AIR-SEA INTERACTION Sergey Gulev gul sail msk ru 33

AIR-SEA INTERACTION Sergey Gulev, gul@sail. msk. ru (+33 -6 -22. 59. 72) Air-sea interaction is the redistribution of the solar energy through the property exchange between the ocean and the atmosphere and associated processes of the energy transformation in the ocean and in the atmosphere. Critically important for: q Hard core of the ocean-atmosphere coupling q Boundary conditions for ocean and atmospheric GCMs q Global and regional energy budgets of the ocean and the atmosphere

General assessment of energy sources in the climate system Incoming solar radiation: 1024 J/year Evaporation: 2 1023 J/year Advection of heat by ocean currents: 5 1022 J/year Anthropogenic energy production: 5 1019 J/year

Sea water and atmospheric air parameter Density Specific heat capacity (p=const) h/L Horizontal velocity Vertical velocity Sea water/ocean Air/atmosphere 1025 kg/m 3 1. 2 kg/m 3 4. 2 103 J/(kg K) 1 103 J/(kg K) ~ 10 -4 ~10 -3 ~0. 1 m/s ~0. 001 m/s ~0. 1 m/s

Ocean and atmosphere Sea surface temperature Surface air temperature Ocean surface currents Surface wind

То, что считается «типичным» механизмом, Ocean’s редко на самом деле происходит очень role in climate – transporting heat from the low latitudes to high latitudes NP Equator SP http: //www. classzone. com/books/earth_science/ terc/content/visualizations/es 2401 page 01. cfm? chapter_no=visualization

Major air-sea interaction processes LW SW Qe h Q α P Gas fluxes wind IMa IHa Ice thickness Ocean heat and mass balance Ekman currents Surface density flux and water mass transformation wind stress curl IMw IHw

Air-sea fluxes: shaping ocean-atmosphere coupling Changing atmospheric state variables and circulation Surface fluxes Forcing the ocean Diabatic sources for the atmosphere Surface fluxes Changing ocean state and circulation

Major sea-air interaction processes 100 6 20 4 6 38 26 16 15 Wind stress precipitation 3 51 waves mechanical mixing 21 7 23 convective mixing

Major sea-air interaction processes Trenberth et al. 2011

Major sea-air interaction processes: our outline 1. Solar radiation (SW): absorption, reflection and scattering 2. Infrared radiation: emission, reflection and absorption 3. Turbulent heat transfer 4. Evaporation 5. Precipitation 6. Buoyancy flux at sea surface 7. Turbulent transfer of kinetic energy by tangential components (stress) 8. Turbulent transfer of kinetic energy by normal components (normal pressure) 9. Ocean surface wave generation and decay 10. Mixing in the atmosphere and generation of atmospheric vorticity in ABL 11. Mixing (mechanical and convective) in the ocean and generation of water masses 12. Gas transfer

Major consequences of sea-air interaction processes: (will not be discussed, but very important) 1. Advection of heat by ocean currents and atmospheric flows 2. Instabilities in the ocean and atmosphere 3. Generation of temperature anomalies in the ocean 4. Generation of circulation anomalies in the atmosphere Annual range of air temperature (Monin 1968)

SHORT-WAVE RADIATION AT SEA SURFACE H = SW - LW - Qh - Qe 100 65 8 27 + - Definition of sign is arbitrary, but important to be set Temperature of the Sun: Tsun 5800 K; Esun= Tsun 4 99% of energy is within 0. 2 -3 Solar constant (S 0) – the amount of solar energy (W/m²) at normal incidence outside the atmosphere (extraterrestrial) at the annual mean sun-earth distance S 0 = 1378 W/m 2 (1359 – 1384 W/m 2)

Sun brightness How much brighter is the Sun as viewed from Mercury as compared to Earth? How much fainter is it at Jupiter? Inverse square law relates the relative distances of two objects as compared to a third. The amount of the Sun's energy reaching Earth is 1 solar constant. The average distance from the Sun to Earth is 149, 597, 870. 66 kilometers, (1 Astronomical Unit or 1 AU). So Earth is 1 AU from the Sun and receives 1 solar constant. The relationship can be expressed as: 1/d 2 where d = distance as compared to Earth's distance from the Sun. At 1 AU, Earth receives 1 unit of sunlight. How much sunlight would a spacecraft receive if it were twice as far from the Sun as Earth? The distance from the Sun to the spacecraft would be 2 AUs so. . . d = 2. If we plug that into the equation 1/d 2 = 1/22 = 1/4 = 25%. The spacecraft is getting only one quarter of the amount of sunlight that would reach it if it were near Earth. This is because the light is being radiated from the Sun in a sphere. As the distance from the Sun increases the surface area of the sphere grows by the square of the distance. That means that there is only 1/d 2 energy falling on any similar area on the expanding sphere. Mercury is at 0. 387 AUs. 1/d 2 = 1/0. 3872 = 1/. 15 = 666. 67%, almost seven times brighter! We can use this method to compare any spot in the Universe if we describe its distance as compared to Earth relative to the Sun. Mars is at a distance of 1. 5 AUs from the Sun. 1/d 2 = 1/1. 52 = 1/2. 25 = 44%. Jupiter is at 5. 2 AUs so 1/d 2 = 1/5. 22 = 1/27 = 3. 7%

