共查询到20条相似文献，搜索用时 15 毫秒
1.
Abstract The relationship between the Arctic and subarctic sea‐ice concentration (SIC) anomalies, particularly those associated with the decadal‐scale Greenland and Labrador Seas “Ice and Salinity Anomalies (ISAs) “, and the overlying atmospheric circulation fluctuations is investigated using the singular value decomposition (SVD) and composite map analysis methods. The data analyzed are monthly SIC and sea level pressure (SLP) anomalies, which cover the northern hemisphere poleward of 45°N and extend over the 41‐year period 1954–1994. The SVD1 (first) mode of the coupled variability, which accounts for 57% of the square covariance, is for the most part an atmosphere‐to‐ice forcing mode characterized by the decadal timescale. The aforementioned ISA anomalies are clearly captured by this mode whose SIC anomalies are dominated by a strong dipole across Greenland. However, as part of the same mode, there is also a weaker SIC dipole in the northern North Pacific which has opposite‐signed anomalies in the Sea of Okhotsk and the Bering Sea. It is also shown that there exists a significant negative correlation between the decadal SIC variability in the Greenland‐Barents Seas region associated with this mode and the North Atlantic Oscillation, whose spectrum also exhibits a quasi‐decadal signal. The SVD2 mode accounts for 12% of the square covariance and shows no evidence of a dominant forcing field of either SIC or SLP. This SVD mode exhibits very low frequency (interdecadal) variability, and its co‐variability is mainly concentrated in the northern North Pacific. It appears to be a high‐latitude extension of the recently investigated interdecadal North Pacific Oscillation. The spatial structure of the second mode complements the case of the first SVD mode whose co‐variability mainly occurs in the northern North Atlantic. 相似文献
2.
《大气与海洋》2013,51(2):85-100
Abstract The sensitivity of the Canadian Regional Climate Model (CRCM), developed at the Université du Québec à Montréal, and the Gulf of St. Lawrence Ocean Model (GOM), developed at the Institut Maurice‐ Lamontagne, to each other is tested with an ensemble of simulations over eastern Canada from 1 November 1989 to 31 March 1990. The goal of this study is to investigate the interaction of the CRCM and GOM with respect to each other's forcing fields. In the first part of the experiment, a series of simulations were performed using an iterative strategy, where both models run separately and alternately, using variables from the other model to supply the needed forcing fields for the computation of surface fluxes. The runs are iterated several times over the same period from the output of the previous run to allow the atmosphere and the ocean to interact several times with each other and to study the evolution of the solutions from one iteration to the next. In the second part of the experiment, a two‐way coupled simulation is performed over the same period. The results indicate that on a monthly or longer timescale, the CRCM is not very sensitive to the details of the oceanic fields from GOM, except locally over the Gulf of St. Lawrence (GSL). However, GOM is quite sensitive to the differences in atmospheric fields from the CRCM. The results of several iterations converge to a unique solution, suggesting that the CRCM and GOM reach equilibrium with respect to each other's forcing fields. Furthermore, the results of the coupled run also converge to this same solution. 相似文献
3.
H.G. Leighton 《大气与海洋》2013,51(1):43-52
Abstract A model to compute rapidly the absorption of solar radiation in the atmosphere is described. The model is based partially on the parameterization of Lacis and Hansen and also makes use of the delta‐Eddington method. In addition to absorption by ozone and water vapour, and scattering by air molecules and clouds, the mode1 includes absorption and scattering by aerosols. Good agreement is found in comparison with the Lacis and Hansen parameterization in the absence of clouds and aerosol. The present model represents an improvement in the treatment of scattering by clouds. Its main advantage though, is in its flexibility in allowing for interactions with the atmospheric aerosol. 相似文献
4.
