2018 exam Flashcards
define absolute instability
parcel of air always warmer than the environment, it will continuously rise as it is less dense than the atmosphere around it
define conditional instability
initially the parcel of air is cooler and more dense, at some point it will saturate and follow the moist adiabatic, crossing the temperature making it unstable
describe the physical source of radiation for visible satellites and why they are useful in meteorology
measures short wave radiation reflected back into space from the surface and clouds ( measures albedo of surface).
dark surfaces appear black
shallow broken clouds - albedo of 0.3-0.4 and appear gray
thicker clouds will have higher albedo 0.65-0.9
snow will appear whit e abedo .095
not available at night
describe the physical source of radiation for IR satellites and why they are usefull in meteorology
measures long wave radiation emitted by: surface atmospehre and clouds
white = low temp
black = high temp
gives a good contrast between high and low clouds
available at night
describe the physical source of radiation for water vapour satellites and why they are useful in meteorology
radiation emitted by water vapour
measures moisture in the upper troposhere
white= humid
black = dry
usefull to pick out dry air in anticycloned and descenting air behind fronts
why is it hard to identify fog at night
fog is low and has a similar temperature to the surface not much contrast in ir
describe how the use of multiple infrared channels might help identify night time fog
using multiple channels can improve the contrast compared to looking
what is thermal wind
cold air is denser than warm air so in a cold column of air , pressure will decrease more rapidly with height
Horixontal pressure gradient s and geostrophic winds will change wiht heights in regions where ther are horizontal pressure grradients
thermal wind is the vector between the difference in surface geostrophic wind and geostrophic wind at a particular hight
sketch a diagram
thermal wind vector from north- westerly - westery
angle diagram to the rigth
How would you expect the temperature of the air mass to change over the
next few hour- regards to ‘The winds from a radiosonde ascent are seen to back with height from northwesterly
to westerly and to increase in speed. Draw a sketch to show the
approximate thermal wind vector and the location of the warm and cold air
This is cold advection (geostrophic wind blowing from direction of cold air) and so
expect temperature to decrease over the next few hours.
Explain how the north-south temperature gradient between polar and midlatutude
air leads to strong westerly winds in the jet stream over the Atlantic.
surface winds blowing south from polar to mid latitude, hot to cold, high level winds will be blowing south easterly meaning thermal winds will blow fromt he west to east causing the strong westerly winds insert diagram
Draw a sketch showing the forces acting on the geostrophic flow around a
high pressure system and the resulting wind direction.
.
) The surface pressure is observed to change by 4 hPa over a distance of 100
km. Estimate the geostrophic wind speed.
ug = 1 1.2×10−4 4×100 100×1000 = 33ms−1
Explain how friction modifies the wind speed and direction in the boundary
layer. You should use sketches to help explain
Friction acts against the wind and reduces the wind speed in the boundary layer,
hence reduces the Coriolis force. Net balance of forces shown in figure 4 with
component of wind blowing outwards from the centre of the high.
Why are high pressure systems associated with subsiding air aloft? [
Component of the wind out from high pressure in the boundary layer results in low
level divergence of the wind from the high pressure. By continuity this must be
matched by subsidence from aloft.
