Temporal coverage: 9 May 2013 - present
The Microwave Limb Sounder (MLS) Water Vapor (H2O) Mixing Ratio layer at 46hPa (hectopascals) indicates water vapor levels at the vertical atmospheric pressure level of 46hPa, and is measured in parts per million by volume (ppmv).
Water vapor is the dominant greenhouse gas in the troposphere. Its greatest influences on climate forcing is in the upper troposphere, and it is generally believed that water vapor amplifies the radiative forcing associated with the anthropogenic increases in carbon dioxide. In the tropics, upper tropospheric water vapor is closely linked to sea surface temperature and thus ocean-atmosphere coupling phenomena such as the El Niño southern oscillation can be observed. Energy is released when water vapor condenses and large values of relative humidity, which is derived from water vapor and temperature, show where cloud formation is likely. Stratospheric water vapor influences stratospheric ozone chemistry both by providing a source of odd-hydrogen that destroys ozone and by influencing the formation of polar stratospheric clouds that trigger processes leading to large ozone loss in polar winter. Water vapor has been increasing in the stratosphere, believed due to changes near the tropical troposphere where water vapor enters the stratosphere.
The MLS Water Vapor (H2O) Mixing Ratio 46hPa layer is derived from the MLS Water Vapor product (ML2H2O_NRT) available from the Microwave Limb Sounder (MLS) instrument on the Aura satellite. The sensor resolution is 5km, imagery resolution is 2km, and the temporal resolution is twice daily (day and night).
References: GES DISC - ML2H2O_NRT: MLS/Aura Near-Real-Time L2 Water Vapor (H2O) Mixing Ratio V004; MLS - H2O Product