Space Shuttle Mission Report Series: Earth Observations during STS-055 April 26 - May 6, 1993

(continued)

Air-Sea Interaction

The warm water of the Timor Sea provides moisture for the popcorn cumulus clouds in the next view. When the photograph in figure 9 was taken, the Shuttle was located at 12.5° south, 125.1° east. In this photograph of the Timor Sea along the south coast of Timor, the sunglint pattern shows a sharp boundary in sea surface temperature, with cooler water along the coast and warmer water offshore. The sunglint brightness reveals water surface roughness: bright areas are smooth water; dark areas are rough water. The cooler water is smoother because it acts to stabilize the atmospheric boundary layer, while the warm water acts to destabilize the atmosphere. The mottled appearance of the sunglint pattern over the warm water indicates low-level turbulence resulting from the destabilizing effect.      Another indication of water temperature is the cloud pattern. Advection within the atmosphere as a result of warming at the sea surface forms small, low-level clouds with the popcorn-like appearance seen in upper right corner of the photograph. The cool water, on the other hand, is relatively free of the popcorn-like clouds. The distribution of the clouds indicates that the wind is blowing toward the upper right corner of the photograph.      Another interesting feature is the line of low-level popcorn clouds situated along the boundary between the two water masses and over the cooler water. This perhaps indicates the presence of a vortex within the atmosphere, where the air over the warm water is rising and the air over the cooler water is sinking. This particular cloud pattern only appears where the water mass boundary is nearly parallel to the wind direction. It does not appear where the boundary shifts orientation (bottom of the photograph) and is nearly perpendicular to the wind direction.

Figure 9: Timor Sea. This sunglint photograph of the south coast of Timor and the Timor Sea (northwest of Darwin, Australia) shows a sharp boundary in sea surface temperature. The cooler water (nearer Timor) is smoother (and hence brighter) because of suppression of atmospheric turbulence; whereas the dark areas (speckled with clouds) are the rougher warmer water. The photo was taken on May 5, 1993, at 04:03:47 GMT. [NASA photograph STS055-151-120] Moderate resolution (150 dpi, 249 Kb) High resolution (300 dpi, 3.8 Mb)

Whitings

The white patches in the waters of the Bahamian Banks (fig. 10) are called whitings, which are areas in the water where CaCO3 in the form of aragonite is thought to be precipitating directly from the water column. The origin of whitings, which look like little lenticular clouds, has been controversial for some time, because the geochemical evidence for in situ aragonite precipitation is difficult to explain. Recent work suggests that the whiting precipitation is induced by blooms of plankton (unicellular algae) in the water (Shinn et al. 1989).      Whitings vary in size and duration. The whitings in this mosaic are unusually large. The largest white patch is roughly 10–12 km long, covering an area more than 100 sq. km. This represents a tremendous quantity of CaCO3 and is crucial to mass-balance calculations of the sediment budget of the Bahamas. Space Shuttle astronauts have the chance to photograph large whitings and thus provide information about their size, frequency, and location from one overpass to the next and from one flight to the next. All are important variables when estimating the importance of the contribution of whitings to the overall CaCO3 budget of the Bahamas and other similar tropical ocean areas.      Figure 10: Whitings in the Waters of the Bahama Banks. In this south-looking view of the Bahamas, we can see many small white smears in the lagoon northeast of the northernmost island, Grand Bahama. These white smears dotting the shallow waters of the Little Bahama Bank are called whitings. There are about 50 of them in this lagoon, each 2-4 km long. Several larger whitings can be seen off the northwest coast of Andros Island, the largest of the Bahamian islands, in the shallow waters of Great Bahama Bank. The largest of these whitings is 10-12 km long and covers an area of more than 100 sq. km. Whitings are areas in the water where CaCO3 in the form of aragonite is thought to be precipitating directly from the water column. [NASA photographs STS055-72-075 and -077] Moderate resolution (150 dpi, 189 Kb) High resolution (300 dpi, 1.8 Mb)

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