that neural network models
were viable for ENSO forecasting even at longer lead times of 9 to 12 months. We hypothesized that at these longer leads,
the underlying relationship between the wind stress and Ni?o 3.4 SSTA became increasingly nonlinear. The neural network results
were interpreted in light of current theories, e.g., the role of the “off-equatorial” Rossby waves in triggering the onset
of an ENSO event and the delayed-oscillator theory in the development and termination of an ENSO event.
Received: 31 October 1995 / Accepted: 25 July 1996 相似文献
6.
Summary The Siberian High is the most important atmospheric centre of action in Eurasia during the winter months. Here its variability
and relationship with temperature and precipitation is investigated for the period 1922 to 2000. The pronounced weakening
of the Siberian High during the last ∼ 20 years is its most remarkable feature. Mean temperature, averaged over middle to
high latitude Asia (30° E–140° E, 30° N–70° N), is correlated with the Siberian High central intensity (SHCI) with correlation
coefficient of − 0.58 (1922–1999), and for precipitation, the correlation coefficient is − 0.44 (1922–1998). Taking the Arctic
Oscillation (AO), the SHCI, the Eurasian teleconnection pattern (EU), and the Southern Oscillation (SO) index into account,
72 percent of the variance in temperature can be explained for the period 1949–1997 (for precipitation the variance is 26
percent), with the AO alone explaining 30 percent of the variance, and the Siberian High contributing 24 percent. The precipitation
variance explained by the Siberian High is only 9.8 percent of the total.
Received January 2, 2001 Revised November 24, 2001 相似文献
7.
Last Glacial Maximum climate of the former Soviet Union and Mongolia reconstructed from pollen and plant macrofossil data 总被引:2,自引:2,他引:0
P. E. Tarasov O. Peyron J. Guiot S. Brewer V. S. Volkova L. G. Bezusko N. I. Dorofeyuk E. V. Kvavadze I. M. Osipova N. K. Panova 《Climate Dynamics》1999,15(3):227-240
An improved concept of the best analogues method was used to reconstruct the Last Glacial Maximum (LGM) climate from a set
of botanical records from the former Soviet Union and Mongolia. Terrestrial pollen and macrofossil taxa were grouped into
broad classes – plant functional types (PFTs), defined by the ecological and climatic parameters used in the BIOME1 model.
PFT scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from Eurasia and North America.
In contrast to individual taxa, which exhibit great variability and may not be present in the palaeoassemblages, even in suitable
climates, PFTs are more characteristic of the vegetation types. The modified method thus allows climate reconstruction at
time intervals with partial direct analogues of modern vegetation (e.g. the LGM). At 18 kBP, mean temperatures were 20–29 °C
colder than today in winter and 5–11 °C colder in summer in European Russia and Ukraine. Sites from western Georgia show negative,
but moderate temperature anomalies compared to today: 8–11 °C in January and 5–7 °C in July. LGM winters were 7–15 °C colder
and summers were 1–7 °C colder in Siberia and Mongolia. Annual precipitation sums were 50–750 mm lower than today across northern
Eurasia, suggesting a weakening of the Atlantic and Pacific influences. Reconstructed drought index shows much drier LGM conditions
in northern and mid-latitude Russia, but similar to or slightly wetter than today around the Black Sea and in Mongolia, suggesting
compensation of precipitation losses by lower-than-present evaporation.
Received: 11 May 1998 / Accepted: 25 September 1998 相似文献
8.