Radiation balance assumption Planet’s average temperature assuming planet is a solid globe with no atmosphere and no albedo Name Mercury Venus (75%) Earth (30%) Mars (15%) Jupiter Saturn Uranus Neptune Temp (K) Albedo T (K) 438. 322. 228. 274. 250. 223. 215. 120. 89. 62. 50.

Is Solar constant a real constant? Long-term change – amounts to ~1 W/m 2

Is Solar constant a real constant? Interannual (e. g. 11 -yr) change is ranging by ~3 W/m 2 (+/-0. 1%)

Seasonal changes in Solar constant (2 factors): (1)The Earth orbit is elliptic (2)(2) The Earth axis is titled

152 x 106 km 147 x 106 km S 0=1443 W/m 2 S 0=1349 W/m 2 Seasonal changes in Solar constant (2 factors): Solar radiation on the top of the atmosphere:

Solar altitude φ is latitude, δ is the Solar inclination angle, h is hourly angle, θ 0 is zenith Sun angle.

TOA (top of atmosphere) SW radiation NASA ERBE spacecraft

Exercise: Solar altitude Compute solar altitude for: 07: 00 GMT 05. 04. 2006 35 N, 55 W Derive the dependence of solar altitude on: latitude for 12: 00, 04. 2006 for 45 N Reproduce this picture for S=1368 W/m 2 F 77: /meolkerg/home/gulev/problems/solar. f to compile: Ifort –o solar. f

Milankovitch Cycles Eccentricity - Jupiter’s gravitational force results in Earth’s orbit varying from nearly circular with eccentricity near 0. 0 to about 0. 06. Current difference in distance to the Sun at perihelion and aphelion is 3 -4%. Periods - Dominate period of 413, 000 and minor period of 100, 000 years 413, 000 years 100, 000 years Milutin Milanković (1879 – 1958) was a Serbian geophysicist "Contribution to the mathematical theory of climate" (1912)

Milankovitch Cycles Obliquity - Change in the tilt of the Earth's axis with a period of 41, 000 years. Changes between ~22. 1° and ~24. 5°

The effect of Milankovitch Cycle on obliquity Change in Ice for past 21, 000 years (1/2 period of the tilt cycle) (Matches change in obliquity from 22. 1° to 23. 5°)

Milankovitch Cycles Precession - Wobble in the tilt of the Earth's axis with a period of 22, 000 years. The mechanism – like spinning top due to non-spherical form of the Earth (and the other planets too) Precession of the equinox over the last 750, 000 years

Milankovitch Cycles: combined effect

To know how much of solar radiation comes to the surface, you should know what happens with the solar energy in the atmosphere Spectral view: What this range is about?

Surface SW radiation Need to quantify the difference between the TOA and surface radiation

Radiation on the top of the atmosphere Radiation on the Earth’s surface

SW radiation at sea surface is determined by: Ø Solar altitude Ø Molecular diffusion Ø Gas absorption Ø Water vapor absorption Ø Aerosols diffusion Measurements Modelling Parameterization

Measurements of SW radiation Downwelling shortwave (SW) radiation can be measured with the pyranometer, facing skyward. Modern pyranometers are still based on the Moll-Gorczynski design (Moll 1923) in which radiation falls on a blackened horizontal receiving surface bonded to a thermopile and protected by two concentric precision hemispheric glass domes. The most important factors affecting the accuracy of these instruments: Ø reliability and stability of calibration, Ø dome temperature effects, Ø cosine response, Ø detector temperature stability. Another source of error, particular to pyranometers used at sea, is caused by the platform motion. For correct measurement the receiving surface must be horizontal, but both ships and buoys can roll through several degrees. Uncertainty of daily average can be as large as 10 -20%. At sea pyranometers must be set in gimbals. Moll-Gorczynski pyranometer Multi-Filter Rotating Shadowband Radiometer (MFRSR)

Measurements of SW radiation in the sea

QSW = f Q 0 sin h, Important: be sure that you measure at a horizontal surface, otherwise, the correction has to be applied

Where to find/buy/order a perfect package? http: //www. arm. gov/instruments/instclass. php? id=radio http: //www. kippzonen. com/pages/1250/3/Howcan. Ikeepb