Abstract The role of sea‐ice in affecting the stability and long‐term variability of the oceanic thermohaline circulation (THC) is studied in this paper. The emphasis is placed on studying how sea‐ice might affect the stability and the long‐term variability of the THC through modulations of the surface heat and freshwater fluxes. A simple box model is analyzed to elucidate qualitatively the distinct physical meanings of these two processes. The analytical solution of this simple model indicates that, for the long timescales considered here, the thermal insulation stabilizes the THC while the freshwater feedback increases the effective inertia of the coupled ice‐ocean system. Sea‐ice insulation lessens the negative feedback between heat flux and the SST, and therefore, allows the SST to play a greater role in counteracting changes of the THC and high latitude salinity field. The freshwater feedback effectively links the surface heat flux to a freshwater reservoir, and thus, increases the effective inertia of the coupled ocean‐ice system. A two‐dimensional ocean model coupled with a thermodynamic sea‐ice model is used to estimate quantitatively the magnitudes of these two feedbacks. The numerical experiments involve the model's responses both to initial anomalies and to changes of forcing fields. For the free response cases (model responses to initial anomalies without changing the forcing fields), the model shows that the decay rate of an initial anomaly is greater when sea‐ice is included. For small perturbations the thermal insulation effect dominates over the freshwater feedback. The latter becomes increasingly more important for larger perturbations. In response to a change of external forcing, the presence of sea‐ice reduces the magnitude and the pace of the model's response. The numerical results are qualitatively consistent with the analytical solution of the box model. 相似文献
5.
Abstract A numerical method for solving the advection‐diffusion equation, based on the semi‐Lagrangian algorithm of Robert (1981, 1982) is described, analysed and evaluated in comparison with other methods through a series of test problems. It is found that this method is generally better than other semi‐Lagrangian methods, and is a viable alternative to existing methods for LRTAP and other meteorological modelling because of its flexibility in application, its computational stability and its accuracy. 相似文献
6.
《大气与海洋》2013,51(4):221-233
Abstract The cell‐to‐cell channel routing schemes used in General Circulation Models (GCMs) and Regional Climate Models (RCMs) are revisited. A simpler parsimonious routing scheme based on Askew's formula (1970) for computing time‐evolving channel lags is implemented and tested against observations and compared with the variable‐velocity scheme of Arora and Boer (1999). The variable‐lag routing scheme agrees very well with the variable‐velocity scheme. The variable‐lag scheme has the advantage of using fewer parameters, which is a major advantage at fine resolution over a large domain, where the uncertainty associated with parameters can be quite large. The spatial resolutions of RCMs are much finer than those of GCMs and hence there is a need for channel routing at fine spatial resolutions. The task of extending the cell‐to‐cell routing schemes developed for large‐scale routing, as in GCMs, to finer spatial scales, as in RCMs, is addressed. The sensitivity of the variable‐lag scheme to the routing time interval is studied. The choice of the routing time interval is very critical and varies with the spatial resolution as in any hydrological model. A simple method for determining the appropriate range of routing intervals at different spatial resolutions for the variable‐lag scheme is presented. 相似文献
7.
R. Krishna Rao Vupputuri 《大气与海洋》2013,51(3):214-236
A mean meridional circulation model of the stratosphere, incorporating radiative heating and photochemistry of the oxygen‐hydrogen‐nitrogen atmosphere, is used to simulate the meridional distributions of O3, HOX, N2O,NOX, temperature and the three components of mean motion for the summer and winter seasons under steady‐state conditions. The results are generally in good agreement with the available observations in the normal stratosphere. The model has been applied to assess the effects of water vapour and nitrogen oxide perturbations resulting from aircraft emissions in the stratosphere. It is found that a fleet of 500 Boeing‐type sst's, flying at 20 km and 45°N in the summer hemisphere and inserting NOx at a rate of 1.8 megatons per year, has the effect of reducing the global total ozone by 14.7%. Similar calculations for 342 Concorde/TU‐114's, cruising at 17 km and injecting NOx at a rate of 0.35 megatons per year, show a global‐average total‐ozone reduction of 1.85%. Although water vapour is considered important, because of its ability to convert NO2 into HNO3, the direct effect on global‐average total‐ozone reduction resulting from the 100% increase in the stratospheric water content is less than 1%. The changes in the chemical structure (HO^NO^), temperature, and mean motions associated with the ozone reduction are also investigated in the case of the 1.8‐megaton‐per‐year NOX perturbation. It is shown that the reduced meridional temperature gradient in the middle and upper stratosphere resulting from the NOx perturbation leads to the weakening of the tropical easterly jet in the summer hemisphere and mid‐latitude westerlies in the winter season. The sensitivity of the model solutions to an alternate choice of input parameters (diffusion coefficients and solar photodissociation data) is tested and the main deficiency of the model is pointed out. 相似文献
8.
