New INCOMPASS observations of the monsoon over southern India with - - PowerPoint PPT Presentation

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New INCOMPASS observations of the monsoon over southern India with - - PowerPoint PPT Presentation

Dec 14, 2023 306 likes •594 views

New INCOMPASS observations of the monsoon over southern India with Doug Parker, Andrew Turner, Arathy Menon, Bob Houze, GS Bhat, G Mrudula, and many others 1 The spatial distribution of monsoon rainfall is strongly associated with

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New INCOMPASS

  • bservations of the monsoon
  • ver southern India

with Doug Parker, Andrew Turner, Arathy Menon, Bob Houze, GS Bhat, G Mrudula, and many others

1

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Jennifer Fletcher -- Indian monsoon

The spatial distribution of monsoon rainfall is strongly associated with orography

03/07/2018 2

  • Rainiest areas are where moist

flow over oceans encounters mountains: the Meghalaya Plateau and upstream of Western Ghats and mountain ranges on Myanmar coast.

  • In South India, the east coast is

in the rain shadow and has a different peak rainfall season.

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Research Questions

  • What processes are associated

with rainfall offshore?

  • What is the boundary layer

structure of the onshore flow?

  • What produces rainfall over the

tops of the Western Ghats and the rain shadow?

3

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INCOMPASS South India IOP, June 2016

  • Six flights over Western Ghats and eastern Arabian Sea
  • Surveyed diurnal cycle and synoptic evolution over ten day period
  • In situ aircraft data supplemented with radiosondes, satellite and

reanalysis for context

4 Photo by Adrian Pingstone

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The IOP was characterised by the passage of an active phase of the MJO/BSISO

5

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Using methods of Roundy et al 2012 and Kikuchi et al 2012

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Two distinctive rainfall regimes associated with large scale mode

  • Offshore phase
  • First half of IOP
  • Heavy rainfall over eastern

Arabian Sea

  • Suppressed rainfall over coast

and mountains

  • Coastal phase
  • Second half of IOP
  • Intermittent rainfall over Arabian

Sea

  • Heavy rainfall over coast and

mountains

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Offshore phase mean Coastal phase mean

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Combined aircraft and radiosonde observations averaged over offshore and coastal phases

theta qv u theta qv u

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Combined aircraft and radiosonde observations averaged over offshore and coastal phases

theta qv u theta qv u

  • Offshore phase
  • Cooler, dryer boundary layer over

Arabian Sea

  • Weak onshore flow, low critical

layer

  • Coastal phase
  • Warmer, moister boundary layer
  • ver Arabian Sea
  • Stronger onshore flow, westerlies

up to about 400 hPa

  • Mid-level dry layer from western

Arabian Sea

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Combined aircraft and radiosonde observations averaged over offshore and coastal phases

theta qv u theta qv u

  • Offshore phase
  • Cooler, dryer boundary layer over

Arabian Sea

  • Weak onshore flow, low critical

layer

  • Coastal phase
  • Warmer, moister boundary layer
  • ver Arabian Sea
  • Stronger onshore flow, westerlies

up to about 400 hPa

  • Mid-level dry layer from western

Arabian Sea

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Combined aircraft and radiosonde observations averaged over offshore and coastal phases

theta qv u theta qv u

  • Offshore phase
  • Cooler, dryer boundary layer over

Arabian Sea

  • Weak onshore flow, low critical

layer

  • Coastal phase
  • Warmer, moister boundary layer
  • ver Arabian Sea
  • Stronger onshore flow, westerlies

up to about 400 hPa

  • Mid-level dry layer from western

Arabian Sea

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Flight number phase Time of day Mean rainfall (mm/h) SST (oC) Fr Amini CAPE Mangl. CAPE Mid-trop q (g/kg) B959 Offshore Day 2.3 28.58 0.6 889.0 156.7 6.5 B961 Offshore Day 1.1 28.78 1.3 510.9 65.5 6.7 B962 Offshore Evening 1.3 28.78 0.9 NA 340.6 6.3 B963 Coastal Night 0.2 28.62 0.9 NA 175.8 5.1 B964 Coastal Day 0.0 28.55 1.1 1370.0 715.0 3.3 B965 Coastal Evening 0.8 28.55 1.0 NA 2158.6 4.5

Controls on offshore rainfall

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Flight number phase Time of day Mean rainfall (mm/h) SST (oC) Fr Amini CAPE Mangl. CAPE Mid-trop q (g/kg) B959 Offshore Day 2.3 28.58 0.6 889.0 156.7 6.5 B961 Offshore Day 1.1 28.78 1.3 510.9 65.5 6.7 B962 Offshore Evening 1.3 28.78 0.9 NA 340.6 6.3 B963 Coastal Night 0.2 28.62 0.9 NA 175.8 5.1 B964 Coastal Day 0.0 28.55 1.1 1370.0 715.0 3.3 B965 Coastal Evening 0.8 28.55 1.0 NA 2158.6 4.5