Jan Esper Lara Klippel Paul J. Krusic Oliver Konter Christoph C. Raible Elena Xoplaki Jrg Luterbacher Ulf Bntgen 《Climate Dynamics》2020,54(3):1367-1382
The Mediterranean has been identified as particularly vulnerable to climate change, yet a high-resolution temperature reconstruction extending back into the Medieval Warm Period is still lacking. Here we present such a record from a high-elevation site on Mt. Smolikas in northern Greece, where some of Europe’s oldest trees provide evidence of warm season temperature variability back to 730 CE. The reconstruction is derived from 192 annually resolved, latewood density series from ancient living and relict Pinus heldreichii trees calibrating at r1911–2015 = 0.73 against regional July–September (JAS) temperatures. Although the recent 1985–2014 period was the warmest 30-year interval (JAS Twrt.1961–1990 = + 0.71 °C) since the eleventh century, temperatures during the ninth to tenth centuries were even warmer, including the warmest reconstructed 30-year period from 876–905 (+ 0.78 °C). These differences between warm periods are statistically insignificant though. Several distinct cold episodes punctuate the Little Ice Age, albeit the coldest 30-year period is centered during high medieval times from 997–1026 (− 1.63 °C). Comparison with reconstructions from the Alps and Scandinavia shows that a similar cold episode occurred in central Europe but was absent at northern latitudes. The reconstructions also reveal different millennial-scale temperature trends (NEur = − 0.73 °C/1000 years, CEur = − 0.13 °C, SEur = + 0.23 °C) potentially triggered by latitudinal changes in summer insolation due to orbital forcing. These features, the opposing millennial-scale temperature trends and the medieval multi-decadal cooling recorded in Central Europe and the Mediterranean, are not well captured in state-of-the-art climate model simulations. 相似文献
9.
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
10.
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
11.
Summary This paper is to promote a further understanding of the interdecadal mode of the South Pacific. With this focus, we will specifically
aim at better understanding the difference between interannual and interdecadal SSTA modes over South Pacific. We define the
difference of the normalization area-averaged SSTA in the southern extratropical Pacific (160° W–110° W, 40° S–25° S) and
the south subpolar Pacific (150° W–110° W, 60° S–45° S) as the South Pacific interdecadal index (I
spd). It is found that the interannual mode is more coherent than the interdecadal mode in the central and eastern tropical Pacific,
and the interdecadal mode is significant only during boreal winter (DJF). The interdecadal variation of SSTA firstly occurring
in the extratropic South Pacific propagates to the western boundary of the South Pacific, then moves northeast to cross the
equator, and finally reaches the central tropic Pacific. It takes about 8 years to propagate from southeast subtropical Pacific
to the north hemisphere. The previous studies have suggested the mechanism of waves in the subsurface in the South Pacific.
Our study also highlights the Rossby waves play important roles in linkage between the extratropics-tropics South Pacific
SSTA on interdecadal time scales. Moreover, the paper shows that the interdecadal variability originated in the extrotropic
southeast Pacific is mainly induced by interannual variability in the tropic Pacific. 相似文献
12.
Based on calculations of data from FGGE Level III b, a discussion is made of the energy balance in the 40-50 day periodic oscillation over the Asian monsoon region during the 1979 summer. It is found that the main source of 40-50 day periodic perturbation is the monsoon region extending from central South Asia to Southeast Asia. In the upper layer over the North Pacific subtropical area (10-20oN, 150oE-150oW) pres-sure work turns into kinetic energy that maintains 40-50 day periodic perturbation associated with the variation in position and intensity of the mid-Pacific trough. The mean energy budget in the three-dimensional space (0-30oE, 30oE-150oW, 100-1000 hPa) indicates that the 40-50 day periodic perturbation transports kinetic energy to a seasonal mean and a transient perturbation wind field. 相似文献
13.
The spatial and temporal variability of land carbon flux over the past one hundred years was investigated based on an empirical
model directly calculating soil respiration rate. Our model shows that during 1901–1995, about 44-89 PgC (equals to 0.5, 0.9
PgC/yr respectively) were absorbed by terrestrial biosphere. The simulated net ecosystem productivity (NEP) after the 1930s
was close to the estimated value of “ missing C sink” from deconvolution analysis. Most of the total carbon sink happened
during 1951–1985 with the estimated value of 33–50 PgC. Three major sinks were located in the tropics (10°S–10°N), Northern
mid-latitudes (30°–60°N) and Southern subtropics (10°–40°S). During 1940s-mid-1970s, carbon sinks by terrestrial ecosystem
increased with time, and decreased after the mid-1970s. These may be due to the changing of climate condition, as during the
1940s–1970s, temperature decreased and precipitation increased, while after the mid-1970s, an opposite climate situation occurred
with evident increasing in temperature and decreasing in precipitation. Usually, warmer and dryer climate condition is not
favor for carbon absorption by biosphere and even induces net carbon release from soil, while cooler and wetter condition
may induce more carbon sink. Our model results show that the net carbon flux is particularly dependent on moisture / precipitation
effect despite of temperature effect. The changing of climate in the past century may be a possible factor inducing increases
in carbon sink in addition to CO2 and N fertilizer.
