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1.
Abstract This paper presents the seasonal dependence of the stationary and transient eddies of the GLAS/UMD GCM from a two‐year annual cycle integration. The simulated Northern Hemisphere stationary waves are realistic in winter (below 250 mb) and in spring and fall; in winter a large anomalous ridge over the date‐line is noted above 250 mb. The model does not simulate the winter barotropic trough over eastern Canada. In summer the mid‐latitude stationary waves are poorly simulated (possibly owing to anomalous summer rainfall), but the monsoonal structure in the tropics is captured. The stationary wave field at 500 mb in the Southern Hemisphere is not well simulated, with the range of season‐to‐season variability being much larger than observed. The zonally averaged stationary wave rms is realistic below 200 mb in winter and spring, but is less so in summer and autumn, possibly due to erroneous summertime precipitation. The geographical distributions of 500‐mb transient and band‐pass height rms, of transient 850‐mb heat flux and of 200‐mb momentum flux in the Northern Hemisphere are well simulated except for summer. The latitude‐height dependence of height rms and low‐level transient heat flux is realistic in both summer and winter, but the transient momentum flux is not well simulated in summer. The mid‐level transient heat flux is too strong. The overall pattern of transient activity at 500 mb in the Southern Hemisphere is reasonable in the GCM, although there is too much variability in the eastern Pacific, while the observed peak in rms in the New Zealand sector is displaced eastwards in the GCM. The latitude‐height dependence of transient height rms and transient fluxes of heat and momentum looks quite realistic, and is similar in accuracy to the Northern Hemispheric results. 相似文献
2.
Kevin Hamilton 《大气与海洋》2013,51(1):40-54
Abstract The zonal wavenumber spectra of the geopotential heights of the 300‐ and 500‐mb surfaces in the Southern Hemisphere were determined for each month between May 1972 and November 1979 using daily operational analyses produced by the Australian Bureau of Meteorology. During over one‐quarter of the “summer” months (November through March) there are very prominent peaks at zonal wavenumber five in the region of the mid‐latitude jet (～35–60°S). Frequently wavenumber five totally dominates the eddy fields in individual daily maps so that height contours in mid‐latitudes take on virtually pentagonal shapes. During periods when wavenumber 5 is prominent, it is observed to propagate eastward in a very regular manner with a period of about eleven days. All these findings are consistent with Salby's (1982) earlier results concerning the Southern Hemisphere height fields during the first few months of the FGGE experiment. There is little evidence for a similar phenomenon in the winter circulation of the Southern Hemisphere. 相似文献
3.
4.
William H. Klein 《大气与海洋》2013,51(2):155-176
Abstract Anomalies of monthly mean surface temperature observed at 55 stations in Canada and 13 in Alaska from 1951 through 1980 are related to concurrent anomalies of monthly mean 700‐mb height at a network of 107 grid points in North America and the surrounding oceans. The data are screened by a stepwise forward selection procedure to yield multiple regression equations for specifying the monthly mean temperature anomaly at each city and for each month from the field of simultaneous 700‐mb heights plus the previous month's local temperature anomaly. On the average, the specification equations explain 70% of the temperature variance and select as predictors approxiamtely 2 heights to the west of the reference station, 1.5 heights in the vicinity, 1 height to the east, and 0.5 previous temperatures. Most of this paper describes various properties of the specification equations and related atmospheric characteristics on a regional, seasonal and month‐to‐month basis. Five statistical features are mapped for the months of January, April, July and October, and marked regional differences are noted. The above features are then averaged for the entire region and graphed month by month; the annual cycle of other properties is also described. Systematic spatial and temporal variations in the characteristics of temperature variability, persistence, correlation with height, and specification equations are illustrated. 相似文献
5.
Abstract The Geosat radar altimeter data from ～60 repeat cycles of the Exact Repeat Mission (ERM) over the period November 1986 to September 1989 have been analysed to show the annual variations of the sea‐surface slopes, corrected for ocean tides, over the Scotian Shelf and the Grand Banks. A coastal tidal model developed at the Bedford Institute of Oceanography, combined with the global tidal model of Schwiderski, is employed to remove the tidal signals from the sea‐surface heights over those regions. Linear regression is used to estimate the sea‐surface slopes over the inner shelf region, the outer shelf region, or a combination of the two along the Geosat ground tracks. Harmonic analysis is applied to the time series of sea‐surface slopes to derive the annual signals, showing that amplitudes are of order of 5 × 10‐7 (5 cm/100 km) with onshore slopes positive in winter and negative in summer. The largest annual cycles occur over the outer portion of the Laurentian Channel and the southern Grand Banks. The annual cycles differ between the eastern and western portions of the Scotian Shelf: in the east, the signal is synchronized with that of the Laurentian Channel, whereas in the west, the phase of the signal is advanced by 2–3 months. The annual signals over the eastern Scotian Shelf are comparable and consistent with historical hydrographie data along the Halifax Hydrographie Section. The amplitude and phase over the western Scotian Shelf are consistent with the adjusted sea level at the Halifax Station. The annual variability of the sea‐surface slopes over the Scotian Shelf and the Grand Banks is thought to be induced by the seasonal outflow from the Gulf of St Lawrence through Cabot Strait, and possibly by an annual cycle in the Slope Water current. 相似文献
6.
