Lidar Site Research Articles

CALIPSO validation using ground-based lidar in Hefei (31.9°N, 117.2°E), China

Validation measurement in collaboration with existing lidar sites is a very important part of CALIPSO validation program, lidar site in Hefei is invited to collaborate in the CALIPSO validation program. In this paper, ground-based lidar measurements in Hefei performed in coincidence with CALIPSO overpass are presented, attenuated backscatter profiles at 532 nm and 1064 nm, as well as volume depolarization ratio profile at 532 nm measured by CALIPSO are compared with the ones measured by ground-based lidar. The comparisons indicate that CALIPSO measurements are consistent with the ground-based lidar measurements. However, due to the fact that horizontal distributions of aerosols in the lower troposphere and clouds are in most cases inhomogeneous, there are some differences between two lidar measurements in the boundary layer and clouds. The aerosol layer below the semi-transparent thick cloud can be detected by the 532 nm channel of CALIPSO in daytime.

Aerosol Observation with Raman LIDAR in Beijing, China

Aerosol observation with Raman LIDAR in NIES (National Institute for Environmental Studies, Japan) LIDAR network was conducted from 17 April to 12 June 2008 over Beijing, China. The aerosol optical properties derived from Raman LIDAR were compared with the retrieved data from sun photometer and sky radiometer observations in the Aerosol Robotic Network (AERONET). The comparison provided the complete knowledge of aerosol optical and physical properties in Beijing, especially in pollution and Asian dust events. The averaged aerosol optical depth (AOD) at 675 nm was 0.81 and the Angstrom exponent between 440 nm and 675 nm was 0.99 during experiment. The LIDAR derived AOD at 532 nm in the planetary boundary layer (PBL) was 0.48, which implied that half of the total AOD was contributed by the aerosol in PBL. The corresponding averaged LIDAR ratio and total depolarization ratio (TDR) were 48.5sr and 8.1%. The negative correlation between LIDAR ratio and TDR indicated the LIDAR ratio decreased with aerosol size because of the high TDR associated with nonspherical and large aerosols. The typical volume size distribution of the aerosol clearly demonstrated that the coarse mode radius located near 3 lTEXg${\mu}m$l/TEXg in dust case, a bi-mode with fine particle centered at 0.2 lTEXg${\mu}m$l/TEXg and coarse particle at 2 lTEXg${\mu}m$l/TEXg was the characteristic size distribution in the pollution and clean cases. The different size distributions of aerosol resulted in its different optical properties. The retrieved LIDAR ratio and TDR were 41.1sr and 19.5% for a dust event, 53.8sr and 6.6% for a pollution event as well as 57.3sr and 7.2% for a clean event. In conjunction with the observed surface wind field near the LIDAR site, most of the pollution aerosols were produced locally or transported from the southeast of Beijing, whereas the dust aerosols associated with the clean air mass were transported by the northwesterly or southwesterly winds.

Polar mesospheric cloud structures observed from the cloud imaging and particle size experiment on the Aeronomy of Ice in the Mesosphere spacecraft: Atmospheric gravity waves as drivers for longitudinal variability in polar mesospheric cloud occurrence

The cloud imaging and particle size (CIPS) experiment is one of three instruments on board the Aeronomy of Ice in the Mesosphere (AIM) spacecraft that was launched into a 600 km Sun‐synchronous orbit on 25 April 2007. CIPS images have shown distinct wave patterns and structures in polar mesospheric clouds (PMCs), around the summertime mesopause region, which are qualitatively similar to structures seen in noctilucent clouds (NLCs) from ground‐based photographs. The structures in PMC are generally considered to be manifestations of upward propagating atmospheric gravity waves (AGWs). Variability of AGW effects on PMC reported at several lidar sites has led to the notion of longitudinal differences in this relationship. This study compares the longitudinal variability in the CIPS‐observed wave occurrence frequency with CIPS‐measured PMC occurrence frequency and albedo along with mesospheric temperatures measured by the sounding of the atmosphere using broadband emission radiometry instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics spacecraft. Our results for the latitude ranges between 70° and 80° show a distinct anticorrelation of wave structures with cloud occurrence frequency and correlations with temperature perturbations for at least two of the four seasons analyzed, supporting the idea of gravity wave‐induced cloud sublimation. The locations of the observed wave events show regions of high wave activity in both hemispheres. In the Northern Hemisphere, while the longitudinal variability in observed wave structures show changes from the 2007–2008 seasons, there exist regions of both low and high wave activities common to the two seasons. These persistent features may explain some of the observed differences in PMC activity reported by ground‐based lidar instruments distributed at different longitudes. The statistical distribution of horizontal scales increases with wavelength up to at least 250 km. We also discuss the possibility of atmospheric tides, especially the nonmigrating semidiurnal tide, aliasing our observations and affecting the results presented in this analysis.

