C-SOLAS Pacific Cruise Summer 2002

Transcription

1 Ulrike Lohmann Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland Thanks to: Silvia Kloster, MPI Hamburg, Germany Richard Leaitch, Meteorological Service of Canada Maurice Levasseur,Univ. Laval, Canada Peter Liss, Univ. of East Anglia, UK Lisa Phinney, Dalhousie University, Canada Simo, 21 (Shaw et al., 1983, Charlson et al., 1987) C-SOLAS Pacific Cruise Summer 22 cloud droplets Lower Surface Chl image courtesy NASA php3?img_id=1793 Surface

2 Inter-species variability in algal DMSP production Fate of DMSP in sea water Simo, TEE, 21 Dinoflagellates Prymnesiophytes (Coccolithophores) & High DMSP quota (smaller ones, r ~ 2 µm) Gonyaulax grindelyi Emiliania huxleyi Diatoms Low DMSP quota (larger ones, r ~ 2 µm, probably most prevalent on Chlorophyll images) Thalassiosira tenera DMSP = dimethylsulphoniopropionate: (CH 3 ) 2 S CH 2 CH 2 COO - cellular precursor for DMS, is a zwitterionic compound found in cells of certain types of marine and seaweeds 2% of total cell carbon in marine can be invested in DMSP Carbonyl sulphide (COS) and carbon disulphide (CS 2 ) are less important (CH 3 ) 2 S CH 2 CH 2 COO - (CH 3 ) 2 S CH 2 CHCOOH Dimethylsulphoniopropionate (DMSP) DMS Acrylic Acid C-SOLAS Pacific iron-enrichment cruise Transect across the patch on July 25 th 22 2,5e6 Nanoflagellates (cells/l) 2,e6 1,5e6 1,e6 NI 12 DMS (nm) Nitrate (um) 1 Fluorescence (X1) 5,e5 OUT, D) DMS (nm) Particulate DMSP (nm) Date (July 22) Date (July 22) Latitude (degree N) Longitude (degree W) Longitude (W) Deficit in DMS inside the patch during the iron-induced diatom bloom!

3 Fate of the DMSP? 25 B) Particulate DMSP (nm) C) Bacterial production 14 (ugc L -1 d -1 ; left) 8 12 & 7 Bacterial S-demand 1 6 (nmol S L -1 d -1 ; right) crash of high DMS producing DMSP-rich nano bloom after day 7 followed by peak in bacterial biomass production with little conversion to DMS (<2%) followed by intermediate DMS producing DMSPpoor diatom bloom A) Bacteria (19 cells L-1) cloud droplets D) DMSP d consumption (nmol L -1 h -1 ) Lower Surface Surface sampling day (Merzouk et al. submitted) (Hale and Rivkin submitted) Fate of DMS HAMOCC5 / DMS cycle in the ocean DMS production: - depends on the destruction of diatoms and coccolithophores DMS consumption (whole euphotic zone -1m): - photo- (8%) f(solar irradiance) - microbial consumption (8%) f(temperature) - flux to the atmosphere (12%) f(temperature, wind speed) flux to the atmosphere Atmosphere Ocean photo DMS DMSPd cell lysis Phytoplankton DMSP Light Liss et al., PTRSL, 1997 microbial consumption zooplankton grazing Nutrients (Kloster et al. submitted)

4 Resulting annual mean DMS sea surface concentration and DMS flux from a coupled model run (ECHAM5-OM/HAMOCC5) Importance of DMS emissions for the global sulfur budget [Bates et al., JAC, 1992] DMS sea surface concentration [nanomol/l] DMS flux into the atmosphere [mg(s)/m 2 * year] DMS flux =.31 w 12 (SC/6) -1/2 (Wanninkhof, 1992) w1 = 1 m wind speed SC = Schmidt number for DMS (after Saltzman et al., 1993) (Kloster et al. submitted) cloud droplets Canadian SOLAS cruise Pacific 22 [Phinney et al., subm. to DSR, 25] OH OH, NO 3 OH, BrO, NO 3 Surface

5 Köhler Curve cloud droplets consists of Raoult s law and Kelvin equation: e(r)/ e ( ) = exp ({2 σ}/{ρ w R v T r}) = exp (a/r) r = droplet radius e (r) = vapor pressure of droplet of size r e ( ) = vapor pressure over a bulk surface of water σ = surface tension = water density ρ w Saturation ratio Critical radius Number of molecules Surface µm.126 µm 1.73 nm.52 nm 2.5 x x Cloud Droplet Formation Köhler Curve (2) Raoult s law: For a plane water surface the reduction in vapor pressure due to the presence of a non-volatile solute may be expressed: e*( )/e ( ) = 1 n s /n w = (3 ν m s M w )/(4 π M s ρ w r 3 ) = 1 - b/r 3 e s ( ) n s, n w M s, M w m s ν = vapor pressure of bulk solution = number of moles of solute, moles of water = molecular weight of the solute, water = mass of the solute, = degree of dissociation

