Maynooth Optical Aeronomical Facility

Ground-based measurements of upper atmospheric parameters, such as temperature and wind velocity, can be made by observing airglow emissions that have a well-defined altitude profile and that are known to be representative of the emitting region. We describe the optical observatory at Maynooth (53.23 deg N, 6.4 deg W) at which two instruments, a Fabry-Perot interferometer and a Fourier transform spectrometer, are used to record atmospheric airglow emissions in Ireland at visible and near-infrared wavelengths, respectively. Descriptions of the instruments, data acquisition, and analysis procedures are provided, together with some sample results

Ground-Based Fabry-Perot Interferometry of the Terrestrial Nightglow with a Bare Charge-Coupled Device: Remote Field Site Deployment

The application of Fabry-Perot interferometers (FPIs) to the study of upper atmosphere thermodynamics has largely been restricted by the very low light levels in the terrestrial airglow as well as the limited range in wavelength of photomultiplier tube (PMT) technology. During the past decade, the development of the scientific grade charge-coupled device (CCD) has progressed to the stage in which this detector has become the logical replacement for the PMT. Small fast microcomputers have made it possible to "upgrade" our remote field sites with bare CCDs and not only retain the previous capabilities of the existing FPls but expand the data coverage in both temporal and wavelength domains. The problems encountered and the solutions applied to the deployment of a bare CCD, with data acquisition and image reduction techniques, are discussed. Sample geophysical data determined from the FPI fringe profiles are shown for our stations at Peach Mountain, Michigan, and Watson Lake, Yukon Territory

Seasonal dependence of northern high‐latitude upper thermospheric winds: A quiet time climatological study based on ground‐based and space‐based measurements

This paper investigates the large‐scale seasonal dependence of geomagnetically quiet time, northern high‐latitude F region thermospheric winds by combining extensive observations from eight ground‐based (optical remote sensing) and three space‐based (optical remote sensing and in situ) instruments. To provide a comprehensive picture of the wind morphology, data are assimilated into a seasonal empirical vector wind model as a function of season, latitude, and local time in magnetic coordinates. The model accurately represents the behavior of the constituent data sets. There is good general agreement among the various data sets, but there are some major offsets between GOCE and the other data sets, especially on the duskside. The assimilated wind patterns exhibit a strong and large duskside anticyclonic circulation cell, sharp latitudinal gradients in the duskside auroral zone, strong antisunward winds in the polar cap, and a weaker tendency toward a dawnside cyclonic circulation cell. The high‐latitude wind system shows a progressive intensification of wind patterns from winter to equinox to summer. The latitudinal extent of the duskside circulation cell does not depend strongly on season. Zonal winds show a mainly diurnal variation (two extrema) around polar and middle latitudes and semidiurnal variation (four extrema) at auroral latitudes; meridional winds are primarily diurnal at all high latitudes. The strength of zonal winds channeling through the auroral zone on the duskside is strongest in the summer season. The vorticity of the wind pattern increases from winter to summer, whereas divergence is maximum in equinox. In all three seasons, divergence is weaker than vorticity.Key PointsFirst ever investigation of the large‐scale seasonal dependence of northern high‐latitude upper thermospheric winds in magnetic coordinatesResults show progressive intensification of wind circulation from winter to equinox to summerThe vorticity increases from winter to summer. In all the seasons, the strongest divergences occur primarily in and above auroral latitudesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136373/1/jgra53329.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136373/2/jgra53329_am.pd

Linkages between the cold summer mesopause and thermospheric zonal mean circulation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95392/1/grl28827.pd

HL‐TWiM Empirical Model of High‐Latitude Upper Thermospheric Winds

We present an empirical model of thermospheric winds (High‐latitude Thermospheric Wind Model [HL‐TWiM]) that specifies F region high‐latitude horizontal neutral winds as a function of day of year, latitude, longitude, local time, and geomagnetic activity. HL‐TWiM represents the large‐scale neutral wind circulation, in geomagnetic coordinates, for the given input conditions. The model synthesizes the most extensive collection to date of historical high‐latitude wind measurements; it is based on statistical analyses of several decades of F region thermospheric wind measurements from 21 ground‐based stations (Fabry‐Perot Interferometers and Scanning Doppler Imaging Fabry‐Perot Interferometers) located at various northern and southern high latitudes and two space‐based instruments (UARS WINDII and GOCE). The geomagnetic latitude and local time dependences in HL‐TWiM are represented using vector spherical harmonics, day of year and longitude variations are represented using simple harmonic functions, and the geomagnetic activity dependence is represented using quadratic B splines. In this paper, we describe the HL‐TWiM formulation and fitting procedures, and we verify the model against the neutral wind databases used in its formulation. HL‐TWiM provides a necessary benchmark for validating new wind observations and tuning our physical understanding of complex wind behaviors. Results show stronger Universal Time variation in winds at southern than northern high latitudes. Model‐data intra‐annual comparisons in this study show semiannual oscillation‐like behavior of GOCE winds, rarely observed before in wind data.Key PointsWe developed a comprehensive empirical model of high‐latitude F region thermospheric winds (HL‐TWiM)Universal Time variations in high‐latitude winds are stronger in the Southern than Northern HemisphereHL‐TWiM provides a necessary benchmark for validating new high‐latitude wind observations and tuning first principal modelsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153588/1/jgra55363_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153588/2/jgra55363-sup-0001-Figure_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153588/3/jgra55363.pd

Short‐Term and Interannual Variations of Migrating Diurnal and Semidiurnal Tides in the Mesosphere and Lower Thermosphere

Among the broad spectrum of vertically propagating tides, migrating diurnal (DW1) and semidiurnal (SW2) are prominent modes of energetic and dynamical coupling between the mesosphere and lower thermosphere and the upper thermosphere and ionosphere. DW1 and SW2 tides are modulated on time scales ranging from days to years. NASA Thermosphere‐Ionosphere‐Mesosphere Energetic and Dynamics (TIMED) is the first observational platform to perform global synoptic observations of these fundamental tides (for nearly two decades) overcoming previous observational limitations. Here we utilize the extensive archive of TIMED Doppler Interferometer wind measurements and exploit the capabilities of tidal theory to estimate short‐term (1 year), and climatological variability in DW1 (1,1), SW2 (2,2), and SW2 (2,3) modes and then compare with tidal estimates derived from the Navy Global Environmental Model‐High Altitude version data assimilation system. Overall, the tidal estimates from TIMED Doppler Interferometer and Navy Global Environmental Model‐High Altitude version are similar and exhibit significant short‐term and intra‐annual variability. The short‐term variability can induce ∼64% change in the DW1 amplitude. Statistically, the short‐term variability in DW1 (1,1), SW2 (2,2), and SW2 (2,3) modes is of the order of ∼9, 33, and 20 m/s, respectively. The biennial oscillations in DW1 and SW2 modes suggest a systematic correlation with the equatorial quasi‐biennial oscillation in the stratosphere and are more apparent in DW1 amplitudes. Although there is significant interannual variability in addition to the apparent biennial signal, there is no clear evidence of any solar cycle dependence or long‐term trend in either DW1 or SW2 modes.Key PointsShort‐term and intra‐annual variability in DW1 and SW2 tidal modes estimated from TIDI and NAVGEM‐HA are in good agreementThe biennial oscillations in DW1 and SW2 modes are systematically correlated with equatorial stratospheric quasi‐biennial oscillationThere is no clear evidence of any solar cycle dependence or long‐term trend in either DW1 or SW2 modesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146276/1/jgra54488_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146276/2/jgra54488.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146276/3/jgra54488-sup-0001-supplementary.pd