This research was funded by CAS One Hundred Talents project and Knowledge Innovation Project of CAS(KZCX2-201). 相似文献
14.
Sensitivity studies of the RegCM3 simulation of summer precipitation, temperature and local wind field in the Caribbean Region 总被引:6,自引:1,他引:6
D. Martínez-Castro R. Porfirio da Rocha A. Bezanilla-Morlot L. Alvarez-Escudero J. P. Reyes-Fernández Y. Silva-Vidal R. W. Arritt 《Theoretical and Applied Climatology》2006,86(1-4):5-22
Summary We present a preliminary evaluation of the performance of three different cumulus parameterization schemes in the ICTP Regional
Climate Model RegCM3 for two overlapping domains (termed “big” and “small”) and horizontal resolutions (50 and 25 km) in the
Caribbean area during the summer (July–August–September). The cumulus parameterizations were the Grell scheme with two closure
assumptions (Arakawa–Schubert and Fritsch–Chappell) and the Anthes-Kuo scheme. An additional sensitivity test was performed
by comparing two different flux parameterization schemes over the ocean (Zeng and BATS).
There is a systematic underestimation of air temperature and precipitation when compared with analyzed data over the big domain
area. Greater (∼2 °C) and smaller (∼0.9 °C) negative temperature biases are obtained in Grell–FC and Kuo convective scheme,
respectively, and intermediate values are obtained in Grell–AS. The small domain simulation produces results substantially
different, both for air temperature and precipitation. Temperature estimations are better for the small domain, while the
precipitation estimations are better for the big domain.
An additional experiment showed that by using BATS to calculate the ocean fluxes in the big domain instead of the Zeng scheme,
precipitation increases by 25% and the share of convective precipitation rose from 18% to 45% of the total, which implies
a better simulation of precipitation. These changes were attributed to an increase of near surface latent heating when using
BATS over the ocean. The use of BATS also reduces the cold bias by about 0.3–0.4 °C, associated with an increase of minimum
temperature.
The behavior of the precipitation diurnal cycle and its relation with sea breeze was investigated in the small domain experiments.
Results showed that the Grell–Arakawa–Schubert closure describes better this circulation as compared with Grell–Fritsch–Chappell
closure. 相似文献
15.
The variations noticed in the atmospheric electric field recorded at Pune (18o32’N, 73o51’E, 559 m ASL), a tropi-cal inland station located in Deccan Plateau, India, during the period 1930-1987, have been examined in relation to the variations observed in the Angstrom turbidity coefficient (β) and selected meteorological parameters. The month-ly and annual mean values of the atmospheric electric field, Angstrom turbidity coefficient (β), rainfall, temperature and relative humidity for the years 1930-1938, 1957-1958, 1964-1965, 1973-1974 and 1987 were considered in the study.The results of the above study indicated gradual increases in the atmospheric electric field over the period of study (1930-1987) which is statistically significant at less than 5% level. The increases noticed during different periods varied from 30 to 109 %. The increase noticed during the period (1930-1938) and (1973-1974) was maximum (109%). The Angstrom turbidity coefficient also showed systematic increases during the period of study, which is consistent. The diurnal curve of the atmospheric electric field at the station by and large, showed a double oscillation, which is generally observed in the continental environments. 相似文献
16.
