Answer sheet 2
1. a) A geostationary satellite orbits the earth directly above the equator at the same speed
as the earth rotates, meaning the satellite remains above the same point on the Earth’s surface. A
polar orbiting satellite circles the earth at near-polar inclination. They pass the equator and each
latitude at the same local solar time each day and cover large parts of the earth’s surface.
b) A polar orbiting satellite because geostationary satellites have very little coverage over high
latitudes and can only make measurements over a fraction of longitudes. Polar orbiting satellites
track almost directly over the poles, pass over several times per day at several different
longitudes.
2. a) and b) See Met Office analysis chart below
c) Any region marked by white. In a thermal image, the colder temperatures are represented by
white and the warmer images by grey/dark grey. A high cloud is colder than clouds closer to the
surface, e.g. over North-West Norway.
The visible channel cannot be used at night!
3. a) and b) see Met Office analysis chart below
c) The thermal image shows warmer temperatures over that region but it is often difficult to be
certain that there is cloud present using only the thermal image. Visible images are essentially a
black and white photo of the surface and clouds above it. The white colour over the region
confirms it is cloud and the thermal image shows it is warm, so therefore low cloud.
4. a) See chart below.
b) See chart, the geostrophic wind is a balance between the pressure gradient force and the
Coriolis force. At the surface, frictional forces slow down the wind, thus reduce the Coriolis
force and reduce the wind’s turning to the right. The surface wind therefore points towards the
centre of the low pressure system.
c) See thermal satellite image below.
d) and e) See chart.
e) The most rain is associated with the passage of the cold and warm fronts.
Geostrophic wind
Surface wind
Warm front
front
Cool
Warm
Cold
B
C
Geostrophic wind
Negligible wind
Cold front
front
Thermal image
5. An analysis chart is the model’s representation of the state of the atmosphere a few hours in
the past, using real observations. Forecasts are made using these analyses and a numerical
weather prediction model to predict how the atmospheric conditions will change. The forecasts
will never be completely accurate so there are always differences between the analysis and
forecast charts. How accurate the forecast is depends on a number of factors, including:
- The quality of observational data,
- Quality of model dynamics and parameterisations,
- How far in advance forecast was for,
- Type of current weather system i.e. is the atmosphere in a predictable or unpredictable state.
6. The geostrophic wind flows the opposite way around low and high pressure systems in the
Southern Hemisphere. This is because the Coriolis force acts to the left of the pressure gradient
force, instead of the right.
B
A
7. The forested land surface creates more friction at the surface than an open plain, therefore
wind speeds over the forested surface will be decreased more than over an open plain. Slower
wind speeds reduce the Coriolis force so the wind veers more strongly towards the centre of the
low pressure.
8. Westerly winds. Strong solar heating around the equator causes air to rise and then sink at
about 30 degrees N/S, creating a high pressure region (horse latitudes) and the Hadley cell. A
similar process occurs at the polar front – relatively warm and moist air rises and moves towards
the pole. The ferrel cell is created in between the two, moving air from south to north in the north
hemisphere. The Coriolis force acts on this air motion creating south-westerly air flow between
30 and 60deg N. The UK is on the northern edge of this cell, where the Coriolis force is strongest
and thus winds are almost westerly.
9. A: Cool temperatures, wind south to southwesterly, falling pressure, light rain but for a long
duration, cirrus clouds at first and then cloud base lowering as the warm front approaches
(altostratus and then stratus clouds).
B: Warm temperatures, wind southwesterly to westerly, pressure falling and then rising, clouds
clear at first and then cumulus and possible cumulonimbus with passage of cold front, short but
intense rain as cold front passes.
C: Cold temperatures, wind north-westerly, rising pressure, no precipitation, cloud clears.
10. a) Pressure decreases by approx. 1 hPa per 7 m, therefore ascending 840 m would cause a
decrease of 120 hPa. The recorded pressure would therefore be 890 hPa.
b) Temperature (in dry air) decreases by approx. 1 oC per 100 m, therefore ascending 840 m
would cause a decrease of 8.4 oC. The recorded temperature would therefore be 11.6 oC.
11. a) At night the air cools and can therefore hold less water vapour. Sometimes the air cools
enough to become saturated and dew will condense out on to surfaces such as grass. After
sunrise the air heats up again and the dew evaporates.
b) A clear night – if there are no clouds to trap in the outgoing long-wave radiation then it is
likely to become colder and therefore more likely for the air to reach its dew point temperature.