Multiparameter Raman Lidar Measurements for the Characterization of a Dry Stratospheric Intrusion Event

Abstract

The UV Raman lidar system (BASIL), operational at University of Basilicata (Potenza-Italy) and capable to perform high-resolution and accurate measurements of atmospheric temperature and water vapour based on the application of the rotational and vibrational Raman lidar techniques in the UV, was recently involved in the LAUNCH 2005 experiment (International Lindenberg campaign for assessment of humidity and cloud profiling systems and its impact on high-resolution modelling) held from 12 September to 31 October 2005. A thorough description of technical characteristics, measurements capabilities and performances of BASIL is given in the paper. Measurements were continuously run between 1 and 3 October 2005, covering a dry stratospheric intrusion episode associated with a tropopause folding event. The measurements in this paper represent the first simultaneous Raman Lidar measurements of atmospheric temperature and water vapour mixing ratio, and consequently relative humidity, reported for an extensive observation period (32 hours). The use of water vapour to trace intruded stratospheric air allows to clearly identify a dry structure (approx. 1 km thick) originated in the stratosphere and descending in the free troposphere down to ~ 3 km. A similar feature is present in the temperature field, with lower temperature values detected within the dry air tongue. Relative humidity measurements reveal values as small as 0.5-1 % within the intruded air. The stratospheric origin of the observed dry layer has been verified by the application of a Lagrangian trajectory model. The subsidence of the intruding heavy dry air may be responsible for the gravity wave activity observed beneath the dry layer. Lidar measurements have been compared with the output of both the PSU/NCAR Mesoscale Model (MM5) and the European Center for Medium range Weather Forecasting (ECMWF) global model. Comparisons in term of water vapour reveal the capability of MM5 to reproduce the dynamical structures associated with the stratospheric intrusion episode and simulate the deep penetration into the troposphere of the dry intruded layer. Moreover, lidar measurements of potential temperature are compared with MM5 output, while potential vorticity from both ECMWF and MM5 is compared with estimates obtained combining MM5 model vorticity and lidar measurements of potential temperature

The water vapour intercomparison effort in the framework of the Convective and Orographically‐induced Precipitation Study: airborne‐to‐ground‐based and airborne‐to‐airborne lidar systems

“…This ratio needs to be calibrated through an independent measurement, which is usually provided by radiosonde, GPS or microwave radiometer measurements. Raman lidar is a very powerful and straightforward technique to measure water vapour mixing ratio profiles, especially at night, but performances are somewhat degraded during the daytime because of the small Raman cross-sections, reducing the covered vertical range to 5 km (Althausen et al, 2000;Whiteman et al, 2006;Di Girolamo et al, 2009a).…”

“…The major feature of the system is represented by its capability to perform high-resolution and accurate measurements of atmospheric temperature and water vapour, both during daytime and night-time, based on the application of the rotational and vibrational Raman lidar techniques in the ultraviolet (Di Girolamo et al, 2004, 2009a, 2009b. Specifically, the water vapour profiles are determined from the Raman backscatter signals at 387 and 407 nm from nitrogen and water vapour molecules, respectively (Melfi et al, 1969;Cooney, 1971;Melfi, 1972).…”

“…Specifically, the water vapour profiles are determined from the Raman backscatter signals at 387 and 407 nm from nitrogen and water vapour molecules, respectively (Melfi et al, 1969;Cooney, 1971;Melfi, 1972). Besides temperature and water vapour, BASIL is 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, 2007;Mona et al, 2007;Bhawar et al, 2008;Di Girolamo et al, 2009a). For the purpose of determining particle size and microphysical parameters, measurements of the particle backscattering coefficient at 355, 532 and 1064 nm, of the particle extinction coefficient at 355 and 532 nm and of the depolarization ratio at 355 nm are used (Di Girolamo et al, 2009c).…”

Long‐range transport of Saharan dust and its radiative impact on precipitation forecast: a case study during the Convective and Orographically‐induced Precipitation Study (COPS)

“…BASIL also provides measurements of atmospheric temperature and multiwavelength measurements of particle backscattering, extinction and depolarization (Di Girolamo et al, 2009). The water-vapour mixing ratio was used together with β par at 1064 nm.…”

Initiation of convection over the Black Forest mountains during COPS IOP15a

“…The University of Basilicata Raman Lidar system (BASIL: Di Girolamo et al, 2009) was deployed at Supersite R. It measures temperature and water-vapour mixing ratio based on the application of the rotational (Di Girolamo et al, 2004) and rotovibrational Raman lidar techniques (Whiteman, 2003;Whiteman et al, 2006), respectively, in the ultraviolet region. The data used in this article were integrated over 15 minutes and have a vertical resolution for water vapour and temperature of 150 m and 300 m, respectively, and a precision for water vapour of less than 5% at 2 km and around 20% at 4 km (Bhawar et al, 2011) and for temperature of 1 K up to 4 km.…”