What is cloudiness?
Clouds are visible masses of condensed water vapor and/or ice crystals. Cloud formation is dependent on the moisture content and temperature of the air. A general rule: when moist air cools enough for the water vapor to condense, clouds can form. We use clouds to help describe and predict weather patterns, but clouds are also vital in creating weather! Although we may think of clouds only when deciding whether to bring an umbrella, it is important to realize that clouds are integral to Earth's overall energy budget.
Gulf of Maine cloudiness
Gulf of Maine skies can vary from crystal clear, to lightly cloudy, to overcast, to foggy or hazy, and everything in-between. Clouds form when moist air cools and water vapor condenses; thus clouds may be seen where warm air is carried over a cooler surface. In the Gulf of Maine, this often occurs at the coastal margins. Clouds also form when air is lifted to higher, cooler levels in the atmosphere, causing moisture within the air to condense.
Note: All satellite images on this page were taken by the SeaWiFS instrument and are available from NASA's "Earth Observatory" website.
Two parameters are estimated from GoMOOS buoys sensors during daylight hours:
- Percentage of sun in comparison to a clear sky
- This parameter is computed hourly by comparing buoy measurements of downwelling irradiance (i.e., sunlight entering the ocean) to a clear sky atmospheric model
- Whether or not sky conditions are cloudy, partly cloudy, or hazy
- This parameter is computed by looking at hour to hour deviations in the sun percentage (described above)
- If hour to hour deviations are large, it likely means that clouds are passing over frequently, and thus the sky conditions are partly cloudy
- If hour to hour deviations are small and the sun percentage is lower than 80%, then there is most likely thin clouds or haze present
- If hour to hour deviations are small and the sun percentage is lower than 30%, these are likely cloudy or overcast conditions
- This parameter is computed by looking at hour to hour deviations in the sun percentage (described above)
Clouds play a major role in our global climate by regulating the amount of solar radiation that reaches Earth's surfce and the energy emitted by Earth into space. Solar energy is the main force driving our climate, but the earth and clouds are also important players. The sun emits short-wave radiation that : 1) reaches earth's surface; 2) is absorbed by clouds; or 3) is reflected by clouds. The earth also emits energy, but as long-wave radiation that either reaches space, or is absorbed or reflected by clouds. Clouds emit their own long-wave radiation to earth's surface and to space. The balance of emitted, absorbed, and reflected radiation is what determines our global climate, and clouds can significantly change that balance. The image at right shows how different types of clouds impact the radiation budget of Earth. Low, thick clouds primarily reflect incoming solar energy back to space causing cooling. On the other hand, thin, high clouds primarily absorb and reflect outgoing energy back and produce warming. Clouds can have a cooling effect or a warming effect; however, the average global effect of clouds is cooling.
Precipitation is perhaps the most well known impact of clouds. Recall that clouds are "collections" of condensed water vapor or ice crystals. When these become too dense to remain suspended in air, they fall to earth as precipitation. Depending on the temperatures encountered during its path, precipitation can reach earth's surface as rain, hail, freezing rain, sleet or snow.
Beyond the Gulf: Where does cloudiness commonly occur?
One of the most consistent band of clouds is the Intertropical Convergence Zone (ITCZ). The ITCZ is found where wind systems of the northern and southern hemispheres meet. In this zone, warm moist air converges, rises, and cools: this causes water vapor to condense and clouds to form. Ever present, the ITCZ shifts north during the northern hemisphere's summer (i.e., southern hemisphere's winter) and shifts south during the southern hemisphere's summer (i.e., northern hemisphere's winter).
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- Conkling, P.W. (ed.). (1995). From Cape Cod to the Bay of Fundy: An Environmental Atlas of the Gulf of Maine. MIT Press.
- Fraser, A. B. (1995). Bad Clouds. URL: http://www.ems.psu.edu/~fraser/Bad/BadClouds.html.
- NASA Facts. (1999). Clouds and the Energy Cycle. URL: http://eospso.gsfc.nasa.gov/ftp_docs/Clouds.pdf.
- NASA Earth Observatory. (2002). Visible Earth. URL: http://visibleearth.nasa.gov/
- Open University Course Team. (1989). Ocean Circulation. Pergamon Press.
- Tropical Rainfall Measuring Mission.(2002). TRMM Instruments: Clouds and the Earth's Radiant Energy System. URL: http://trmm.gsfc.nasa.gov/overview_dir/ceres.html.