Estimation of the microphysical aerosol properties over Thessaloniki, Greece, during the SCOUT‐O3 campaign with the synergy of Raman lidar and Sun photometer data

An experimental campaign was held at Thessaloniki, Greece (40.6°N, 22.9°E), in July 2006, in the framework of the integrated project Stratosphere‐Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere (SCOUT‐O3). One of the main objectives of the campaign was to determine the local aerosol properties and their impact on the UV irradiance at the Earth's surface. In this article, we present vertically resolved microphysical aerosol properties retrieved from the inversion of optical data that were obtained from a combined one‐wavelength Raman/two‐wavelength backscatter lidar system and a CIMEL Sun photometer. A number of assumptions were undertaken to overcome the limitations of the existing optical input data needed for the retrieval of microphysical properties. We found acceptable agreement with Aerosol Robotic Network retrievals for the fine‐mode particle effective radius, which ranged between 0.11 and 0.19 for the campaign period. It is shown that under complex layering of the aerosols, general assumptions may result in unrealistic retrievals, especially in the presence of aged smoke aerosols. Furthermore, with this instrument setup, the inversion algorithm can also be applied successfully for the complex refractive index in cases of vertically homogeneous layers of continental polluted aerosols. For these inversion cases, the vertically resolved retrievals for the single‐scattering albedo resulted in values around 0.9 at 532 nm, which were in very good agreement with estimates from airborne in situ observations obtained in the vicinity of the lidar site.

Aerosol load study in urban area by Lidar and numerical model

Vertical profiles of particle mass concentration in the urban canopy above the city of Lyon have been obtained from Lidar measurements of atmospheric backscattering, over a period of three days. The concentrations measured at 50 m above the ground have been compared with the mass concentration of PM10 measured by a ground-based sampler located near the Lidar site. At certain times during the measurement campaign, the Lidar concentration measurements at 50 m agree reasonably well with the concentrations at ground level but at other times the differences between the two sets of measurements are so great that they cannot be explained by possible uncertainties in the data processing. Even when the Lidar and ground-based measurements coincide, there are significant differences between the two signals. To explain these differences we have computed the trajectories of the air parcels that pass over the Lidar, using a numerical model for the wind field that takes into account surface features such as relief and changes in roughness. This analysis showed that the differences can be explained by the meteorological conditions (wind speed and direction, vertical profiles of temperature) and the positions of the different sources of particulate matter relative to the measurement site. The combination of Lidar, ground-based sampler and air mass trajectory calculations is shown to be a powerful tool for discriminating between different sources of pollution, which could be useful in enforcing an urban air quality policy.

Calibration of a Multichannel Water Vapor Raman Lidar through Noncollocated Operational Soundings: Optimization and Characterization of Accuracy and Variability

