Role of Tibetan Plateau and other topography in Indian weather


Gp Capt (Dr) B Nandi

1. Introduction

Tibetan plateau has enormous impact on the weather pattern over Asia. We need to understand its role in influencing the weather so that we can forecast weather better. It towers over southwestern China at an average elevation of 4000 m above sea level and is known as “the roof of the world”, covering more than 2.5 million sq km and spans approximately 1000 km north to south and 2500 km east to west.  The great Himalayan Mountain range lies on the southern periphery with world’s highest peak Mount Everest As the Third Pole of the earth, the Tibetan Plateau is an important water source of Asia. The 10 major rivers in China and abroad developed from the Tibet Plateau and provide living and production water for 1/3 of the world’s population in East Asia and South Asia. Tibet is not only a place of gigantic mountains, but it is also a land of beautiful lakes. Despite its high elevation, it is surprisingly littered with 1500 lakes, among which 787 scenic lakes are as big or larger than a square kilometer.

2. Features

Note worthy features about Tibetan Plateau are

  • (a) Capable of inducing local/regional circulations.
  • (b) It acts as barrier to low level wind flow being solid earth up to a height more than 4000m
  • (c) The roof top like Tibetan plateau is a vast source of heat (summer) and sink (winter) in the middle troposphere
  • (d) Elevated sink of moisture and source of many rivers. Major rivers are Yellow river (China), Arun river (Nepal), Bhote Kosi river( Nepal), Mekong river (China, Myanmar, Laos, Thailand, Combodia, Vietnam ), east flowing Yangtse river (China), Brahmaputra river (India, Bangladesh), Indus river (India, Pakistan), Ganga (India, Bangladesh), Chambal river (Nepal, India), Karnali river (Nepal, India), Irrawaddy River (Myanmar), Salween river( China, Myanmar).

3. Tibetan Plateau as circulation inducer.

Elevated place with gentle slope at the edge is capable of inducing local circulation through Anabatic and Katabatic wind. Let us look into the topographic map of Pakistan as shown below

Compare with the afternoon satellite image for the clouding over the elevated hill top.

It is evident from the clouding that the Afternoon Anabatic wind being moist and rising wind has given rise to the visible cloud at the hill top all over the Middle East and Himalayan region.

Night Katabatic wind being descending motion it does not have visible evidence, except that similar clouding is not seen during morning. The NWP chart for 925hPa will confirm that the synoptic scale flow is not the cause of such clouding.

4. Barrier

On a regional scale it forces the air to flow parallel to the topography and maintains the same pattern up to certain height though thermal wind as being source of elevated heated hill. That is how we have westerlies over north Arabian coast line and SWlies over Pakistan, deflected as NWly and blow parallel to Himalayan range over NW India and Gangetic plain. Ridge over NW India is due to Coriolis force turning the wind to the right.

Himalayan range being massive the flow pattern of NWly parallel to Himalayan range over Gangetic plains continued up to 600hPa chart and wind started climbing over the barrier at 500hPa chart. This a scenario before full onset of monsoon and shown in below two charts 600hPa and 500hPa

After the onset of monsoon SWly wind on impinging over Arakan hills, along the east coast of Bay of Bengal turns SELy and then easterlies by Khashi hills to meet the NWlies and form a circulation over Bihar ( As seen in 06UTC 925hPa chart for 14JUN2024). With the progress of the season and heating, heat low shifts to Pakistan and the SElies/Elies spreads to NW India forced by the West-East oriented Barrier of Himalayas.

Easterlies are maintained north of Monsoon trough and south of Himalayan barrier. This can go up even up to 500hPa.

