• MODIS Pic of the Day 23 December 2022

    From Dan Richter@1:317/3 to All on Fri Dec 23 11:02:04 2022
    December 23, 2022 - Fog in the Central Valley

    Fog
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    Thick fog frequently fills California’s Central Valley in late fall and
    winter, often creating a risk for drivers as visibility plummets. The
    Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s
    Terra satellite acquired a false-color image of a huge bank of fog on
    December 15.

    In this type of false-color image, infrared and visible light (MODIS
    Bands 7,2,1) are combined to help separate snow, which appears electric
    blue, from cloud and fog. Fog and most clouds look bright white,
    although high, cold clouds which contain ice crystals, may be tinted
    with electric blue. Vegetation appears green, open land looks tan,
    while water shows up as inky-black.

    The formation of fog requires three ingredients: wet ground, still air,
    and cold temperatures. Conditions are ripe after the ground has become
    damp from a recent rain. During the day, the warmth of the Sun causes
    the moisture to evaporate into the air. After sunset, air temperature
    slowly drops. Because cool air can hold less moisture than warm air the
    many tiny moisture droplets suspended in the air during the day combine
    into large droplets, creating “low cloud”, or fog.

    The Central Valley winter fog, also called Tule (too-le) tends to
    form—often rapidly— after sunset, become thickest just before dawn,
    then slowly thins as air warms in the morning. Tule fog season
    typically begins in December and ends in February.

    Image Facts
    Satellite: Terra
    Date Acquired: 12/21/2022
    Resolutions: 1km (474.1 KB), 500m (1.1 MB), 250m (684.2 KB)
    Bands Used: 1,4,3
    Image Credit: MODIS Land Rapid Response Team, NASA GSFC



    https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2022-12-23

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