2. Air Mass Weather Lesson 33/34

3. What is an Air Mass? An air mass is a large volume of air covering many thousands of square miles and having fairly uniform properties. The characteristic of the air mass depends upon: a) the source region b)the surface over which it is travelling

4. What is an Air Mass? The main source regions are the stable high pressure belts: –Sub-tropical –Polar

5. Air Mass Modification As air masses move away from their source region, they are affected by moisture and heat exchanges from the surface. –They may be heated from below, this causes instability. –They may be cooled from below, this increases the stability. –A sea track increases the moisture at low level, –A land track will not modify the moisture content to any great degree.

6. Air Masses Affecting the UK

7. Source Regions of Air Masses Worlds stable high pressure regions. –Classified chiefly on the basis of two primary factors: Temperature »Polar »Arctic »Tropical Surface of origin: »Maritime »Continental

8. Cold Air-masses Polar Maritime –Between Greenland and N. Canada Arctic Maritime –From above the Arctic Circle Polar Continental –From the Siberian High over central Asia.

9. Warm Air-masses Tropical Maritime –From the Azores High in the mid Atlantic Ocean. Tropical Continental –from the North African sub-tropical high pressure belt.

10. Summary of Air Masses Summer & Winter Air Masses: –Tropical Maritime –Polar Maritime –Returning Polar Maritime

11. Summary of Air Masses Winter Only –Polar Continental Short sea track. Long sea track. –Arctic Maritime Summer Only –Tropical Continental

12. Air Mass Properties Characteristic properties are: –Uniform mean temperature –Moisture content –ELR –Stability –Weather –Visibility

13. Air Mass Characteristics Tropical air cooled from below Polar air heated from below

14. Tropical Continental L H

15. Tc Air Mass Properties

16. Polar Continental (Short Sea Track) L H

17. Pc (Short Sea Track) Air Mass Properties Very dry

18. Polar Continental (Long Sea Track)

19. Pc(Long Sea Track)Air Mass Properties

20. Tropical Maritime

21. Tm Air Mass Properties

22. Polar Maritime

23. Pm Air Mass Properties

24. Arctic Maritime

25. Am Air Mass Properties

26. Returning Polar Maritime

27. rPm Air Mass Properties