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The edge of the winter polar vortex is thought to isolate chemistry between inside and outside. A way to test how accurately it is estimated is to examine chemical mixing ratios along a path that crosses its edge. Two edge methods are tested, one is the “Q-edge” (Harvey et al., 2002), which chooses a specific streamline; the other is scaled potential vorticity, “sPV”, which identifies an inner and outer edge depending on the local value of potential vorticity scaled according to the static stability (Manney et al., 1994). Aura MLS mixing ratios show that, statistically overall, sPV edge area agrees better with the N 2 O mixing ratio gradient below ∼700 K, albeit with more scatter. Finally direct comparison statistics on a few 10 day winter intervals show that the Q-edge is usually outside the sPV outer edge below potential temperature levels ∼400–500 K, agrees up to ∼700 K, and inside to ∼1200 K. Above that, both methods tend to agree again. [ABSTRACT FROM AUTHOR]

Abstract: Polar Mesosphere Summer Echoes (PMSE) are now a well recognized summer phenomenon in the polar regions. For more than a decade, the echoes have been continuously monitored at Resolute Bay (75.0°N, 95.0°W) using a 51.5MHz VHF radar, which has a narrow vertically pointing beam as well as four tilted beams at 10.9° from zenith. The radar site is located inside the northern polar cap, and remains a true polar cap radar at any level of geomagnetic activity. PMSE at this location show some unique features compared with other high latitude radars operating at similar frequencies. In this paper, we investigate the aspect-sensitivity of the PMSE at Resolute Bay. This feature of PMSE, which led to debate among researchers regarding the scattering mechanisms of these echoes, has not been extensively studied, especially on a long-term basis. In this study, we use a decade-long data-set collected during 1998–2009 to investigate the aspect-sensitivity parameter by comparing the absolute backscattered powers in four off-zenith beams with the vertical beam. We concentrate on conditions when electron precipitation is weak or not present, in order to simplify comparison (precipitation is present less than 8% of the time during PMSE). It was found that the aspect-sensitivity of PMSE can be broadly categorized into three groups based on the PMSE signal strengths of strong, moderate and weak. The height profiles of the calculated aspect angle show a good agreement among all four off-zenith beams, especially in the cases of strong and moderate PMSE strengths. Our long-term investigation reveals that when PMSE are strong, they show a median aspect angle of 8° at around 84km and a 11° at around 88km, meaning lower PMSE layers are associated with more anisotropic scattering. These values are about 2–3° higher, when PMSE are only “moderate” strength at Resolute Bay. The height dependence of aspect-sensitivity remains consistent in the cases of strong and moderate PMSE strengths. The results are compared with the observations made by a similar radar at another polar cap location at Eureka (80.0°N, 86.0°W). The comparison shows agreement in terms of the shape of the aspect-sensitivity height profiles, but the values are about 2–3° smaller. Possible explanations are discussed. [Copyright &y& Elsevier]

Abstract: The ACE-MAESTRO (Atmospheric Chemistry Experiment–Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) instrument on the SCISAT satellite is able to measure solar occultation absorption in the - and -bands of molecular oxygen with a spectral resolution of 2nm. Profiles of total atmospheric density are derived by exploiting the constant and known mixing ratio of , and are used to determine profiles of pressure and temperature using hydrostatic balance and the ideal gas law. A highly accurate combined fast-line-by-line and extended correlated- technique is implemented to fast forward model MAESTRO''s absorption measurements, which ensures that errors in pressure and temperature resulting from the forward model approximation are essentially negligible. Estimated errors in pressure and temperature are determined for the -, -, and combined –-band retrievals for a typical retrieval, and demonstrate that pressure profiles should be derivable to within 1% and temperature to within 2K over most altitudes using a combined – retrieval. The combined retrieval provides an improvement of up to 0.25% in pressure and 0.5K in temperature over the -band retrieval alone. The -band could also be used alone below about 50km, where its independent retrieval produces error estimates of 1–1.5% in pressure and 2–3K in temperature. [Copyright &y& Elsevier]