6 Köhler Curve (3) Combination of Kelvin and Raoults equation evaluated for e*(r)/e s ( ) yields the Köhler curve: r c, S c e*(r)/e s ( ) = exp(a/r) * (1 - b/r 3 ) ~ 1 a/r - b/r 3 1. term: surface molecules possess extra energy 2. term: solute molecules displacing surface water molecules a ~ /T [m] b ~ i M s /m s [m 3 /mol] m s = mass of salt [kg] M s = molecular mass of salt [kg/mol] The critical radius r c and critical supersaturation S c are given by: r c = (3b/a) 1/2, S c = (4 a 3 /[27 b]) 1/2 Effect of Organics on Effect of other compounds on SS=.34%, r=.67 SS=.19%, r=.73 Phinney et al., manuscript in prep. Phinney et al., DSR, 25 [SO4] well-correlated with at both.19% SS (r c =86 nm) and.34% SS (r c =58 nm) Low values of the intercepts indicate that at low mass, and still determine O Dowd/Facchini et al., Nature, 24

7 (V) Organics < 1% of total (V) Effect of Organics on Organics < 1% of total.19%.34% Linear (.19%) Linear (.34%) y =.38x.34 r =.64 y =.94x.78 r =.56 r =.6 Phinney et al., manuscript in prep..34%.19% Importance of organic aerosols off the coast of Nova Scotia [Leaitch et al., subm. to JGR, 25] [SO4] ( g m -3 organics > 25% of total ) [ ] (µg m -3 ) Presence of internally-mixed organics: increases the correlation of [SO4] with increases sensitivity to [SO4] at higher supersaturations (i.e. smaller ) [] (V) %.34% Linear (.19%) Linear (.34%) Organics > 25% of total r =.8 y =.51x.31 r =.82 y = 2.17x.48 r = [SO4] ( g m -3 ) [ ] (µg m -3 ) Slope 1% higher Slope 3% higher Importance of organic aerosols off the coast of Nova Scotia [Leaitch et al., subm. to JGR, 25] Explained fraction of aerosol number concentrations during summer 1996 in the Arctic Ocean Updraft (cm/s) Flight 1 organic solubility 5 g/l 2 g/l As H 2 Flight 2 organic solubility 5 g/l 2 g/l As H 2 [Lohmann and Leck, Tellus, 25] Internal mixture Internal mixture External mixture Station2: 12 h from open ocean 14 5 Obs: 2-3 cm -3 cloud droplets Obs: cm -3 Station 3: 38 h from open ocean The higher cloud droplet number on flight 2 is caused to 7% by the increased aerosol conc. (mainly organics) and to 3% by larger updraft velocities Station 19: 1 h from open ocean

8 in the Arctic [Lohmann and Leck, Tellus, 25] Ref: reference sim Sol: all aerosols are soluble Ref/NA15/65: 15/65% of the organics are surface active cloud droplets Station 2: 12 h from open ocean Station 3: 38 h from open ocean Lower Surface Surface Station 19: 1 h from open ocean Cloud evolution in a clean and polluted atmosphere Aerosol modifica- tion of marine stratus clouds Durkee et al., 2

9 Aerosol modification of marine clouds observed during the Monterey Area Ship Track Experiment Evidence for the 1 st indirect aerosol effect in marine stratus clouds off the coast of Nova Scotia Durkee et al., JAS, 2 Peng et al., 22 Evidence of the 2 nd indirect aerosol effect Aerosol - cloud droplet relationships Onset of the drizzle drop formation Peng et al., 22 Penner et al., IPCC, 21

10 Temporal evolution of sulphur emission and direct and indirect radiative forcing of sulfate aerosols Top panel: Direct effect of sulphate aerosols (.4 W/m 2 ) Lower panel: Indirect cloud albedo effect ( 1.o W/m 2 ) Boucher and Pham, GRL, 22 Boucher and Pham, GRL, 22 Cloud lifetime effect calculations The autoconversion rate (precipitation formation rate in clouds with no ice) in climate models depends on the cloud water content q l and the number concentration of cloud droplets N: Q aut ~ q la N b with a=2-5 b=-1 to -3.3 Aerosol effects on cloud water content between preindustrial and present-day times more cloud droplets decrease drizzle formation

11 Indirect aerosol effect Difference between two 5-year simulations one with pre-industrial and one with present-day aerosol emissions [Global mean change in top-of-the-atmosphere net radiation: -1.4 W/m 2 ] Global mean indirect aerosol effect (Twomey vs. lifetime) from different climate models Sulfate Soot (BC) and sulfate Organic aerosols (OC) and sulfate BC, OC and sulfate Peng and Lohmann, GRL, 23 Lohmann and Feichter, ACP, 25 of cloud droplets Surface energy budget effect from pre-industrial times to present-day: ECHAM4/MLO with increasing GHG and aerosols [Courtesy: Hans Feichter] aerosols greenhouse gases Lower Surface Surface

12 control on DMS? of cloud droplets El Nino El Nino Surface Bates and Quinn, GRL, 1997?? cloud droplets? Surface