eo.ucar.edu https://eo.ucar.edu/basics/wx_1_b.html eo.ucar.edu Layers of the Atmosphere eo.ucar.edu National Center for Atmospheric Research atmosphere https://eo.ucar.edu/basics/wx_1_b.html https://eo.ucar.edu/basics/wx_1_b.html Atmospheric Layers Site 1 National Center for Atmospheric Research ucar.edu