Abstract: The horizontal wind data from the standard version of Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) have been analyzed to obtain the diurnal wind structures in the mesosphere. In the standard version of CMAM-DAS, meteorological observations from radiosondes, aircraft, surface measurements, and satellites are assimilated only in the troposphere and stratosphere (below 1-hPa) with no increments applied in the mesosphere. Results for the years 2006–2008 are being used here as part of the Canadian International Polar Year (IPY) program and the Canadian Network for the Detection of Atmospheric Change (CANDAC) Research Program. The CMAM-DAS shows good overall agreement with radar observations for the seasonal characteristics of the diurnal tides at single stations from low-middle latitudes. The most prominent nonmigrating diurnal tides revealed by the CMAM-DAS winds at 88km include the westward propagating component with zonal wavenumber 2 (DW2), the standing oscillation (D0), and the eastward propagating wavenumbers 3 (DE3) and 2 (DE2). A detailed discussion of the latitudinal and seasonal variations and Hough modes is provided for these predominant nonmigrating components and the migrating tide (DW1). The modeled nonmigrating diurnal tides, on both monthly (60-day windows) and annual time scales, are generally in good agreement with those determined from TIDI (TIMED Doppler interferometer) and from UARS-HRDI (High Resolution Doppler Imager)/WINDII (Wind Imaging Interferometer). This work provides further evidence for the tidal forcing from below. [Copyright &y& Elsevier]

Abstract: This study assesses the relation between the year-to-year variability of the semidiurnal tides (SDT) observed at high latitudes of both hemispheres and the global stratospheric stationary planetary wave (SPW) with zonal wavenumber S=1 (SPW1) derived from the UKMO temperature data. No significant positive correlation can be identified between the interannual variability of the Northern Hemisphere (NH) SDT and the Southern Hemisphere (SH) SPW1 for austral late-winter months. In contrast, a good consistency is evident for the interannual variations between the SDT observed at Rothera (68°S, 68°W) and the Arctic SPW1 for NH mid-winter months. Since it has been observed that during austral summer the non-migrating SDT often plays a significant role at the latitude of Rothera, a physical link between the SH SDT and the NH SPW is suggested. This asymmetry in the interhemispheric link is also noted in a recent study. [Copyright &y& Elsevier]

Abstract: The collisional shifts and widths of several P-branch spectral lines in the fundamental band of CO–Ar have been measured at temperatures between 214 and 324K and pressures between 0.025 and 1atm. The widths have been determined using a line shape model based on the solution of the transport/relaxation equation for the appropriate off-diagonal element of the density matrix. The model uses a realistic molecular potential energy surface to calculate the speed dependence of the collisional broadening, and a rigid sphere potential to calculate the translational motion. It is found that both the shifting and broadening coefficients follow a power law dependence on the temperature. Additionally, it is demonstrated that studies have tended to overestimate the accuracy of collisional widths when the line shape model used to obtain the widths involves multiple fitted line shape parameters or fails to fit the measured spectra within the experimental noise. [Copyright &y& Elsevier]

Abstract: The shapes of Dicke-narrowed spectral lines in the fundamental P-branch of CO in Ar are studied by comparing high-resolution measurements and theoretical calculations. The measured spectra were recorded at temperatures between 214 and 324K, and at pressures between 0.025 and 1atm. The calculations are based on solving a transport/relaxation equation for the appropriate off-diagonal element of the density matrix; they use a realistic intermolecular potential to determine the speed-dependent collisional broadening, and a rigid sphere potential to determine the Dicke narrowing. It is found that the calculations can reproduce the measured spectra within the experimental noise under all conditions, but that the magnitude of the Dicke narrowing in the measured spectra is 70–90% less than predicted from the mass diffusion constant. A revised view of the collision operator resolves the discrepancy in principle, and leads to a better understanding of the line shape problem in general. [Copyright &y& Elsevier]

