Comparative Analysis of the Measured and Modeled Equatorial Thermospheric Wind Climatology

<p>The thermospheric winds play an important role in the vertical and horizontal couplings of the upper atmosphere by modulating neutral and plasma dynamics. A large variety of observation techniques and numerical as well as empirical models have been developed to understand the behavior of thermospheric winds. The Fabry-Perot interferometer (FPI) is a widely used ground- and satellite-based optical instrument for the thermospheric winds observations in the upper atmosphere. Due to solar contamination of the fainter airglow emission during the daytime, most of the ground-based interferometric wind measurements are limited to the nighttime period only. Despite these constraints, the Second&#8208;generation, Optimized, Fabry&#8208;Perot Doppler Imager (SOFDI) is designed for both daytime and nighttime measurements of thermospheric winds from OI 630&#8208;nm emission and is currently operating at the Huancayo, Peru, near the geomagnetic equator.&#160;In this study, we present a comparative analysis of the observed SOFDI wind climatological data and several other modeled results including, but not limited to, Horizontal Wind Model 2014 (HWM-14), Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model with and without implementing Prompt Penetration Electric Field (PPEF), Whole Atmosphere Model (WAM), SAMI3 model, and Magnetic mEridional NeuTrAl Thermospheric (MENTAT) model. We examine the relative performances of these models in the context of the direct-measured thermospheric winds. The day and nighttime modeled winds show an excellent agreement with the SOFDI wind data at the equatorial latitude, except for the daytime zonal winds. Further, this analysis gives a comprehensive picture of how well the measured winds provided by the SOFDI instrument and various models represent the features of the equatorial thermosphere.&#160;We also investigate and give an overview of the sources, drivers, effects, and possible mechanisms of the wind variability in the low-latitude thermosphere.</p>

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New results on equatorial thermospheric winds and the midnight temperature maximum

Annales Geophysicae ◽

10.5194/angeo-26-447-2008 ◽

2008 ◽

Vol 26 (3) ◽

pp. 447-466 ◽

Cited By ~ 48

Author(s):

J. Meriwether ◽

M. Faivre ◽

C. Fesen ◽

P. Sherwood ◽

O. Veliz

Keyword(s):

Local Time ◽

Wind Field ◽

General Circulation ◽

Circulation Model ◽

Meridional Wind ◽

Optical Observations ◽

Horizontal Wind ◽

Temporal Sampling ◽

The Mean ◽

Thermospheric Winds

Abstract. Optical observations of thermospheric winds and temperatures determined with high resolution measurements of Doppler shifts and Doppler widths of the OI 630-nm equatorial nightglow emission have been made with improved accuracy at Arequipa, Peru (16.4° S, 71.4° W) with an imaging Fabry-Perot interferometer. An observing procedure previously used at Arecibo Observatory was applied to achieve increased spatial and temporal sampling of the thermospheric wind and temperature with the selection of eight azimuthal directions, equally spaced from 0 to 360°, at a zenith angle of 60°. By assuming the equivalence of longitude and local time, the data obtained using this technique is analyzed to determine the mean neutral wind speeds and mean horizontal gradients of the wind field in the zonal and meridional directions. The new temperature measurements obtained with the improved instrumental accuracy clearly show the midnight temperature maximum (MTM) peak with amplitudes of 25 to 200 K in all directions observed for most nights. The horizontal wind field maps calculated from the mean winds and gradients show the MTM peak is always preceded by an equatorward wind surge lasting 1–2 h. The results also show for winter events a meridional wind abatement seen after the MTM peak. On one occasion, near the September equinox, a reversal was observed during the poleward transit of the MTM over Arequipa. Analysis inferring vertical winds from the observed convergence yielded inconsistent results, calling into question the validity of this calculation for the MTM structure at equatorial latitudes during solar minimum. Comparison of the observations with the predictions of the NCAR general circulation model indicates that the model fails to reproduce the observed amplitude by a factor of 5 or more. This is attributed in part to the lack of adequate spatial resolution in the model as the MTM phenomenon takes place within a scale of 300–500 km and ~45 min in local time. The model shortcoming is also attributed in part to the need for the model to include a hydrodynamical mechanism to describe the merging of the zonal wind with the meridional tidal winds that converge onto the geographical equator. Finally, a conclusion of this work is that the MTM compressional heating takes place along the perimeter of the pressure bulge rather than within the bulge, an issue previously not appreciated.

