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Optical properties of long-range transported volcanic ash over Romania and Poland during Eyjafjallajökull eruption in 2010

Nemuc A., Stachlewska I.S., Vasilescu J., Górska A, Nicolae D, Talianu C

Acta Geophysica

2014

Vol. 62, no. 2

350--366

After Eyjafjallajökull volcano eruption on 14 April 2010, due to a complex air mass circulation, Romania was exposed to volcanic ash and its mixture with continental aerosols. Ash particles with an average Ångström (UV-VIS) exponent of 1.4 ± 0.2 and (VIS-IR) of 1.2 ± 0.3, a color ratio (VIS-UV) of 0.54 and (IR-VIS) of 0.49, an average particle depolarization value ~9.4%, and a lidar ratio of 50 sr were retrieved on 18 April from multiwavelength Raman lidar measurements in Bucharest. Mixed volcanic ash with mineral dust particles advected from Sahara, depolarization ~12%, Ångström (UV-VIS) exponent of 1.25 ± 0.25 and (VIS-IR) of 1.45 ± 0.25, an increased color ratio (VIS-UV) of 0.61, (IRVIS) of 0.39 and lidar ratio of 53 sr were identified on 28 April. From observations in Poland conducted by an elastic lidar at 532 nm and a ceilometer at 1064 nm we retrieved an average backscatter related Ångström (VIS-IR) exponent of 1.25 ± 0.35, and a color ratio (IR-VIS) of 0.53 in the layer at about 5.5 km during the night of 16/17 April, indicating fresh ash over Warsaw.

Evaluation of the boundary layer morning transition using the CL-31 ceilometer signals

Sokół P, Stachlewska I.S, Ungureanu I., Stefan S.

Acta Geophysica

2014

Vol. 62, no. 2

367--380

The morning transition of the atmospheric boundary layer from nighttime to daytime conditions was investigated using the Vaisala’s CL-31 ceilometer, located at Magurele, Romania (44.35°N, 26.03°E). Based on the 5-days backward trajectories, we rejected those measurements which were related to the intrusions of long-range transported particles. In the several discussed cases, which are representative for the morning transition in spring and summer seasons over Magurele, the increasing depth of the boundary layer related to the local aerosol load was well discernible. The dynamic change of its depth was estimated with errors using a simple method based on finding the minimum of the first derivative of the ceilometer signal. In the summer, the increase of the boundary layer depth due to the morning transition from the nighttime to daytime conditions starts on average of about 80 min earlier and the growth rate of this depth is 143 ± 6 m/h and about 37% slower than in the spring case.

Ceilometer observations of the boundary layer over Warsaw, Poland

Stachlewska I., Piądłowski M., Migacz S., Szkop A., Zielińska A., Swaczyna P.

Acta Geophysica

2012

Vol. 60, no. 5

1386-1412

Jenoptik's CHM 15k ceilometer was used to monitor the vertical structure of the atmospheric boundary layer (ABL) over Warsaw, from 2008 until 2011, on Mondays and Thursdays, in 24h periods. Hereby, we present an assessment of the signal-to-noise ratio along with a sensitivity study of signal smoothing methods developed in-house. With the proposed averaging, ceilometer attenuated-backscatter signals reached the high troposphere, which makes this sensor competitive to a single-wavelength elastic lidar. The smoothed signals were employed as an input for algorithms developed to automatically detect the ABL height, clouds, fog, and precipitation in the lower troposphere. The classification of weather conditions was validated by the METAR reports from the Warsaw Airport. The obtained ABL heights were compared to those assessed from radiosoundings from a nearby meteorological station WMO12374 in Legionowo. An inter-comparison of the ABL heights, derived by using the Jenoptik's automated routine against the in-house developed algorithms, is in favor of the latter. The presented four annual cycles of the ABL height, obtained with various derivative-based methods, are the first such longterm results reported using the CHM 15k sensor in Eastern Europe.