The 0310 ← 0110 parallel Q branch of N2O has been studied at 297 K and over the pressure range 1–130 torr. Absorption spectra were recorded using a high resolution (1.5 MHz or 5 × 10-5 cm-1) and high signal-to-noise (>3500:1) mid-infrared spectrometer based on difference-frequency infrared generation in AgGaS2. In the low-pressure range (1–11 torr) we obtained accurate values for the line strengths, the broadening coefficients, the weak mixing coefficients, and the overall shifting of the branch. The medium pressure results, ranging from 23 to 130 torr, were analyzed by treating the band as a whole, using a relaxation matrix formalism, based on an energy gap scaling law. We find, effectively, that only 36% of the rotationally inelastic collisions are associated with Q branch mixing, the rest presumably being associated with Q–P and Q–R mixing in the same vibrational band. The pressure shifting coefficient of the 0310 ← 0110 Q branch as a whole was also determined and found to be 5.8 × 10-3 cm-1/atm towards lower frequencies. [Copyright &y& Elsevier]

A variable-temperature single-pass absorption gas cell with an optical pathlength of 147.5 cm was designed and built for spectroscopic measurements of gases of atmospheric interest. The cell is optically matched to a Bomem DA8.3 Fourier transform spectrometer. A heating/cooling system enveloping the cell, used together with a Neslab ULT-80 thermal bath, allows spectroscopic studies of gas samples at temperatures ranging from 205 to 350 K and at pressures up to 1 atm. Tests of the optical, thermal, and vacuum operation of the system were performed. Spectra of the 3←0 vibrational–rotational band of carbon monoxide were recorded from 225 to 348 K and used to determine the rotational gas temperatures. These results were compared with values obtained using thermocouples, in order to assess the thermal performance of the new system. A second temperature-controlled cell 25-cm long, able to withstand pressures up to 30 atm, was also used to record CO spectra. We have recorded high-resolution FTIR spectra of CO and CO perturbed by N2 at temperatures from 295 to 348 K. The spectra were analyzed to determine pressure broadening and pressure-induced shift coefficients, along with their temperature dependence for several transitions in the second overtone band of CO. The results, especially for self-broadening, are in excellent agreement with other recent measurements reported in the literature. [Copyright &y& Elsevier]

Weak mixing coefficients for D[sub 2] and D[sub 2] –He mixtures at 305.2 and 100.7 K are reported and compared with ab initio quantal calculations. The measurements support but do not provide a critical test of the calculations. Measurements of 50% D[sub 2] in Ar at 305.2 K are at variance with the measurements in the pure gas and in mixtures with He and below 20 amagat exhibit an increasing line asymmetry with decreasing density. The results are also at variance with the asymmetries measured in 5% H[sub 2] in Ar. PACS No.: 33.70.Jg, 33.20.FbNous présentons les coefficients de mélange faible pour D[sub 2] et D[sub 2] –He à 305,2 et à 100,7 K et les comparons avec le résultat de calculs quantiques complets (ab initio). Mesures et calculs agréent, mais les premiers ne constituent pas un test critique des seconds. Les mesures pour 50% de D[sub 2] dans Ar à 305,2 K sont en déaccord avec les mesures dans le gaz pur et dans des mélanges avec He sous 20 amagat, elles montrent une asymétrie de ligne croissant avec la diminution de la densité. Les résultats sont aussi en déaccord avec les asymétries mesurées pour 5% de H[sub 2] dans Ar. [Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Line widths and shifts of the S[sub 1] (0), S[sub 1] (1), S[sub 1] (2), and the O[sub 1] (2) Raman lines in pure D[sub 2] at 100.7 K are reported. These measurements, made with a high-resolution cw Raman gain spectrometer, can be used to test future theoretical calculations.PACS Nos.: 33.70-w 33.20FbNous présentons des mesures de largeur et de déplacement des lignes Raman S[sub 1] (0), S[sub 1] (1), S[sub 1] (2) et O[sub 1] (2) du D[sub 2] pur à 100,7 K. Ces résultats ont été obtenus avec un spectromètre à gain Raman continu de haute résolution et pourront être utilisés pour tester de futurs calculs théoriques. [Traduit par la rédaction] [ABSTRACT FROM AUTHOR]

