Atlas, Elliot

Fiehn, Alina

Hepach, Helmke

Krüger, Kirstin

Quack, Birgit

Tegtmeier, Susann

OceanRep

  Transport of halogenated VSLS from the Indian Ocean to the stratosphere through the Asian monsoon circulation   Alina Fiehn (GEOMAR, Kiel, Germany)  Helmke Hepach (GEOMAR), Elliot Atlas (RSMAS), Birgit Quack (GEOMAR), Susann Tegtmeier (GEOMAR), Kirstin Krüger (UiO) CT3LS Meeting, Boulder, CO, 7/22/2015 (Tegtmeier et al., in prep.) Modelled CHBr3 mixing ratio @ 17 km JJA Stratospheric entrainment of oceanic bromine (VSLS) (Liang et al. 2014, ACP) Modelled Bry mixing ratio @ 13 km 2 The tropical Indian Ocean is projected to be a strong source region for  stratospheric bromine based on climatological emission estimates.  Bromoform emission climatologies 3 Bottom-up climatology (after Ziska et al., 2013, ACP) nmol m-2 h-1 ? (Ziska et al., 2013, ACP) Bromoform water concentrations No measurements exist in the Indian Ocean except for the Bay of Bengal (Ziska et al., 2013; Yamamoto et al., 2001). (Liang et al., 2010, ACP) Top-down climatology global: 5.32 Gmol Br yr-1 global: 2.5 Gmol Br yr-1 OASIS-SONNE cruise • July and August 2014 • West Indian Ocean • VSLS concentrations measured in air and water every 3 h • Emissions calculated after Nightingale et al. (2000): Bromoform (CHBr3) emissions CkF ∆⋅=4 The Indian Ocean is a strong source region for VSLS.  OASIS-SONNE  ship (JA 2014) Ziska et al.      (2013)  IO August 2014  Monsoon circulation during NH summer How much does the Indian Ocean contribute to stratospheric bromine? 5 Strong surface wind above IO during  monsoon; flow towards India/ Bay  of Bengal.  Polluted air in the stratosphere through Asian monsoon circulation (Randel et al. 2010). Surface winds, July 2014 - ERA-Interim HCN VMR (ppbv) - ACE satellite FLEXPART model • Lagrangian transport model with convection scheme       (Stohl et al., 2005) using 6-hourly ERA-Interim fields • Forward and backward trajectories, run for 3 month  • Output: 6 hourly 1. Bromoform emissions from OASIS-SONNE cruise 10,000 forward trajectories from measurement sites Atmospheric lifetime profile for emitted VSLS 2. General transport from Indian Ocean  Forward trajectories from 1°x1° grid over West Indian Ocean surface 961 trajectories released every day during July 3.  Source regions of Asian monsoon anticyclone Backward trajectories from 1°x1° grid at 17 km 27,000 trajectories released on July 31st Simulations for 2014: 6 OASIS-SONNE transport regimes Subtropical westerlies Monsoon circulation Tropical convection 1. OASIS-SONNE simulations 10 day forward trajectories  7 Entrainment of bromoform @17km  Low efficiency of transport (0-1%) High efficiency of transport (≈2%) Subtropical westerlies Monsoon circulation Tropical convection Highest efficiency of transport (≈3%) 8 More entrainment from the Indian Ocean than from the equatorial Atlantic (1 %) but less than from the tropical West Pacific (3-10 %; Tegtmeier et al. 2012, ACP). 1. OASIS-SONNE simulations Entrainment of air from the Indian Ocean Trajectories (fwd) after 30 days - Entrainment @17 km convection Convective outflow 8.2 % Trajectories after 10 days: Release from the sea surface Main entrance region to the stratosphere is above India, Bangladesh, and Myanmar.  July 2014 10 2. Indian-Ocean simulations Density of trajectories @17 km Median age: 35 days Asian monsoon anticyclone Vertical velocity and geopotential height anomaly at 100 hPa ERA-I July 2014 ERA-I July 2014 Geopotential height anomaly and  horizontal winds at 100 hPa Strong anticyclone in July at  100 hPa.  Upward movement above Bay of Bengal, Tibetan Plateau, Southeast Asia, and China. up down 11 H 3. Anticyclone simulations Anticyclone - air masses 70% of the air masses at 17 km origin from the boundary layer. From this, 48% origin from the oceanic boundary layer and 52% from land. 10 day backward trajectories  Release at 17 km Boundary layer (BL) source regions Median age:  25 days Transit time: BL to 17 km 12 3. Anticyclone simulations July 2014 July 2014 Days Anticyclone - oceanic source regions Anticyclonic entrainment from Bay of Bengal and tropical West Pacific is even larger than from tropical West Indian Ocean. Oceanic boundary layer source region, July 2014 13 3. Anticyclone simulations Anticyclonic bromoform source regions 14 Strong bromoform emissions from Bay of Bengal, Arabian Sea and equatorial Indian Ocean combined with effective transport are projected to lead to intense stratospheric entrainment of bromoform above Asian monsoon circulation.  Global FLEXPART/ERA-I simulations with Ziska-climatology (Tegtmeier et al. talk) [%] Conclusions • The subtropical and tropical Indian Ocean is a strong source region for VSLS (bromoform, dibromomethane, and methyl iodide). • The Asian monsoon circulation provides an effective pathway for oceanic VSLS to the stratosphere. • High modeled stratospheric bromine mixing ratios result from high bromoform emissions from the Bay of Bengal, Arabian Sea and tropical Indian Ocean. 15 

