Abstract
Abstract. We present tropospheric water vapor profiles measured with a Raman lidar during three field campaigns held in Finland. Co-located radio soundings are available throughout the period for the calibration of the lidar signals. We investigate the possibility of calibrating the lidar water vapor profiles in the absence of co-existing on-site soundings using water vapor profiles from the combined Advanced InfraRed Sounder (AIRS) and the Advanced Microwave Sounding Unit (AMSU) satellite product; the Aire Limitée Adaptation dynamique Développement INternational and High Resolution Limited Area Model (ALADIN/HIRLAM) numerical weather prediction (NWP) system, and the nearest radio sounding station located 100 km away from the lidar site (only for the permanent location of the lidar). The uncertainties of the calibration factor derived from the soundings, the satellite and the model data are < 2.8, 7.4 and 3.9 %, respectively. We also include water vapor mixing ratio intercomparisons between the radio soundings and the various instruments/model for the period of the campaigns. A good agreement is observed for all comparisons with relative errors that do not exceed 50 % up to 8 km altitude in most cases. A 4-year seasonal analysis of vertical water vapor is also presented for the Kuopio site in Finland. During winter months, the air in Kuopio is dry (1.15±0.40 g kg−1); during summer it is wet (5.54±1.02 g kg−1); and at other times, the air is in an intermediate state. These are averaged values over the lowest 2 km in the atmosphere. Above that height a quick decrease in water vapor mixing ratios is observed, except during summer months where favorable atmospheric conditions enable higher mixing ratio values at higher altitudes. Lastly, the seasonal change in disagreement between the lidar and the model has been studied. The analysis showed that, on average, the model underestimates water vapor mixing ratios at high altitudes during spring and summer.
Highlights
The radiative balance between incoming solar radiation and outgoing longwave radiation is the primary regulator of Earth’s climate
As its concentration mostly depends on the air temperature, climate models suggest an amplified initial warming effect in global warming scenarios (Boucher et al, 2013)
Hearty et al (2014) report on instrumental biases of Advanced InfraRed Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU) concluding to up to 2 K for the temperature measurements and 10 % wet for the water vapor, where the bias is largest within the boundary layer
Summary
The radiative balance between incoming solar radiation and outgoing longwave radiation is the primary regulator of Earth’s climate. As its concentration mostly depends on the air temperature, climate models suggest an amplified initial warming effect in global warming scenarios (Boucher et al, 2013) This important feedback roughly doubles the amount of warming caused by carbon dioxide (Held and Soden, 2000; Soden et al, 2002, 2005). While microwave radiometers and photometers can accurately deliver the total precipitable water vapor (TPW), lidars (DIAL and Raman) are the only instruments available for high temporal and vertical resolution of continuous WVMR measurements. Foth et al (2017) proposed a methodology to retrieve water vapor mixing ratios during daytime by using a microwave radiometer and the Raman lidar profiles. We calibrate Raman lidar WVMR profiles using in situ, satellite and model data.
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