Abstract This paper presents a parametric automatic procedure to calibrate the multichannel Rayleigh–Mie–Raman lidar at the Institute for Atmospheric Science and Climate of the Italian National Research Council (ISAC-CNR) in Tor Vergata, Rome, Italy, using as a reference the operational 0000 UTC soundings at the WMO station 16245 (Pratica di Mare) located about 25 km southwest of the lidar site. The procedure, which is applied to both channels of the system, first identifies portions of the lidar and radiosonde profiles that are assumed to sample the same features of the water vapor profile, taking into account the different time and space sampling. Then, it computes the calibration coefficient with a best-fit procedure, weighted by the instrumental errors of both radiosounding and lidar. The parameters to be set in the procedure are described, and values adopted are discussed. The procedure was applied to a set of 57 sessions of nighttime 1-min-sampling lidar profiles (roughly about 300 h of measurements) covering the whole annual cycle (February 2007–September 2008). A calibration coefficient is computed for each measurement session. The variability of the calibration coefficients (∼10%) over periods with the same instrumental setting is reduced compared to the values obtained with the previously adopted, operator-assisted, and time-consuming calibration procedure. Reduction of variability, as well as the absence of evident trends, gives confidence both on system stability as well as on the developed procedure. Because of the definition of the calibration coefficient and of the different sampling between lidar and radiosonde, a contribution to the variability resulting from aerosol extinction and to the spatial and temporal variability of the water vapor mixing ratio is expected. A preliminary analysis aimed at identifying the contribution to the variability from these factors is presented. The parametric nature of the procedure makes it suitable for application to similar Raman lidar systems.

Characteristics of cirrus clouds and its radiative properties based on lidar observation over Chung-Li, Taiwan

In this paper, characterization of cirrus clouds are made by using data from ground based polarization lidar and radiosonde measurements over Chung-Li (24.58°N, 121.10°E), Taiwan for a period of 1999–2006. During this period, the occurrence of cirrus clouds is about 37% of the total measurement nights over the lidar site. Analysis of the measurement gives the statistical characteristics about the macrophysical properties such as occurrence height, ambient temperature, and its geometrical thickness while the microphysical properties are interpreted in terms of extinction coefficient, optical depth, effective lidar ratio and depolarization ratio. The effective lidar ratio has been retrieved by using the simulation technique of backscattered lidar signals. The effect of multiple scattering has been taken into the account by a model calculation. Summer (Jun–Aug) shows the maximum appearances of cirrus due to its formation mechanism. It is shown that tropopause cirrus clouds may occur with a probability of about 24%. These clouds are usually optically thin and having laminar in structure with some cases resembling the characteristics similar to that of polar stratospheric clouds (PSCs). The radiative properties of the cirrus clouds are also discussed in detail by the empirical equations with results show a positive feedback on any climate change.

Vertically resolved dust optical properties during SAMUM: Tinfou compared to Ouarzazate

Vertical profiles of dust key optical properties are presented from measurements during the Saharan Mineral Dust Experiment (SAMUM) by Raman and depolarization lidar at two ground-based sites and by airborne high spectral resolution lidar. One of the sites, Tinfou, is located close to the border of the Sahara in Southern Morocco and was the main in situ site during SAMUM. The other site was Ouarzazate airport, the main lidar site. From the lidar measurements the spatial distribution of the dust between Tinfou and Ouarzazate was derived for 1 d. The retrieved profiles of backscatter and extinction coefficients and particle depolarization ratios show comparable dust optical properties, a similar vertical structure of the dust layer, and a height of about 4 km asl at both sites. The airborne cross-section of the extinction coefficient at the two sites confirms the low variability in dust properties. Although the general picture of the dust layer was similar, the lidar measurements reveal a higher dust load closer to the dust source. Nevertheless, the observed intensive optical properties were the same. These results indicate that the lidar measurements at two sites close to the dust source are both representative for the SAMUM dust conditions.

Ten years of multiwavelength Raman lidar observations of free‐tropospheric aerosol layers over central Europe: Geometrical properties and annual cycle