Transport of halogenated VSLS from the Indian Ocean to the stratosphere through the Asian monsoon circulation

  Transport of halogenated VSLS from the Indian Ocean to the stratosphere through the Asian monsoon circulation Alina Fiehn  Helmke Hepach, Elliot Atlas (RSMAS), Birgit Quack,  Susann Tegtmeier, Kirstin Krüger (UiO) ACAM Workshop, 10.06.2015 Asian monsoon transport  to the stratosphere HCN concentration from ACE satellite (Randel et al. 2010, Science) Tropospheric pollution Measured bromoform (CHBr3) concentration in the surface oceans (Ziska et al. 2013, ACP) Are oceanic VSLS entrained via the Asian monsoon circulation ? JJA ? 2 Oceanic halogen containing very short lived substances (VSLS, lifetime <0.5 a) How much is emitted? Asian monsoon transport Ocean Troposphere Stratosphere Tropical Tropopause Layer (TTL) Halogen loading Lifting by deep convection Anticyclone How much reaches the stratosphere? How fast is the transport? Suggested VSLS transport VSLS emissions CHBr3   CH2Br2   CH3I 17 d      150 d     3.5 d    3 VSLS emissions CHBr3   CH2Br2   CH3I 17 d      150 d     3.5 d    OASIS cruise • July and August 2014 • West Indian Ocean • Trace gas concentrations measured in air and water every 3 h • Emissions calculated Bromoform (CHBr3) emissions CkF Elevated at coasts, banks and in upwelling regions 4 Strong source region for VSLS.  FLEXPART • Lagrangian transport model with convection scheme • Input: 6 hourly ERA-Interim fields • Forward or backward trajectories  • Output every 6 hours for 3 months 1. Bromoform emissions from OASIS cruise 10,000 forward trajectories from measurement sites Atmospheric lifetime profile for emitted VSLS 2. General transport from Indian Ocean  Forward trajectories from 1°x1° grid over West Indian Ocean surface 1404 trajectories released every day in July 2014 3.  Source regions of monsoon anticyclone Backward trajectories from 1°x1° grid at 17 km 27,000 trajectories released on July 31st, 2014 Simulations Stohl et al. 2005 5 ERA Interim input Vertical velocity and geopotential anomaly at 100 hPa July 2014 July 2014 Geopotential anomaly and  horizontal winds at 100 hPa Strong anticyclone in July  at 100 hPa  Upward movement above Bay of Bengal, Tibetan Plateau, Southeast Asia, and China up down 6 OASIS transport regimes Subtropical westerlies Monsoon circulation Tropical convection 1. Simulation: OASIS 10 day forward trajectories  7 Entrainment of bromoform at 17km  Low efficiency of transport (0-1%) High efficiency of transport (≈2%) Subtropical westerlies Monsoon circulation Tropical convection Highest efficiency of transport (≈3%) 8 1. Simulation: OASIS More than in the Equatorial Atlantic (1 %) but less than in the West Pacific (3-10 %, Tegtmeier et al. 2012). Entrainment of air masses  from the Indian Ocean Stratospheric entrainment at 17 km convection Convective outflow 7.2 % 10 day forward trajectories  20 day forward trajectories  Release from the sea surface Main entrance region to the stratosphere is above India, Bangladesh, and Myanmar.  Median age: 35 days Trajectory distribution at 17 km July 2014 9 2. Simulation: Indian Ocean Anticyclone at 17 km 70% from boundary layer. 48% origin from oceanic boundary layer, 52% from land. 10 day backward trajectories  Release at 17 km Boundary layer source regions Median age: 25 days Time needed from boundary layer to 17 km 10 3. Simulation: Anticyclone July 2014 July 2014 Oceanic source regions Anticyclonic entrainment from Bay of Bengal and West Pacific is even greater than from Tropical West Indian Ocean. Oceanic boundary layer source region, July 2014 11 3. Simulation: Anticyclone Conclusions • Tropical Indian Ocean is a strong source region for VSLS. • Monsoon transport is fast enough for VSLS from the Indian Ocean to reach the stratosphere. • ≈50% of the tropospheric air masses in the anticyclone have oceanic boundary layer source region. • Expected high entrainment from Bay of Bengal during Asian monsoon season. 12 Potential temperature Indian Ocean transport 14 Month of release Run Reach 17 km Median age [d] June 2012 18 6.0 % 28.5 June 2013 19 5.9 % June 2014 20 5.9 % Anticyclone source regions 15 Month in 2014 Boundary layer Land Ocean Arabic Sea Bay of Bengal West Pacific Middle America July 70 52 48 15 21 53 11 August 69 52 48 9 16 61 13 September 71 34 66 5 13 70 12 Emissions and entrainment 16 Campaign Ocean Mean CHBr3 emissions (pmol m-2 h-1) Mean CHBr3 entrainment OASIS West Indian 1520 12.3 nmol 2-3 % TransBrom Open West Pacific 463 ≈15 nmol 3-10 % SHIVA Coastal West Pacific 1338 ≈50 nmol 5-10 % DRIVE Northeast Atlantic ≈700 10 nmol 2 % MSM 18-3 Equatorial Atlantic 643 2.9 nmol 1 % 

Transport of halogenated VSLS from the Indian Ocean to the stratosphere through the Asian monsoon circulation

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