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1.
Daily rainfall variability over southern Africa (SA) and the southwest Indian Ocean (SWIO) during the austral summer months
has recently been described objectively for the first time, using newly derived satellite products. The principle mode of
variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region.
These represent the location of cloud bands associated with tropical temperate troughs (TTT). This study objectively identifies
major TTT events during November to February, and on the basis of composites off NCEP reanalysis data describes the associated
atmospheric structure. The two phases of the rainfall dipole are associated with markedly contrasting circulation patterns.
There are also pronounced intra-seasonal variations. In early summer the position of the temperate trough and TTT cloud band
alternates between the SWIO and southwest Atlantic. In late summer the major TTT axis lies preferentially over the SWIO, associated
with an eastward displacement in the Indian Ocean high. In all months, positive events, in which the TTT cloud band lies primarily
over the SWIO, are associated with large-scale moisture flux anomalies, in which convergent fluxes form a pronounced poleward
flux along the cloud band. This suggests that TTT events are a major mechanism of poleward transfer of energy and momentum.
Moisture transport occurs along three principle paths: (1) the northern or central Indian Ocean (where anomalous fluxes extend
eastward to the Maritime Continent), (2) south equatorial Africa and the equatorial Atlantic, (3) from the south within a
cyclonic flow around the tropical-temperate trough. The relative importance of (2) is greatest in late summer. Thus, synoptic
scale TTT events over SA/SWIO often result from large-scale planetary circulation patterns. Hovmoeller plots show that TTT
development coincides with enhanced tropical convection between 10°–30°E (itself exhibiting periodicity of around 5 days),
and often with convergence of eastward and westward propagating convection around 40°E. Harmonic analysis of 200 hPa geopotential
anomalies show that TTT features are forced by a specific zonally asymmetric wave pattern, with wave 5 dominant or significant
in all months except February when quasi-stationary waves 1, 2 and 3 dominate. These findings illustrate the importance of
tropical and extratropical dynamics in understanding TTT events. Finally, it is suggested that in November–Januar TTT rainfall
over SA/SWIO may be in phase with similar rainfall dipole structures observed in the South Pacific and South Atlantic convergence
zones.
Received: 11 August 1998 / Accepted: 28 May 1999 相似文献
2.
Tropical-extratropical cloud band systems over southern Africa, known as tropical temperate troughs (TTTs), are known to contribute substantially to South African summer rainfall. This study performs a comprehensive assessment of the seasonal cycle and rainfall contribution of TTTs by using a novel object-based strategy that explicitly tracks these systems for their full life cycle. The methodology incorporates a simple assignment of station rainfall data to each event, thereby creating a database containing detailed rainfall characteristics for each TTT. This is used to explore the importance of TTTs for rain days and climatological rainfall totals in October–March. Average contributions range from 30 to 60 % with substantial spatial heterogeneity observed. TTT rainfall contributions over the Highveld and eastern escarpment are lower than expected. A short analysis of TTT rainfall variability indicates TTTs provide substantial, but not dominant, intraseasonal and interannual variability in station rainfall totals. TTTs are however responsible for a high proportion of heavy rainfall days. Of 52 extreme rainfall events in the 1979–1999 period, 30 are associated with these tropical-extratropical interactions. Cut-off lows were included in the evolution of 6 of these TTTs. The study concludes with an analysis of the question: does the Madden-Julian Oscillation influence the intensity of TTT rainfall over South Africa? Results suggest a weak but significant suppression (enhancement) of intensity during phase 1(6). 相似文献
3.
This study examines southern African summer rainfall and tropical temperate troughs (TTTs) simulated with three versions of an atmospheric general circulation model differing only in the convection scheme. All three versions provide realistic simulations of key aspects of the summer (November–February) rainfall, such as the spatial distribution of total rainfall and the percentage of rainfall associated with TTTs. However, one version has a large bias in the onset of the rainy season. Results from self-organizing map (SOM) analysis on simulated daily precipitation data reveals that this is because the occurrence of TTTs is underestimated in November. This model bias is not related to westerly wind shear that provides favorable conditions for the development of TTTs. Rather, it is related to excessive upper level convergence and associated subsidence over southern Africa. Furthermore, the model versions are shown to be successful in capturing the observed drier (wetter) conditions over the southern African region during El Niño (La Niña) years. The SOM analysis reveals that nodes associated with TTTs in the southern (northern) part of the domain are observed less (more) often during El Niño years, while nodes associated with TTTs occur more frequently during La Niña years. Also, nodes associated with dry conditions over southern Africa are more (less) frequently observed during El Niño (La Niña) years. The models tend to perform better for La Niña events, because they are more successful in representing the observed frequency of different synoptic patterns. 相似文献
4.
