Radiosonde Humidity Retrieval by Simultaneous Radiation Measurements

Abstract

A radiometric method for the retrieval of moisture data at altitudes above the radiosonde hygristor cutoff region or in situations where a malfunction of the hygristor occurs is described. The method was applied to BOMEX radiation soundings. Regardless of the exact moisture profile, the method is designed to radiometrically infer the average decrease of moisture through the entire atmospheric column through a solution of the radiative transfer equation. This enables recovery of the total mass of atmospheric water vapor. In at least 25% of all BOMEX radiometersonde ascents, humidity retrieval did produce a more realistic moisture profile and total mass of precipitable water vapor. In these cases, the radiosonde hygristor humidity deficiencies averaged from ?45% at 800 mb to ?30% at 600 mb. For such pressure levels, the optical mass of water vapor retrieved for the soundings discussed averaged 1.68 gm cm?2. This represents 56% of the hygristor-measured optical mass. Above 400 mb the optical mass recovered averaged 0.7 gm cm?2 for all BOMEX radiometer soundings. It is suggested that a simple radiometer could be used to improve moisture measurements for soundings requiring the best possible water vapor data.