We present geometrical properties and seasonal variations of appearance of aerosol particle pollution in the free troposphere over the central European lidar site at Leipzig, Germany. The data set has been acquired with Raman lidar in the past 10 years in the framework of the German Lidar Network (1997–2000) and since 2000 in the framework of the European Aerosol Research Lidar Network (EARLINET). In summary we analyzed 1028 measurements. Geometrical depth of the pollution layers was ≤1 km in 33% of all cases. Geometrical depths >5 km were found in 10% of all cases. Traces of particle pollution were detected up to the height of the tropopause. Forest‐fire burning in North America causes intrusion of particles into the stratosphere. Seven hundred seventeen of all observations were carried out on the basis of a regular measurement schedule which allows us to establish a statistic on the frequency of particle transport in the free troposphere. In 43% of the regular measurements we observed pollution above the continental boundary layer. The lofted particle layers largely result from intercontinental long‐range transport. We use backward trajectory analysis to identify the main source regions of the lofted pollution layers. In 19% of all regular measurements, free‐tropospheric pollution was advected from North America. Forest‐fire smoke from Canada and anthropogenic pollution from urban areas of the United States of America and Canada were the sources of the particle layers. We find a strong seasonal dependence of occurrence of these layers with a peak in June–August of each year. In a few cases we observed forest‐fire smoke advected from Siberia and east Asia with winds from westerly directions. Pollution advected from areas north of 70°N presents another transport channel. That pollution consists of Arctic haze or mixtures of haze with anthropogenic pollution. The main occurrence of such particle layers is around springtime of each year. Import of mineral dust from the Sahara represents another transport path. Most of such cases are observed during late springtime and summertime. Free‐tropospheric pollution advected from east and southeast Europe and Russia presents one transport channel from within the Euro‐Asian continent.

Interannual variations of middle atmospheric temperature as measured by the JPL lidar at Mauna Loa Observatory, Hawaii (19.5°N, 155.6°W)

The Jet Propulsion Laboratory Rayleigh‐Raman lidar at Mauna Loa Observatory (MLO), Hawaii (19.5°N, 155.6°W) has been measuring atmospheric temperature vertical profiles routinely since 1993. Linear regression analysis was applied to the 13.5‐yearlong (January 1994 to June 2007) deseasonalized monthly mean lidar temperature time series for each 1‐km altitude bin between 15 and 85 km. The regression analysis included components representing the Quasi‐Biennial Oscillation (QBO), El Niño‐Southern Oscillation (ENSO), and the 11‐year solar cycle. Where overlapping was possible, the results were compared to those obtained from the twice‐daily National Weather Service (NWS) radiosonde profiles at Hilo (5–30 km) located 60 km east‐north‐east of the lidar site, and the four‐times‐daily temperature analysis of the European Centre for Medium Range Weather Forecast (ECMWF). The analysis revealed the dominance of the QBO (1–3 K) in the stratosphere and mesosphere, and a strong winter signature of ENSO in the troposphere and lowermost stratosphere (∼1.5 K/MEI). Additionally, and for the first time, a statistically significant signature of ENSO was observed in the mesosphere, consistent with the findings of recent model simulations. The annual mean response to the solar cycle shows two statistically significant maxima of ∼1.3 K/100 F10.7 units at 35 and 55 km. The temperature responses to QBO, ENSO, and solar cycle are all maximized in winter. Comparisons with the global ECMWF temperature analysis clearly showed that the middle atmosphere above MLO is under a subtropical/extratropical regime, i.e., generally out‐of‐phase with that in the equatorial regions, and synchronized to the northern hemisphere winter/spring.

Cirrus optical properties observed with lidar, radiosonde, and satellite over the tropical Indian Ocean during the aerosol‐polluted northeast and clean maritime southwest monsoon

