Partitioning of net radiation 581 Characteristics over sea ice

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Figure 5.10, also from Persson et al. (2002), illustrates annual cycles of the turbulent energy fluxes and conduction at the SHEBA site in comparison with other estimates. Recall that our convention is that non-radiative fluxes are positive when directed away from the surface and negative when directed toward the surface. The SHEBA results are representative of reasonably thick ice. They show the sensible heat flux as directed toward the surface in winter and variously toward or away from the surface in the other months. The salient point, however, is that the fluxes are small, peaking in February at about -8 W m-2. The latent heat flux is also quite small, ranging from essentially zero in the winter months to about 7 W m-2 upward (i.e., evaporation and sublimation is occurring) in June. Again, there are some considerable differences with respect to other estimates. As with the radiative fluxes, the turbulent terms show large day-to-day variability. Typically, observed peaks correspond to synoptic events associated with increased wind speed.

Figure 5.9 Monthly radiation balance components (Wm-2) for the central Arctic Ocean. Shown are (a) net radiation (heavy lines) and albedo (thin lines); (b) incoming shortwave radiation; (c) incoming longwave radiation. In each panel, results from the SHEBA experiment are shown along with those from other studies (adapted from Persson et al., 2002, by permission of AGU).

Figure 5.9 Monthly radiation balance components (Wm-2) for the central Arctic Ocean. Shown are (a) net radiation (heavy lines) and albedo (thin lines); (b) incoming shortwave radiation; (c) incoming longwave radiation. In each panel, results from the SHEBA experiment are shown along with those from other studies (adapted from Persson et al., 2002, by permission of AGU).

Figure 5.10 Monthly non-radiative energy balance components (W m-2) for the central Arctic Ocean. Shown are (a) sensible heat flux; (b) latent heat flux; (c) conductive heat flux. In each panel, results from the SHEBA experiment are shown along with those from other studies (adapted from Persson et al., 2002, by permission of AGU).

Figure 5.10 Monthly non-radiative energy balance components (W m-2) for the central Arctic Ocean. Shown are (a) sensible heat flux; (b) latent heat flux; (c) conductive heat flux. In each panel, results from the SHEBA experiment are shown along with those from other studies (adapted from Persson et al., 2002, by permission of AGU).

During winter, the sea ice and its overlying snow cover separate the cold atmosphere from the relatively warm Arctic Ocean at its freezing point (-1.8 °C for typical ocean salinities). Hence there is a temperature gradient in the snow and ice cover and an upward heat flux to the surface, which in our framework is negative, consistent with what is seen in Figure 5.10. This conductive flux includes the effects of latent heat release at the ice-ocean interface associated with ice growth. The amount of ice growth (or ablation) at the bottom of the ice is represented by the sum of the ocean heat flux, Fw, and the conductive heat flux through the snow and ice, Ki(dTi/dz):

Fw has a mean annual value of about 2 W m-2, determined almost entirely by shortwave input through leads and areas of thin ice. Compared to previous studies, the winter conductive flux at the SHEBA site is rather small, peaking at about -5 W m-2. Annually, the conductive heat flux to the surface of multiyear ice estimated from different studies ranges from 2 to 8 W m-2, with the SHEBA year falling in the low end. According to Maykut (1986), the annual upward conductive flux is up to 40 W m-2 in the marginal ice zone of the northern North Atlantic. During summer, as air temperatures increase, the conductive flux becomes small or non-existent. For July, the SHEBA turbulent fluxes and conduction taken together are quite small, meaning that the bulk of the radiation surplus is going into melt. These issues are reviewed in more detail in Chapter 7.

Although the turbulent fluxes are quite small for the SHEBA region, over areas of thin ice and open water they can be large. In such areas, strong temperature gradients are formed in the boundary layer, and winter sensible heat fluxes may reach 600 W m-2. Measurements over and near freezing leads and polynyas (Badgley, 1966; Smith et al., 1983; Makshtas, 1984) suggest that heat is transferred only 10-15 m above the surface (Andreas et al., 1979) and is relayed back to the ice downwind by condensation, ice crystal precipitation, the sensible heat flux and longwave radiation from cloud formation downwind of the lead. However, condensate plumes emanating from wide (>10 km) open-water areas (leads) that extend to 4 km in the atmosphere and persist for up to 200 km downwind have been identified using backscatter measurements from an airborne downward pointing lidar (Schnell et al., 1989; Andreas et al., 1990). Such deep convection events appear to require a combination of a large air-sea temperature contrast (providing a large sensible heat flux), low wind speeds, and a weak Arctic temperature inversion. This combination, however, is rare in Arctic conditions (Serreze et al., 1992a). Shallow convection (< 1 km) above narrow leads is believed to result in locally high concentrations of ice crystals near the surface, substantially augmenting the downwelling radiation flux (Curry et al., 1990).

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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