Abstract The climatologies of upper‐air persistent circulation anomalies found in observations of the Northern Hemisphere and in a General Circulation Model (GCM) integration are compared with each other and with those found in previous studies. The model simulation is that of the Canadian Climate Centre GCM run at resolution T20. The objective criteria that define the persistent events differ from those of some earlier investigations in that the anomalies are not required to be as nearly stationary. It is found that the GCM generates persistent circulation anomalies downstream of the synoptic‐scale storm tracks, in very nearly the correct geographical locations, but that the frequency of occurrence is too low in the model. A kinetic energy and streamfunction variance analysis is presented for both dataseis to clarify the differences between the observed and simulated distributions of circulation anomalies. It is evident that, apart from the mean annual cycle, the middle‐latitude transient eddies of the model are too weak. 相似文献
7.
Abstract The relationship between sea surface temperature (SST) and rainfall index anomalies over sub‐Saharan Africa for the 15‐year period, 1970–84, has been examined. The objectively analysed monthly mean SST data were used for the global oceans between 40°S and 60°N. The rainfall data consist of annual mean rainfall indices for the Sahel and Soudan belts over north Africa. An Empirical Orthogonal Function analysis of the SST data has been carried out for the Atlantic, Indian and global ocean regions. The results show that the most dominant eigenmode, EOF1, is characterized by warming over the central eastern Pacific, cooling over the eastern mid‐latitude Pacific and warming over the entire Atlantic and Indian ocean basins. The second EOF for the Atlantic Ocean SST analysis shows a dipole (north‐south see‐saw) pattern. The third EOF for the Atlantic SST analysis has the same sign over the entire Atlantic basin. Global SST EOF2 and EOF3 correspondió Atlantic SST EOF3 and EOF2, respectively. The correlation between the sub‐Saharan annual rainfall index, which mainly represents the summer season rainfall from June to September, and SST EOFs shows that EOF1 has statistically significant monthly correlations for the Sahel and Soudan regions and that the warm El Niño‐like phases of SST EOF1 correspond to drought conditions. This result suggests that the large‐scale SST anomalies may be responsible for a significant component of the observed vacillation of sub‐Saharan rainfall. Some preliminary GLA GCM simulation results that support the above findings are also presented. 相似文献
8.
Abstract This study reports on the implementation of an interactive mixed‐layer/thermodynamic‐ice lake model coupled with the Canadian Regional Climate Model (CRCM). For this application the CRCM, which uses a grid mesh of 45 km on a polar stereographic projection, 10 vertical levels, and a timestep of 15 min, is nested with the second generation Canadian General Circulation Model (GCM) simulated output. A numerical simulation of the climate of eastern North America, including the Laurentian Great Lakes, is then performed in order to evaluate the coupled model. The lakes are represented by a “mixed layer” model to simulate the evolution of the surface water temperature, and a thermodynamic ice model to simulate evolution of the ice cover. The mixed‐layer depth is allowed to vary spatially. Lake‐ice leads are parametrized as a function of ice thickness based on observations. Results from a 5‐year integration show that the coupled CRCM/lake model is capable of simulating the seasonal evolution of surface temperature and ice cover in the Great Lakes. When compared with lake climatology, the simulated mean surface water temperature agrees within 0.12°C on average. The seasonal evolution of the lake‐ice cover is realistic but the model tends to underestimate the monthly mean ice concentration on average. The simulated winter lake‐induced precipitation is also shown, and snow accumulation patterns on downwind shores of the lakes are found to be realistic when compared with observations. 相似文献
9.
H. Jean Thiébaux 《大气与海洋》2013,51(3):219-233
Abstract Study of vertical extrapolations of the errors in forecast values of pressure‐level heights and temperatures indicates that they do not provide accurate off‐level information. Indeed it appears that, above 850 mb, forecast errors interpolated from observed 1000‐mb values are less accurate than level‐specific monthly mean differences. These results suggest that the de facto function of vertically interpolated single‐level forecast errors, in numerical forecast model updating, is the provision of vertical consistency rather than the injection of time‐specific information – except at the level of observation. 相似文献
10.
