Interference of the Equatorial Waves on the 2017 Indian Monsoon Northward Progression

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Steven Harvey
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1 F5BCC0A4E13BBD103123C&thid=OIP.4gaj08EcIqXuIdGNdiwwUAEsDI&q=monsoon+pi ctures&simid= &selectedindex=119&mode=overlay&first=1 Interference of the Equatorial Waves on the 2017 Indian Monsoon Northward Progression Sue Chen, Maria Flatau, Jerome Schmidt, Craig Bishop Naval Research Laboratory Monterey, CA Sixth WMO International Workshop on Monsoons, November 2017, Singapore

2 Outlines Background for the bogus ISM onset Large-scale conditions of the 2017 Indian Summer Monsoon (ISM) onset Modeling approach: full-physics Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) idealized equatorial wave framework Results from the idealized COAMPS equatorial wave experiments

3 Flatau et al. (J. of Climate, 2001, JGR 2003) The bogus ISM onset can be triggered by a sequence of events 1. Warm Bay of Bengal (BoB) SST in late spring, Cooling of in May from ISO, TC, or monsoon depression 2. Equatorial westerly vertical shear 3. Presence of MJO, Kelvin, or Rossby waves at the equator

1. Through what mechanisms do the Equatorial Waves interfere with the ISM onset? Scientific Questions 2. What is the role of the reversal of SST in the Bay of Bengal for the bogus ISM onset?

4 1. Through what mechanisms do the Equatorial Waves interfere with the ISM onset? Scientific Questions 2. What is the role of the reversal of SST in the Bay of Bengal for the bogus ISM onset? 2BFZplaF&id=978CEB450E0FA8C DB16F90B3012CD5F20&t hid=oip._-fzplafqfvjflh1bgw1aesdh&q=monsoon+pictures&simid= &selectedindex=137&mode=overlay&first=1

5 India Meteorological Department (IMD) June 1 June 6

6 Rainfall of 2017 ISM NOAA CPC rain analysis May 25 June 6 June 1 Multiple rain maxima followed by a one week dry period May 25 June 1

7 MJO & Equatorial wave activity during the 2017 Indian Summer Monsoon TC Mora NOAA CPC OLR analysis

8 US Navy Global Environmental Model (NAVGEM) Analysis: May 29 TC Mora CC Kelvin Wave

9 US Navy Global Environmental Model (NAVGEM) Analysis: June 1 CC Rossby Wave

10 US Navy Global Environmental Model (NAVGEM) Analysis: June 12 ISM

11 NAVGEM Zonal and Meridional Vertical Wind Shear ( hpa) 5S-5N, E Meridional Hadley Circulation index

(ANALYSIS) NAVDAS COAMPS GALWEN-LIS Atmosphere Setup LSM Hydrology connector NCODAQC CICE SST, SSH ICE, PROF SHIP,

12 Air-Ocean-Wave-ICE-LSM-Hydro Coupled COAMPS Forecast and Data Assimilation System Atmos OBS obs, remote sensing, text GLOBE WVS Climo User configurable 6 or 12 hr atmosphere update cycle ESMF/NUOPC NAVGEM ATMOSPHERE BC (ANALYSIS) NAVDAS COAMPS GALWEN-LIS Atmosphere Setup LSM Hydrology connector NCODAQC CICE SST, SSH ICE, PROF SHIP, GLDR NCODA NCOM/ROMS SWAN/ WW3 Ocean OBS NCODA QC DATABASE GDEM MODAS DBDBV DBDB2 OSUTide Rivers Ocean Setup WAVE Setup GOFS gww3

Idealized COAMPS Kelvin Wave Experiments May 1 SST Initial 10 m Wind May 28

13 Idealized COAMPS Kelvin Wave Experiments May 1 SST Initial 10 m Wind May 28 SST - May 1 SST Bay of Bengal (BoB) Analytical Kelvin wave initialization (Schmidt et al. 2018) E-W periodic boundary conditions 45 km horizontal resolution Aqua planet Full nonlinear physics 1. Dry (no convective feedback), no vertical shear, no radiation 2. Time-invariant (fixed) SST a) Uniform (~30 C) b) Real pre-monsoon NCODA May 1 SST (warm BoB) c) Real May 28 SST from NCODA (cold BoB)

Chimeric Kelvin Wave Experiments U Wind Chimeric

14 Idealized COAMPS 10 day idealized dry Kelvin wave simulation No vertical shear No surface flux No radiation Chimeric Kelvin Wave Experiments U Wind Chimeric Equatorial waves (Chao, J. of Met. Soci. Japan, 2007) 10 days simulation

Coriolis induces a Rossby wave response behind the idealized, no vertical wind shear,

toward equator and strengthen the Kelvin wave structure at the equator and suppress the

the Rossby wave component of Chimeric Kelvin wave Idealized COAMPS Kelvin Wave Experiments U

15 Coriolis induces a Rossby wave response behind the idealized, no vertical wind shear, dry-kelvin wave dynamic effect The role of surface enthalpy flux is to advect enthalpy flux toward equator and strengthen the Kelvin wave structure at the equator and suppress the Coriolis induced Rossby wave growth Cold late May SST condition in the BoB favors the growth of the Rossby wave component of Chimeric Kelvin wave Idealized COAMPS Kelvin Wave Experiments U wind, 10 Days simulation, no surface flux Poleward SW flow U wind, 10 Days simulation with surface flux, uniform 32 C SST

2 m/s) SW flow from 0-10N V wind difference May 28 SST-May 1 SST 4-day simulation 10 days idealized

16 U wind, May 1 SST, 4-day simulation Real SST Experiments Unstable dry Rossby Wave emerged after 4 days and last less than 1 day Increased N-S SST gradient in late May 2017 enhanced a small (< 0.2 m/s) SW flow from 0-10N V wind difference May 28 SST-May 1 SST 4-day simulation 10 days idealized dry Kelvin wave simulation No vertical shear With surface flux May 1 and May 28, 2017 real SST No radiation

17 Dry-Kelvin experiment with May 1 N-S SST gradient Enhanced the poleward meridional flow in the Rossby Wave component of the Chimeric Kelvin wave The poleward meridional flow only reaches ~ 12 N

18 Rain and 200hPa-800hPa shear difference

19 Summary The large-scale conditions for the 2017 ISM onset is similar to the bogus ISM onsets discussed by Flatau et al. (2001, 2003) The role of SST (cooling in the BoB) on the Chimeric dry Kelvin wave growth and its influence on induced poleward flow is systematically investigated using four COAMPS idealized experiments in the no vertical shear condition The no surface flux experiment show the Chimeric dry Kelvin wave structure (Kelvin & Rossby) emerged due to the beta effect The real SST idealized experiments showed for Chimeric dry Kelvin wave, the increased SW flow in Rossby wave is not due to colder BoB SST but from increased 0-20N SST gradient in late May A similar result from the moist Chimeric Kelvin wave but is stronger than the dry Chimeric Kelvin wave

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Understanding El Nino-Monsoon teleconnections Dr Neena Joseph Mani Earth & Climate Science INSA Anniversary General meeting, Session: Science in IISER Pune 27 th December 2017 Mean State of the equatorial