5. Source of heat in middle atmosphere.

After the vernal equinox (20/21March) sun starts moving northward into Northern Hemisphere. Sensible heat starts rising over the elevated plateau making it like an oven and also making mid troposphere much warmer than the atmosphere over the plains in the south and north of the plateau. Apart from general plateau TP has Karakoram range on the west and Himalayan ranges on the south which are higher than the general plateau.  These two zones have glaciers and this makes the diabatic heating little different from general TP. A feature Karakorum vortex (or Western Tibetan Vortex) has recently been recognized as a large-scale atmospheric circulation system related to warmer (cooler) near-surface and mid-lower troposphere temperatures above the Karakoram in the western Tibetan Plateau (TP). WTV came to be known as while doing research on why glaciers are growing in this third pole of the earth. This WTV induces anticyclonic anomaly to the wind flow in (JJA) summer and Cyclonic anomaly in (DJF) winter.  Warmest position will depend on

  • (a) Diabatic heating -Sensible heating by solar radiation, turbulent heat flux, long-wave radiation and latent heat release associate with Convective clouds.
  • (b) Adiabatic heating – subsidence(warming)/upward motion(cooling)
  • (c) Thermal Advection by wind
  • (d) Cloud coverage for reduction in insolation

A heat low develops over the Tibetan plateau. This warm core low will obviously have anticyclonic thermal wind as a part temperature pressure relationship. This anticyclonic thermal wind will turn the wind above warm core low to anticyclonic wind. Warm core is maintained by the latent heat release by the convection thus we get warm core anticyclone over Tibet. This part of anticyclone supports convective cloud development as its genesis and diverge out the air from the top of cloud layer as see in case of cyclones to maintain the upper tropospheric anticyclone.

The feature to be noted that during Monsoon we have Tibetan high and West Asian High, usually over Iran/Afganisthan. Of late with stream function analysis of 15 years reanalysis data it has been shown that there is a massive anticyclone extending from 400E to 1200E and it has been given the name as South Asian High (SAH), shown in the figure.

Observational thermodynamic structure for (a) northern summer (June–August) and (b) southern summer (December–February). Black contours are the 200-hPa streamfunction (1.0 × 106 m2 s−1). Negative contours are indicated by dashed lines. Shading with white contours shows vertically integrated diabatic heating 〈Q1〉 (W m−2) calculated as a residual in the thermodynamic energy equation. Red contours are estimates of mass-weighed vertical mean temperature for 500–200 hPa (K).

Citation: Journal of Climate 35, 3; 10.1175/JCLI-D-21-0004.1

The decoupling of TA up to 300hPa with 200hPa and above anticyclone, shifting of the anticyclone centre and even to the extent that TA is not seen suggest that there has to be a role of general circulation dynamics through Rossby wave teleconnection or monsoon_ desert mechanism. The diabatic heating due latent heat release from the massive rainfall over Indian continent must be having relation in maintaining the SAH. Let us see the position of anticyclone as captured by the analysis GFS, India model for 00UTC/01JUL2024.

There are two anticyclone centre at 400hPa, one marked over Iraq and the other is marked at 290N/820E, west of Kathmandu and north of Lucknow. The maximum temperature is located at 500hPa chart as shown by Windy (ECMWF) chart. Location of maximum temperature of 70C at 300N/810E. This indicates that sensible heating is responsible for anticyclone at 400hPa as clouding was reported minimum in the region as seen in cloud top alert image.

This indicates that sensible heating is responsible for anticyclone at 400hPa as clouding was reported minimum in the region as seen in cloud top alert image for 00UTC/01JUL2024 by

TA location at 300hPa is over Chattagram (220N/920E) not exactly a location of coldest cloud top, indicates the role of latent heat release and temperature advection. 300hPa chart is shown below.

The major high is over Afghanistan from 600hPa to 150hpa. Charts are shown below.

