adiabatic process arden buck equation atmospheric pressure atmospheric thermodynamics bar baroclinity capillary action celsius cloud cloud condensation nuclei condensation convection convective instability dew point dry-bulb temperature fog gas heat index humidex humidity lapse rate lifted condensation level lightning mean radiant temperature physical system physics pressure relative humidity surface weather analysis temperature thermometer vapor visibility vorticity water vapor wet-bulb potential temperature wet bulb globe temperature wind wind chill