摘要:

This paper analyses the sensitivity of wintertime precipitation and soil hydrology over the western United States to coastal ocean sea surface temperature (SST), inland soil moisture and coastal topography representation, as simulated with a coupled limited‐area meterological model‐soil hydrology model. The period simulated is 1–30 January 1979, comprising nine storm episodes over the western United States. The main source of moisture feeding precipitation over the western United States is found to be the westerly advection of water vapour from the Pacific Ocean. Evaporation from coastal ocean waters is also significant, whereas land evaporation is of secondary importance. Coastal SST anomalies of ±1.5 K affect inland precipitation only weakly. However, for an anomaly of + 3 K, precipitation increases significantly. Because of the precipitation shadowing effect of the Sierra Nevada and Coastal ranges the precipitation enhancement mostly occurs over California and the Pacific Northwest. Regional precipitation averages increase by 10–20% there, with local effects being larger over coastal areas. Farther inland the effect is of the order of 5–7%. Precipitation is only minimally affected by variations in soil wetness and land evaporation (effects not exceeding 5%), but the efficiency of other components of the hydrologie budget, such as water infiltration to deep soil and surface runoff, strongly increases with soil water content. Problems related to the initialization of soil moisture for simulations of soil hydrology on scales of one to several weeks are examined. Finally, the precipitation simulation is sensitive to adjustments in the description of the complex western United States coastal topography, but effects are generally local and do not propagate far over the continental regions.

ISSN:0705-5900    

DOI:10.1080/07055900.1990.9649365

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The multigrid principle producesfast solversfor systems of algebraic equations, particularly those that arise from discretizing elliptic boundary‐value problems. A multigrid solver is developed for the discretized two‐dimensional elliptic equation on the sphere that arises from a semi‐implicit time discretization of the global shallow‐water equations. We experiment with different formulations of the semi‐implicit scheme that result in variable‐coefficient Helmholtz‐type equations for which nofast direct solversare available. The efficiency of the multigrid solver is optimal, in the sense that the total operation count is proportional to the number of unknowns. Numerical experiments using initial data derived from actual 300‐mb height and wind velocity fields indicate that our semi‐implicit global shallow‐water model has very good accuracy and stability properties.

ISSN:0705-5900    

DOI:10.1080/07055900.1990.9649366

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Our model studies of light non‐methane hydrocarbons (NMHCs) in the troposphere and lower stratosphere for seasonally varying insolation and transport conditions indicate that NMHC mixing ratios (MRs) are generally highest in the winter. These results reflect our assumptions of a constant surface source for each season. Comparisons of these calculated NMHC MRs with measurements suggest that the sources of the light NMHC may vary seasonally. There is a serious discrepancy between calculated and observed values of formic and acetic acids. It appears that the direct emissions or the aqueous phase chemistry of these acids, or their precursors, are of importance. An injection of NMHCs into the upper troposphere to stimulate transport of boundary‐layer air by rapid vertical convection in clouds, has a significant impact on the local chemistry on a time‐scale of a few days. The most important effects besides the increase in NMHCs and their products are the generation of peroxyacetyl nitrate precursors and the local depletion of NOx. The magnitude of the NOxdepletion would be enhanced if the rate coefficients for the loss of the peroxyacetyl radical, which are currently not well determined, were slower.

ISSN:0705-5900    

DOI:10.1080/07055900.1990.9649367

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In this paper the drift and spread of theExxon Valdezoil spill that occurred on 24 March 1989 are simulated using a modified version of the Canadian Atmospheric Environment Service oil spill behaviour model. The model simulations show that the movement of the oil out of Prince William Sound and beyond is sensitive to the wind/ocean current combination. The net drift of the oil with wind and ocean currents taken into account is three to four times that with either wind or ocean currents alone. Although a 12‐d drift of the spill containing the higher concentrations of oil parcels is in very good agreement with observations, model simulations show the presence of oil farther to the south, albeit in lower concentrations. The lateral spread of the oil is also very well simulated by the model.

ISSN:0705-5900    

DOI:10.1080/07055900.1990.9649368

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Feedback mechanisms among decadal oscillations of Northern Hemisphere atmospheric circulation, Arctic‐subarctic ice cover and ocean circulation are studied. Decadal oscillations of the ice cover have been observed since 1950, most significantly in the Barents Sea and on the Labrador Shelf. The extreme southward extent of Labrador ice is explained by local weather conditions, such as low air temperatures and strong northwesterly winds. This weather pattern is attributed to an atmospheric circulation with low sea‐level pressure anomalies over the Eurasian Basin in the Arctic. Barents Sea ice is also highly (but inversely) correlated with this atmospheric circulation, i.e. Barents Sea ice is inversely correlated with Labrador ice. Barents Sea ice is weakly correlated with local air temperature.

ISSN:0705-5900    

DOI:10.1080/07055900.1990.9649369

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The changes in normal precipitation amounts from 1931–60 to 1951–80 are examined for stations in Eastern Canada. The area covered comprises the Maritime Provinces and those parts of Ontario and Quebec south of a line approximately 200 km north of Lakes Erie and Ontario and the St Lawrence River. Changes are computed for each of the four seasons and for the entire year. On the whole, precipitation has increased, especially in winter and summer. However, there is considerable variation throughout the area, with precipitation decreasing in some regions. General circulation models that simulate the effect of doubling atmospheric CO2also show an increase in precipitation.

ISSN:0705-5900    

DOI:10.1080/07055900.1990.9649370

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor