1. Whitecaps, sea-salt aerosols, and climate Magdalena D. Anguelova Oceans and Ice Branch Seminar College of Marine Studies University of Delaware18 October, 2001

2. Outline n Sea-salt aerosols and climate n Sea spray n Whitecap coverage estimation

3. Climate studies © Ocean Drilling Program

4. Cloud feedbacks - 20 W m -2

5. Modeling cloud feedback Cess et al., 1990

6. “I used to think of clouds as the Gordian knot of the problem,” says cloud specialist V. Ramanathan of Scripps. “Now I think it’s the aerosols. We are arguing about everything.” R. A. Kerr, Science, 1997, 276

7. Aerosol radiative forcing n Anthropogenic aerosol loading; n Aerosol radiative forcing: Negative 0.5 to 2 W m -2

8. Aerosol effects n Direct; Radiative forcing on climate in 2 distinct ways:

9. Aerosol effects n Indirect; Radiative forcing on climate in 2 distinct ways: Cloud properties; Cloud lifetime. n Direct;

10. Include aerosol direct and indirect forcing in climate models. Recognized Need

11. Types of aerosols n Natural n Anthropogenic

12. Baseline Clean atmosphere is affected only by natural background aerosols. Sea-salt aerosols are the dominant aerosol species in background atmosphere.

13. Direct effect of sea-salt aerosols n Cooling 0.6 to 2 W m -2 (Winter and Chýlek, 1997) n Potential of –4 W m -2 (Quinn et al., 1996)

14. Andreae (1995) Indirect effect of sea-salt aerosols n Dominate the activation of CCN; n Compete with SO 4 2- aerosols. Activation of CCN begins on the largest and most soluble particles. Larger; More hygroscopic. SS concentrations; SO 4 2- concentrations Cloud updraft: Total CCN  Total CCN 

15. Halogen chemistry n Multiphase reactions n Site for chemical reactions

16. Halogen chemistry n Multiphase reactions n Site for chemical reactions Reactive Cl and Br; Cl, Br CH 4 DMS OH

17. Halogen chemistry n Multiphase reactions n Site for chemical reactions Reactive Cl and Br; Tropospheric O 3 : –Greenhouse gas; –Pollutant; Cl, Br Clean air Polluted air NO x

18. Halogen chemistry n Multiphase reactions n Site for chemical reactions Reactive Cl and Br; Tropospheric O 3 : –Greenhouse gas; –Pollutant; Sink of S. H 2 SO 4 O3O3 DMS SO 2 SO 4 2- Industrial SO 4 2-

19. Sea-salt aerosol effects must be accounted for.

20. Outline n Sea-salt aerosols and climate n Sea spray n Whitecap coverage estimation

21. n As waves break, n air blobs break up, nand forms clouds of bubbles. Wave breaking

22. The fate of the bubbles n …dissolve and disappear… n …stabilize and join… n …rise and burst…

23. The fate of the bubbles n …dissolve and disappear… n …stabilize and join… n …rise and burst…

24. n Upon bursting, bubble caps shatter Film drops Resch and Afeti (1991)

25. n As the bubble cavity collapses... Jet drops MacIntyre (1974)

26. n Under very high winds drops are torn from the wave crests and blown directly into the air. Spume drops

27. Sea spray n In the air: Moisture equilibrium; Change of size and phase state; sea-salt aerosols.

28. r,  m 5001001010.1 Andreas (1998) Sea spray sizes n Residence time (Andreas, 1992) Heat exchangeAerosol forcing > 20  m < 20  m film jet spume

29. Modeling sea-salt aerosols n Many processes: Generation; Transport; Diffusion and convection; Chemical and physical transformations: –in clear air; –in clouds; –below clouds; Wet and dry deposition. Generation;

30. Sea spray generation function, F Monahan et al. (1986) r,  m 5001001010.1 Via bubblesTearing = dF 0 /dr + dF 1 /dr Rate of production of sea spray per unit area per increment of droplet radius, r (s -1 m -2  m -1 ). dF /dr

31. Best generation function n Among 14 proposed functions (Andreas, 2001) Explicit forms for 4 size regions covering 1 to 500  m range. (Monahan and O’Muircheartaigh, 1980)

32. Improved generation function? W (U 10,  T, T s, S, f, d, C ) W (U 10 ) Best available (Monahan and O’Muircheartaigh, 1986)

33. Improved generation function? W (U 10,  T, T s, S, f, d, C ) W (U 10 ) Best available (Monahan and O’Muircheartaigh, 1986)

34. Improved generation function? W (U 10,  T, T s, S, f, d, C ) W (U 10 ) Best available (Monahan and O’Muircheartaigh, 1986)

35. Improved generation function? W (U 10,  T, T s, S, f, d, C ) W (U 10 ) Best available (Monahan and O’Muircheartaigh, 1986)

36. Improved generation function? W (U 10,  T, T s, S, f, d, C ) W (U 10 ) Best available (Monahan and O’Muircheartaigh, 1986)

37. Improved generation function? W (U 10,  T, T s, S, f, d, C ) W (U 10 ) Best available (Monahan and O’Muircheartaigh, 1986)

38. Improved generation function? W (U 10 ) Best available W (U 10,  T, T s, S, f, d, C ) (Monahan and O’Muircheartaigh, 1986)

39. Need of database W (U 10,  T, T s, S, f, d, C ) 477 points n Existing database 16 cruises (1969 – 1984); Photographs.

40. Need of database W (U 10,  T, T s, S, f, d, C ) 477 points n Existing database 16 cruises (1969 – 1984); Photographs.

41. Need of database W (U 10,  T, T s, S, f, d, C ) 477 points 307 points n Existing database 16 cruises (1969 – 1984); Photographs.

42. Need of database W (U 10,  T, T s, S, f, d, C ) 477 points 307 points n Existing database 16 cruises (1969 – 1984); Photographs. New method

43. Outline n Sea-salt aerosols and climate n Sea spray n Whitecap coverage estimation

44. Whitecaps signature High Reflectivity High Emissivity Reflectivity Emissivity VisIRmWUV

45. e = (e s +  e r )(1-W ) + W e f The concept n Ocean composite emissivity e – e s –  e r e f – e s –  e r W = e, e s,  e r, e f e  as W  n The task

46. t Top of the atmosphere eTseTs T CB T BU T BD Ocean TsTs TBTB Radiometer TB =TB = teT s + t 2 (1 - e) T CB + T BU + t(1 - e) T BD Calculate composite emissivity e eT s = T B

47. e = T B - T BU - t T BD - t 2 T CB t T s - t T BD - t 2 T CB T B -- SSM/I T s -- AVHRR T CB = 2.7 K T BU T BD t Wentz (1997) V, L (SSM/I) Calculate composite emissivity e

48. e s = 1 - r s 1 + i    =   +  s -    0 0 - i  Fresnel formula: r s = f ( ,  ) Calculate specular emissivity e s Debye equation : Klein and Swift (1977)  = 2  f, f = 19 GHz  ,  0, ,   s,  = f (T s, S ) T s -- AVHRR S -- NOAA Atlas

49. 3  -  Q + Q  f =  2  Q - 2Q + 3 Rosenkranz and Staelin (1972) e f = 1 - r f Fresnel formula: r f (  f,  ) Calculate foam emissivity e f Q = Volume of water Volume of mixture Q = 2 %

50. Calculate rough sea emissivity  e r  e r = (A + B  2 )   U 10 TsTs Pandey and Kakar (1982) ,  -- known A, B -- given coefficients U 10 -- SSM/I T s -- AVHRR

51. What else? n Analytical expressions; n Data (T B, U 10, V, L, T s, S ); n Preparation; n Error analysis; n Calculate W;

52. Results n Emissivities

53. All emissivities vs. T s

54. All emissivities vs. V e = T B - T BU - t T BD - t 2 T CB t T s - t T BD - t 2 T CB

55. All emissivities vs. V e = T B - T BU - t T BD - t 2 T CB t T s - t T BD - t 2 T CB

56. All emissivities vs. V e = T B - T BU - t T BD - t 2 T CB t T s - t T BD - t 2 T CB

57. All emissivities vs. V e = T B - T BU - t T BD - t 2 T CB t T s - t T BD - t 2 T CB

58. Retrieved emissivities 27 March (86), 1998

59. Restrictions for W estimation 2 – 10 % W < 0 e < e s +  e r

60. Results n Whitecap coverage

61. W = 0 to 24% W = 3.16% 3.4% (Blanchard, 1963) Whitecap coverage 27 March (86), 1998

62. Validation: W = 0 to 17% W = 1.43%

63. Validation New method – Wind Formula

64. The effect of T s n W  as T s  ; n  as T s  ;

65. The effect of T s n Suppress at high latitudes; n Boosts at mid latitudes; Wind speed, U 10 (m s -1 ) Sea surface temperature, T s ( o C)

66. Validation: in situ data

68. Another hour to talk about n Database organization; n Regressions; n Modified formula; n Global distribution of sea-salt aerosols; n Estimations for climate processes.

69. Questions