Outflow Events Flashcards
What is onshore wind?
wind flowing in from the sea
Where are outflow events most likely to occur
Areas where there are high mountain ranges. Moving air travelling over the mountain ranges are subject to a warming effect due to the adiabatic lapse rate.
What is offshore wind?
Wind that flows out to sea from land.
Define adiabatic lapse rate?
rate at which surface air changes temp with changing elevation
cools at 2 degrees per 300 m of rise
warms at 3 degrees per 300m of descent
Why does air warm as it descends?
the compression effect creates heating
What do we call onshore winds in fire management?
Inflow winds
Why does RH decrease as air descends
why is this dangerous?
Because the air is expanding due to the warming effect of adiabatic lapse rate.
Dries out fine fuels, making them more susceptible to ignition and spread.
What is crossover?
When RH drops below Temperature in summer
a.k.a The Black CROSS
Very volatile situation for fires!
What causes outflow winds?
Pressure imbalance where there is a High Pressure system on land and a low over the sea.
Primarily a winter time occurrence… but can happen in the summer
What does trough mean?
Low pressure system
What is a thermal trough?
How do they affect Fire management?
A low pressure system resulting from intense heating of the surface of the land.
They are dangerous because they can travel out to sea and generate outflow winds due to the pressure being lower than the on land pressure. These thermal lows pull the high pressure air over the mountains which creates bad crossover situations.
Catastrophic potential
Why are Fjords, canyons and gullies an issue?
They create situations where wind velocity is increased due to a funnel effect. This can happen in both outflow and inflow wind events but more dangerous in outflow events due to lower RH.
What is subsidence
Refers to air falling in relation to the land around it. Also includes to the compression associated with descending air masses.
What is the fire behaviour triangle?
Weather Topography Fuels
WTF