Abstract Observations of the changes in mean annual and seasonal precipitation with time in British Columbia and western Alberta between the periods 1931–60 and 1951–80 indicate that more stations show an increase than a decrease. Changes tend to be positive on the coast, negative in south‐central British Columbia, positive on the west slopes of the Rockies, and negative to the east. This suggests an orographic influence and increased flow from the southwest at mountain‐top. The possibility that these changes in precipitation are associated with CO2 warming is considered. Both the surface air temperature and sea surface temperature were raised by 2°C for cyclogenesis events over the northeastern Pacific and the consequences were investigated with the aid of a limited‐area, 8‐level primitive equations model. The lows are deepened by as much as 6 mb and precipitation amounts are increased up to 8 mm owing to the increased mixing ratio and the feedback of latent heat energy. 相似文献
11.
Abstract An analysis of variance of the 1000–500 mb thickness field is performed to investigate the possibility of seasonal change in climatic variability during the period 1949 to 1975. The mean thickness and measures of transient eddy, standing eddy and north‐south variance, averaged over the region from 25°N to the Pole, are analysed for the annual average and for each of the four seasons. For the annually averaged data, the only statistically significant trend is a linear decrease in mean thickness. None of the variability measures display significant trends in annually averaged values. On a seasonal basis, a significant trend in mean thickness is found in three of the four seasons. Several seasonal measures of variability show statistically significant trends. The most notable result of the analysis is an apparent increasing trend in summer season values of both transient and standing eddy measures of variability. The results of this study reiterate those of a previous study that found no overall change in climatic variability during the period. In addition, however, the data suggest an increase in variability during the summer season although this increase is not sufficient to affect the overall annually averaged value. 相似文献
12.
Abstract Current understanding of the possible nature of climatic change at the regional scale is limited by the spatial resolution of General Circulation Models (GCM). The use of GCM outputs without correction linked to the spatial variability of the variables can bring significant errors in their utilization at the regional scale. The potential of the Canadian GCM for regional applications in Quebec has been analysed by comparison to the climatic normals of temperature and precipitation, measured over the Quebec climatological network, on an annual and seasonal basis. This analysis has been undertaken with the support of a geographical information system (GIS) (PAMAP). In summary, a difference between the climatic normal and the GCM output has been estimated at 20% for temperature and 30% for precipitation. We present an analysis of a corrected regionalized scenario for the province of Quebec of the possible climatic change simulated by the Canadian GCM under the hypothesis of a doubling of atmospheric CO2. Results show an increase of the annual average temperature of 4° C for summer and 6°C for winter, associated with an average increase of 80 mm (10%) in annual precipitation, reaching 25% in some regions. 相似文献
13.
Abstract The medium‐scale wave regime, consisting largely of zonal wavenumbers 5–7, frequently dominates the summer Southern Hemisphere tropospheric circulation. We perform a diagnostic study of this circulation as simulated by the Canadian Climate Centre (CCC) general circulation model (GCM). The analysis of Hövmöller diagrams, space‐time and zonal wavenumber spectra shows that the CCC GCM is able to simulate the observed medium‐scale wave regime. The zonally averaged meridional eddy heat and momentum transports and the associated baroclinic and barotropic energy conversions are also examined. The distributions of the transports on the vertical plane agree well with the observations. After comparison with the observed December‐January‐February 1979 distributions, some quantitative differences remain: the heat transport is too weak aloft and too large near the surface, whereas the momentum transport tends to be too weak. The baroclinic and barotropic conversions show a maximum in the medium‐scale waves. The time evolution of the Richardson number of the mean flow suggests that the medium‐scale wave is due to a baroclinic instability. 相似文献
14.