The southwestern Indian Ocean (SWIO) is characterized by significant climate variability and frequent tropical cyclones (TC). Year-to-year fluctuations of TC and associated oceanic and atmospheric fields in the period 1961–2002 are studied with reanalysis data as composites and cross-correlations, with wavelet filtering and cross-modulus analysis, and by hovmoller analysis and multi-variate statistical modeling. Observational limitations in the early part of the record are recognized. An intense TC-days index is formed and is characterized by quasi-biennial to decadal cycles that relate to ocean Rossby waves and high latitude atmospheric circulations, respectively. New variables are uncovered that significantly improve the seasonal prediction of SWIO TC. One predictor is the geopotential height in the SE Pacific, which explains 31% of SWIO TC variability. It foretells of downstream oscillations in the sub-tropical jet stream, which govern wind shear, an equatorial duct and attendant circulation anomalies over the SWIO. An anti-phase association between Amazon convection and intense TCs is found to be related to the Atlantic Zonal Circulation. Drought across the Amazon is related to an increase in TC activity in the SWIO, when zonal wind anomalies over the Atlantic become upper easterly/lower westerly. This feature is related to Pacific Ocean El Niño Southern Oscillation phase. A La Niña signal favors TC development through a westward propagating cyclonic circulation and downweling Rossby wave in the South Indian Ocean that enhances thermodynamic energy. It is recommended to repeat this analysis every few years to determine whether teleconnections evolve due to climate drift or improving observations. 相似文献
5.
This study aims at presenting various methodologies to separate the reproducible and irreproducible components of seasonal and intraseasonal climate variability simulated by a regional climate model over Southern Africa (south of 15°S), during an austral summer rainy season representative of the climatology. To that end, a 30-member ensemble simulation is performed using WRF laterally forced by the ERA40 reanalyses. Retained metrics include the analysis of weather regimes, signal-to-noise ratio, inter-member standard deviation and coefficient of variation. At the seasonal timescale, simulated rainfall amounts generally show a strong reproducibility, except in the subtropics and over the southern part of the Mozambique Channel. There, the number of rainy days is roughly similar in all members, while their average intensity varies extensively. At the intraseasonal timescale, the chronology of weather regimes, derived from the 500?hPa geopotential height, is highly reproducible. Rainfall variability is much less reproducible, especially in the central parts of the domain and near its outflow boundaries. Analysis of a South African regional index nonetheless indicates that both wet and dry spells tend to be accurately simulated and occur in phase in most members, demonstrating that they are embedded in large-scale variability patterns. Internal variability is lastly related to the lateral forcings along the domain boundaries. An objective classification of inflow/outflow mass fluxes allows identification of the recurrent synoptic configurations that favor strong or weak regional reproducibility. The main uncertainties concern the basic morphological features of rain-bearing systems (i.e., their spatial extension, location and propagation speed). Consequences for tropical-temperate interactions are then discussed. 相似文献
6.
The capability of a current state-of-the-art regional climate model for simulating the diurnal and annual cycles of rainfall over a complex subtropical region is documented here. Hourly rainfall is simulated over Southern Africa for 1998–2006 by the non-hydrostatic model weather research and forecasting (WRF), and compared to a network of 103 stations covering South Africa. We used five simulations, four of which consist of different parameterizations for atmospheric convection at a 0.5 × 0.5° resolution, performed to test the physic-dependency of the results. The fifth experiment uses explicit convection over tropical South Africa at a 1/30° resolution. WRF simulates realistic mean rainfall fields, albeit wet biases over tropical Africa. The model mean biases are strongly modulated by the convective scheme used for the simulations. The annual cycle of rainfall is well simulated over South Africa, mostly influenced by tropical summer rainfall except in the Western Cape region experiencing winter rainfall. The diurnal cycle shows a timing bias, with atmospheric convection occurring too early in the afternoon, and causing too abundant rainfall. This result, particularly true in summer over the northeastern part of the country, is weakly physic-dependent. Cloud-resolving simulations do not clearly reduce the diurnal cycle biases. In the end, the rainfall overestimations appear to be mostly imputable to the afternoon hours of the austral summer rainy season, i.e., the periods during which convective activity is intense over the region. 相似文献
7.
