Ice Nucleation and Dehydration in the Tropical Tropopause Layer

Optically thin cirrus near the tropical tropopause regulate the humidity of air entering the stratosphere, which in turn has a strong influence on the Earth's radiation budget and climate. Recent highaltitude, unmanned aircraft measurements provide evidence for two distinct classes of cirrus formed in the tropical tropopause region: (i) vertically extensive cirrus with low ice number concentrations, low extinctions, and large supersaturations (up to approx. 70%) with respect to ice; and (ii) vertically thin cirrus layers with much higher ice concentrations that effectively deplete the vapor in excess of saturation. The persistent supersaturation in the former class of cirrus is consistent with the long time-scales (several hours or longer) for quenching of vapor in excess of saturation given the low ice concentrations and cold tropical tropopause temperatures. The low-concentration clouds are likely formed on a background population of insoluble particles with concentrations less than 100 L1 (often less than 20 L1), whereas the high ice concentration layers (with concentrations up to 10,000 L1) can only be produced by homogeneous freezing of an abundant population of aqueous aerosols. These measurements, along with past high-altitude aircraft measurements, indicate that the low-concentration cirrus occur frequently in the tropical tropopause region, whereas the high-concentration cirrus occur infrequently. The predominance of the low-concentration clouds means cirrus near the tropical tropopause may typically allow entry of air into the stratosphere with as much as approx. 1.7 times the ice saturation mixing ratio

Black carbon aerosol characterization in a remote area of qinghai–tibetan plateau, western china

AbstractThe concentrations, size distributions, and mixing states of refractory black carbon (rBC) aerosols were measured with a ground-based Single Particle Soot Photometer (SP2), and aerosol absorption was measured with an Aethalometer at Qinghai Lake (QHL), a rural area in the Northeastern Tibetan Plateau of China in October 2011. The area was not pristine, with an average rBC mass concentration of 0.36μgSTP-m−3 during the two-week campaign period. The rBC concentration peaked at night and reached the minimal in the afternoon. This diurnal cycle of concentration is negatively correlated with the mixed layer depth and ventilation. When air masses from the west of QHL were sampled in late afternoon to early evening, the average rBC concentration of 0.21μgSTP-m−3 was observed, representing the rBC level in a larger Tibetan Plateau region because of the highest mixed layer depth. A lognormal primary mode with mass median diameter (MMD) of ~175nm, and a small secondary lognormal mode with MMD of 470–500nm of rBC were observed. Relative reduction in the secondary mode during a snow event supports recent work that suggested size dependent removal of rBC by precipitation. About 50% of the observed rBC cores were identified as thickly coated by non-BC material. A comparison of the Aethalometer and SP2 measurements suggests that non-BC species significantly affect the Aethalometer measurements in this region. A scaling factor for the Aethalometer data at a wavelength of 880nm is therefore calculated based on the measurements, which may be used to correct other Aethalometer datasets collected in this region for a more accurate estimate of the rBC loading. The results present here significantly improve our understanding of the characteristics of rBC aerosol in the less studied Tibetan Plateau region and further highlight the size dependent removal of BC via precipitation

Solar PAR and UV radiation affects the physiology and morphology of the cyanobacterium Anabaena sp PCC 7120

Solar UV radiation (280-400 nm) may affect morphology of cyanobacteria, however, little has been evidenced on this aspect while their physiological responses were examined. We investigated the impacts of solar PAR and UVR on the growth, photosynthetic performance and morphology of the cyanobacterium Anabaena sp. PCC7120 while it was grown under three different solar radiation treatments: exposures to (a) constant low PAR (photosynthetic active radiation, 400-700 nm), (b) natural levels of solar radiation with and (c) without UV radiation (290-400 nm). When the cells were exposed to solar PAR or PAR + UVR, the photochemical efficiency was reduced by about 40% and 90%, respectively, on day one and recovered faster under the treatment without UVR over the following days. Solar UVR inhibited the growth up to 40%, reduced trichome length. by up to 49% and depressed the differentiation of heterocysts. Negligible concentrations of UV-absorbing compounds were found even in the presence of UVR. During the first 2 d of exposure to natural levels of PAR, carotenoid concentrations increased but no prolonged increase was evident. Heterocyst formation was enhanced under elevated PAR levels that stimulated quantum yield and growth after an initial inhibition. Higher concentrations of carotenoids and a twofold increase in the carotenoid to chlorophyll a ratio provided protection from the high levels of solar PAR. Under radiation treatments with UVR the relatively greater decrease in chlorophyll a concentrations compared with the increase in carotenoids was responsible for the higher carotenoid: chlorophyll a ratio. Heterocyst formation was disrupted in the presence of solar UVR. However, the longer term impact of heterocyst disruption to the survival of Anabaena sp. requires further study. (c) 2007 Elsevier B.V. All rights reserved

