Forcing of the Ocean: tides, winds, and heating Tides

Result from the gravitational forces of the moon and the sun

For the Earth-moon-sun system there is a balance of gravitational forces very close to the center of the Earth.

At any point on the Earth’s surface there is a slight imbalance, giving a tide generating potential.

The horizontal component of the tide generating potential gives TWO tidal bulges. Tides

-There are two places of high tide at any one time. These regions are planar with the moon.

-Earth rotates once per day, so have 2 high tides per day.

-Forcing is semi-diurnal

The horizontal component of the tidal force on Earth when the tide- generating body is above the Equator at Z. From Dietrich, et al. (1980). tides: combined effect of Spring-NeapMoon and Sun cycle http://www.bayoffundy.com

“Beating” of lunar M2 tide “Beating” of lunar M2 tide and solar S2 tide and solar S2 tide leads to “spring”leads tidesto “spring” and “neap” tides andtides “neap” tides Tides are dynamic

Tidal “bulges” travel at the surface of the Earth as “shallow-water waves” of maximum speed 230 m s-1 which is less than 448 m s-1 predicted by celestial mechanics Bottom drag causes the dynamic tides to lag the equilibrium tides by several hours Shapes of ocean basin prevent the tidal bulges from circumnavigating the globe (except in the Southern Ocean) lateral ocean movements are subject to Coriolis force Animation of M2 tidal constituent (0-400 mm) from Tim Jupp. Cotidal lines indicating phase every 30 degrees originate at amphidromic points where the tidal range is zero.

http://empslocal.ex.ac.uk/people/staff/tej202/tideomatic/ani_World_M2.gif Global mean wind system

Polar cell westerlies 60 Ferrel cell

30 Text Hadley cell trade winds ITCZ: 30 Intertropical Convergence westerlies 60 Zone

Circulation is Air circulation deflected by driven by uneven Earth’s rotation heating by ocean (and land) Global mean wind system

subpolar gyre subtropical gyre

Figure 4.3(b) Simplified schematic of Earth's atmospheric circulation driven by solar heating in the tropics and cooling at high latitudes. Cross-section through the atmosphere showing the two major cells of meridional circulation. From The Open University (1989a). Mean 10-m winds in boreal summer (top) and winter (bottom) from ECMWF 40-year re-analysis. (Kallberg et al, 2005). -Stronger westerlies in winter. -Asian monsoon affects wind direction in north Indian Ocean and NW Pacific Winds Now!

earth

https://earth.nullschool.net/ Heat fluxes short wave long wave

Figure 5.6 The mean annual radiation and heat balance of the Earth. From Houghton et al., (1996: 58), which used data from Kiehl and Trenberth (1996). Annual-mean heat flux at surface

To p : n et s o lar, QSW = incoming- reflected

Bottom: net infrared, QLW = greenhouse- outgoing

From the ECMWF 40-year reanalysis. Units are W m-2. From Kallberg et al 2005. Annual-mean heat flux at surface

Top: latent heat flux, QL

Bottom: sensible heat flux, QS

From the ECMWF 40-year reanalysis. Units are W m-2. From Kallberg et al 2005. Net cloud radiative effect High clouds are thin Thick low and cold and transmit clouds reflect SW freely, but absorb SW radiation outgoing LW and and COOL WARM surface surface

from CERES data (credit : Willis Eschenbach, WUWT

Clouds both reflect solar SW radiation AND absorb terrestrial LW radiation. Their net effect is currently cooling ~ 13 W/m2, but could be changing with climate. Net Annual-mean heat flux Q through the sea surface in W m-2, calculated from the ECMWF 40-year reanalysis. From Kallberg et al 2005.

Max into ocean in tropics and upwelling regions. Max loss from ocean over WBCs. (Few measurements in Southern Ocean) Heat flux through sea surface -insolation greatest in tropics -evaporation + LW primarily balances insolation -sensible heat flux is smallest -what balances total heat flux?