Cirrus formation and geometrical and optical properties of tropical cirrus as a function of height and temperature are studied on the basis of INDOEX (Indian Ocean Experiment) lidar and radiosonde measurements and satellite observations of deep convection causing the generation of anvil cirrus. Lidar and radiosonde measurements were conducted at Hulule (4.1°N, 73.3°E), Maldives, during four field campaigns carried out in February–March 1999 and March 2000 (northeast (NE) monsoon season, characterized by increased concentrations of anthropogenic aerosols over the Indian Ocean) and in July and October 1999 (southwest (SW) monsoon season, characterized by clean maritime conditions). As a result of a stronger impact of deep convection on cirrus formation during the SW monsoon season, cirrus clouds covered the sky over the lidar site in only 35% (NE), but 64% (SW) of the measurement time. Subvisible cirrus (optical depth ≤0.03), thin (optical depth from 0.03 to 0.3), and opaque cirrus (optical depth ≥0.3) were observed in 18%, 48%, and 34% (NE) and in 8%, 52%, and 40% (SW) out of all cirrus cases, respectively. Mean midcloud heights were rather similar with values of 12.9 ± 1.5 km (NE) and 12.7 ± 1.3 km (SW). In 25% of the cases the cirrus top height was found close to the tropopause. Mean values of the multiple‐scattering‐corrected cirrus optical depth, cirrus layer mean extinction coefficient, and extinction‐to‐backscatter ratio were 0.25 ± 0.26 (NE) and 0.34 ± 0.29 (SW), 0.12 ± 0.09 km−1 (NE) and 0.12 ± 0.10 km−1 (SW), and 33 ± 9 sr (NE) and 29 ± 11 sr (SW), respectively. A functional dependency of the extinction coefficient of the tropical cirrus on temperature is presented. All findings are compared with several other cirrus lidar observations in the tropics, subtropics, and at midlatitudes. By contrasting the cirrus optical properties of the different seasons, a potential impact of anthropogenic particles on anvil cirrus optical properties was examined. Differences in the cirrus extinction‐to‐backscatter ratio suggest that NE monsoon anvil cirrus originating from deep‐convection cumulus clouds had more irregularly shaped and thus slightly larger ice crystals than respective SW monsoon anvil cirrus. Because the meteorological conditions were found to vary significantly between the seasons, an unambiguous identification of the influence of Asian haze on cirrus optical properties is not possible.

Comparisons of Raman Lidar Measurements of Tropospheric Water Vapor Profiles with Radiosondes, Hygrometers on the Meteorological Observation Tower, and GPS at Tsukuba, Japan

Abstract The vertical distribution profiles of the water vapor mixing ratio (w) were measured by Raman lidar at the Meteorological Research Institute, Japan, during the period from 2000 to 2004. The measured values were compared with those obtained with radiosondes, hygrometers on a meteorological observation tower, and global positioning system (GPS) antennas near the lidar site. The values of w obtained with the lidar were lower than those obtained with the corrected Meisei RS2-91 radiosonde by 1.2% on average and higher than those obtained with the corrected Vaisala RS80-A radiosonde by 17% for w ≥ 0.5 g kg−1. The lidar data were higher than those radiosondes’ data by 19% or 33% for w < 0.5 g kg−1. The vertical variations of w obtained with the lidar differed from those obtained with the Meisei RS-01G radiosonde and Meteolabor Snow White radiosonde by 5% on average for w ≥ 0.5 g kg−1. The lidar data were lower than those radiosondes’ data by 37% or 39% for w < 0.5 g kg−1. The temporal variations of w obtained with the lidar and the hygrometers on the meteorological tower agreed to within 0.4% at a height of 213 m, although the absolute values differed systematically by 9%–14% due to the incomplete overlap of the laser beam and the receiver’s field of view at heights between 50 and 150 m. The precipitable water vapor obtained with the lidar indicated a mean positive bias of 2 mm (9%–11%) relative to those obtained with GPS. The lidar water vapor calibration coefficient that was calculated using RS2-91 radiosonde data varied by 11% during an 18-month period. Therefore, it is necessary to develop an accurate, yet convenient, method for determining the calibration coefficient for the use of the lidar.

Volcanic ash plume identification using polarization lidar: Augustine eruption, Alaska

During mid January to early February 2006, a series of explosive eruptions occurred at the Augustine volcanic island off the southern coast of Alaska. By early February a plume of volcanic ash was transported northward into the interior of Alaska. Satellite imagery and Puff volcanic ash transport model predictions confirm that the aerosol plume passed over a polarization lidar (0.694 μm wavelength) site at the Arctic Facility for Atmospheric Remote Sensing at the University of Alaska Fairbanks. For the first time, lidar linear depolarization ratios of 0.10–0.15 were measured in a fresh tropospheric volcanic plume, demonstrating that the nonspherical glass and mineral particles typical of volcanic eruptions generate strong laser depolarization. Thus, polarization lidars can identify the volcanic ash plumes that pose a threat to jet air traffic from the ground, aircraft, or potentially from Earth orbit.

