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1.
Summary The precipitation variability over the eastern Amazon (EAM) and northeast Brazil (NEB) during the autumn rainy season (March to May) is diagnosed using raingauge-based weekly data from 1982 to 2001. Since precipitation in this region is remarkably modulated by the combined effects of the Pacific and Atlantic Sea Surface Temperature (SST) anomalies, two extreme and contrasting large-scale climatic scenarios are considered in this study. The unfavorable (UNFAV) scenario, defined by the simultaneous occurrences of the El Niño and northward SST gradient in the intertropical Atlantic and the favorable (FAV) scenario, by the simultaneous occurrence of the La Niña and southward SST gradient in the intertropical Atlantic. UNFAV (FAV) composites with unfiltered data show remarkable changes in both the Walker and the Hadley cells associated with the Atlantic Intertropical Convergence Zone (ITCZ) anomalously weakened (enhanced) thus with deficient (abundant) seasonal rainfall in most of the EAM/NEB. Precipitation variability is identified objectively through EOF analyses performed on the (30–70 day) intraseasonal and submonthly (蠄21 day) filtered weekly precipitation anomalies for 18 autumn seasons (1983 to 2000). The principal components (PC) of the first mode of each analysis show strong oscillations. In particular, the oscillations of the PC series during UNFAV and FAV years reveal that events with anomalously deficient and abundant precipitation over the EAM/NEB occur alternately, even under extreme climatic conditions in the tropical Pacific and Atlantic. Composites based on events with anomalously increased precipitation (objectively selected from the PC series) on intraseasonal and submonthly scales are analyzed separately for the UNFAV and FAV years. These analyses show that for both scenarios the more important rainfall-producing atmospheric mechanism over the EAM/NEB on intraseasonal time scales consists of the establishment of deep convective bands trigged by South Atlantic Convergence Zone events or persistent frontal systems over northeast Brazil. Such a regional pattern is embedded in a large-scale dynamic environment related to the propagation of the Madden-Julian Oscillation over tropical South America. On the other hand, the main rainfall-producing atmospheric mechanism over the EAM/NEB on submonthly time scales is the Atlantic ITCZ during FAV years, whilst weakened Atlantic ITCZ activity may be forced by meridionally elongated mid-latitude wave trains in the upper troposphere during UNFAV years. 相似文献
2.
Future change of climate in South America in the late twenty-first century: intercomparison of scenarios from three regional climate models 总被引：2，自引：1，他引：1
Jose A. Marengo Tercio Ambrizzi Rosmeri P. da Rocha Lincoln M. Alves Santiago V. Cuadra Maria C. Valverde Roger R. Torres Daniel C. Santos Simone E. T. Ferraz 《Climate Dynamics》2010,35(6):1073-1097
Regional climate change projections for the last half of the twenty-first century have been produced for South America, as
part of the CREAS (Cenarios REgionalizados de Clima Futuro da America do Sul) regional project. Three regional climate models
RCMs (Eta CCS, RegCM3 and HadRM3P) were nested within the HadAM3P global model. The simulations cover a 30-year period representing
present climate (1961–1990) and projections for the IPCC A2 high emission scenario for 2071–2100. The focus was on the changes
in the mean circulation and surface variables, in particular, surface air temperature and precipitation. There is a consistent
pattern of changes in circulation, rainfall and temperatures as depicted by the three models. The HadRM3P shows intensification
and a more southward position of the subtropical Pacific high, while a pattern of intensification/weakening during summer/winter
is projected by the Eta CCS/RegCM3. There is a tendency for a weakening of the subtropical westerly jet from the Eta CCS and
HadRM3P, consistent with other studies. There are indications that regions such of Northeast Brazil and central-eastern and
southern Amazonia may experience rainfall deficiency in the future, while the Northwest coast of Peru-Ecuador and northern
Argentina may experience rainfall excesses in a warmer future, and these changes may vary with the seasons. The three models
show warming in the A2 scenario stronger in the tropical region, especially in the 5°N–15°S band, both in summer and especially
in winter, reaching up to 6–8°C warmer than in the present. In southern South America, the warming in summer varies between
2 and 4°C and in winter between 3 and 5°C in the same region from the 3 models. These changes are consistent with changes
in low level circulation from the models, and they are comparable with changes in rainfall and temperature extremes reported
elsewhere. In summary, some aspects of projected future climate change are quite robust across this set of model runs for
some regions, as the Northwest coast of Peru-Ecuador, northern Argentina, Eastern Amazonia and Northeast Brazil, whereas for
other regions they are less robust as in Pantanal region of West Central and southeastern Brazil. 相似文献
3.
Santos RG Martins AS Farias Jda N Horta PA Pinheiro HT Torezani E Baptistotte C Seminoff JA Balazs GH Work TM 《Marine pollution bulletin》2011,62(6):1297-1302
To show the influence of coastal habitat degradation on the availability of food for green turtles (Chelonia mydas), we assessed the dietary preferences and macroalgae community at a feeding area in a highly urbanized region. The area showed low species richness and was classified as degraded. We examined stomach contents of 15 dead stranded turtles (CCL = 44.0 cm (SD 6.7 cm)). The diet was composed primarily of green algae Ulva spp. (83.6%). In contrast, the macroalgae community was dominated by the green alga Caulerpa mexicana. We found a selection for red algae, seagrass and Ulva spp., and avoidance for C. mexicana and brown alga Dictyopteris delicatula. The low diversity of available food items, possibly a result of environmental degradation, likely contributed to the low dietary diversity. The nutritional implications of this restricted diet are unclear. 相似文献
4.
5.
J. A. Marengo T. Ambrizzi G. Kiladis B. Liebmann 《Theoretical and Applied Climatology》2002,73(3-4):223-242
Summary ?An examination is made of the relationships between circulation and convection over South America as related to strong cooling
in southern and southeastern Brazil during austral wintertime. Correlations between sub monthly (2–30 days) near-surface air
temperature in southeastern Brazil reveal the preferred path of a quasi-stationary Rossby wave impinging on to the region
from mid-latitudes and emanating from the tropical western Pacific. The large amplitude upper-level trough in middle latitudes,
which extends into the tropics, has been pointed out as one of the major features of the cold situation. These waves embedded
in westerly flow are an example of wintertime tropical-extratropical interactions leading to cooling in southeastern South
America. This is suggested by the results from the observational and baroclinic-modeling studies presented here. However,
in addition to the right synoptic situation associated with this intermediate modulation, local controls are important on
determining the degree of cooling and the occurrence of freezes.
Received August 25, 2000; revised September 1, 2001; accepted December 1, 2001 相似文献
6.
Based on previous observational studies of the mean atmospheric circulation leading to generalized frosts (GF) in central
Southern South America, it is possible to establish a hypothesis that specific large scale patterns are associated to the
frequency of occurrence of these events through the propagation of Rossby waves remotely excited. This hypothesis is tested
here through a teleconnection analysis for austral winters which present an extreme frequency of occurrence of GF in southeastern
South America, particularly over the Wet Pampa area in Argentina. Rossby wave propagation regions are identified for two basic
states given by the composition of winters with maximum and minimum frequency of GF occurrence, during the 1961–1990 period.
The stationary wavenumber K
s
indicates the regions where the Rossby wave propagation is permitted and those where it will be inhibited (K
s
= 0), highlighting the importance of the jets as waveguides. Nevertheless, differences exist between both basic states analyzed.
These differences indicate that the locations for wave generation and its later evolution are conditioned by the basic state.
Results are validated through a baroclinic model, which simulates the Rossby wave patterns responsible for the teleconnection.
Numerical experiments confirm that the principal wave activity takes place inside the subtropical and polar jets. In particular,
for the basic state with maximum frequency of GF occurrence, the wave trains propagating inside the subtropical and polar
waveguides merge just before entering the continent, as shown by the observations prior to the occurrence of GF events. This
configuration favors the development of an intense south wind anomaly with large meridional extension which results in the
intensification of anticyclonic circulation in southern South America. A conceptual model is presented to summarise all these
results. 相似文献
7.
