摘要:

Climatological aspects of Arctic cyclones are examined for winter and summer over a 20‐year (1973–1992) period. The primary objective is to characterize patterns of cyclone distribution examined in previous studies in terms of cyclone sea level pressure tendency (SLPT), maximum deepening rates and the frequency of cyclogenesis and cyclolysis. Results rely on output from a system detection and tracking algorithm applied to twice‐daily National Meteorological Center sea level pressure fields.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649522

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The passage of a winter storm is accompanied by changes in many surface and near‐surface parameters including temperature, humidity, wind, pressure, precipitation rate and type, cloud base height, visibility and accretion. These parameters were measured in association with the passage of precipitation‐type transitions over Newfoundland during the Canadian Atlantic Storms Program II field experiment. Three simple summaries of the observed weather events were developed. These summaries depend on the observed large‐scale synoptic conditions, which include warm fronts, a cold front and a trough.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649523

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

On 3 November 1993 a new higher‐resolution version of the regional forecast system was implemented into operations at the Canadian Meteorological Centre. The changes include modifications to the regional data assimilation system and to the regional finite‐element (RFE) forecast model. The main features of the new version of the RFE model include an increase in resolution from 100 to 50 km and to 25 σ levels in the vertical. The fields that describe the surface characteristics are generated directly on the 50‐km grid of the model from high‐resolution global geophysical datasets, yielding more details and a much better definition of the orography and coastlines. The new RFE model also includes an improved package of physical parametrizations, notably for condensation and radiation processes. The major changes to the data assimilation are a higher‐resolution analysis, and the assimilation of humidity profiles retrieved from satellite imagery.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649524

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The characteristics of the Northern Hemisphere low‐frequency temperature variability (periods 10 to 120 d) are examined using 700‐hPa analyses for 5 winters. Of particular interest is the relationship between the evolution of the low‐frequency temperature field and that of the higher‐frequency synoptic‐scale flow. The latter produces a low‐frequency heat flux divergence that can interact with the low‐frequency temperature field. The nature of this interaction is investigated by examining the relative position, both in space and in time, of the low‐frequency temperature and the heat flux divergence. The maximum temporal variance of the low‐frequency temperature is found to occur over Canada and Siberia. Although not negligible in these regions, the low‐frequency component of the heat flux divergence by the synoptic‐scale flow reaches a maximum somewhat farther to the east, near the storm track regions. The low‐frequency temperature variations are positively correlated in time with the in situ synoptic‐scale heat flux divergence, implying that the synoptic‐scale eddies act to dissipate the low‐frequency temperature variability.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649525

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Three‐time‐level semi‐implicit semi‐Lagrangian discretizations are used in many meteorological centres around the world. Following the work of Rivest et al. (1994) on two‐time‐level schemes, it is essential to modify existing three‐time‐level schemes to avoid orographically induced spurious resonance. A four‐time‐level scheme targeted as a rapidly implemented retrofit for the conventional three‐time‐level scheme, is proposed, analyzed, and evaluated in the context of the shallow‐water equations.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649526

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Summertime energy budgets of contiguous wetland tundra and forest near Churchill, Manitoba along the coast of Hudson Bay were measured over a five year period, 1989–1993. An examination of differences in energy budgets between the two sites showed that net radiation was similar in all years. Soil heat flux was greater at the tundra site in most, but not all, years. However, sensible heat flux was always larger at the forest site and latent heat flux was always greater at the tundra site. Mean daily Bowen ratios at both sites were less than unity in all years. Average Bowen ratios for the five years were 0.45 for tundra and 0.66 for forest. Wind direction is used as an analogue for changing climatic conditions where onshore winds are cooler and moister than offshore winds. Sensible and latent heat fluxes at both sites varied significantly between onshore and offshore wind regimes. However, differences between onshore and offshore fluxes at the tundra site were larger than for the forest. Thus, Bowen ratios also varied more at the tundra site. We have plotted the ratio of tundra‐to‐forest Bowen ratios as a measure of the relative sensitivity of energy partitioning to climatic change. The ratio decreases with increasing vapour pressure deficit (and increasing air temperature). We interpret these results as suggesting that energy partitioning over the wetland tundra is more sensitive to changes in climate than the treeline forest environment. Thus, as the climate warms and becomes drier, more additional energy goes into evaporation of water from the wetland tundra than from the forest.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649527

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The hydrography and circulation of Conception Bay (Newfoundland) are described based on hydrographic, current‐meter and drifter data collected over four years (1988–1991). The seasonal cycles of temperature (‐1.6 to 13–17°C) and salinity (31–32.5) in the bay closely follow those on the adjacent shelf. Exchange of bottom water was observed in April 1989. Deepwater exchange was observed from late fall to early winter of 1989–90. Tidal currents are weak, 1–2 cm s‐1for the M2and K1constituents. Observed Eulerian mean currents (<3 cm s‐1) are smaller than the standard deviation (1–11 cm s‐1); however, there is a persistent outflowing current of 10 to 20 cm s‐1within 2 km of the shoreline on the eastern side of the outer bay. The Lagrangian correlation length scale is from 4 to 10 km, in agreement with the weak coherence squared (≤0.4) found between the fixed current‐meter sites separated by greater than 4–5 km. The variable currents (up to 20 cm s‐1) tend to be cyclonic. Cyclonic eddies were observed near the mouth on the eastern side of the bay, adjacent to the outflow. A simplified fractal dispersion model gives residence times of 42 d similar to those obtained from a scaling analysis (30–40 d) and a diagnostic numerical model (30 d).

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649528

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We look at the development of the first plumes that emerge from a convectively unstable boundary layer by modelling the process as the instability of a fluid with a time‐dependent mean density field. The fluid is semi‐infinite, rotating, dissipative ‐ characterized by the ratio of its viscosity to thermal diffusivity (Prandtl number Pr = ν/κ) ‐ and initially homogeneous. A constant destabilizing heat flux is applied at the boundary and the stability of the evolving density field is investigated both mathematically and in laboratory experiments.

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649529

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649530

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0705-5900    

DOI:10.1080/07055900.1995.9649531

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor