Naked Science Forum
Life Sciences => The Environment => Topic started by: IzzieC on 24/08/2018 14:00:24
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Bernard asks:
"There is a song that indicates that it only rains at night in Camelot, and it seems to me that thunderstorms (with their heavy precipitation) are more likely in the late afternoon and evening. However I really don’t know how much of a statistically significant variation occurs during each day – can anyone tell me please?"
What do you think?
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Convective clouds produce most shortlived summer thunderstorms over a wide area all at once. Sun shines on moist ground, damp air rises rapidly into cold upper atmosphere and accelerates upwards because it doesn't cool as quickly as the rate of ambient temperature decrease with height ("lapse rate"). Once above the condensation level this accelerates faster and forms towering cumulus or cumulonimbus clouds, and convection within these clouds makes water droplets and ice crystals rise and fall, creating a potential difference between the top and bottom of the cloud (see the Kelvin electrostatic generator on this forum https://www.thenakedscientists.com/get-naked/experiments/electricity-water-kelvin-water-drop-generator ). Eventually this will discharge to another cloud or to ground.
Summer "fine weather" cumulus clouds take time to grow, so at UK latitudes are unlikely to reach electrical instability until some time after the maximum solar heating, say 2 - 3 pm (local time is distorted by ridiculous "daylight saving" clock aberrations) but it may happen quicker at lower latitudes. They usually disperse after sunset.
Advected frontal storms last for a longer period and form in a moving line rather than a static area as a cold polar air mass rolls over warm (and therefore moist) tropical air. In the UK the line usually moves west to east at about 20 - 30 knots and can hit any point at any time of day or night. Most likely to be found along a cold front on a weather map, but a real nasty can occur when the cold front (which generally moves faster than a warm front) overtakes a warm front to produce an occlusion. This can look from below like harmless mist and drizzle with a benign covering of stratus so off we go into the wide grey yonder, only to break through the stratus at 5000 ft and find all hell going on upstairs - "embedded CuNim" chucking snow, hail and lightning all around you, up to 60,000 ft, in the middle of the night. Study and avoid.
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Hi Alan, Many thanks. My question was somewhat modified by Izzie when she posted it for me! My actual question (by email - I am new to this forum) was:
"Does rain fall more heavily at different times of the day in Cambridgeshire?
There is a song that indicates that it only rains at night in Camelot, and it seems to me that thunderstorms (with their heavy precipitation) are more likely in the late afternoon and evening. However I really don’t know how much of a statistically significant variation occurs during each day – can you and your colleagues tell us please?"
So this is a general query about precipitation, not just that during thunderstorms.
Regards,
BernardG.
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Yes. Particularly in summer, more rain falls in mid-afternoon (thanks to convective cloud precipitation) than at other times, but the difference is less noticeable in winter when most of the rain is advective rather than convective. However it is also the case that official daytime in Cambridge lasts almost 17 hours in June and less than 8 in December, so if the rain fell continuously, it would mostly fall at night in winter.
PS. The Camelot myth having now been assigned to Tintagel, "it do rain there most of the bloody time, me dear."
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Yes, i think in afternoon the weather temperature is quiet low which makes it easier for the storm to blow.
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Hi Alan, Many thanks. My question was somewhat modified by Izzie when she posted it for me! My actual question (by email - I am new to this forum) was:
"Does rain fall more heavily at different times of the day in Cambridgeshire?
There is a song that indicates that it only rains at night in Camelot, and it seems to me that thunderstorms (with their heavy precipitation) are more likely in the late afternoon and evening. However I really don’t know how much of a statistically significant variation occurs during each day – can you and your colleagues tell us please?"
So this is a general query about precipitation, not just that during thunderstorms.
Regards,
BernardG.
In the summer the atmosphere is affected by the solar heat, which moisture then rises in and precipitates out suddenly. In general, the solar heat sustains clouds during the day and in the early evening, as the sun dissapears the water precipitates out giving heavier rain.