Daytime ClO over McMurdo in September 1987: Altitude profile retrieval accuracy

During the 1987 National Ozone Expedition, mm-wave emission line spectra of the 278.6 GHz rotational stratospheric ClO were observed at McMurdo Station, Antarctica. The results confirm the 1986 discovery of a lower stratospheric layer with approximately 100 times the normal amount of ClO; the 1987 observations, made with a spectrometer bandwidth twice that used in 1986, make possible a more accurate retrieval of the altitude profile of the low altitude component of stratospheric ClO from the pressure broadened line shape, down to approximately 16 km. The accuracy of the altitude profile retrievals is discussed, using the daytime (09:30 to 19:30, local time) data from 20 to 24 September, 1987 as an example. The signal strength averaged over this daytime period is approx. 85 percent of the midday peak value. The rate of ozone depletion implied by the observed ClO densities is also discussed

Quantitative observations of the behavior of anomalous low altitude ClO in the Antarctic spring Stratosphere, 1987

During the second National Ozone Expedition ground-based observations at McMurdo Station Antarctica were performed which resulted in a second season's measurement of abnormally large amounts of ClO in the Antarctic spring stratosphere. The original measurements of 1986, in which the presence of this anomalous layer was first discovered, were limited in low altitude recovery of the ClO mixing ratio profile by the restrictions of the spectral bandwidth (256 MHz) which was used to measure the pressure-broadened ClO emission line shape. The 1987 measurements were marked by the use of twice the spectral bandpass employed the previous year, and allow a better characterization of the ClO mixing ratio profile in the critical altitude range 18 to 25 km. In-situ aircraft measurements of ClO made over the Palmer Peninsula during Aug. and Sept. of 1987 by Anderson, et al. effectively determined the important question of the ClO mixing ratio profile at altitudes inaccessible to our technique, below approximately 18 to 18.5 km. These flights did not penetrate further than 75 deg S, however, (vs 78 deg S for McMurdo) and were thus limited to coverage near the outer boundaries of the region of severest ozone depletion over Antarctica in 1987, did not reach an altitude convincingly above that of the peak mixing ratio for ClO, and were not able to make significant observations of the diurnal variation of ClO. The two techniques, and the body of data recovered by each, thus complement one another in producing a full picture of the anomalous ClO layer intimately connected with the region of Antarctic spring ozone depletion. An analysis is presented of the mixing ratio profile from approximately 18 to 45 km, the diurnal behavior, and the secular change in ClO over McMurdo Station during Sept. and early Oct. 1987

Measurements of the vertical profile, diurnal variation, and secular change of ClO in the stratosphere over Thule, Greenland, February-March, 1992

We report observations of stratospheric chlorine monoxide over the altitude range approx. 16 to 50 km at Thule, Greenland from Feb. 8 to Mar. 24, 1992. A new, more sensitive ground-based mm-wave spectrometer was employed for these measurements, similar in principle to that used earlier for the discovery of low altitude ClO in the Antarctic springtime. In this report, we discuss different aspects of vertical distribution, secular trends, and diurnal variation of ClO in the Arctic stratosphere, based on a preliminary analysis of our Thule data. We see no evidence for large (approx. 1.2-1.5 ppb) amounts of ClO in the lower stratosphere at any time during February or March, in agreement with UARS-MLS findings for this period, and in marked contrast to findings reported for the Arctic in January. We have some evidence for small enhancements (approx. 0.2-0.5 ppb) in the 18-30 km range in late February-early March, which might be associated with volcanic aerosol, rather than PSC, processing

Observed changes in the vertical profile of stratopheric nitrous oxide at Thule, Greenland, February - March 1992

Using a ground-based mm-wave spectrometer, we have observed stratospheric N2O over Thule, Greenland (76.3 N, 68.4 W) during late February and March, 1992. Vertical profiles of mixing ratio ranging from 16 to 50 km were recovered from molecular emission spectra. The profiles of early March show an abrupt increase in the lower-stratosphere N2O mixing ratio similar to the spring-to-summer change associated with the break up of the Antarctic polar vortex. This increase is correlated with changes in potential vorticity, air temperature, and ozone mixing ratio

A new high-sensitivity superconducting receiver for mm-wave remote-sensing spectroscopy of the stratosphere

We describe a recently constructed ground-based mm-wave spectrometer incorporating a superconducting tunnel junction as a heterodyne mixer-receiver. Under conditions of low tropospheric water vapor, the superior sensitivity of this receiver allows spectral line measurements of stratospheric molecules with mixing ratios as small as a few tenths of a part per billion (e.g., ClO, HCN) to be made in 4 to 6 hours, with a signal to noise ratio of at least 30:1. We expect to be able to halve this time by further improvement of the mixer's intrinsic noise level

Search for Interstellar Furan and lmidazole

Results are reported of an unsuccessful 6-cm search for the hetrocyclic carbon ring molecules furan and imidazole. Upper limits in brightness temperature of 0.25 K or less are found for furan in 11 galactic sources, and of less than 0.1 K for imidazole in Sgr A and Sgr B2

A Spectroscopic study of laser-induced Tin-Lead plasma: transition probabilities for spectral lines of Sn I

In this paper, we present transition probabilities for 97 spectral lines of Sn I, corresponding to transitions n(n = 6,7,8)s → 5p2, n(n = 5,6,7)d → 5p2, 5p3 → 5p2, n(n = 7)p → 6s, determined by measuring the intensities of the emission lines of a Laser-induced breakdown (emission) spectrometry (LIBS). The optical emission spectroscopy from a laser-induced plasma generated by a 10 640 Å radiation, with an irradiance of 1.4 × 1010 Wcm− 2 on an Sn–Pb alloy (an Sn content of approximately 20%), in vacuum, was recorded at 0.8 µs, and analysed between 1900 and 7000 Å. The population-level distribution and corresponding temperature were obtained using Boltzmann plots. The electron density of the plasma was determined using well-known Stark broadening parameters of spectral lines. The plasma under study had an electron temperature of 13,200 K and an electron number density of 2 × 1016 cm− 3. The experimental relative transition probabilities were put on an absolute scale using the branching ratio method to calculate Sn I multiplet transition probabilities from available radiative lifetime data of their upper states and plotting the Sn I emission spectrum lines on a Boltzmann plot assuming local thermodynamic equilibrium (LTE) to be valid and following Boltzmann's law. The LTE conditions and plasma homogeneity have been checked. Special attention was paid to the possible self-absorption of the different transitions. The experimental results obtained have been compared with the experimental values given by other authors