排序方式： 共有10条查询结果，搜索用时 15 毫秒
1
1.
2.
A study of long term temperature data for fourteen Canadian cities showed that the length of the annual frost free season has increased by average of 7 days since 1940. Change in individual stations ranged from 26 to -17 days resulting in significant shifts in the mean probable dates for the first and the last frost of the season at most stations. No similar trend was shown in three non-urban control stations. Three urban factors: heat island effect, enhanced cloud cover and the rate of population growth - together accounted for 80% of the explained variance in the phenomenon. A multiple regression model was developed to describe the relationship between the change in the season and the urban factors. It is shown that for any appreciable gains to be made in the length of the season at reasonably predictable changes in temperature, such changes in temperature should be accompanied by a modest increase in cloud cover. 相似文献
3.
L. C. Nkemdirim 《Theoretical and Applied Climatology》1991,43(3):123-128
Summary Evaporation rates determined by energy balance and bulk transfer equations and confirmed with soil moisture sampling was regressed against average daytime temperature, vapour pressure deficit and wind speed over several chinook events between 1986 and 1988. The equationE = 0.45 exp (0.35
+ 0.025 — 0.133 [e
* —e]) yielded reasonable estimates of evaporation with surface soil moisture between saturation and near wilting point.E is evaporation in mmd
–1,T, u ande
* ande are temperature (°C), wind speed (ms–1), saturation vapour pressure and vapour pressure (mb) respectively. The overbar denotes daytime average.With 8 Figures 相似文献
4.
L. C. Nkemdirim 《Theoretical and Applied Climatology》1991,43(3):129-136
Summary Chinooks are warm mountain winds which occur in the foothills of southern Alberta. They are often blamed for encouraging droughts in the western prairies because of the link believed to exist between them and excessive surface and subsurface evaporation. Measurements made over four winters show that evaporation rates during a chinook exceed the net radiation flux when there is water standing over the surface. However, the vapour flux fraction reduces to a level below the potential rate once the moisture content drops below saturation level within the upper subsurface layer no thicker than 2 mm. Meanwhile, the soil moisture reservoir below that layer remains virtually undepleted even in the face of persistently strong chinook events.With 6 Figures 相似文献
5.
Data on CO, wind velocity and mixing depths collected over a five-year period show a definite association between higher levels of air pollution and SW winds in Calgary (pop. 610,000), a city 110 km E of the Canadian Rockies. The phenomenon most pronounced at wind speeds lower than 3m sec–1 is present during winds of up to 10 m sec–1. The shallow mixing depth associated with southwesterlies in this area appears to be a strong factor in the maintenance of the discrepancy. In addition, a climatological assessment of the distribution of mean mixing depths in the city shows that mixed layers are shallowest and least frequent in the S end of the city thereby increasing the potential for air pollution hazard in that part of the city. 相似文献
6.
7.
8.
Lawrence C. Nkemdirim 《The Professional geographer》1988,40(1):65-76
Results of analyses of 86 years of precipitation records for Calgary, Canada, showed that there were three periods of above normal precipitation and three periods of precipitation significantly below normal. This pattern gave the precipitation climate a quasi-periodic appearance. The average number of precipitation-days was 134 per annum. The reduction in the frequency of precipitation-days in dry years was not as significant as the equivalent reduction in precipitation amounts. A significant upward trend in the frequency of precipitation-days, which correlated with a similar trend in cloud cover, was not repeated in precipitation amounts. The upward trend in both cloud cover and precipitation-day frequency is believed to be related to urban growth and the corresponding heat island. This enhancement is more pronounced in the fall and winter months than in the spring and summer. 相似文献
9.
10.
1