8.
The total ozone column is well correlated with tropospheric fields such as the heights of the upper tropospheric geopotential
surfaces and thus it can provide useful information on temporal variability in the troposphere. The global availability of
long period satellite measurements of the total ozone column, taken by the TOMS instruments since 1978, provides a valuable
and independent data set for use in studies of seasonal and interannual climate variability. In this study, the global low-frequency
seasonal teleconnections in the observed TOMS data from 1979–91 have been investigated using seasonal teleconnectivity maps
and empirical orthogonal function analysis. They have also been compared with the results from a simulation made with the
atmospheric GCM at Météo-France, having prescribed observed sea surface temperatures for the same period. In the observed
total ozone, strong ENSO-related wave number one longitudinal dipole patterns are seen in both the tropics and in the Southern
Hemisphere extratropics. The model shows much weaker variability in total ozone yet appears to be able to capture similar
teleconnection patterns in the tropics related to ENSO. In the SH extratropics, the model total ozone shows a strong wave
number 3 response rather than the wave number one dipole seen in the observations. A wave number 3 response is also evident
in the 200 hPa geopotential height simulated by the model and in the NCEP analysis, and is consistent with the response in
a linearised barotropic model forced in the Indonesian region. The different responses in the modelled and observed total
ozone, suggest that tropopause effect is not the major factor in the SH extratropics, and it is likely that horizontal ozone
transport also plays a role in this region. Despite a generally poor simulation of the zonal mean total ozone, the model was
able to capture the anomalous strengthening of the SH stationary waves during austral spring of 1988, related to an intense
stratosphere sudden warming.
Received: 21 October 1996 / Accepted: 11 September 1997 相似文献
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10.
Gyrlene Aparecida Mendes da Silva Anita Drumond T��rcio Ambrizzi 《Theoretical and Applied Climatology》2011,106(3-4):307-319
In austral summer, the observed El Ni?o (EN) events during warm Pacific Decadal Oscillation (PDO) phases (PDO(+)) exhibited large anomalous upper level wave patterns in response to larger Sea Surface Temperature (SST) anomalies in the Equatorial Pacific and Atlantic Oceans compared with SST anomalies in EN events during cold PDO phases (PDO(?)). The precipitation anomalies in PDO(+) EN are increased over Southeastern South America (SESA) associated with the intensification of the moisture flux convergence in this region. The PDO(?) EN events exhibit positive precipitation anomalies only over southern SESA, while negative anomalies were observed in the north. Downward motion and anomalous divergence over central eastern Brazil may have contributed to the weakening of the northwesterly moisture flux convergence associated with the South American Low Level Jet (SALLJ) over the subtropics. The extratropical cyclones showed higher frequency and lower central pressures in southern Brazil, Uruguay, northeastern Argentina, and Southwest Atlantic Ocean during the PDO(+) EN events compared with the PDO(?) EN events. Such increase in the frequency and intensity of cyclogenesis cases seems to be in accordance with the anomalous moisture flux convergence over the SESA and associated reduction in the Sea Level Pressure observed during PDO(+) EN events. In order to investigate the impact of a canonical El Ni?o event over South America under different PDO phases, two numerical experiments were done with an Atmospheric General Circulation Model. Global SST and ice sea fields average over years characterized by (a) PDO(+) and (b) PDO(?) were considered as climatologically fields, and a composite of anomalies of SST of all El Ni?o events observed in 1950?C1999 was added in the region 20oS?C20oN;120oW?C175oW of both ??climatologies.?? The differences in experiments suggest that a canonical EN may produce significant different anomalous atmospheric patterns associated with distinct PDO climatologies. The more significant differences are simulated over extreme northern and eastern Brazil. Additional numerical experiments isolating the observed variability of SST over several oceanic basins during different PDO phases will be conducted to study their particular role on the South American climate. 相似文献