Jacques Derome Gilbert Brunet André Plante Normand Gagnon George J. Boer Francis W. Zwiers 《大气与海洋》2013,51(4):485-501
Abstract Two dynamical models are used to perform a series of seasonal predictions. One model, referred to as GCM2, was designed as a general circulation model for climate studies, while the second one, SEF, was designed for numerical weather prediction. The seasonal predictions cover the 26‐year period 1969–1994. For each of the four seasons, ensembles of six forecasts are produced with each model, the six runs starting from initial conditions six hours apart. The sea surface temperature (SST) anomaly for the month prior to the start of the forecast is persisted through the three‐month prediction period, and added to a monthly‐varying climatological SST field. The ensemble‐mean predictions for each of the models are verified independently, and the two ensembles are blended together in two different ways: as a simple average of the two models, denoted GCMSEF, and with weights statistically determined to minimize the mean‐square error (the Best Linear Unbiased Estimate (BLUE) method). The GCMSEF winter and spring predictions show a Pacific/North American (PNA) response to a warm tropical SST anomaly. The temporal anomaly correlation between the zero‐lead GCMSEF mean‐seasonal predictions and observations of the 500‐hPa height field (Z500) shows statistically significant forecast skill over parts of the PNA area for all seasons, but there is a notable seasonal variability in the distribution of the skill. The GCMSEF predictions are more skilful than those of either model in winter, and about as skilful as the better of the two models in the other seasons. The zero‐lead surface air temperature GCMSEF forecasts over Canada are found to be skilful (a) over the west coast in all seasons except fall, (b) over most of Canada in summer, and (c) over Manitoba, Ontario and Quebec in the fall. In winter the skill of the BLUE forecasts is substantially better than that of the GCMSEF predictions, while for the other seasons the difference in skill is not statistically significant. When the Z500 forecasts are averaged over months two and three of the seasons (one‐month lead predictions), they show skill in winter over the north‐eastern Pacific, western Canada and eastern North America, a skill that comes from those years with strong SST anomalies of the El Niño/La Niña type. For the other seasons, predictions averaged over months two and three show little skill in Z500 in the mid‐latitudes. In the tropics, predictive skill is found in Z500 in all seasons when a strong SST anomaly of the El Niño/La Niña type is observed. In the absence of SST anomalies of this type, tropical forecast skill is still found over much of the tropics in months two and three of the northern hemisphere spring and summer, but not in winter and fall. 相似文献
15.
Abstract The Canadian Regional Climate Model (CRCM) has been nested within the Canadian Centre for Climate Modelling and Analysis ‘ second generation General Circulation Model (GCM), for a single month simulation over the Mackenzie River Basin and environs. The purpose of the study is to assess the ability of the higher resolution CRCM to downscale the hydrological cycle of the nesting GCM. A second 1‐month experiment, in which the CRCM was nested within analyzed fields of a global data assimilation system, was also performed to examine the sensitivity of the basin moisture budget to atmospheric lateral boundary forcing. We have found that the CRCM can produce realistic lee cyclogenesis, preferentially in the Liard sub‐basin, along with associated circulation and precipitation patterns, as well as an improved rainshadow in the lee of the Rocky Mountains compared to the GCM. While these features do quantitatively affect the monthly average climate statistics, the basin scale moisture budgets of the models were remarkably similar, though some of this agreement is due to compensating errors in the GCM. Both models produced excessive precipitation compared to a recent climatology for the region, the cause of which is traced to lateral boundary forcing. A second experiment, identical to the first except that the CRCM was forced with analyzed fields at the lateral boundaries, produced a qualitatively different basin moisture budget, including a much more realistic precipitation field. Errors in the moisture budget of the first experiment appear to be associated with the poor representation of the Aleutian Low in the GCM, and do not appear to be strongly connected to (local) surface processes within the models. This suggests that an effective strategy for modelling the hydrological cycle of the Mackenzie Basin on the fast climate timescale ‐ a major requirement of the Mackenzie GEWEX Study ‐ will involve nesting the CRCM within analyzed (or re‐analyzed) atmospheric fields. 相似文献
16.
Belmadani Ali Dalphinet Alice Chauvin Fabrice Pilon Romain Palany Philippe 《Climate Dynamics》2021,56(11):3687-3708
Tropical cyclones are a major hazard for numerous countries surrounding the tropical-to-subtropical North Atlantic sub-basin including the Caribbean Sea and Gulf of Mexico. Their intense winds, which can exceed 300 km h−1, can cause serious damage, particularly along coastlines where the combined action of waves, currents and low atmospheric pressure leads to storm surge and coastal flooding. This work presents future projections of North Atlantic tropical cyclone-related wave climate. A new configuration of the ARPEGE-Climat global atmospheric model on a stretched grid reaching ~ 14 km resolution to the north-east of the eastern Caribbean is able to reproduce the distribution of tropical cyclone winds, including Category 5 hurricanes. Historical (1984–2013, 5 members) and future (2051–2080, 5 members) simulations with the IPCC RCP8.5 scenario are used to drive the MFWAM (Météo-France Wave Action Model) spectral wave model over the Atlantic basin during the hurricane season. An intermediate 50-km resolution grid is used to propagate mid-latitude swells into a higher 10-km resolution grid over the tropical cyclone main development region. Wave model performance is evaluated over the historical period with the ERA5 reanalysis and satellite altimetry data. Future projections exhibit a modest but widespread reduction in seasonal mean wave heights in response to weakening subtropical anticyclone, yet marked increases in tropical cyclone-related wind sea and extreme wave heights within a large region extending from the African coasts to the North American continent.