Abstract. Tunable diode laser absorption spectroscopy has been employed by our group at the National Center tot Atmospheric Research to study a number of important trace atmospheric gases and processes over the past 10 years. This paper presents an overview of these studies along with details on instrument hardware and software features implemented for high sensitivity. The merits of four different approaches in assessing instrument performance are presented with formaldehyde (CH[sub 2]O) used as the target gas. One method utilizes the Allan variance. When our present aircraft system is operated in the laboratory, the Allan variance indicates a CH[sub 2]O detection limit of 0.031 ppbv for integration times of 25 s. This sensitivity corresponds to a minimum detectable absorbance of 1.0 x 10[sup -6], and this is within a factor of two of that reported by Werle et al. who used high-frequency modulation spectroscopy. The present instrument utilizes conventional low-frequency (2f = 100 kHz) wavelength modulation. Instrument performance, obtained from replicate measurements of CH[sub 2]O standards acquired over time periods as long as 1.5 hours, on average resulted in a factor of two poorer precision than indicated by the Allan variance. Since replicate measurements precisely simulate the acquisition procedures... [ABSTRACT FROM AUTHOR]

• OSIRIS and ACE-FTS ozone agrees well, ACE-MAESTRO ozone shows low bias. • Satellite ozone data agree with ground-based measurements to within 0.1–12.0%. • Satellite NO 2 data agree with ground-based measurements to within 0.7–33.2%. • Results are consistent with previous validation studies. • No significant drift found in the satellite datasets. This paper presents long-term intercomparisons (2003–2017) between ozone and NO 2 measured by the Optical Spectrograph and Infra-Red Imager System (OSIRIS) and the Atmospheric Chemistry Experiment (ACE) satellite instruments, and by ground-based instruments at the Polar Environment Atmospheric Research Laboratory (PEARL), near Eureka, Nunavut, Canada (80∘N, 86∘W). The ground-based instruments include four zenith-sky differential optical absorption spectroscopy (DOAS) instruments, two Fourier transform infrared (FTIR) spectrometers, and a Brewer spectrophotometer. Comparisons of 14–52 km ozone partial columns show good agreement between OSIRIS v5.10 and ACE-FTS v3.5/3.6 data (1.2%), while ACE-MAESTRO v3.13 ozone is smaller than the other two datasets by 6.7% and 5.9%, respectively. Satellite profiles were extended to the surface using ozonesonde data, and the resulting columns agree with the ground-based datasets with mean relative differences of 0.1–12.0%. For NO 2 , 12–40 km partial columns from ACE-FTS v3.5/3.6 and 12–32 km partial columns from OSIRIS v6.0 (scaled to 40 km) agree with ground-based partial columns with mean relative differences of 0.7–33.2%. Dynamical coincidence criteria improved the ACE to ground-based FTIR ozone comparisons, while little to no improvements were seen for other instruments, and for NO 2. A ± 1∘ latitude criterion modestly improved the spring and fall NO 2 comparisons. The results of this study are consistent with previous validation exercises. In addition, there are no significant drifts between the satellite datasets, or between the satellites and the ground-based measurements, indicating that the OSIRIS and ACE instruments continue to perform well. [ABSTRACT FROM AUTHOR]

Presents letter from readers of the periodical 'British Dental Journal' concerning dentistry in Great Britain. Prescription of fluoride mouthwash; Protection from needle stick injury; Community dental care.

Using a difference frequency spectrometer we have measured the Q(2) to Q(38) 20[sup 0]0←01[sup 1]0,Σ←Π transitions of carbon dioxide at 296 K and pressures up to 15 kPa. These low pressure spectra were analyzed using both the Voigt model, and an empirical line shape that blends together a hard collision model and a speed dependent Lorentzian profile. The broadening coefficients were obtained with an accuracy of 1% or better. The low density or first order low pressure line mixing parameters were also determined. We have compared both our measured low pressure line-mixing parameters and the complete band spectrum at high pressures with those predicted by a relaxation matrix calculated from an EPG fitting law. Spectra at the highest pressures were recorded using both the difference frequency spectrometer and an FTIR spectrometer, the temperature for the latter experiments being 303 K. The vibrational band intensity and linear pressure shift of the branch as a whole were also measured. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]