Paolo Di Girolamo

Volcanic aerosol layers observed by lidar at South Pole, September 1991–June 1992

During 1991 the terrestrial stratosphere went through a substantially increased aerosol load, due mainly to the eruptions of Mt. Pinatubo in the Philippines, and, to a lesser extent, to those of Mt. Hudson in Chile. This paper reports lidar observations of the stratospheric aerosols at South Pole. Two layers were present at different altitudes during the austral summer, but only the higher one persisted in the stratosphere until the onset of the polar stratospheric cloud (PSC) phenomenon. Data have been analyzed in terms of the integrated backscattering coefficient and the aerosol mass content has been estimated.

Lidar observations of the Pinatubo aerosol layer at Thule, Greenland

Lidar measurements of the stratospheric aerosol content have been carried out in Thule (Greenland), in connection with the European Arctic Stratospheric Ozone Experiment (EASOE). Aerosols attributable to the Pinatubo eruption were detected in the stratosphere late in September; during autumn and early winter the stratospheric aerosol load slowly increased. In the region above approximately 18 km the aerosol load depended on the location of the station relative to the polar vortex. A temporary increase of the aerosol concentration was detected up to about 26 km at the beginning of February, when Thule was located for a few days outside the vortex. A final increase of the aerosol load was related with the final breakup of the vortex. The aerosol integrated backscatter values ranged between 0.001 and 0.005 sr−1 during most of the winter, and increased up to 0.007 sr−1 in early spring; in this period the aerosol columnar mass was estimated to be as high as 0.1 g m−2.

The Evolution of the Pinatubo Stratospheric Aerosol Layer Observed by Lidar at South Pole, Rome, Thule: a Summary of Results

Stratospheric aerosol observations have been carried out with three lidars, in the period preceeding and following the eruption of Mt. Pinatubo. The lidars were located at South Pole, Rome and Thule. The detailed analysis of the results is still under way: their general features and highlights are summarised in this paper. The aerosol backscattering data show the global evolution of the volcanic aerosol cloud in relation to the general circulation of the atmosphere and to microphysical processes. Other inferred parameters are the mass, the center of mass of the cloud. and the size distribution of the aerosol. Correlations between the aerosol and the ozone contents. found after all main eruptions since 1962, have been confirmed. Large effects on polar stratospheric cloud activity have been recorded.

On the temperature dependence of polar stratospheric clouds

Polar stratospheric clouds were frequently observed by lidar at the Amundsen-Scott South Pole Station during May–October 1988. The dependence of the bakscattering cross section on the temperature can be referred to transitions of the HNO3/H2O system: it appears possible to distinguish the pure trihydrate from the mixed ice-trihydrate phase in the composition of the aerosol and, in some cases, to bracket the HNO3 and H2O content of the ambient gas, and to provide indications on the size of the particles.

Characterization of PBL height and structure by Raman lidar: Selected case studies from the convective and orographically-induced precipitation study

The planetary boundary layer includes the portion of the atmosphere which is directly influenced by the presence of the Earths surface. Aerosol particles trapped within the PBL can be used as tracers to study boundary-layer vertical structure and time variability. The PBL height and structure can be estimated based on the use of Raman lidar data. A first method is based on the first order derivative of the range-corrected elastic signal (RCS). Estimates of the PBL height and structure obtained from the above mentioned approach are compared with simultaneous estimates obtained from potential temperature profiles determined from the radiosondes launched simultaneously to lidar operation. Additional estimates of the boundary layer height are obtained from rotational Raman lidar signals used for temperature measurements signals, this latter approach being preferable in the decaying phase of the boundary layer, when effectiveness of the approach based on the elastic lidar signals may be altered by the presenc...

Lidar observations of low-level wind reversals over the Gulf of Lion and characterization of their impact on the water vapour variability

Water vapour measurements from a ground-based Raman lidar and an airborne differential absorption lidar, complemented by high resolution numerical simulations from two mesoscale models (Arome-WMED and MESO-NH), are considered to investigate transition events from Mistral/Tramontane to southerly marine flow taking place over the Gulf of Lion in Southern France in the time frame September-October 2012, during the Hydrological Cycle in the Mediterranean Experiment (HyMeX) Special Observation Period 1 (SOP1). Low-level wind reversals associated with these transitions are found to have a strong impact on water vapour transport, leading to a large variability of the water vapour vertical and horizontal distribution. The high spatial and temporal resolution of the lidar data allow to monitor the time evolution of the three-dimensional water vapour field during these transitions from predominantly northerly Mistral/Tramontane flow to a predominantly southerly flow, allowing to identify the quite sharp separation ...