Tropical cyclone genesis frequency over the western North Pacific simulated in medium-resolution coupled general circulation models 总被引:4,自引:0,他引:4
This study examines the tropical cyclone (TC) genesis frequency over the western North Pacific simulated in atmosphere–ocean
coupled general circulation models from the World Climate Research Programme’s Coupled Model Intercomparison Project phase
3. We first evaluate performances of eight models with atmospheric horizontal resolution of T63 or T106 by analyzing their
daily-mean atmospheric outputs of twentieth-century climate simulations available from the Program for Climate Model Diagnosis
and Intercomparison database. The genesis frequency is validated against the best-track data issued by the Japan Meteorological
Agency. Five of the eight models reproduce realistic horizontal distribution of the TC genesis with a large fraction over
the 10°–20°N, 120°–150°E area. These five high-performance models also realistically simulate the summer–winter contrast of
the frequency. However, detailed seasonal march is slightly unrealistic; four of the models overestimate the frequency in
the early season (May–June) while all of them underestimate the frequency in the mature season (July–September). Reasons for
these biases in the seasonal march for the five high-performance models are discussed using the TC genesis potential (GP)
index proposed by Emanuel and Nolan (in Am Meteor Soc, pp 240–241, 2004). The simulated GP has seasonal biases consistent with those of the TC genesis frequency. For all five models, the seasonal
biases in GP are consistent with those in environmental lower-tropospheric vorticity, vertical wind shear, and relative humidity,
which can be attributed to the simulated behavior of monsoon trough. The observed trough migrates northward from the equatorial
region to reach the 10°–20°N latitudinal band during the mature season and contributes to the TC frequency maximum, whereas
the simulated trough migrates northward too rapidly and reaches this latitude band in the early season, leading to the overestimation
of the TC genesis frequency. In the mature season, the simulated trough reaches as far as 15°–25°N, accompanied by a strong
vertical shear south of the trough, providing an unfavorable condition for TC genesis. It is concluded that an adequate simulation
of the monsoon trough behavior is essential for a better reproduction of the TC frequency seasonal march. 相似文献
17.
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
18.
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
19.
Upper-level cut-off lows in southern South America 总被引:2,自引:0,他引:2
Summary This paper presents a statistical study of the spatial and seasonal distribution and duration of cut-off low systems over
the southern South American region based on the NCEP- NCAR reanalysis data for the period 1979–1988. Cut-off lows were first
objectively determined as minimum geopotential values at the 250 hPa level and then subjectively imposing a cut-off circulation
and a cold core. A total of 171 cut-off low events were detected, being more frequent in austral autumn followed by winter,
spring and summer. There is a preferential region of occurrence in spring and autumn located between 68°–80° W and 30°–45° S.
The Pacific area showed the greatest frequency of occurrence followed by the Atlantic and the continental areas. Most of the
cut-off lows last 2 or 3 days (around 90% of the cases) though there is a tendency of the continental events to be longer.
The cut-off low event developed upwind the Andes on 22–28 September 1986 was selected as a case study. Low-level cold air
advection was the main forcing of the deepening of the upper level low system. 相似文献
20.
Alpine ecosystems in permafrost region are extremely sensitive to climate change. The headwater regions of Yangtze River and
Yellow River of the Qinghai-Tibet plateau permafrost area were selected. Spatial-temporal shifts in the extent and distribution
of tundra ecosystems were investigated for the period 1967–2000 by landscape ecological method and aerial photographs for
1967, and satellite remote sensing data (the Landsat’s TM) for 1986 and 2000. The relationships were analyzed between climate
change and the distribution area variation of tundra ecosystems and between the permafrost change and tundra ecosystems. The
responding model of tundra ecosystem to the combined effects of climate and permafrost changes was established by using statistic
regression method, and the contribution of climate changes and permafrost variation to the degradation of tundra ecosystems
was estimated. The regional climate exhibited a tendency towards significant warming and desiccation with the air temperature
increased by 0.4–0.67°C/10a and relative stable precipitation over the last 45 years. Owing to the climate continuous warming,
the intensity of surface heat source (HI) increased at the average of 0.45 W/m2 per year, the difference of surface soil temperature and air temperature (DT) increased at the range of 4.1°C–4.5°C, and
the 20-cm depth soil temperature within the active layer increased at the range of 1.1°C–1.4°C. The alpine meadow and alpine
swamp meadow were more sensitive to permafrost changes than alpine steppe. The area of alpine swamp meadow decreased by 13.6–28.9%,
while the alpine meadow area decreased by 13.5–21.3% from 1967 to 2000. The contributions of climate change to the degradation
of the alpine meadow and alpine swamp was 58–68% and 59–65% between 1967 and 2000. The synergic effects of climate change
and permafrost variation were the major drivers for the observed degradation in tundra ecosystems of the Qinghai-Tibet plateau. 相似文献