Slightly cooler SST during coastal phase

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Flight number phase Time of day Mean rainfall (mm/h) SST (oC) Fr Amini CAPE Mangl. CAPE Mid-trop q (g/kg) B959 Offshore Day 2.3 28.58 0.6 889.0 156.7 6.5 B961 Offshore Day 1.1 28.78 1.3 510.9 65.5 6.7 B962 Offshore Evening 1.3 28.78 0.9 NA 340.6 6.3 B963 Coastal Night 0.2 28.62 0.9 NA 175.8 5.1 B964 Coastal Day 0.0 28.55 1.1 1370.0 715.0 3.3 B965 Coastal Evening 0.8 28.55 1.0 NA 2158.6 4.5

Flow is mostly unblocked in both phases

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Flight number phase Time of day Mean rainfall (mm/h) SST (oC) Fr Amini CAPE Mangl. CAPE Mid-trop q (g/kg) B959 Offshore Day 2.3 28.58 0.6 889.0 156.7 6.5 B961 Offshore Day 1.1 28.78 1.3 510.9 65.5 6.7 B962 Offshore Evening 1.3 28.78 0.9 NA 340.6 6.3 B963 Coastal Night 0.2 28.62 0.9 NA 175.8 5.1 B964 Coastal Day 0.0 28.55 1.1 1370.0 715.0 3.3 B965 Coastal Evening 0.8 28.55 1.0 NA 2158.6 4.5

CAPE is anti correlated with offshore rainfall due to buildup of BL humidity

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Flight number phase Time of day Mean rainfall (mm/h) SST (oC) Fr Amini CAPE Mangl. CAPE Mid-trop q (g/kg) B959 Offshore Day 2.3 28.58 0.6 889.0 156.7 6.5 B961 Offshore Day 1.1 28.78 1.3 510.9 65.5 6.7 B962 Offshore Evening 1.3 28.78 0.9 NA 340.6 6.3 B963 Coastal Night 0.2 28.62 0.9 NA 175.8 5.1 B964 Coastal Day 0.0 28.55 1.1 1370.0 715.0 3.3 B965 Coastal Evening 0.8 28.55 1.0 NA 2158.6 4.5

Mid-tropospheric drying associated with reduced rainfall offshore

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Data from low level runs (below 500 m)

theta qv u rainfall

  • ffshore

coastal

Arabian Sea boundary layer: during the coastal phase, when convection was suppressed offshore, boundary layer humidity built up to the highest levels observed in the campaign.

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Observations in the Western Ghats

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Afternoon rainfall during coastal phase

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Upslope easterlies stronger, earlier in coastal phase

Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

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Dry intrusion

Relatively weak

  • nshore flow

(a) Offshore phase

+ θ a n

  • m

a l y + θ a n

  • m

a l y u = 0

Relatively strong

  • nshore flow

cooler, drier boundary layer warmer, moister boundary layer

(b) Coastal phase

u = 0 Dry intrusion Afternoon Afternoon

drying of mixed layer drying of mixed layer drying of mixed layer drying of mixed layer 400 500 700 900 950 400 500 700 900 950

Art by Beth Tully

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Hypotheses to investigate further

  • Local thermodynamic properties play

a more important role in offshore rainfall than orographic blocking does.

  • Mid-tropospheric dry intrusions are a

major determinant of offshore rainfall and in the thermodynamics of the

  • nshore flow.
  • Upslope flow on the lee side of the

Western Ghats occurs in the afternoon and can contribute to convective triggering on the mountain tops and rain shadow if other conditions permit.

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Thank you

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Are these precipitation responses over ocean and land generally seen with the passage of the BSISO?

  • New results:

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS

  • IOP. QJRMS, in review.

Met7/GPM IR and reflectivity

  • Precipitation shifts from stratiform to

convective over the course of the IOP

  • Offshore rainfall in the evening is

congestus-like.

25

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Data from low level runs (below 500 m)

theta qv u rainfall

  • ffshore

coastal

  • Arabian Sea boundary

layer: low level drying

  • bserved in all flights as

the onshore flow approached the coast.

  • Boundary layer moisture

budget analysis suggests this is due to entrainment of free tropospheric air/ downdrafts

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Fletcher et al, 2018: The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. QJRMS, in review.

Data from low level runs (below 500 m)

theta qv u rainfall

  • ffshore

coastal

There is considerable variability in temperature and winds, especially in the offshore phase when convection was active