《大气与海洋》2013,51(3):129-139
Abstract Both the earth‐reflected shortwave and outgoing longwave radiation (OLR) fluxes at the top of the atmosphere (TOA) as well as surface‐absorbed solar fluxes from Canadian Regional Climate Model (CRCM) simulations of the Mackenzie River Basin for the period March 2000 to September 2003 are compared with the radiation fluxes deduced from satellite observations. The differences between the model and satellite solar fluxes at the TOA and at the surface, which are used in this paper to evaluate the CRCM performance, have opposite biases under clear skies and overcast conditions, suggesting that the surface albedo is underestimated while cloud albedo is overestimated. The slightly larger differences between the model and satellite fluxes at the surface compared to those at the TOA indicate the existence of a small positive atmospheric absorption bias in the model. The persistent overestimation of TOA reflected solar fluxes and underestimation of the surface‐absorbed solar fluxes by the CRCM under all sky conditions are consistent with the overestimation of cloud fraction by the CRCM. This results in a larger shortwave cloud radiative forcing (CRF) both at the TOA and at the surface in the CRCM simulation. The OLR from the CRCM agrees well with the satellite observations except for persistent negative biases during the winter months under all sky conditions. Under clear skies, the OLR is slightly underestimated by the CRCM during the winter months and overestimated in the other months. Under overcast conditions the OLR is underestimated by the CRCM, suggesting an underestimation of cloud‐top temperature by the CRCM. There is an improvement in differences between model and satellite fluxes compared to previously reported results largely because of changes to the treatment of the surface in the model. 相似文献
9.
Abstract A static decision‐analytic method is used to investigate the economic value of bivariate ‐ precipitation and temperature ‐ seasonal forecasts of the form currently issued by the U.S. National Weather Service. This method is applied to a corn versus spring wheat choice‐of‐crop decision‐making problem by considering a transect of four counties across the northwestern margin of the North American corn belt. Numerical results indicate that seasonal forecasts of current quality can be of appreciable value (≥$1/ha) for some locations when the optimal action chosen on the basis of climatological information is only marginally preferred to another action. Increases in forecast value follow from hypothetical increases in the quality of both the precipitation and temperature components of the forecasts in the spring wheat region, whereas forecast value increases primarily as a function of the quality of the precipitation forecasts alone in the corn belt region. The results are very sensitive to absolute and relative crop prices. 相似文献
10.
《大气与海洋》2013,51(4):283-299
Abstract The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) series of high‐altitude balloon flights is being undertaken to investigate changes in the concentrations of northern hemisphere mid‐latitude stratospheric ozone, and of nitrogen and chlorine compounds that play a role in ozone chemistry. Four campaigns have been carried out to date, all from Vanscoy, Saskatchewan, Canada (52°01'N, 107°02'W, 511.0 m). The first MANTRA mission took place in August 1998, with the balloon flight on 24 August 1998 being the first Canadian launch of a large high‐altitude balloon in about fifteen years. The balloon carried a payload of instruments to measure atmospheric composition, and made measurements from a float altitude of 32–38 km for one day. Three of these instruments had been flown on the Stratoprobe flights of the Atmospheric Environment Service (now the Meteorological Service of Canada) in the 1970s and early 1980s, providing a link to historical data predating the onset of mid‐latitude ozone loss. The primary measurements obtained from the balloon‐borne instruments were vertical profiles of ozone, NO2, HNO3, HCl, CFC‐11, CFC‐12, N2O, CH4, temperature, and aerosol backscatter. Total column measurements of ozone, NO2, SO2, and aerosol optical depth were made by three ground‐based spectrometers deployed during the campaign. Regular ozonesonde and radiosonde launches were also conducted during the two weeks prior to the main launch in order to characterize the local atmospheric conditions (winds, pressure, temperature, humidity) in the vicinity of the primary balloon flight. The data have been compared with the Model for Evaluating oZONe Trends (MEZON) chemical transport model, the University of California at Irvine photochemical box model, and the Canadian Middle Atmosphere Model (CMAM) to test our current understanding of model photochemistry and mid‐latitude species correlations. This paper provides an overview of the MANTRA 1998 mission, and serves as an introduction to the accompanying papers in this issue of Atmosphere‐Ocean that describe specific aspects and results of this campaign. 相似文献
11.
