# Presentation: 054658

##   Annual cycle of inferred equivalent ocean heat content

**  ****Annual cycle of inferred equivalent ocean heat content**

- Net surface fluxes into or out of the ocean have been computed as residuals of the total heat budget of the Earth using top-of-atmosphere radiation and complete heat and energy budgets for the atmosphere.  The focus is on departures from the annual mean and the implied annual cycle in “equivalent ocean heat content”.  We use the term “equivalent” because it includes any annual cycle in ocean heat transports, but those effects are relatively small outside of the tropics and they are especially noticeable from about 5 to 15N in association with the annual cycle in wind stress curl and North Equatorial Current. These estimates, together with actual ocean heat content estimates, provide a more holistic view of the heat budget and suggest that, with modest improvements, divergent ocean heat transports may be deduced as a residual.

**Kevin E. Trenberth and David P. Stepaniak **
**National Center for Atmospheric Research, Boulder, CO 80307**

**Annual cycle of equivalent ocean heat content**

- There is good evidence for an annual cycle of heat transports by the ocean (cf. WOCE assumptions) in the Tropics. Heat transports evidently contribute to amplify annual cycle in heat content somewhat owing to larger poleward heat transport in summer than winter (mainly Ekman):  Zhang et al. (JGR 2002).
- WOA results exhibit  small  spotty features,  often of wrong sign  in southern hemisphere,  and a physically unreasonable second harmonic.     Results agree better with first harmonic.   Another issue is depth of integration of 275 m.

**3.**  Departures from annual mean of net surface heat flux: Change in  **Equivalent **
**	****ocean heat content  **=
- 	actual ocean heat content  if annual cycle in ocean heat transports ignored.

**Annual mean net surface flux**

**1.** There is a large annual cycle in net radiation  at the  top-of-atmosphere, mostly from solar radiation.  It makes for a large annual cycle in net surface heat  flux,   which  is  computed  by subtracting  out  the  divergence in atmospheric energy transports  and allowing  for  changes  in storage in atmosphere.

**2.** It is assumed that the annual mean surface flux is balanced by the divergence in ocean heat transport;
- see Trenberth and Caron (2001 JC).

**4.** The rates of change are converted  into  equivalent ocean  heat  content  and compared  with  Antonov, Levitus and Boyer, 2004.
- Note: Antonov et al.  use  incorrect values for density and specific heat (4.4%  too l arge for heat content).
- Biggest   differences   from actual ocean heat content occur in Tropics, especially 10N with North Equatorial Current in Pacific.

**7.** In Pacific, the zero wind stress curl line migrates from 11° N in March to 20°N in September causing major annual cycle in NEC,  heat content and heat transports.
- 	C.f. Qiu and Lukas (1996 JGR);
- 	Kobayashi and Imasato (1998 JGR).
**8.** 	Some fine structure arises from bottom topography, islands, and associated currents.

**Antonov et al. 2004 GRL**
**Levitus and Antonov 1997**

**Atlantic          Indian          Pacific**