Ch 5 - Pressure Systems Flashcards
Cyclones
Low pressure systems
Depressions
Rotate Anti clockwise
Quick to form and separate
Smaller than high
Few 100 to a few 1000km across
Convergence at surface
Convection
Weather Associated with Cyclones
Showers
Cloudy
Unstable - CU CB
Windy
High humidity
High Temp
Surface heating
Orographic / Lee Depressions
When the air is forced around a mountain instead of over can cause a lack of ai on the lee side of the mountain - an orographic low
CU SH Convection
If cold front passes over the top it can lead to more convective activity - TS
Thermal or Warm Depressions
Caused by thermal heating - can have -
Thermal Lows - follow the ITCZ
Warm anticyclone
Cold Anticyclone
Troughs
Extension of low pressure systems
More convergence which means more instability
Will experience SEV low pressure wx;
- Cu Cb TS +RA +SH
- Wind shear
Anticyclones (High pressure system)
Around 1500nm across
Associated with;
Stable conditions - Clear sky / calm wind
Subsidence and Divergence at the surface
Haze and decreased visibility (suspended particles)
Can cause a subsidence inversion
Rotates clockwise in the northern hemisphere
Blocking High
Blocking anticyclone
Massive high pressure system sitting on top or in between two pressure systems
Warm anticyclone
Forcing low pressure systems around it
Quasi-Stationary (not moving)
Weather Summer; poor vis, clear, calm. Winter; Clear, calm, fog / stratus
Cols
High pressure system (usually)
In between 2 lows and 2 highs
Usually show instability - intense heating at the surface - CB TS
Ridges
Extension of the H extending away
Shows H pressure system weather conditions
Flat Pressure Pattern
Exact same as col-conditions
No isobars over a massive area
CBs TS
Jan - Temp and Pressures (NH)
EQ lows follow the ITCZ
Sub-tropical pressure system and polar front depressions move slightly according to season
Jan - SH
ICTZ down to 20’ S up to 5-7’N(Dakar)
Africa, S. America, Northern Aus
Low pressure systems over land masses
high pressure subtropical highs over the oceans 22-45’S averaging 30C
N Hemisphere Winter
Russia and Siberia - V. Cold (cold anticyclone) cold High
Cold anticyclone over Canada (Canadian high)
Warm anticyclone over Azores (Azores high)
Warm high over California
Massive low over Iceland and Scandinavia
July NH
ITCZ 25-28’N
Africa, Siberia, Japan, N America
Siberia - Low pressure system (Baluchistan low/Asian low)
Canada - Canadia Low - Thermal Low
Azores Anticyclone - reaches florida and Western Europe
Icelandic Low splits into three - Greenland, Iceland and Baltics (cold lows)
Winter SH
Subtropical high over the whole area
Polar lows at ~60’S