Predictability of the subtropical dipole modes is assessed using the SINTEX-F coupled model. Despite the known difficulty in predicting subtropical climate due to large internal variability of the atmosphere and weak ocean–atmosphere coupling, it is shown for the first time that the coupled model can successfully predict the South Atlantic Subtropical Dipole (SASD) 1 season ahead, and the prediction skill is better than the persistence in all the 1–12 month lead hindcast experiments. There is a prediction barrier in austral winter due to the seasonal phase locking of the SASD to austral summer. The prediction skill is lower for the Indian Ocean Subtropical Dipole (IOSD) than for the SASD, and only slightly better than the persistence till 6-month lead because of the low predictability of the sea surface temperature anomaly in its southwestern pole. However, for some strong IOSD events in the last three decades, the model can predict them 1 season ahead. The co-occurrence of the negative SASD and IOSD in 1997/1998 austral summer can be predicted from July 1st of 1997. This is because the negative sea level pressure anomalies over the South Atlantic and the southern Indian Ocean in September–October (November–December) that trigger the occurrence of the negative SASD and IOSD are related to the well predicted tropical Indian Ocean Dipole (El Niño/Southern Oscillation). Owing to the overall good performances of the SINTEX-F model in predicting the SASD, some strong IOSD, and El Niño/Southern Oscillation, the prediction skill of the southern African summer precipitation is high in the SINTEX-F model. 相似文献
8.
Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF 总被引：2，自引：2，他引：0
This study aims at quantifying seasonal biases of regional climate model outputs during southern African summer, against a dense in situ measurement network (daily rain-gauge and surface air temperature records, and 12?h UTC radiosondes), and uncertainties associated with some physical parameterizations. Using the non-hydrostatic Advanced Research Weather Forecast (WRF) laterally forced by ERA40 reanalysis, twenty-seven experiments configured with three schemes of cumulus (CU), planetary boundary layer (PBL) and microphysics (MP), are performed at 35?km horizontal resolution during the core of a summer rainy season (December 1993 to February 1994 season) representative of the South African rainfall climatology. WRF simulates accurately seasonal large-scale rainfall patterns, as well as seasonal gradients of South African rainfall and 2-m temperature, and seasonal vertical profiles of the air temperature and humidity. However seasonal biases fluctuate strongly from an experiment to another, denoting considerable uncertainties generated by the physical package. Rainfall amounts are the most sensitive parameter to the tested schemes. Their geography, intensity, and intraseasonal characteristics are predominantly sensitive to CU schemes, and much less to PBL and MP schemes. Some CU-PBL combinations produce additive effects, which can dramatically either reduce or increase biases. Satisfactory configurations are found for South African climate, which would not have been possible without testing numerous physical parameterizations. 相似文献
9.
Moisture exchange between the South Atlantic and southern Africa is examined in this study through zonal moisture transport.
Along the west coast of southern Africa, a multivariate analysis of the zonal flow of moisture computed from NCEP-DOE AMIP
II Re-analyses reveals a primary mode of variability typical of variations in intensity and of the latitudinal migration of
the circulation associated with the midlatitude westerlies and the South Atlantic anticyclone. In austral summer (January–February),
this mode, referred to as the South Atlantic midlatitude mode, is found to be well correlated with rainfall over southern
Africa (i.e. to the south of the upper lands surrounding the Congo basin). Its positive/negative phases are found to correspond
with surface pressures changes over the South Atlantic region in austral summer when the South Atlantic anticyclone is shifted
northward/southward respectively. Such changes are accompanied by dipole-like SST anomalies in the midlatitude South Atlantic
Ocean, while simultaneous SST anomalies with a similar structure are also found over South Indian Ocean regions. In January–February,
positive/negative events linked to the South Atlantic midlatitude mode are marked by meridional shifts (northward/southward)
and weakening/strengthening of the ITCZ over the southern tropics, together with modulations in intensity (weakened/sustained)
of the Angola low, which could act as a tropical source of moisture for Tropical Temperate Troughs (TTTs). In association
with a strengthened/weakened zonal component of the southern extension of the African Easterly Jet (AEJ), this could modulate
the meridional transfer of moisture south of 15°S to the advantage/detriment of Angolan coastal regions, where above/below
rainfall are expected. Variations in the latitudinal position (northward/southward) of the South Atlantic anticyclone, and
thus of the midlatitude westerlies, are also found to reduce/favour moisture advection towards southern Africa subtropics
allowing the southern Indian trades to penetrate less/more over the subcontinent south of 25°S. This would create a situation
where convection processes are inhibited/supported within the SICZ/TTTs region resulting in drier/wetter conditions locally
for positive/negative events respectively. 相似文献
10.