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Comparative analysis of the accessibility and connectivity of public transport in the city districts of Krakow

Prace Komisji Geografii Komunikacji PTG ◽

10.4467/2543859xpkg.20.016.12784 ◽

2020 ◽

Vol 23 (3) ◽

pp. 7-14

Author(s):

Martin Bárta

Keyword(s):

Comparative Analysis ◽

Public Transport ◽

Spatial Inhomogeneity ◽

Urban Mobility ◽

City Center ◽

Specific Identification ◽

Transport Services ◽

Comprehensive Picture ◽

The City

A properly functioning public transport is one of the most important components of urban mobility for the population. Due to spatial inhomogeneity and overall socio-economic differences within a city, there are often considerable disproportions in the quality of transport services within its districts. Also, the city of Krakow is no exception in this case. For a comparison of public transport accessibility in 18 Krakow districts, 7 major quantitative and 5 minor indicators were created. These indicators include the most important characteristics of transport services such as accessibility, frequency, connectivity of connections, and ratios of tram public transport subsystem. The resulting values give a fairly comprehensive picture of the quality of the transport services. Overall higher values for most indicators occur in the central districts of the city. However, due to the complexity of the observed characteristics, it is possible to discover significant differences in the structure of individual indicators. Peripheral districts reach higher amplitudes, which means that in some aspect they have even better transport services than the city center. Yet, at the same time, we also find opposite extremes here, highly below-average values for most other indicators. A detailed analysis of the results provides a unique perspective on the disparities among districts. It can also serve for specific identification of strengths and weaknesses of transport services and its possible optimization.

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A possible influence of the Great White Spot on Saturn kilometric radiation periodicity

Annales Geophysicae ◽

10.5194/angeo-32-1463-2014 ◽

2014 ◽

Vol 32 (12) ◽

pp. 1463-1476 ◽

Cited By ~ 19

Author(s):

G. Fischer ◽

S.-Y. Ye ◽

J. B. Groene ◽

A. P. Ingersoll ◽

K. M. Sayanagi ◽

...

Keyword(s):

Gravity Waves ◽

Upper Atmosphere ◽

White Spot ◽

Time Interval ◽

Unusual Behavior ◽

Cassini Mission ◽

Large Jump ◽

Modulation Signal ◽

Thermospheric Winds ◽

Energy And Momentum

Abstract. The periodicity of Saturn kilometric radiation (SKR) varies with time, and its two periods during the first 5 years of the Cassini mission have been attributed to SKR from the northern and southern hemisphere. After Saturn equinox in August 2009, there were long intervals of time (March 2010 to February 2011 and September 2011 to June 2012) with similar northern and southern SKR periods and locked SKR phases. However, from March to August 2011 the SKR periods were split up again, and the phases were unlocked. In this time interval, the southern SKR period slowed down by ~ 0.5% on average, and there was a large jump back to a faster period in August 2011. The northern SKR period speeded up and coalesced again with the southern period in September 2011. We argue that this unusual behavior could be related to the so-called Great White Spot (GWS), a giant thunderstorm that raged in Saturn's atmosphere around that time. For several months in 2011, the visible head of the GWS had the same period of ~ 10.69 h as the main southern SKR modulation signal. The GWS was most likely a source of intense gravity waves that may have caused a global change in Saturn's thermospheric winds via energy and momentum deposition. This would support the theory that Saturn's magnetospheric periodicities are driven by the upper atmosphere. Since the GWS with simultaneous SKR periodicity measurements have only been made once, it is difficult to prove a physical connection between these two phenomena, but we provide plausible mechanisms by which the GWS might modify the SKR periods.