相似文献17.
P. J. Michaels D. E. Sappington D. E. Stooksbury B. P. Hayden 《Theoretical and Applied Climatology》1990,42(3):149-154
Summary We developed a statistical model relating cyclone track eigenvectors over the U.S., southern Canada, and nearby oceans to a record of mean annual 500 mb heights. The length of the cyclone track record allowed us to calculate mean heights back to 1885. Use of mean annual surface pressure data allowed us to estimate the mean 1 000-500 mb thickness, which was related to mean annual temperature. This temperature calculation is unique in that it cannot suffer from urban or site bias. We find a warming of 1.5°C from the late 19th century to 1955, followed by a drop of 0.7° to 1980. By 1987, the calculated temperatures were 0.3° above the mean for 103 years of record.As an example of regional application, we examine results over the southwestern U.S.With 8 Figures 相似文献
18.
Wang Shaowu 《大气科学进展》1984,1(1):7-29
The most effective technique in long-range weather forecasting in China is teleconnection. Summer rainfall and temperatures are closely correlated to the preceding winter 500 mb heights over the Northern Hemisphere and sea surface temperatures over the North Pacific, so the former can be predicted from the latter. This kind of connection is called rhythm. In this paper, four examples of rhythm are outlined. The manifestation of rhythm and its universal significance is demonstrated. The mechanism of rhythm is discussed. 相似文献
19.
The hydrological cycle in the ECMWF short range forecasts 总被引：1，自引：0，他引：1
Precipitation and latent heat flux forecasts by the European Centre for Medium Range Weather Forecasts (ECMWF) model have been compared with other estimates of these quantities. In the Northern Hemisphere extra-tropics the latent heat flux over oceans and the precipitation over continents in the short range forecasts are probably good estimates of the truth. The day-to-day as well as the interannual variability in these latitudes seem to be realistic.In the Southern Hemisphere extra-tropics there is a strong spin-up in the precipitation forecasts probably with too low precipitation amounts in the short range forecasts. It is speculated that inconsistent use of satellite data leads to a weakening of large-scale rising motions between 40 and 60°S. Also the latent heat flux in these latitudes is probably too low due to a too moist 1000 mb humidity analysis.Over subtropical deserts the precipitation amounts in the forecasts agree with climatological estimates. Contrary to climatological estimates this precipitation is not evaporated but runs off.In the tropics, especially over mountainous areas, the short range forecasts (average for the first 24 h) with the present model tend to overpredict precipitation amounts, but still with reasonable distributions. Averages between days 1 and 2 probably give a good estimate of the truth except over the eastern Pacific where there is an overestimation, also in the medium range forecasts. Strong underestimation of latent heat fluxes over tropical oceans in the short range forecasts have been considerably reduced with a recent model change. There are still areas, e.g. the Southern Hemisphere subtropical Pacific, with too low evaporation due to too moist 1000 mb analyses probably in connection with an inconsistent use of satellite observations.The interannual variability of monthly mean evaporation and precipitation in the short range forecasts reflects partly atmospheric anomalies, but especially in the tropics, and also larger amplitude variations due to changes in the analysis/forecasting scheme. 相似文献
20.
Abstract In order to assess the ability of a GCM to simulate regional to synoptic scale atmospheric structures, a correlation‐based computer‐assisted gridded map typing procedure is used to compare daily pressure (MSL) and geopotential height fields (500 hPa) from a GCM simulation of the present climate to a decade of NMC analyses. The model is able to reproduce the entire range of synoptic circulation types. However, statistically significant differences in the seasonal frequencies and variances of the main circulation types are evident. These differences, which are most pronounced in the winter (at 500 hPa) and in spring and autumn in the MSL fields, are consistent with subtle errors in the predicted fields at the hemispheric scale. The lack of agreement between the NMC climatology and the “control” simulation precludes extension of this approach to investigation of climate change impacts in western north America, and to more meteorologically dynamic extra‐tropical regions. The map‐typing procedure is shown to be an appropriate GCM synoptic‐scale validation tool that permits direct comparison of GCM output and observed fields. As such, it has the potential to elucidate the regional‐scale impacts of global climatic change through established synoptic circulation environment relationships. 相似文献