Satyaban B. Ratna Swadhin Behera J. Venkata Ratnam Keiko Takahashi Toshio Yamagata 《Climate Dynamics》2013,41(2):421-441
Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like structure in the lower troposphere over southern Africa and the adjoining Indian Ocean. Therefore, the index considers physical processes that occur over southern Africa, adjoining the Atlantic and Indian Oceans to depict the variability of the TTT events. Unusually strong TTT events are identified when the standard deviations of the TTT indices defined by the OLR and wind anomalies in the selected regions are above 1.5 and 0.5 respectively. After applying this criterion and filtering out consecutive events, 55 TTT events are identified during the study period of December–January–February seasons from 1980–1981 to 2009–2010. From the composite analyses of those 55 events, it is found that the TTTs evolve with suppressed (enhanced) convection over the southwest Indian Ocean adjacent to Madagascar (southern Africa). The suppressed convection is, in turn, found to be associated with the enhanced convection around Sumatra in the southeast tropical Indian Ocean. This may explain why more TTT events occur in La Niña years as compared to El Niño years. Time evolution of the canonical TTT event shows that it starts 3 days prior to the mature phase of the event, suggesting possible predictability. After reaching a matured state, the system moves east toward the Indian Ocean and decays within the subsequent couple of days. In addition, the intertropical convergence zone (ITCZ) structure changes over Southern Africa/Madagascar during the TTT event and remains similar to climatology over other regions. The results indicate that the continental part of the ITCZ intensifies prior to the TTT event and then spreads southward following the mid-latitude influence during and after the event. 相似文献
11.
We present an analysis of a regional simulation of present-day climate (1981–1990) over southern South America. The regional
model MM5 was nested within time-slice global atmospheric model experiments conducted by the HadAM3H model. We evaluate the
capability of the model in simulating the observed climate with emphasis on low-level circulation patterns and surface variables,
such as precipitation and surface air mean, maximum and minimum temperatures. The regional model performance was evaluated
in terms of seasonal means, seasonal cycles, interannual variability and extreme events. Overall, the regional model is able
to capture the main features of the observed mean surface climate over South America, its seasonal evolution and the regional
detail due to topographic forcing. The observed regional patterns of surface air temperatures (mean, maxima and minima) are
well reproduced. Biases are mostly within 3°C, temperature being overestimated over central Argentina and underestimated in
mountainous regions during all seasons. Biases in northeastern Argentina and southeastern Brazil are positive during austral
spring season and negative in other seasons. In general, maximum temperatures are better represented than minimum temperatures.
Warm bias is larger during austral summer for maximum temperature and during austral winter for minimum temperature, mainly
over central Argentina. The broad spatial pattern of precipitation and its seasonal evolution are well captured; however,
the regional model overestimates the precipitation over the Andes region in all seasons and in southern Brazil during summer.
Precipitation amounts are underestimated over the La Plata basin from fall to spring. Extremes of precipitation are better
reproduced by the regional model compared with the driving model. Interannual variability is well reproduced too, but strongly
regulated by boundary conditions, particularly during summer months. Overall, taking into account the quality of the simulation,
we can conclude that the regional model is capable in reproducing the main regional patterns and seasonal cycle of surface
variables. The present reference simulation constitutes the basis to examine the climate change simulations resulting from
the A2 and B2 forcing scenarios which are being reported in a separate study. 相似文献
12.