Optical and Microphysical Properties of the Hunga-Tonga Stratospheric Aerosol Plume derived from Lidar and In Situ Measurements at Reunion Island (21°S, 55°E)

International audienceThe highly-explosive eruption of the Hunga-Tonga Hunha Ha’apai volcano, that occurred on 15 Jan. in the South Pacific, was associated with a powerful blast that injected gases, steam and aerosols to unprecedentedly high altitudes. The Tonga Rapid Response Experiment (TR²Ex) was triggered few days after in La Réunion island (21°S, 55°E), directly downwind of the eruptive plume. Two lidars, operating at 355 nm and 532 nm, sampled the overflying plume every night from 19 Jan. until 28 Jan. During the same period, more than 15 balloons have been launched to perform in situ measurements of the stratospheric plume. These observations involved ozone, water vapor, aerosol size distribution and SO2 sondes. These efforts allowed to assess both the vertical structure, the optical and microphysical properties of the aerosol stratospheric burden. In particular, a wide plume altitude range from 36 km down to 18 km has been highlighted along time, with heterogeneous aerosol optical depth that reached 0.84 at 532 nm and Angström exponents from -0.8 to 1.2. Such temporal evolution is related to both the injection heights of the volcanic material and the stratospheric dynamic and chemistry. Findings resulting from the synergistic use of the TR²Ex dataset will be presented and discussed

Optical and Microphysical Properties of the Hunga-Tonga Stratospheric Aerosol Plume derived from Lidar and In Situ Measurements at Reunion Island (21°S, 55°E)

International audienceThe highly-explosive eruption of the Hunga-Tonga Hunha Ha’apai volcano, that occurred on 15 Jan. in the South Pacific, was associated with a powerful blast that injected gases, steam and aerosols to unprecedentedly high altitudes. The Tonga Rapid Response Experiment (TR²Ex) was triggered few days after in La Réunion island (21°S, 55°E), directly downwind of the eruptive plume. Two lidars, operating at 355 nm and 532 nm, sampled the overflying plume every night from 19 Jan. until 28 Jan. During the same period, more than 15 balloons have been launched to perform in situ measurements of the stratospheric plume. These observations involved ozone, water vapor, aerosol size distribution and SO2 sondes. These efforts allowed to assess both the vertical structure, the optical and microphysical properties of the aerosol stratospheric burden. In particular, a wide plume altitude range from 36 km down to 18 km has been highlighted along time, with heterogeneous aerosol optical depth that reached 0.84 at 532 nm and Angström exponents from -0.8 to 1.2. Such temporal evolution is related to both the injection heights of the volcanic material and the stratospheric dynamic and chemistry. Findings resulting from the synergistic use of the TR²Ex dataset will be presented and discussed

Optical and Microphysical Properties of the Hunga-Tonga Stratospheric Aerosol Plume derived from Lidar and In Situ Measurements at Reunion Island (21°S, 55°E)

International audienceThe highly-explosive eruption of the Hunga-Tonga Hunha Ha’apai volcano, that occurred on 15 Jan. in the South Pacific, was associated with a powerful blast that injected gases, steam and aerosols to unprecedentedly high altitudes. The Tonga Rapid Response Experiment (TR²Ex) was triggered few days after in La Réunion island (21°S, 55°E), directly downwind of the eruptive plume. Two lidars, operating at 355 nm and 532 nm, sampled the overflying plume every night from 19 Jan. until 28 Jan. During the same period, more than 15 balloons have been launched to perform in situ measurements of the stratospheric plume. These observations involved ozone, water vapor, aerosol size distribution and SO2 sondes. These efforts allowed to assess both the vertical structure, the optical and microphysical properties of the aerosol stratospheric burden. In particular, a wide plume altitude range from 36 km down to 18 km has been highlighted along time, with heterogeneous aerosol optical depth that reached 0.84 at 532 nm and Angström exponents from -0.8 to 1.2. Such temporal evolution is related to both the injection heights of the volcanic material and the stratospheric dynamic and chemistry. Findings resulting from the synergistic use of the TR²Ex dataset will be presented and discussed

An overview of aircraft observations from the Pacific Dust Experiment campaign

International audienc