"Waghorn" wrote in message
...
One of my clients reported rather unusual wind speeds during a flight
from
Bedford last night. Thought I'd throw this open to ideas....
Hi Chris,
sounds like a 'nocturnal low level jet'
but I toiught these were strongest in the early morning hours,

--
regards,
david
(add 17 to waghorne to reply)

Hi David,

I was thinking along similar lines but there are some conditions lacking to
confirm it is. With a nocturnal LLJ, unlike one induced by a mid-latitude
cyclone, the cooling aloft (900-850hPa) can only occur through land at a
higher elevation. For example, the Great Plains is often used in examples
from papers I have read. However, is it possible that the urban heat from
London could have triggered an effect, such that there was a thermal
gradient between Bedford and London even to that height ? The nocturnal LLJ
is strongest in the early hours, rather than early evening.

There's a paper here, well it is used as a lecture presentation I think,
which is useful - Xuw, Ming "Chapter 2. Planetary Boundary Layer and Related
Phenomena, 2.3 Low-level Jet"
http://twister.caps.ou.edu/MM2004/Chapter2.3.pdf

And another, Blackardar (1957), Boundary Layer Wind Maxima and Their
Significance for the Growth of Nocturnal Inversions,
http://twister.caps.ou.edu/MM2004/Bl...ar1957BAMS.pdf (14.3MB)

Have you read the latter ?

Joe