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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]

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]

• 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]