Yuanhong Guan Bohua Huang Jieshun Zhu Zeng-Zhen Hu James L. Kinter III 《Climate Dynamics》2014,43(3-4):1141-1157
The mechanism of the South Pacific Ocean Dipole (SPOD) mode is examined, using a 50-year simulation of the Climate Forecast System, version 2 (CFSv2) and 50-year observation-based ocean–atmosphere analyses (1961–2010). It is shown that the SPOD, a sea surface temperatures (SST) seesaw between the subtropics and extratropics, is the dominant mode of the interannual variability in the South Pacific in both observations and CFSv2 simulation. CFSv2 also reproduces the seasonal phase-locking of the observed SPOD, with the anomaly pattern developing in austral spring, peaking in summer, and decaying in autumn. Composite analyses based on both observational and model data suggest that in the warm phase of SPOD, positive SST anomaly (SSTA) is initiated by weakened westerly winds over the central South Pacific in austral spring, which suppress the surface evaporative heat loss and reduce the oceanic mixed layer depth, both contributing to the SST warming. The wind-SST-mixed layer anomalies then evolve coherently over the next two seasons while the cold SSTA develops to the north. The wind perturbations are in turn a response to El Niño-Southern Oscillation (ENSO), which forces an atmospheric planetary wave train, the Pacific-South American pattern, emanating from an anomalous heat source in the tropical western Pacific. Moreover, SPOD is significantly correlated with the southern annular mode (SAM) while the latter is also significantly correlated with the ENSO index. This suggests that ENSO’s influence on the SPOD may be partially conveyed through SAM. 相似文献
13.
Performance assessment of three convective parameterization schemes in WRF for downscaling summer rainfall over South Africa 总被引：2，自引：1，他引：1
Satyaban B. Ratna J. V. Ratnam S. K. Behera C. J. deW. Rautenbach T. Ndarana K. Takahashi T. Yamagata 《Climate Dynamics》2014,42(11-12):2931-2953
Austral summer rainfall over the period 1991/1992 to 2010/2011 was dynamically downscaled by the weather research and forecasting (WRF) model at 9 km resolution for South Africa. Lateral boundary conditions for WRF were provided from the European Centre for medium-range weather (ECMWF) reanalysis (ERA) interim data. The model biases for the rainfall were evaluated over the South Africa as a whole and its nine provinces separately by employing three different convective parameterization schemes, namely the (1) Kain–Fritsch (KF), (2) Betts–Miller–Janjic (BMJ) and (3) Grell–Devenyi ensemble (GDE) schemes. All three schemes have generated positive rainfall biases over South Africa, with the KF scheme producing the largest biases and mean absolute errors. Only the BMJ scheme could reproduce the intensity of rainfall anomalies, and also exhibited the highest correlation with observed interannual summer rainfall variability. In the KF scheme, a significantly high amount of moisture was transported from the tropics into South Africa. The vertical thermodynamic profiles show that the KF scheme has caused low level moisture convergence, due to the highly unstable atmosphere, and hence contributed to the widespread positive biases of rainfall. The negative bias in moisture, along with a stable atmosphere and negative biases of vertical velocity simulated by the GDE scheme resulted in negative rainfall biases, especially over the Limpopo Province. In terms of rain rate, the KF scheme generated the lowest number of low rain rates and the maximum number of moderate to high rain rates associated with more convective unstable environment. KF and GDE schemes overestimated the convective rain and underestimated the stratiform rain. However, the simulated convective and stratiform rain with BMJ scheme is in more agreement with the observations. This study also documents the performance of regional model in downscaling the large scale climate mode such as El Niño Southern Oscillation (ENSO) and subtropical dipole modes. The correlations between the simulated area averaged rainfalls over South Africa and Nino3.4 index were ?0.66, ?0.69 and ?0.49 with KF, BMJ and GDE scheme respectively as compared to the observed correlation of ?0.57. The model could reproduce the observed ENSO-South Africa rainfall relationship and could successfully simulate three wet (dry) years that are associated with La Niña (El Niño) and the BMJ scheme is closest to the observed variability. Also, the model showed good skill in simulating the excess rainfall over South Africa that is associated with positive subtropical Indian Ocean Dipole for the DJF season 2005/2006. 相似文献
14.