Abstract Teleconnections between sea surface temperature (SST) anomalies over the Pacific and the dominant patterns of wintertime Northern Hemisphere 500‐hPa height are examined by applying statistical techniques such as rotated principal component analysis and composite analysis. It is shown that the Pacific/North American (PNA) patterns in December through March are correlated most significantly with the ENSO‐related SST anomalies in the previous October, while the western Pacific (WP) patterns in December through February are most closely linked to the ENSO‐related SST anomalies in the same season. In addition, the PNA response to the ENSO signal during La Niña events is more significant than that during El Niño events, while the WP response is stronger during El Niño events than during La Niña events. A composite analysis shows that in the El Niño winters the North Pacific centre of the PNA pattern is located about 10 degrees east of its normal position, leading to a less significant correlation between the ENSO signal and the PNA pattern in these winters. The ENSO‐related SST anomalies include a large centre of action over the tropical Pacific and an oppositely signed anomaly centre over the North Pacific. The North Pacific centre appears to the west of the dateline in September and October. This ENSO‐related seed of SST anomalies slowly moves eastward in the following months, gradually cutting off its connection with SST anomalies over the tropical Pacific and being coupled with the PNA pattern. It is pointed out that, although the wintertime SST anomaly over the North Pacific may appear as a mode linearly independent of the ENSO signal in the same season, it is partially related to the ENSO signal in the preceding autumn. Possible dynamical explanations of the above results are discussed. It is suggested that the WP pattern can be linked to the tropical Pacific heat source via advection of vorticity by the upper‐tropospheric divergent/convergent flow, and the intensification of vorticity gradients associated with a stronger east Asian jet is likely to be responsible for a more significant WP pattern response to the ENSO signal in the El Niño winters. On the other hand, the ENSO‐related PNA pattern could be considered a manifestation of the eastward extension (El Niño) or westward withdrawal (La Niña) of the east Asian jet stream due to the local Hadley cell over the Pacific. In addition, the ENSO‐related seed of extratropical SST anomaly over the western Pacific in autumn may also play an important role in the development of the PNA pattern in the following winter. 相似文献
12.
《大气与海洋》2013,51(4):239-266
Abstract The resonance of semi‐diurnal tidal elevations is investigated with a forward numerical forced damped global tide model and an analytical model of forced‐damped tides in a deep ocean basin coupled to a shelf. The analytical model contains the classical half‐wavelength and quarter‐wavelength resonances in the deep ocean and shelf, respectively, as well as a forcing‐scale dependence which depends on the ratio of the phase speed of open‐ocean gravity waves to that of the astronomical forcing. In the analytical model, when the deep ocean and shelf resonate separately at the same frequency, the resonance in the coupled system shifts to frequencies slightly higher and lower than the original frequency, such that a ‘double bump’ is seen in plots of elevation amplitude versus frequency. The addition of a shelf to a resonant open ocean tends to reduce open‐ocean tides, especially when the shelf is also near resonance. The magnitude of this ‘back‐effect’ is controlled by shelf friction. A weakly damped resonant shelf has a larger back‐effect on the open‐ocean tide than does a strongly damped shelf. Numerical simulations largely bear out the analytical model predictions, at least qualitatively. Idealized simulations show that continents enhance tides by enabling the half‐wavelength resonance. Simulations with realistic geometry and topography but varying longitudinal structure in the astronomical forcing display an influence of the forcing scale on tidal amplitudes somewhat similar to that seen in the analytical model. A frequency sweep in the semi‐diurnal band in experiments with realistic geometry and topography reveals weakly resonant peaks in the amplitudes of several shelf regions and in the globally averaged open‐ocean amplitudes. Finally, the back‐effect of the shelf upon the open ocean is seen in simulations in which locations of resonant coastal tides are blocked out and open‐ocean tidal elevations are significantly altered (increased, generally) as a result. 相似文献
13.
