WEATHER MAPS Flashcards
Four properties of the atmosphere
Pressure, density, temperature, humidity
Define pressure
The total weight of the column of air up to the upper limits of the atmosphere above a reference point.
= 1kg per square cm.
Measured in Hectopascal (Hpa)
Define Isobars
Lines on a wx map that joint together areas of equal pressure.
When drawn, wx systems become apparent (Lows, highs etc.)
Buys Ballots Law
If you stand with your back to the wind, the Low pressure is on your right. (SH only)
Wind flow around pressure systems (SH)
Clockwise around LOW (cyclones)
Anti clockwise around HIGH (anticyclones)
Define Anticyclone
A region of relatively high pressure, surrounded by enclosed isobars, at the centre the pressure is highest.
Define Cyclone
A region of relatively low pressure, more or less circular & concentric Isobars surrounding central L where pressures are lowest.
Define ridge
Associated weather?
A ridge of high pressure is an extension of isobars away from the parent High. Never marked on wx charts.
Associated with wx conditions similar to High pressure systems.
Define trough
Associated wx conditions?
A trough of low pressure is an extension of isobars away from the parent Low. The pressure at any point along the trough is LOWER than the pressure either side of the trough.
Sharp change of wind direction, conditions variable - can be like wx associated with a Low pressure system, NSW, or a region of severe TS.
Trough vs. front?
Sharp change in wind direction.
All fronts of any kind mark troughs. Other troughs are marked by a solid bold line on a wx chart.
(All fronts are troughs, not all troughs are fronts)
Define Col
Associated weather?
Area of opposing Highs and Lows (two of each), where a region of almost even pressure results between the systems.
Light & variable winds, moisture fed into converging axis may produce TS in summer, or fog in winter.
Define a front
Fronts mark the boundaries between air masses that have different temp & moisture characteristics.
Define a tropical cyclone
A low pressure system in the tropics, that with the right conditions, will develop to become a depression, and may become a tropical cyclone.
Are named (unlike mid-lat/polar cells).
Describe wind-flow in relation to Isobars
The spacing of isobars dictates the strength of wind. If isobars a close together, then there is a sharp increase/decrease of pressure over that area. High pressure will flow to low pressure, and therefore the sharp change in pressure gradient will result in strong winds.
Curvature of isobars however will dictate direction of wind flow (doesn’t just go direct from high to low pressure).
Describe winds in relation to Anticyclones
High pressure systems have more spaced apart isobars, and therefore have light winds.
Wind circulation is Anticlockwise in the SH.
