High Temperature at Leh

During the second half of July 2024 and first week of August saw quite high temperature over Leh arfield. This high temperature over the already rarified atmosphere created problem for aircraft operations. Maximum temperatures are shown belowon the graph from 16July2024 to 07Aug2024.

Thehighest temperature 37⁰C was seen on 29th July2024. we like to study the occurrence of this high temperature. Clouding report on 24July2024 and29July2024 was same before and during the occurence of maximum temperature. so we are choosing these two dates for pilot study. METARs on 24July2024 are as follows

The day  (29 JUL 2024)  when maximum temperature was 37⁰C,  METARs from 000UTC till maximum temperature occurrence are

Both the day reported clouding in METARs are FEW070 SCT120 meaning that as far as sensible heating (balance of shortwave radiation and outgoing long wave radiation) was concerned, it is more or less same. But what made the ultimate surface heating more and early maximum temperature on 29JUL2024. Is it thermal advection? Cannot be, as winds were light at surface as well as 500hPa GFS charts. Then there can be only one agency like the adiabatic heating due to subsidence that can make the difference. At 0530UTC on 24JUL2024 the surface wind was 17004KT and temperature dewpoint was 29/03 and on 29JUL2024 the surface wind was also 17004KT and temperature dewpoint was 34/03. That is 5⁰C higher. This difference has to be due subsidence.

If we have anticyclonic circulation at surface we are bound to get subsidence to feed the diverging air of anticyclone. So we can examine the 10m wind chart and 500hPa chart, Which can be regarded very close to the ground and in PBL due terrain elevation of Ladakh. 10 wind charts of 24JUL2024 for 0600UTC is shown below.

10 wind chart do not have any anticyclone in the vicinity of Leh and 500hPa chart of 24JUL2024 for 0600UTC is presented below

Anticyclone at 500hPa is at 37⁰N/86⁰E and it was not influencing the Ladakh region. Now let us see the 10m wind charts at 0600UTC of 29JUL2024.

North-South ridge can be marked along 82⁰E east of Leh, bringing Subsiding easterlies. Now let us see 500hPa chart of 0600UTC of 29JUL2024.

There is an anticyclone at 36⁰N/80.5⁰E directly influencing Ladakh region and providing subsidence over Leh. Subsidence air descends at a very weak speed say 5cm/sec meaning that it takes  hours to descend from even only 900m. From upper troposphere (say 300hPa~9800m) it will take 18hours to descend to 3200m (approximately the elevation of Leh). at the rate of 5cm/sec. So we examine first the 500hPa chart of 1800UTC of 28JUL2024 to see whether subsidence is there or not (12hours prior chart), then we will see 300hPa chart of 18 hours prior to the occurrence of Maximum temperature of 37⁰C.

There is an anticyclone at 36⁰N/79.5⁰E directly influencing Ladakh region and providing subsidence over Leh. This means that at least we had 12hours of subsidence time for air to reach ground from higher level. Confirming that we had subsidence on 29JUL2024 which was missing on 24JUL2024.

Subsidence is from higher level is required to produce
high temperature at surface level of Leh and 500hPa. Usually, temperature over Leh at 300hPa is around -22⁰C, with 6.0km descend and adiabatic compression air will acquire temperature of approximately 38⁰C. So let us examine the anticyclones at 300hPa. 300hPa chart of 1200UTC of 28JUL (18 hours prior to occurrence of maximum tempaerature) is shown below.

There is an anticyclone at 35.5⁰N/77⁰E at 300hPa directly influencing Ladakh region and providing subsidence over Leh which can reach ground by 18 hours. The anticyclone at 300hPa needs a feeder form level below tropopause to reach 300hpa. Means there must be convergence at tropopause level which cannot go up,therefore, must descend. So we look for convegence at 100hPa (close to tropopause) 54hours prior to occurrence. 100hpa chart of 0000UTC of 27July2024 is shown below.

Ladhak is in SE quadrant of elliptical anticyclone confirming the convergence zone and descend of air. This descend must continue to feed 300hpa subsidence through 200hPa level. So we examine 00UTC chart of 28July2024at 200hPa(30 hours prior)

At 200hPa chart there is trough in the westeries along 93⁰E and anticyclone is 35⁰N/70⁰E. Ladhak is in the region of strong NWly of the trough and can be said confluenting with weak NWlies of the anticyclone. Thus have the subsidence and working as feeder to 300hPa subsidence.

Water Vapour image provides information of zone of subsidence as black image, whitish portion show mid-tropospheric moisture. It can be seen in the following water vapour images that subsidence over Ladakh and specifically over Leh was there from 26Jul2024 but on 29Jul2024 had whitish region.

Images starting from upper left corner and clockwise are of 0812UTC of 26Jul2024, 0612UTC of 27Jul2024, 0612UTC of 29Jul2024, 0612UTC of 28Jul2024.

Whitish back gound of mid day image of WV on 29July2024 started somme where around 0200UTC. This indicates that subsiding air has already crossed the mid tropospheric level and closing for descend to surface level. around the midday this mid tropospheric level moisture intervened with the terristerial cooling at 6.5 micron and returned the radiation to ground giving a shade higher temperature than 36⁰C of 28July2024.