Abstract Cloudless‐sky solar fluxes calculated by the radiative transfer algorithm used in the Canadian Climate Centre's general circulation climate model are compared with measurements of upwelling radiation at the top of the atmosphere (TOA) and downwelling radiation at the surface. The 12‐layer model partitions the solar spectrum into two broad wavebands (0.25–0.68 and 0.68–4.00 μm). The comparison utilized TOA fluxes estimated from Nimbus‐ 7 measurements and measured downwelling fluxes at the surface for Kalgoorlie, West Australia, and downwelling fluxes at the surface for Woodbridge, Ontario. Model estimates and measurements agreed to within experimental error for most solar zenith angles. Estimates improved, especially at Woodbridge, when aerosol effects were included. The mean bias error was less than 4% for surface irradiance and less than 6% for upwelling TOA irradiance, which produces a TOA albedo error of about 0.01. 相似文献
14.
Abstract The present study examines sources of the interannual variability in salinity on the Newfoundland continental shelf observed in a 40‐year time series from an oceanographic station known as Station 27. Specifically, we investigate, through lag‐correlation analysis, the a priori hypotheses that the salinity anomalies at Station 27 are determined by freshwater runoff anomalies from Hudson and Ungava bays and by ice‐melt anomalies in Hudson Bay and on the Labrador Shelf. Interannual variations of summer runoff into Hudson Bay were significantly negatively correlated with salinity anomalies on the Newfoundland Shelf with a lag (9 months) that is consistent with expected travel times based on known current velocities in Hudson Bay and along the Labrador Shelf. Sea‐ice extent over the Labrador and northern Newfoundland shelves was significantly negatively correlated with salinity at a lag of 3 to 4 months, corresponding to the time of minimum salinity at Station 27. It appears that ice‐melt over the Labrador‐northern Newfoundland Shelf is primarily responsible for the seasonal salinity minimum over the Newfoundland Shelf. Interannual variability in runoff into Ungava Bay and ice‐melt in Hudson Bay were not correlated with interannual salinity variations on the Newfoundland Shelf. 相似文献
15.
We discuss here a mistake in the analysis of Previdi and Liepert (Clim Dyn, 2011). In that article, the surface albedo radiative kernels were calculated incorrectly. We present in this brief comment the corrected albedo kernels. We then use these kernels to compute the surface albedo radiative feedback in climate model simulations driven by increasing carbon dioxide, as in Previdi and Liepert (Clim Dyn, 2011). We find that the use of the corrected albedo kernels does not change the conclusions of our earlier work. 相似文献
16.
Abstract Airborne measurements of mean wind velocity and turbulence in the atmospheric boundary layer under wintertime conditions of cold offshore advection suggest that at a height of 50 m the mean wind speed increases with offshore distance by roughly 20% over a horizontal scale of order 10 km. Similarly, the vertical gust velocity and turbulent kinetic energy decay on scales of order 3.5 km by factors of 1.5 and 3.2, respectively. The scale of cross‐shore variations in the vertical fluxes of heat and downwind momentum is also 10 km, and the momentum flux is found to be roughly constant to 300 m, whereas the heat flux decreases with height. The stability parameter, z/L (where z = 50 m and L is the local Monin‐Obukhov length), is generally small over land but may reach order one over the warm ocean. The magnitude and horizontal length scales associated with the offshore variations in wind speed and turbulence are reasonably consistent with model results for a simple roughness change, but a more sophisticated model is required to interpret the combined effects of surface roughness and heat flux contrasts between land and sea. Comparisons between aircraft and profile‐adjusted surface measurements of wind speed indicate that Doppler biases of 1–2 m s?1 in the aircraft data caused by surface motions must be accounted for. In addition, the wind direction measurements of the Minimet anemometer buoy deployed in CASP are found to be in error by 25 ± 5°, possibly due to a misalignment of the anemometer vane. The vertical fluxes of heat and momentum show reasonably good agreement with surface estimates based on the Minimet data. 相似文献
17.
