Chapter 3: Red Sea Trough

Question 1

Rainy season in Middle east:

Answer 1

october to april

• during this period: cyclones associated with cold upper trough
  
  • move from west to east over the med. sea
    
    • associated with RST sometimes

Question 2

Red Sea trough:

Answer 2

• tongue of low pressure
  
  • extending northward from southern red sea towards eastern mediteranean and levant at lower atmosphere levels
    
    • RST attains its largest amplitude in low level atm.

Question 3

Red sea trough origin:

Answer 3

• sudan monsoon low
  
  • part of:
    
    • large scale subtropical/ Equatorial low pressure thermal system
  • center oscillate from ethiopia - sudan (in summer) to the red sea (winter)

Question 4

Red sea trough is regarded as extension of:

Answer 4

• African Monsoon trough
  
  • large scale subtropical - tropical low pressure thermal synoptic system

Question 5

The development, intensity and northward extension of RST:

Answer 5

due to:

• topography
• thermal forcing factors

over the red sea region

Question 6

Types of Red Sea trough (first type)

Answer 6

• Non active:
  
  • hot dry weather
    
    • over middle east and vicinity
  • results from:
    
    • east south easterly flow at lower atmosphere
• Active:
  
  • major cause of flash floods in Arid southern levant
  • RST accompanied by upper trough from north over EM
    
    • trough enhances upward motion and unstable conditions which results in
      
      • Development of convective storms
      • (Heavy torrential rain, intense precipitation) heavy showers and thunderstorms E and S part of middle east

Question 7

Months:

Answer 7

• Most frequent: Oct - Nov
• second most frequent: April
• RST shift westward: Sep - Jan
• RST shift eastward: Feb - May
• Frequency of occurance negligible: June - Aug

Question 8

Types of Red Sea trough:

Answer 8

• Wet:
  
  • (all months except oct) located east of Dry RST
    
    • at sea level RST is east of 500 hPa trough
      
      • under the inflection point where
        
        • PVA and upward motion take place
  • pronounced diurnal variation
  • northward and westward (over EM) extension of RST more pronounced than dry RST
  • sea level pressure is lower by 3 hPa (except oct)
  • pronounced trough at 500 hpa from black sea towards northern egypt
    
    • thermal low at sea level is weakening with height
      
      • replaced by relatively high pressure aloft
• Dry:
  
  • A ridge or zonal flow at 500 hPa accompanies dry RSTs