The location of high is connected with general circulation mode with STJ to the North and ETJ to the South and subsidence over the region from monsoon-desert mechanism. Subsidence is shown by the Water vapour image from

when SAH takes the mode of West Asian High the subsidence becomes quite evident with the rise in Maximum Temperature at Leh during 27JUN2024 to 04JUL2024 given in the table

Leh Max Temperature290C310C310C310C320C310C320C320C

An anticyclone over the surface of earth when diverging air outward must be associated with subsidence to compensate the diverging air. But, an anticyclone at a particular level in free atmosphere can be associated with descending motion or ascending motion to diverge the air horizontally outward. As we have
seen the anticyclone at 400hPa is associated with surface heating (elevation of Himalayan range itself is close to 500hpa) should be having descending motion and minimum clouding. This means anticyclone at 400hPa when close to foot hills of Himalayas must be associated with minimum clouding. 300hPa anticyclone must
associated with ascending motion and cloud with latent heat liberation for its existence. Above 300hPa mostly it will be cold core due evaporation cooling of the cloud and anticyclonic circulation must reduce or vanish or even may turn to cyclonic circulation in still higher level. Deep layer anticyclone from near tropopause must be associated with subsidence and convergence of air near tropopause to supplement the descending and diverging air.

It is clear that there is a South Asian High (SAH) extending from 400E to 1200E and 100N to 400N. Within this domain of high there can be single centre of anticyclone there can be multiple centre of anticyclones during SW monsoon over Asia. By its location we may refer it as West Asian Anticyclone (WAA)or Tibetan Anticyclone (TA). 100hPa to 200hPa anticyclone is quite related by their position with usually westward slope with height. 300hPa anticyclone may be relatd with the100-200hPa counterpart or may not be. Following table provides the date wise location of anticyclone centre at 100, 200 and 300hPa for the period of 01Jun2024 to 05Jul2024

Table for location of upper tropospheric Anticyclone Centre by Latitude (deg E) /Longtude by deg N)

100hPa29/59 29/9426/66 29/9724/109Ridge at 2524/56 24/9825/9424/70 25/9026/9126/9628/96
200hpa23/84 24/10121/67 25/9917/8219/67 21/10919/58 21/10421/10118/56 21/9516/50 24/9518/55 25/9419/64 25/97
300hPa25/51 19/76 26/10525/50   21/10325/51 17/79 22/9822/59 17/74 19/8619/54 21/10422/10320/9620/82 22/9924/9025/95

100hPa26/94 25/6926/8628/8528/9429/9128/8527/7726/7127/65 27/8626/64 27/95
200hpa24/9625/95 20/6725/9425/9426/9027/9025/8525/8024/7525/67
300hPa25/9924/10417/60 21/9723/9716/54 21/78 25/9424/9125/8526/8023/60 24/9523/74 23/94
100hPa25/69 27/9227/51 28/8527/64 30/8427/74  30/8030/79 27/6030/65  30/65  30/6430/60
200hpa23/66 26/9725/50 26/10625/46 26/9528/8926/48 28/8726/41 28/8527/8527/7027/6230/60
300hPa25/9724/9726/9028/8928/8628.8627/8028/78 24/9528/7930/55 22/91
300hPa31/65  30/65