Hydrological issues in lateral boundary conditions for regional climate modeling: simulation of east asian summer monsoon in 1998 总被引：1，自引：0，他引：1
The atmospheric branch of the hydrological cycle associated with the East Asian summer monsoon is intricate due to its distinct
land-sea configurations: the highest mountains are to its west, the oceans are to its south and east, and mid-latitude influences
come from its north. Here we use the weather research and forecast (WRF) model to demonstrate that using two different large-scale
driving fields, derived from the NCEP/DOE R2 and ERA40 reanalysis data and the same model configuration yielded remarkable
differences. We found that the differences are primarily caused by uncertainties in the water vapor influx across the lateral
boundaries in the reanalyses. The summer-mean water vapor convergence into the model domain computed from the ERA40 reanalysis
is 47% higher than that from the R2 reanalysis. The largest uncertainties in moisture transport are found in the regions of
the Philippine Sea and the Bay of Bengal, where the moisture transport has the most significant impacts on the East Asian
summer monsoon rainfall distribution. The sensitivity test results suggest that the biases in the seasonal mean, seasonal
march of the rain band, and individual rainfall events may be reduced by using an “ensemble” average of R2 and ERA40 as lateral
boundary forcing. While the large-scale forcing field does not conserve water vapor, the WRF simulation conserves water vapor
in the inner model domain. The regional model simulation has corrected the biases in the total amount and the month-to-month
distribution of precipitation in the large-scale driving field. However, RCM’s daily precipitation is poorer than that in
the reanalysis filed. Since the RCM solutions may sensitively depend on the reanalysis forcing, intercomparison of models’
performance based on a single set of the reanalysis may not be reliable. This calls for attention to reshape our strategy
for validation of RCMs. 相似文献
15.
Distinct quasi-biweekly features of the subtropical East Asian monsoon during early and late summers 总被引：2，自引：0，他引：2
Jing Yang Qing Bao Bin Wang Dao-Yi Gong Haozhe He Miao-Ni Gao 《Climate Dynamics》2014,42(5-6):1469-1486
Using Global Precipitation Climatology Project daily rainfall and ERA interim reanalysis data, we investigate the distinct characteristic of quasi-biweekly variation (QBV: 12–20 days) over East Asia (EA) during early (June 10–July 20) and late (July 21–August 31) summer. The QBV maximum variance is found over the core region of EA (30°–40°N, 110°–130°E), which includes eastern China (lower reaches of the Yellow, Huaihe, and Yangtze rivers) and the Korean Peninsula. At both its peak wet and dry phases, QBV over the core region has a baroclinic structure, but with different spatial distributions, different lower-level prevalent wind anomalies, and different upper-level major circulation anomalies in the two subseasons. Meanwhile, the two subseasons have different propagating tracks prior to reaching the peak phase, and different precursors associated with the local genesis of QBV. Furthermore, during the transition from the peak dry to peak wet phase of QBV, the major monsoon circulations have different behaviors that tropical monsoon trough extends eastward in early summer but retreats westward in late summer and the South Asia high (SAH) and western North Pacific (WNP) subtropical high move toward (away from) each other in early (late) summer. The abrupt change of mean state in mid to late July, which includes the northward migration of westerly jet, SAH and WNP, and the weakening and broken of westerly jet, is considered the root cause of the change in behavior of QBV. Finally, we indicate that the tropical monsoon trough and midlatitude westerly jet are possible sources of QBV over subtropical EA in both subseasons and provide useful guidance for 2–3 week predictions over EA. 相似文献
16.
M. T. Kayano 《Meteorology and Atmospheric Physics》2003,83(3-4):263-276
Summary ?Evolving aspects of the dominant high-frequency modes of the 925-hPa v-component and precipitable water in the Tropical South
American and Atlantic sector are studied for the austral summer and winter seasons. Their relations to the precipitation anomalies
over the equatorial South America are also investigated. The highest percentages of the total variance contained in the high-frequency
time-scale for the 925-hPa v-component have a clear seasonal dependency such that they are confined in the Tropical South
Atlantic (TSA) during the austral summer and in the Tropical North Atlantic (TNA) during the austral winter. The high-frequency
variability for the TSA during the austral summer stems from the combined effects of equatorward incursions of midlatitude
synoptic and transient wave systems, equatorial trades and westward traveling disturbances in equatorial latitudes. All these
systems together have a pronounced effect in modulating the summer precipitation over northeastern South America, though the
isolated effect of the easterly waves is weak. In contrast, the high-frequency variability for the TNA during the austral
winter is mainly due to wave-type westward traveling tropical disturbances. These disturbances have an important role in modulating
the daily precipitation of northern part of the South America during the austral winter.
Received June 28, 2002; accepted July 24, 2002
Published online: March 20, 2003 相似文献
17.