Characterization of turbulent processes by the Raman lidar system BASIL during the HD(CP)2 observational prototype experiment – HOPE

Measurements carried out by the Raman lidar system BASIL are reported to demonstrate the capability of this instrument to characterize turbulent processes within the Convective Boundary Layer (CBL). In order to resolve the vertical profiles of turbulent variables, high resolution water vapour and temperature measurements, with a temporal resolution of 10 sec and a vertical resolution of 90 and 30u2005m, respectively, are considered. Measurements of higher-order moments of the turbulent fluctuations of water vapour mixing ratio and temperature are obtained based on the application of spectral and auto-covariance analyses to the water vapour mixing ratio and temperature time series. The algorithms are applied to a case study (IOP 5, 20 April 2013) from the HD(CP)2 Observational Prototype Experiment (HOPE), held in Central Germany in the spring 2013. The noise errors are demonstrated to be small enough to allow the derivation of up to fourth-order moments for both water vapour mixing ratio and temperature fluctu...

Characterization of particle hygroscopicity by Raman lidar: Selected case studies from the convective and orographically-induced precipitation study

The characterization of particle hygroscopicity has primary importance for climate monitoring and prediction. Model studies have demonstrated that relative humidity (RH) has a critical influence on aerosol climate forcing. Hygroscopic properties of aerosols influence particle size distribution and refractive index and hence their radiative effects. Aerosol particles tend to grow at large relative humidity values as a result of their hygroscopicity. Raman lidars with aerosol, water vapor and temperature measurement capability are potentially attractive tools for studying aerosol hygroscopicity as in fact they can provide continuous altitude-resolved measurements of particle optical, size and microphysical properties, as well as relative humidity, without perturbing the aerosols or their environment. Specifically, the University of Basilicata Raman lidar system (BASIL) considered for the present study, has the capability to perform all-lidar measurements of relative humidity based on the application of both...

Characterization of convection-related parameters by Raman lidar: Selected case studies from the convective and orographically-induced precipitation study

An approach to determine the convective available potential energy (CAPE) and the convective inhibition (CIN) based on the use of data from a Raman lidar system is illustrated in this work. The use of Raman lidar data allows to provide high temporal resolution measurements (5 min) of CAPE and CIN and follow their evolution over extended time periods covering the full cycle of convective activity. Lidar-based measurements of CAPE and CIN are obtained from Raman lidar measurements of the temperature and water vapor mixing ratio profiles and the surface measurements of temperature, pressure and dew point temperature provided by a surface weather station. The approach is applied to the data collected by the Raman lidar system BASIL in the frame of COPS. Attention was focused on 15 July and 25-26 July 2007. Lidar-based measurements are in good agreement with simultaneous measurements from radiosondes and with estimates from different mesoscale models.

Raman Lidar Observations of a MCS in the frame of the Convective and Orographically‐induced Precipitation Study

The Raman lidar system BASIL was deployed in Achern (Supersite R, Lat: 48.64°u2009N, Long: 8.06°u2009E, Elev.: 140 m) in the frame of the Convective and Orographically‐induced Precipitation Study. On 20 July 2007 a frontal zone passed over the COPS region, with a Mesoscale Convective System (MCS) imbedded in it. BASIL was operated continuously during this day, providing measurements of temperature, water vapour, particle backscattering coefficient at 355, 532 and 1064 nm, particle extinction coefficient at 355 and 532 nm and particle depolarization at 355 and 532 nm. The thunderstorm approaching determined the lowering of the anvil clouds, which is clearly visible in the lidar data. A cloud deck is present at 2 km, which represents a mid‐level outflow from the thunderstorm/MCS. The mid‐level outflow spits out hydrometeor‐debris (mostly virga) and it is recycled back into it. The MCS modified the environment at 1.6–2.5 km levels directly (outflow) and the lower levels through the virga/precipitation. Wave structur...