Let us first concentrate on tables for 100hPa. At this level we have

(a) Single anticyclone mode dominating the entire domain of SAH

(i) WAH west of 800E

(ii) TA east of 800E

(b) Two different centres one east of 800E and other west of 800E

(c) Two different centres west of 800E

  • When West Asian high dominates the entire domain we have both the STJ and TEJ. The width of the STJ with 40kts wind in the periphery extends from 350N to 450N and lies west of 950E with core speed 80kts or so. The width he width of the TEJ with 40kts wind in the periphery extends from equator to 250N and covers entire domain from 1100E to 500E with core speed 100kts or so. Strong subsidence is seen over the northen half of the anticyclone. Erxample is given below with the chart of 02Jul2024 00UTC GFS-India analysis.
  • When TA dominates the entire domain we have STJ with 40kts wind in the periphery extends from 350N to 450N and lies East of 950E with core speed 60kts or so. The width of the TEJ with 40kts wind in the periphery extends from 50N to 200N and westward coverage is seen mainly up to 700E with core speed 60-80kts. Deep Convective cloud is seen around the centre of the anticyclone. Example is given below with the chart of 14Jun2024 00UTC GFS-India analysis and WV image from for the same time .
  • When there are Two different centres one east of 800E and other west of 800E, STJ is hardly seen with 40kts wind in the periphery extends from 350N to 400N and lies East of 900E with core speed 50-60kts. The width he width of the TEJ with 40kts wind in the periphery extends from 50N to 200N and covers the entire domain with core speed 60-80kts. Strong subsidence is seen over the centre of western the anticyclone and upper level clouding is seen over the centre of the anticyclone on the eastern side with subsidence north of the eastern centre. Example is given below with the chart of 21Jun2024 00UTC GFS-India analysis and WV image from for the same time .
  • When Two different centres both west of 800E, STJ is not seen and 40kts wind in extends from 350N to 400N and lies East of 1000E. The width of the TEJ with 40kts wind in the periphery extends from 50N to 230N and covers entire domain from 1100E to 500E with core speed 100kts or so with at least three wind maximum. Example is given below with the chart of 26Jun2024 00UTC GFS-India analysis and WV image from for the same time .

Mostly North of the anticyclone centre 40kts or stronger winds associate with STJ at 100hPa are seen. TEJ extends to Oman with dominance of West Asian anticyclone; with Tibetan Anticylone TEJ extends up to central Arabian Sea. This indicates that 100hPa anticyclone cntre is closely related to strong wind belt north and south of it.

Now we would like to concentrate on 200hPa anticyclone centres. It remains close to the 100hPa centre position with few degrees slope. 100hPa centre is usually found NW of centre at 200hPa . Position is related to wind maxima of STJ to north and wind maxima of TEJ to the south, with major difference that STJ is much stronger at this level and TEJ is weaker in comparision to 100hPa. Cross equatorial flow to southern Hemispher is prominent at 200hPa.

300hPa centre of anticyclone may be related with 200hPa position keeping 200hPa position to the NW. that is the snticyclone slpes towards NW. 300hPa anticyclone can be unrelated with 200hPa anticyclone. like on 30Jun2024 the centre of anticyclone at 220N/910E is related with latent heat release due clouding and warm advection. There was no anticyclone centre near by at 200hPa. There be three anticyclone centres within the domain of SAH. The col co zone between the anticyclones at 300hPa are prone for heavy rainfall and cloud burst as thoudanderstorm develop in this zone hardly can move and pour down the precipitaion over a limites area.

6 Other important Topography

Besides Somalia Coast at equator, there are three peninsulas north of South Indian ocean, the home of Mascarene High. This are the most unique features for formation of Monsoon. Namely, the three peninsulas are Arab peninsula, Indian peninsula and Indochina peninsula which includes two major seas – Arabian sea and Bay of Bengal. During the summer these land masses gets heated up by direct solar radiation and heat Low with North-South trough over peninsula forms with the interaction of these three lows two zones of subsidence that is low level anticyclone forms over Arabian Sea and Bay of Bengal by April-May.

06UTC analysis chart of 925hPa of 16May2024 shows anticyclone over west Arabian sea (170N/620E) and central Bay of Bengal (160N/880E). ITCZ around 50S with low pressure at (070S/540E). Westerly winds prevail north of equator. The Northerlies of Arabian sea anticyclone meets the Southerlies of Bay of Bengal anticyclone with a cyclonic turning of wind around the Peninsular India. Between Arabian sea anticyclone and equatorial westerlies there is a cyclonic circulation (060N/640E). Let us see when cross equatorial flow starts at Somali coast on 06UTC analysis chart of 925hPa of 21May2024.