Simulation of China Summer Precipitation Using a Regional Air-Sea Coupled Model 总被引：1，自引：0，他引：1 
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下载免费PDF全文 A regional air-sea coupled model based on the regional climate model(RegCM3)and the regional oceanic model POM(Princeton Ocean Model)is developed and a series of experiments are performed to verify the ability of the coupled model in simulating the summer precipitation over China from 1963 to 2002.The results show that the space correlation coefficients between the GISST(Global Ice and Sea Surface Temperature)data and the simulated SST by RegCM3-POM exceed 0.9.Compared with the uncoupled experiments,the coupled model RegCM3-POM has a better performance in simulating the mean summer(June to August)precipitation over China,and the distribution of the rainband in the coupled model is more accurate.The improvement of the rainfall simulation is significant over the Yangtze River Valley and in South China.The rainbelt intraseasoaal evolution over eastern China in summer indicates that the simulation ability of RegCM3-POM is improved in comparison with the uncoupled model.The interannual summer rainfall variation over eastern China simulated by RegCM3-POM is in accordance with observation,while the spatial pattern of the interannual summer rainfall variation in the uncoupled model is inaccurate.The simulated correlation coefficient between the summer rainfall in the uncoupled model RegCM3 and observation is0.30 over the Yangtze River Valley and 0.29 in South China.The coefficient between the rainfall in the coupled RegCM3-POM and observation is 0.48 over the Yangtze River Valley and 0.61 in South China.The RegCM3-POM has successfully simulated the correlation coefficients between summer rainfall in the Yangtze River Valley and SST anomalies of the Bay of Bengal,South China Sea,and the Kuroshio area,whereas the uncoupled model RegCM3 fails to reproduce this relationship.The study further shows that the monsoon circulation and the path of the moisture transport flux simulated by RegCM3-POM are in good agreement with the NCEP/NCAR data. 相似文献
18.
亚澳季风异常与ENSO准四年变化的联系分析 总被引：2，自引：0，他引：2
分析了赤道地区纬向风的年际变化特征，以及亚澳季风与ENSO在各个位相的联系。结果表明：赤道纬向风变化与中东太平洋海温变化在准四年周期上是强烈耦合的；在El Eino期间东亚冬季风弱，夏季风强，而南亚夏季风弱，反之，在La Nina期间东亚冬季风强，夏季风弱，而南亚夏季风强；东亚地区的异常北风有利于西太平洋西风异常爆发，使得东太平洋海温升高，但只有随后在中东太平洋出现持续性西风异常，El Nino才能发展，其中来自太平洋中部的异常北风（并不是来自东亚大陆地区）和南太平洋中部的异常南风的辐合对中东太平洋出现持续性西风异常起重要的作用，尤其是澳大利亚东北部的季风异常的影响更为显。 相似文献
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Regional coupled modeling is one of the frontiers of regional climate modeling, but intercomparison has not been well coordinated. In this study, a community regional climate model, WRF4, with a resolution of 15 km, was coupled with a high-resolution(0.1°) North Pacific Ocean model(LICOM_np). The performance of the regional coupled model,WRF4_LICOM, was compared to that of another regional coupled model, RegCM4_LICOM, which was a coupling of version 4 of the Regional Climate Model(RegCM4) with LICOM_np. The analysis focused on the 2005 western North Pacific summer monsoon rainfall. The results showed that the regional coupled models with either RegCM4 or WRF4 as their atmospheric model component simulated the broad features over the WNP reasonably well. Quantitative intercomparison of the regional coupled simulations exhibited different biases for different climate variables.RegCM4_LICOM exhibited smaller biases in its simulation of the averaged June–July–August SST and rainfall, while WRF4_LICOM better captured the tropical cyclone(TC) intensity, the percentage contributions of rainfall induced by TCs to the total rainfall, and the diurnal cycle of rainfall and stratiform percentages, especially over land areas. The different behaviors in rainfall simulated by the two models were partly ascribed to the behaviors in the simulated western North Pacific subtropical high(WNPSH). The stronger(weaker) WNPSH in WRF4_LICOM(RegCM4_LICOM) was driven by overestimated(underestimated) diabatic heating, which peaked at approximately 450 hPa over the region around the Philippines in association with different condensation–radiation processes. Coupling of WRF4 with LIOCM is a crucial step towards the development of the next generation of regional earth system models at the Chinese Academy of Sciences. 相似文献