depressions

Question 1

how does a depression form

Answer 1

• a mid-latitude depressions forms when warm tropical maritime air mass from the North Atlantic meets a cold polar maritime air mass along the front between 30 degrees and 60 degrees in latitude
• the westerly flowing jet stream in the upper atmosphere plays a vital role in the anticlockwise uplift of air which produces a well-defined warm front, warm sector and a cold front
• as the upper air jet moves upwards, from a trough to a ridge it accelerates, diverges and draws air upwards creating low pressure centre at the ground surface with an anticlockwise pattern of winds
• the path of the depression follows the westerly movement of the jet stream and is associated with a sequence of weather with the passage of a the warm front, warm sector and the cold front.

Question 2

general weather conditions associated with depressions

Answer 2

RAINFALL
- Area of low pressure, Tropical maritime air rising, cools, reaches dew point (RH 100%) and condenses = cloud formation.
WINDY
- isobars close together= steep pressure gradient
-Therefore, winds quickly move from high to low pressure
-Air accelerates as it moves from trough to ridge (sharp uplift of air molecules)
LOW/MILD TEMPERATURES
-Clouds, restrict the level of solar radiation the therefore temperatures may be cooler.

Question 3

1. before the warm front

Answer 3

• cirrus clouds
• dry and cold
• wind is light southerly
• air pressure falling high (1002)

Question 4

2. at the warm front

Answer 4

• nimbostratus clouds
• consistent rain
• warm
• wind is strong and more westerly
• air pressure falling

Question 5

3. at warm sector

Answer 5

• dull, low, flat, stratus
• relatively dry
• warm
• winds moderate and westerly
• air pressure steady

Question 6

4. as cold front passes

Answer 6

• cumulonimbus
• heavy downpour
• temp falls rapidly
• wind is more northernly
• air pressure rising

Question 7

5. after cold front

Answer 7

• cumulus
• showers cold temperature
• wind north or north west
• air pressure rising

Question 8

how does a depression end?

Answer 8

• the cold front has a steeper pressure gradient and moves faster than the warm front
• when the cold front catches up with the warm front it forms an occluded front
• the tropical air by this stage will have been squeezed upwards leaving no warm sector at ground level
• as uplift of air is reduced, so too is the amount of condensation and cloud formation
• air pressure begins to rise, and wind speeds decrease.
• the colder air replaces the uplifted air and infills the depression