B

                     

                A weather map is an important tool for geographers. A series of three or four maps presents a continuous picture of weather changes. Weather forecasters are able to determine the speed of air masses and fronts; to determine whether a pressure area is deepening or becoming shallow and whether a front is increasing or decreasing in intensity (强度) .They are also able to determine whether an air mass is keeping its original characteristics or taking on those of the surface over which it is moving. Thus,a most important function of the map is to show a general picture of conditions in the atmosphere at a given time.

                All students of geography should be able to interpret a weather map accurately. Weather maps contain a large amount of information about weather conditions existing at the time of observation over a large geographical area. They reveal in a few minutes what otherwise would take hours to describe. The United States Weather Bureau issues information about approaching storms,floods,frosts and all climatic conditions in general. Twice a month it issues a 30-day “out-look” which is a rough guide to weather conditions likely to occur over broad areas of the United States. These 30-day outlooks are based upon an analysis of the upper air levels which often set the stage for the development of air masses,fronts,and storms.

                Much effort is being made today to achieve more accurate weather predictions. With the use of electronic instruments and earth satellites,big gains have taken place recently in recognizing and tracking storms over regions which have few meteorological stations(气象台). A lot of experiments are also in progress for weather modification(人工改变天气) studies. But the limitations of weather modification have produced few results except in the seeding(撒干冰) of super cooled,upslope mountainous winds which have produced additional rainfall on the windward(上风的) side of mountain ranges.

6. Paragraph 1 mainly deals with .

   A. the functions of weather maps

   B. the work of weather forecasters

   C. the importance of weather forecast

   D. the relationship among weather elements

7. What's the advantage of using weather maps?

   A. It uses electronic instruments.

   B. It enables man to control the weather.

   C. It gives general information about climate.

   D. It offers much information about the weather.

8. The 30-day forecast is determined by examining.

   A. air masses           B. upper air levels

   C. satellite reports    D. changing fronts

9. At the present time,experiments are being performed in .

   A. 30-day outlooks

   B. controlling storms

   C. controlling weather

   D. accurate weather predictions

10. Artificial rainfall has been most successful in the .

   A. lake areas

   B. grasslands

   C. western slopes of mountains

   D. windward sides of mountains

违法和不良信息举报电话:027-86699610 举报邮箱:58377363@163.com

精英家教网