Regional Meteorology

1
Regional Meteorology

• Mean circulation types
• South
• North
• Associated weather patterns
• Study period (Oct 2000 Apr 2001)

2
Introduction

• Study area incorporates tropic, sub-tropics and
  temperate latitudes
• Detailed information for South Africa, southern
  Mozambique, southern Botswana and Zimbabwe (SAWS)
• Information lacking regarding circulation in
  northern section of study area

3
Mean Circulation

• Dominated by anticyclonic circulation except
  during summer
• Mean circulation controls climate
• Weather driven by synoptic and smaller scale
  disturbances
• Surface features but not forgetting importance of
  upper air features

4
Mean Circulation

• Tropical controls
• easterly flows (waves and lows)
• Sub-tropical controls
• South Indian and South Atlantic anticyclones
• Continental high
• Temperate controls
• Westerly flows (waves and lows)

5
Weather Sequences Classification

• Fine weather mildly disturbed
• subtropical anticyclones, coastal lows berg
  winds
• Tropical disturbance
• easterly waves and lows
• Temperate disturbance
• westerly waves, cut-off lows, southerly flows,
  ridging anticyclones, west coast trough, cold snap

6
Circulation Types

• Those relevant to CAPIA study
• sub-tropical anticyclones
• ridging anticyclones
• easterly waves lows
• cut-off lows
• southerly flows

7
Subtropical Anticyclones

• High pressure system centered over the
  subcontinent
• Strong subsidence clear fine conditions
• Temperature inversions are more likely to occur
• Poorly mixed boundary layer leading to elevated
  pollution levels
• If this condition occurs for extended periods
  during summer drought

8
Ridging Anticyclones

• Associated with the westerly wave
• Leads to widespread rain over the eastern part of
  South Africa
• Can penetrate above the escarpment
• General rains and thunderstorm activity occurs

9
Easterly Flow

• Semi-stationary wave
• Warm, humid air flows from the ITCZ down to the
  subtropics
• Low level convergence at the surface and
  divergence at 500 hPa
• Strong uplift resulting in good rain over a wide
  area
• Associated with northerly winds

10
Easterly Low

• Cool cored low pressure at low levels
• Leads to good rains over the plateau
• Accounts for a high percentage of the summer
  rainfall received
• Occurs as thunderstorms and squall lines

11
Cut-off low

• Intense form of westerly trough
• Cold cored depression
• Unstable systems
• Associated with strong convergence and vertical
  motion
• Responsible for flooding

12
Southerly Meridional Flow

• Strong pressure gradient between a high to the
  west and a low to the east
• Vertical motion leads to cloud formation and
  rainfall
• System occurs mostly over coastal areas and
  Mpumalanga
• Associated with low temperatures

13
Observed vs Expected

• Meteorological parameters
• Rainfall, temperature
• Work in progress
• Extreme weather events
• Assessment of the study period
• Validation of MM5 results vs actual
• next presentation

14
Results
15
Way Forward

• Additional information required around tropical
  meteorology
• Detailed assessment of the weather patterns
  during the study period southern and northern
  areas
• Reporting of the findings in the form of a
  journal publication (co-authorship)