Abstract
Abstract. In this paper, we compare the diurnal variations in middle-atmospheric water vapor as measured by two ground-based microwave radiometers in the Alpine region near Bern, Switzerland. The observational data set is also compared to data from the chemistry–climate model WACCM. Due to the small diurnal variations of usually less than 1%, averages over extended time periods are required. Therefore, two time periods of five months each, December to April and June to October, were taken for the comparison. The diurnal variations from the observational data agree well with each other in amplitude and phase. The linear correlation coefficients range from 0.8 in the upper stratosphere to 0.5 in the upper mesosphere. The observed diurnal variability is significant at all pressure levels within the sensitivity of the instruments. Comparing our observations with WACCM, we find that the agreement of the phase of the diurnal cycle between observations and model is better from December to April than from June to October. The amplitudes of the diurnal variations for both time periods increase with altitude in WACCM, but remain approximately constant at 0.05 ppm in the observations. The WACCM data are used to separate the processes that lead to diurnal variations in middle-atmospheric water vapor above Bern. The dominating processes were found to be meridional advection below 0.1 hPa, vertical advection between 0.1 and 0.02 hPa and (photo-)chemistry above 0.02 hPa. The contribution of zonal advection is small. The highest diurnal variations in water vapor as seen in the WACCM data are found in the mesopause region during the time period from June to October with diurnal amplitudes of 0.2 ppm (approximately 5% in relative units).
Highlights
IntroductionThe diurnal variations from the observational data agree tent heat release in the troposphere
Comparing our observations with tides and propagate westward with the apparent motion of Whole Atmosphere Community Climate Model (WACCM), we find that the agreement of the phase of the di- the sun, and all tides that are not sun-synchronous are called urnal cycle between observations and model is better from December to April than from June to October
This study focuses on diurnal variations in water vapor from the upper stratosphere to the upper mesosphere as observed by two independent ground-based microwave radiometers located in the Alpine region
Summary
The diurnal variations from the observational data agree tent heat release in the troposphere. These tidal waves propwell with each other in amplitude and phase. Comparing our observations with tides and propagate westward with the apparent motion of WACCM, we find that the agreement of the phase of the di- the sun, and all tides that are not sun-synchronous are called urnal cycle between observations and model is better from December to April than from June to October. The amplitudes of the diurnal variations for both time periods increase non-migrating tides. The dominating processes were found to be meridional advection below 0.1 hPa, vertical advectiiedsaol namtidpelistuindetsemmpaexriamtOuizreeciaennadthnwisirnSedgciioninet.hnOe cbMseeLrTvarteigoinoanl studwere tion between 0.1 and 0.02 hPa and (photo-)chemistry above done with satellite instruments The Zhang et al, 2006) and from ground-based wind and temhighest diurnal variations in water vapor as seen in the perature measurements (meteor radars and lidars)
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