Above chart shows cross-equatorial wind at Somali coast is taking place and the Inertial anticyclone has merged with Arabian sea anticyclone leaving it as ridge along 630E. Now the warm equatorial westerlies meet the cold northerlies of east Arabian sea west of Srilanka region which helps realeasing large sensible heat and in turn helps the existing vortex, NE of Srilanka to become well marked and MOV (Monsoon Onset Vortex). This MOV created the onset of monsoon into south Andaman Sea.

Subsequently this MOV grown into Severe Cyclonic storm called “REMAL” which had a landfall over Bangladesh near West Bengal border and moved over NE India, taking the SW Monsson to NE Bay of Bengal. See below the northern limit of monsoon advancement.

7. Rossby wave generation

Tropics being mostly barotropic Rossby wave generation depends on Conservation of Potential vorticity and potential vorticity is defined as

Potential Vorticity=(ζ + f)/h

This means if there is gradient in ‘f’, the coriolis force, which infact exists over earth. ‘f’ is zero at equator and maximum at pole. So, for any north-south (meridonial) flow ‘ζ’, the relative vorticity, will be changing with the flow generating a wave motion

(a) Simple wave formation during monsoon

Let us look at the chart of 925hPa on 01Jun2024 for 00UTC

A meridonial flow across Somalia coast as SWly wind can be seen. as this flow moves northward ‘f’ increases. so to preserve the potential vorticity(PV), ‘ζ’ must decrease, meaning acquiring anticyclonic vorticity and we see the wind turning anticyclonically and becomes NWly over west coast of India and even over Madhya Pradesh region. Once we have NWly, it flows into a region of decreasing ‘f’ . Therefore, ‘ζ’ must must increase to preserve the PV, ‘ζ’ must increase, meaning acquiring cyclonic vorticity that is how SWly wind off east coast of India devlops. Even Sly can be seen over Chhatrisgarh and east of it. this completes the wave generation and the combination of north-south ridge and trough across India (Mp and peninsula) This wave motion can be seen in good depth. let us look at the chart of 600hPa on 01Jun2024 for 00UTC.

Wave motion is there but at southern at comparitively souther latititude with generation of anticyclone and cyclonic vortex.

(b) Mid tropospheric circulations

In the above chart of 600hPa on 01Jun2024 for 00UTC, we can see strong NEly flow along the east coast of Africa, This Nly flow generates Cyclonic Vorticity by conserving PV. So we find a long cyclonic shear line between the NEly and SWly of monsoon current off east coast of Arica.

In the above chart of 600hPa on 01Jun2024 for 00UTC, we can also see strong NWly flow over Afganisthan this generates the Cyclonic circulation over Pakistan and adjoining Rajasthan. Simlarly many a occassion Mid-tropospheric cyclonic circulation over Gujrat and adjoining region develops whenever we have good anticyclonic flow over Aganisthan.

In the above chart of 600hPa on 01Jun2024 for 00UTC, we can also see strong NEly flow (Due to anticyclone over Telengana nad Andhra Pradesh) over Bay of Bengal generating Cyclonic circulation over North Andaman Sea.

8. Arabian Sea Inversion

An low-level inversion is created by the upwelling of ocean current at least up to central Arabian sea. . Upwelling of ocean current forms due to strong Ekman pumping due to Somali jet. Close to west coast of India ocean temperature is higher and the trapped moisture by inversion over the central Arabian Sea burst into atmosphere, giving rise to copious rainfall over west coast along with the impact of western ghat.

9. Cross Equatorial Flow (CEF)

As widely agreed, relatively predominant channels of CEFs lie over the Asian–Australian Monsoon (AAM) region in the lower troposphere (near 925 hPa) in summer, including the Somali CEF at around 45°E, Bay of Bengal (BOB) CEF at around 90°E, South China Sea (SCS) CEF at around 105°E, Celebes Sea CEF at around 125°E, and New Guinea CEF at around 150°E. All of these five CEF channels are named by their geographic location of their climatological state, among which the Somali CEF exhibits the strongest magnitude but weakest interannual variance compared with the other four channels.

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