《大气与海洋》2013,51(4):391-404
Abstract An experimental study was conducted to investigate the transition of two‐layer stratified flow from the slope of bottom topography to a horizontal channel. Three experiments, with a reduced gravity of g’ = 1.64, 6.47 and 18.0 cm s?2, were performed. Particle image velocimetry and planar laser‐induced fluorescence were used to obtain the measurements of velocity and concentration fields. The flow rate, obtained from the measured velocity field, increases significantly toward the toe of the topography by almost 40% from that at the sill crest due to the interfacial wave activities. In the horizontal channel, however, the flow rate only increases marginally. Estimates of the composite Froude number indicate that the supercritical flow on the slope of the topography goes through the transition to the subcritical flow in the horizontal channel. The transition is mainly due to the increase in the lower‐layer thickness because of increasing interfacial friction caused by the breaking of interfacial waves, and no internal hydraulic jumps are observed. The measured mean concentration field showed the formation of an intermediate layer of medium density, which increased its thickness with g’ and helped to suppress turbulence. Spectral analysis of the density interfacial fluctuations indicated that the interfacial waves that developed on the slope of the topography broke up downstream of the toe into smaller amplitude waves at larger frequencies. The waves at several channel cross‐sections were also examined. 相似文献
18.
The need to adapt to climate change impacts, whilst simultaneously limiting greenhouse gas emissions, requires that the government’s efforts are joined by public action. In England and Wales, housing contributes significantly to the emissions and many properties are at risk of flooding. This paper investigates the preparedness of homeowners in England and Wales to make changes to their homes in response to the predicted effects of climate change. A telephone survey of 961 homeowners investigated their interest in purchasing mitigation and adaptation improvements against their concern about climate change, awareness of flood risk and attribution of responsibility for action. Whilst the majority of homes had some energy-saving improvements, few were found to have property-level flood protection. The high levels of awareness about climate change and flooding were coupled with the perception of risks as low. Whilst some respondents accepted personal responsibility for action, most believed that the authorities were responsible for flood protection, and would not pay the costs required to make their home more energy-efficient and better prepared for the eventuality of floods. The results suggest that there is scope for further improvement of energy-saving measures, and that the levels of adoption of flood-protection measures are very low. Multi-faceted strategies, including more effective communication of risks and responsibilities, incentives, and material support for the poorest, will need to be developed to overcome the current reluctance by homeowners to invest in flood-protection measures and further energy conservation solutions in the future. 相似文献
19.
G. P . Williams 《大气与海洋》2013,51(1):23-24
Abstract A detailed examination has been made of the relationship between the space and time variations of the Indian summer monsoon rainfall and the equatorial eastern‐Pacific sea surface temperature (SST) anomaly in different seasons for the 108‐year period, 1871–1978. There is a strong inverse relationship between the two. The correlation coefficients between All‐India monsoon rainfall and the sea surface temperature anomaly for the concurrent season; June, July and August (JJA) and for the succeeding seasons; September, October and November (SON) and December, January and February (DJF) are consistently and highly significant. Even a random sample of 50 years gave values significant at the 0.1 percent level. The sliding window correlation analysis of 10‐, 20‐ and 30‐year widths indicates that the relationships between All‐India monsoon rainfall and the sea surface temperature anomaly for the concurrent JJA and the succeeding SON and DJF seasons exhibit stability and consistency in significance. For contiguous meteorological sub‐divisions west of longitude 80°E the relationship is highly significant for JJA and for succeeding SON and DJF seasons. 相似文献
20.
An Overview of the Madden-Julian Oscillation and Its Relation to Monsoon and Mid-Latitude Circulation 总被引：2，自引：0，他引：2
In the past decade there has been extensive research into tropical intraseasonal variability, one of the major components of the low frequency variability of the general atmospheric circulation. This paper briefly reviews the state-of-the-art in this research area: the nature of the Madden-Julian Oscillation, its relation to monsoonal and extratropical circulations, and the current theoretical understandings. 相似文献