Retrieval of aerosol properties from combined multiwavelength lidar and sunphotometer measurements

Simulation studies were carried out with regard to the feasibility of using combined observations from sunphotometer (SPM) and lidar for microphysical characterization of aerosol particles, i.e., the retrieval of effective radius, volume, and surface-area concentrations. It was shown that for single, homogeneous aerosol layers, the aerosol parameters can be retrieved with an average accuracy of 30% for a wide range of particle size distributions. Based on the simulations, an instrument combination consisting of a lidar that measures particle backscattering at 355 and 1574 nm, and a SPM that measures at three to four channels in the range from 340 to 1020 nm is a promising tool for aerosol characterization. The inversion algorithm has been tested for a set of experimental data. The comparison with the particle size distribution parameters, measured with in situ instrumentation at the lidar site, showed good agreement.

The effect of the 11-year solar-cycle on the temperature in the upper-stratosphere and mesosphere—Part III: Investigations of zonal asymmetry

The response to the 11-year solar cycle is investigated using a 3-D mechanistic stratosphere–mesosphere model, in particular the zonal asymmetry in the solar signal. Two model simulations are performed, one using solar forcing corresponding to solar minimum and the other corresponding to solar maximum. It is seen that the solar signal is strongly zonally asymmetric in northern hemisphere winter, with variations of up to 20 K at 25 km. The model results are compared to the solar signal seen from five rocket-sonde sites and one lidar site, all located at mid-latitude, but at different longitudes. Although there are some significant differences between the model results and the observations, the model results help to explain why there are significant variations in the solar signal in the observations made at different longitudinal positions. Such longitudinal dependence obviously does not appear in zonal mean results, hence this raises questions about the meaning of comparing zonal mean model results with results from local observations.

Risk management practices of Australasian BRCA1 and BRCA2 mutation carriers

Dust storms are significant contributors to ambient levels of particulate matter (PM) in many areas of the world. Central Asia, an area that is relatively understudied in this regard, is anticipated to be affected by dust storms due to its proximity to several major deserts that are in and generally surround Central Asia (e.g., the Aral Sea region, the Taklimakan desert in Western China). To investigate the relative importance of mineral dust (dust specifically composed of soil related minerals and oxides) in Central Asia, PM10 and PM2.5, and by difference, coarse particles (particles with diameters between 2.5 and 10 μm) were measured at two sites, Bishkek and Lidar Station Teplokluchenka (Lidar), in the Kyrgyz Republic. Samples were collected every other day from July 2008 to July 2009. Daily samples were analyzed for mass and organic and elemental carbon. Samples were also composited on a bi-weekly basis and analyzed for elemental constituents and ionic components. In addition, samples collected on days with relatively high and low PM concentrations were analyzed before, and separately, from the biweekly composites to investigate the chemical differences between the episodic events. Data from the episodic samples were averaged into the composited averages. Using the elemental component data, several observational models were examined to estimate the contribution of mineral dust to ambient PM levels. A mass balance was also conducted.Results indicate that at both sites, mineral dust (as approximated by the “dust oxide” model) and organic matter (OM) were the dominant contributors to PM10 and PM2.5. Mineral dust was a more significant contributor to the coarse PM (PM10-2.5) during high event samples at both sites, although the relative contribution is greater at the Lidar site (average ± standard deviation = 42 ± 29%) as compared with the Bishkek site (26 ± 16%). Principal Components Analysis (PCA) was performed using data from both sites, and PCA indicated that mineral dust explained the majority of the variance in PM concentrations, and that the major apportioned factors of PM10 and PM2.5 were chemically similar between sites.

A comprehensive study on middle atmospheric thermal structure over a tropic and sub-tropic stations

The general characteristics of middle atmospheric thermal structure have been studied by making use of the Rayleigh lidar data collected over the period of about four years (1998–2001). Here, the data has been used from two different stations in the Indian sub-continent in tropics (Gadanki; 13.5°N, 79.2°E) and in sub-tropics (Mt. Abu; 24.5°N, 72.7°E). The observed monthly mean temperature profiles are compared with different model atmospheres (CIRA-86 and MSISE-90). We observed, the mean temperature profiles have closer agreement with MSISE-90 than CIRA-86. The temperature profiles measured by lidar and HALOE satellite overpass nearby lidar site are generally in agreement with each other. The systematic and statistical errors in deriving temperature are found to be uniform for both the stations, as ∼1 K at 50 km, ∼3 K at 60 km and ∼10 K at 70 km. The special features of mesospheric temperature inversion (MTI) and double stratopause structure (DBS) are also addressed for both the stations.

Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling

Abstract. The day-long observation of a polar stratospheric cloud (PSC) by two co-located ground-based lidars at the Swedish research facility Esrange (67.9° N, 21.1° E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale modeling is utilized to simulate the meteorological setting of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC is in good agreement with simulations for irregular-shaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 µm, and a number density from 8 to 12 cm-3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 µm, a refractive index of 1.39 and a number density from 7 to 11 cm-3. The total amount of condensed HNO3 was in the range of 8–12 ppbv. The data provide further observational evidence that NAT forms via deposition nucleation on ice particles as a number of recently published papers suggest. By early afternoon the mountain-wave ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 3 to 1.9 µm with time. Later on, following the weakening of the mountain wave, wave-induced LTA was observed only. Our study demonstrates that ground-based lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.

Variation of the aerosol stratification over the Rhine Valley during Foehn development: a backscatter lidar study

The vertical aerosol stratification within and above the Rhine Valley was studied with a backscatter lidar during FORM (Foehn in the Rhine Valley during MAP) IOPs 4-5, October 1-3, 1999. The lidar site was in Trubbach, 9° 28 E, 47° 04 N, 490 m asl. Two scintillometers were used to monitor the horizontal and the vertical wind velocity at 600 m above the Rhine Valley floor. A number of surface stations were operational in the valley, as well as a set of radiosounding stations. This provides a possibility to correlate the measurements of the aerosol stratification with the variation of the meteorological parameters defining the Foehn development. The backscatter lidar measurements during the Foehn development show the variation of the aerosol backscatter at different altitudes of the valley PBL. The combination of lidar signal gradient and lidar signal variance presents the cold-pool as an aerosol-rich layer and suggests a likely mechanism for cold-pool erosion by the Foehn air.

A study of ozone variability and its connection with meridional transport in the northern Pacific lower stratosphere during summer 2002

A preliminary study of the impact of the north‐central Pacific circulation in the subtropical stratosphere on ozone variability locally observed by lidar is presented. The results from the upper tropospheric and stratospheric ozone measurements of the Jet Propulsion Laboratory lidars located at Mauna Loa Observatory (MLO), Hawaii, and Table Mountain Facility (TMF), California, during summer 2002 were compared to isentropic potential vorticity (IPV) advected on 54 levels from 320 to 1500 K by the high‐resolution model MIMOSA. The correlation between ozone measured by lidar, and the origin of the 10‐day backward trajectories of the air parcels sampled, was also investigated. Near the tropopause, strong positive correlation between ozone mixing ratio and IPV was observed at both MLO and TMF lidar sites. The largest fluctuations were centered near 350 K and are associated with the meridional displacement of the tropopause by Rossby waves north or south of the observing sites. These large displacements were occasionally accompanied by Rossby wave breaking (RWB), as was identified several times during the summer in the vicinity of the Hawaiian Islands. Using IPV maps, a case study of the 13 July event is briefly presented. This event appears to be typical of breaking events previously investigated at midlatitudes, including the southward intrusion of high‐PV air originating in the high‐latitude lower stratosphere. This time the intrusion was observed to extend deep in the subtropics. Strong positive ozone anomalies were simultaneously measured by the MLO lidar. Positive correlation between ozone and the equivalent latitude averaged along the parcels' trajectories was seen up to 475 K in the stratosphere. At and above 750 K, negative correlation was calculated for both TMF and MLO. For TMF the altitude dependence of the correlation is similar to that already observed for summer and winter midlatitudes For MLO the observed negative correlation was found to be the result of opposite seasonal and interannual tendencies in ozone and equivalent latitude throughout the summer. All other correlations are associated with a higher intraseasonal variability of both ozone and the parcels' origin, as compared to their seasonal tendencies.