UV Raman lidar measurements of relative humidity for the characterization of cirrus cloud microphysical properties

Abstract

RRaman lidar measurements performed in Potenza by the Raman lidar system BASIL in the presence of cirrus clouds are discussed. Measurements were performed on 6 September 2004 in the frame of Italian phase of the EAQUATE Experiment. The major feature of BASIL is represented by its capability to perform high-resolution and accurate measurements of atmospheric temperature and water vapour, and consequently relative humidity, both in daytime and night-time, based on the application of the rotational and vibrational Raman lidar techniques in the UV. BASIL is also capable to provide measurements of the particle backscatter and extinction coefficient, and consequently lidar ratio (at the time of these measurements only at one wavelength), which are fundamental to infer geometrical and microphysical properties of clouds. A case study is discussed in order to assess the capability of Raman lidars to measure humidity in presence of cirrus clouds, both below and inside the cloud. While air inside the cloud layers is observed to be always under-saturated with respect to water, both ice super-saturation and under-saturation conditions are found inside these clouds. Upper tropospheric moistening is observed below the lower cloud layer. The synergic use of the data derived from the ground based Raman Lidar and of spectral radiances measured by the NAST-I Airborne Spectrometer allows to determine the temporal evolution of the atmospheric cooling/heating rates due to the presence of the cirrus cloud anvil. Lidar measurements beneath the cirrus cloud layer have been interpreted using a 1-D cirrus cloud model with explicit microphysics. The 1-D simulations indicates that sedimentation-moistening has contributed significantly to the moist anomaly, but other mechanisms are also contributing. This result supports the hypothesis that the observed mid-tropospheric humidification is a real feature which is strongly influenced by the sublimation of precipitating ice crystals. Results illustrated in this study demonstrate that Raman lidars, like the one used in this study, can resolve the spatial and temporal scales required for the study of cirrus cloud microphysical processes and appears sensitive enough to reveal and quantify upper tropospheric humidification associated with cirrus cloud sublimation

Multi‐scale observations of atmospheric moisture variability in relation to heavy precipitating systems in the northwestern Mediterranean during HyMeX IOP12

“…The system was deployed in an atmospheric “supersite” located in Candillargues (43°N, 4°E, elevation: 1 m) and operated from 5 September to 5 November 2012 (Figure ). Besides atmospheric temperature and water vapour, BASIL also provides measurements of particle backscatter at 355, 532 and 1,064 nm, particle extinction at 355 and 532 nm, and particle depolarization at 355 and 532 nm (Di Girolamo et al, ; ). During HyMeX SOP1, water vapour mixing‐ratio measurements were calibrated based on the comparison with the simultaneous radiosondes, with the radiosonde launching facility being located approximately 100 m southeast of the lidar station.…”

A review of the remote sensing of lower tropospheric thermodynamic profiles and its indispensable role for the understanding and the simulation of water and energy cycles

“…[, ] showed that high‐power Raman lidar can even be applied for monitoring profiles of turbulent moments up to the third order in the daytime convective atmospheric boundary layer (CBL). Additionally, the combined use of the WVRL and TRRL techniques has been exploited to perform measurements of relative humidity [ Mattis et al ., ; Di Girolamo et al ., ; Hammann et al ., ], e.g., for the characterization of cloud condensation levels in the CBL and cirrus cloud microphysical properties.…”

Observation of low‐level wind reversals in the Gulf of Lion area and their impact on the water vapour variability

“…The major feature of BASIL is represented by its capability to perform high‐resolution and accurate measurements of atmospheric temperature and water vapour, both in daytime and night‐time, based on the application of the rotational and vibrational Raman lidar techniques in the ultraviolet (Di Girolamo et al , , , ; Bhawar et al , ). Besides temperature and water vapour, BASIL is also capable of providing measurements of particle backscatter at 355, 532 and 1064 nm, particle extinction at 355 and 532 nm, and particle depolarization at 355 and 532 nm (Griaznov et al , ; Di Girolamo et al , , , ).…”

“…Concerning water vapour mixing ratio measurements, BASIL provides daytime and night‐time profiles with a maximum vertical and temporal resolution of 7.5 m and 10 s, respectively. The typical daytime precision is 0.2 g kg −1 up to 3 km and 0.3 g kg −1 up to 5 km, while the typical night‐time precision is 0.05 g kg −1 up to 3 km and 0.005 g kg −1 at 10 km, based on an integration time of 5 min and a vertical resolution of 150 m (Di Girolamo et al , ). Water vapour mixing ratio measurements by BASIL were calibrated based on the comparison with the radiosondes launched from the lidar site, with the radiosonde launching facility being located approximately 100 m away from the lidar station.…”