Ground‐based measurements of water vapor in the middle atmosphere

Abstract

We present measurements of the middle atmospheric water vapor mixing ratio profile obtained using the ground‐based Naval Research Laboratory water vapor millimeter‐wave spectrometer (WVMS) instrument at the Jet Propulsion Laboratory Table Mountain Observatory. The measurements cover a period of 262 days from January 23, 1992, to October 13, 1992. During this campaign it was possible to retrieve useful daily mixing ratio profiles for 186 days. We thus have a nearly continuous record of water vapor mixing ratios for altitudes from ≈35 to 75 km. The retrievals are obtained using the optimal estimation method. Details of the error analysis are presented, and a technique is introduced that reduces baseline effects and helps to estimate the baseline error. The high‐altitude (≳65 km) data show a sharp rise prior to the expected maximum near the summer solstice and a gradual decline in the following months. The mixing ratios generally peak between 55 and 65 km, at which point the mixing ratios are 6–7 parts per million by volume. The highest peaks occur in January, May, and October.