Figure 5.7 Upper: Zonal averages of heat transfer to the ocean by insolation Qsw, and loss by longwave radiation Qlw, sensible heat flux Qs, and latent heat flux Ql, calculated by DaSilva, Young, and Levitus (1995) using the COADS data set. Lower: Net heat flux through the sea surface calculated from the data above (solid line) and net heat flux constrained to give heat and fresh-water transports by the ocean that match independent calculations of these transports. Global energy budget at top of atmosphere with latitude Oceanic and atmospheric meridional heat flux 2552 MeridionalJOURNAL OF oceanic PHYSICAL OCEANOGRAPHY heat fluxes VOLUME 37

FIG. 1. Global box model geometry: 25 WOCE hydrographic sections (Table 1) form 18 boxes in which various properties are conserved and other constraints, such as the strengths of western boundary currents, are satisfied. Heat transports across the sections (red bars; units are 1015 W) are from the inverse model solution. Sections at a nominal latitude of 32°S separate the Atlantic, Indian, and Pacific basins from the Southern Ocean; a nearly circumpolar composite section at 62Lumpkin°S separates theand bottom-water Speer formation(2007) regions against Antarctica from the rest of the Southern Ocean. to within Ϯ1Sv(Svϵ 106 m3 sϪ1) [see Ganachaud straints on deep layer transports in various overflows (2003a) for a detailed discussion of the sources of this and subbasins based on direct current measurements model error]. Heat and salt anomaly conservation in and tracer observations (Fahrbach et al. 1995; Orsi et al. the layers is constrained to within Ϯ1 Sv times the sum 2002; LS03). In the case of the Weddell Sea we have of the mean property, plus twice the standard deviation reanalyzed direct current measurements (updated from of the property in the box (see appendix B in LS03). Yaremchuk et al. 1998) to produce new boundary cur- Net silicate is conserved to Ϯ500 kmol sϪ1 in boxes rent constraints on circulation. north of 32°S. Each of the 45 model layers contains an Interior diapycnal fluxes, reference velocity adjust- equal volume of the world’s water (LS03); 45 layers ments, and adjustments to the air–sea heat and fresh- proved necessary to resolve the global range of water water fluxes are found that satisfy the imposed con- masses experiencing significant transformation. Previ- straints. The model’s adjusted air–sea heat fluxes are ous observation-based studies of hydrographic sections generally consistent within error to the products, with have not included explicit air–sea buoyancy transfor- the following exceptions: unadjusted National Ocean- mation (Ganachaud and Wunsch 2000; Talley et al. ography Centre (NOC) fluxes are too hot (ocean heat 2003; Ganachaud 2003b) or were not global (Sloyan gain significantly larger than model results) in all tropi- and Rintoul 2001; LS03). The inversion presented here cal and subtropical boxes (cf., Grist and Josey 2003); is also novel as it includes a circumpolar Southern adjusted NOC fluxes are too cold in all three Southern Ocean section (WOCE S4) that helps distinguish trans- Ocean boxes (32°S–S4); NCEP fluxes are slightly too formation sites of the upper and lower meridional over- hot in Atlantic and Indian sectors of the Southern turning cells. Ocean boxes; ERA-15 fluxes are too hot in the coastal Within the Arctic–Nordic seas box and Antarctic Antarctica boxes and Arctic Sea box; and the Univer- coastal margin boxes, none of the air–sea flux products sity of Wisconsin—Milwaukee/Comprehensive Ocean– includes sufficient ocean heat loss to accommodate the Atmosphere Data Set (UWM/COADS) fluxes are too observed Denmark Strait and Faroe Banks overflows cold in the Arctic box. Model-derived transports across or Antarctic Bottom Water export across 62°S. In the key sections are given in Table 2. Net global meridional ocean these fluxes are typically associated with rela- salt and volume (freshwater) fluxes are not well deter- tively intense air–sea exchange in narrow boundary cur- mined at any latitude. Net global ocean heat transports rent regions or at small scales in leads and polynyas. are consistent with earlier results within errors, which Air–sea fluxes in these regions are not imposed upon are typically of the same order as earlier studies. Unlike the inverse solution and, instead, are derived via con- in the North Atlantic (LS03), where various air–sea flux