Observations of extremely thin clouds in the tropical tropopause region by a ship based lidar.

During the cruises ANT XVII/4 (Punta Arenas Bremerhaven, 2000) and ANT XX1/1 (Bremerhaven - Cape Town, 2003) continuous measurements of clouds and aerosol have been performed by a Mobile Aerosol Raman Lidar (MARL). This system measures backscatter of light at 355 nm and 532 nm and is able to detect even extremely thin layers of particles in the atmosphere. Cloud base and top height, depolarisation optical depth and color index can be deduced from this data. During the Polarstern cruises very thin layers of ice particles have been observed frequently in the tropical tropopause layer (TTL). Cases of persistent cloud layers with an optical depth below 10^-3 are reported. Based on the data of radiosondes which were launched daily aboard the vessel, the conditions at which these type of clouds form are analysed. It is shown, that these clouds form in a layer below the cold point, but above the lapse rate tropopause. The relation between cloud occurrence and temperature and wind in the TTL as well as state of the QBO are discussed

Cirrus clouds, contrails, and ice supersaturated regions: observations by lidar and radiosonde in Lindenberg/Germany

From April to October 2003 measurements have been performed with a mobile Aerosol Raman Lidar (MARL) at the Meteorological Observatory in Lindenberg(14.5 E, 52.5 N) . The aim of this extensive campaign was the investigation of tropospheric water vapour, cirrus clouds and contrails over a longer period of time. The lidar system detects aerosols and clouds in the troposphere and lower stratosphere. Cirrus clouds are detected by the large depolarisation of the backscattered laser beam. The lidar operates day and night, during daytime contrails may be identified with the help of a video camera. In the upper troposphere cirrus has been detected in 55% of the measured time. Radiosonde (Vaisala RS 80) data are available four times a day form the routine observational program at the site. They frequently detect ice supersaturatedregions (ISSR) in the upper troposphere. The comparison of the RS 80 andthe MARL data shows that the correlation between ISSR and the occurrence of cirrus and contrails is rather week. On the other hand there is a strong link between the occurrence of subvisual cirrus and contrails in the upper troposphere

Probing the Complex and Variable X-ray Absorption of Markarian 6 with XMM-Newton

We report on an X-ray observation of the Seyfert 1.5 galaxy Mrk 6 obtained with the EPIC instruments onboard XMM-Newton. Archival BeppoSAX PDS data from 18-120 keV were also used to constrain the underlying hard power-law continuum. The results from our spectral analyses generally favor a double partial-covering model, although other spectral models such as absorption by a mixture of partially ionized and neutral gas cannot be firmly ruled out. Our best-fitting model consists of a power law with a photon index of 1.81+/-0.20 and partial covering with large column densities up to 10^{23} cm**-2. We also detect a narrow emission line consistent with Fe Kalpha fluorescence at 6.45+/-0.04 keV with an equivalent width of ~93+/-25 eV. Joint analyses of XMM-Newton, ASCA, and BeppoSAX data further provide evidence for both spectral variability (a factor of ~2 change in absorbing column) and absorption-corrected flux variations (by ~60%) during the ~4 year period probed by the observations.Comment: 7 pages, 2 figures. accepted for publication in the Astronomical Journa

An Early and Comprehensive Millimetre and Centimetre Wave and X-ray Study of SN 2011dh: a Non-Equipartition Blast Wave Expanding into a Massive Stellar Wind

Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3–12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (ϵe/ϵB ∼ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R−2. Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s−1, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (∼1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ϵe/ϵB

An Early & Comprehensive Millimeter and Centimeter Wave and X-ray Study of Supernova 2011dh: A Non-Equipartition Blastwave Expanding into A Massive Stellar Wind

Only a handful of supernovae (SNe) have been studied in multi-wavelength from radio to X-rays, starting a few days after explosion. The early detection and classification of the nearby type IIb SN2011dh/PTF11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at the youngest phase ever of a core-collapse supernova (days 3 to 12 after explosion) in the radio, millimeter and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding supernova shockwave does not exhibit equipartition (e_e/e_B ~ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R^-2. Within modeling uncertainties we find an average velocity of the fast parts of the ejecta of 15,000 +/- 1800 km/s, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast-wave regime between the previously defined compact and extended SN IIb subtypes. Our results highlight the importance of early (~ 1 day) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio e_e/e_B.Comment: 9 pages, 5 figures, submitted to Ap

Fluorescing aerosol from Siberian forest fires in the lowermost stratosphere.

During a measuring campaign in Lindenberg/Germany (14.5 E, 52.5 N), we observed in June 2003 an extended aerosol layer at 13 km altitude in the lowermost stratosphere with a mobile Aerosol Raman Lidar (MARL). The stratospheric layer created an inelastic backscatter signal that we detected with a water vapour Raman channel, but that was not produced by Raman scattering. Also, we find evidence for inelastic scattering by a smoke plume from a forest fire that we observed in the troposphere. We interpret the unexpected properties of these aerosols as fluorescence induced by the laser beam at organic components of the aerosol particles. Fluorescence from ambient aerosol had not yet been considered detectable by lidar systems. However, organic compounds such as polycyclic aromatic hydrocarbons sticking to the aerosol particles, or bioaerosol such as bacteria, spores or pollen fluoresce when excited with UV-radiation in a way that is detectable by our lidar system. Therefore, we conclude that fluorescence from organic material released by biomass burning creates, inelastic backscatter signals that we measured with our instrument and thus demonstratea new and powerful way to characterize aerosols by a remote sensing technique.In spring 2003 heavy fires burned around 18 million hectares of boreal forest inSiberia, the smoke plume from these fires travelled eastwards around the globe and was detected in Europe in late May 2003. The stratospheric aerosol layer that we have observed in Lindenberg for three consecutive days is likely to be a remnant from theseSiberian forest fire plumes that was lifted across the tropopause

Lidar observations of extremely thin clouds at the tropical tropopause

Our two lidar systems MARL (Mobile Aerosol Raman Lidar) and ComCAL (Compact Cloud and Aerosol Lidar) have been operated during measurement campaignsaboard the research vessel Polarstern (2003 and 2005) and at Paramaribo/Suriname (5.8°N, 55°W) in 2004/2005. The lidar systems detect cirrus in the upper troposphere with a very high sensitivity by the depolarization measurement. Cirrus properties like altitude, optical depth, particle phase are derived from the lidar signals. Using scattering theory and an estimate of the particle size, the number concentration of ice particles can be calculated. In almost 90% of the measurements performed at Paramaribo thin or subvisible cirrostratus were detected in the tropical transition layer (TTL). Occasionally, extremely thin clouds with optical depths below 10-4 were observed at the cold point tropopause (CPT). The condensed mass concentration was 0.5 ŠÌg/m3. If we assume a particle size of 5 ŠÌm (effective radius) this corresponds to a number density of only a few particle per liter. The extremely thin clouds which were observed at - or even slightly above - the cold point tropopause seem to dwell in subsaturated air. Our findings indicate that these thin layers of particles, are not composed of pure water ice

Measurements of aerosol and cirrus clouds in the UTLS by a shipborne lidar.

Measurements of cirrus clouds and aerosol in the lower stratosphere and upper troposphere have been performed with a mobile lidar system aboard the German research vessel Polarstern. The aerosol load in the lower stratosphere is higher in the tropics compared to the midlatitudes. Our data reveal a high frequency of occurrence of subvisual cirrus clouds in the tropical tropopause region. Based on the data of radiosondes the temperature of the clouds as well as the structure of the tropical tropopause is characterized. The mean optical depth was 0.02 and a mean temperature of 198 K was determined. Cloud tops are often found at the thermal tropopause. In some cases these clouds are extemely thin with an optical depth below 10-3

Vertical profiles, optical and microphysical properties of Saharan dust layers determined by a ship-borne lidar.

A unique data set of ship-borne lidar measurements of Saharan dust layers above the Atlantic ocean has been collected aboard the research vessel Polarstern with a mobile Aerosol Raman Lidar (MARL) during the LIMPIDO-campaign in June 2000. Extended Saharan dust layers have been observed in the region between 8.5° N and 34° N in an altitude range between 2 and 6 km. The continental, North African origin of the probed air masses is confirmed by 8-day backward trajectories. The Saharan dust is characterized by an optical depth in the range of 0.1 and 0.3, a depolarization around 10% and high lidar ratios of 45 sr at 532 nm and 75 sr at 355 nm. The backscattering by the dust particles at the UV-wavelength is relatively weak, resulting in a negative color index.From the measured optical properties the effective radius and the refractive index of the dust particles are derived using a new approach based on Mie Theory and non-spherical scattering calculations. The low backscatter coefficient observed at 355 nm is due to significant absorption which increases with decreasing wavelength. This finding agrees very well with results from satellite and sun photometer measurements. The effective radii decrease from about 3um base to 0.6 um at the top of the dust plumes. The non-spherical shapes of the dust particles are responsible for the high values of the lidar ratios