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Comparing high-latitude thermospheric winds from FPI and CHAMP accelerometer measurements

10.5194/angeo-2019-57 ◽

2019 ◽

Author(s):

Anasuya Aruliah ◽

Matthias Förster ◽

Rosie Hood ◽

Ian McWhirter ◽

Eelco Doornbos

Keyword(s):

High Latitude ◽

Auroral Oval ◽

Horizontal Wind ◽

Champ Satellite ◽

Fabry Perot ◽

Wind Velocities ◽

Height Dependence ◽

Statistical Sense ◽

Thermospheric Winds

Abstract. It is generally assumed that horizontal wind velocities are independent of height above the F1-region (> 300 km) due to the large viscosity of the upper thermosphere. This assumption is used to compare two completely different methods of thermospheric neutral wind observation, using two distinct locations in the high-latitude Northern Hemisphere. The measurements are from ground-based Fabry-Perot Interferometers (FPI), and from in-situ accelerometer measurements onboard the CHAMP satellite, which was in a near polar orbit. The UCL KEOPS FPI is located in the vicinity of the auroral oval at the ESRANGE site near Kiruna, Sweden (67.8° N, 20.4° E). The UCL Longyearbyen FPI is a polar cap site, located at the Kjell Henriksen Observatory on Svalbard (78.1° N, 16.0° E). The comparison is done in a statistical sense, comparing a longer time series obtained during nighttime hours in the winter months (November to January); with overflights of the CHAMP satellite between 2001 and 2007 over the observational sites, within ±2° (±220 km horizontal range). The FPI is assumed to measure the Doppler shift along the line-of-sight of winds at ~ 240 km height, i.e. the peak emission height of the atomic oxygen 630.0 nm emission. The components of winds at right angles to the CHAMP orbit are derived from state-of-the-art precision accelerometer measurements at altitudes. CHAMP was at altitudes between 450 km (in 2001) to 330 km (in 2007); i.e. 100–200 km above the FPI wind observations. We show that CHAMP winds at high latitudes are systematically 1.5–2 times larger than FPI winds. In addition to testing the consistency of the different measurement approaches, the study aims to clarify the effects of viscosity on the height dependence of thermospheric winds.

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Parameterization of Overwater Horizontal Wind Variability

10.21236/ada169331 ◽

1986 ◽

Cited By ~ 1

Author(s):

Gordon E. Schacher

Keyword(s):

Horizontal Wind ◽

Wind Variability

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Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

Annales Geophysicae ◽

10.5194/angeo-27-2225-2009 ◽

2009 ◽

Vol 27 (5) ◽

pp. 2225-2235 ◽

Cited By ~ 10

Author(s):

C. Anderson ◽

M. Conde ◽

P. Dyson ◽

T. Davies ◽

M. J. Kosch

Keyword(s):

Large Scale ◽

Atmospheric Model ◽

Horizontal Wind ◽

Data Set ◽

Average Behavior ◽

Wind Speeds ◽

Zonal Winds ◽

F Region ◽

Fabry Perot ◽

Thermospheric Winds

Abstract. A new all-sky imaging Fabry-Perot spectrometer has been installed at Mawson station (67°36' S, 62°52' E), Antarctica. This instrument is capable of recording independent spectra from many tens of locations across the sky simultaneously. Useful operation began in March 2007, with spectra recorded on a total of 186 nights. Initial analysis has focused on the large-scale daily and average behavior of winds and temperatures derived from observations of the 630.0 nm airglow line of atomic oxygen, originating from a broad layer centered around 240 km altitude, in the ionospheric F-region. The 1993 Horizontal Wind Model (HWM93), NRLMSISE-00 atmospheric model, and the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model were used for comparison. During the geomagnetically quiet period studied, observed winds and temperatures were generally well modelled, although temperatures were consistently higher than NRLMSISE-00 predicted, by up to 100 K. CTIP temperatures better matched our data, particularly later in the night, but predicted zonal winds which were offset from those observed by 70–180 ms−1 westward. During periods of increased activity both winds and temperatures showed much greater variability over time-scales of less than an hour. For the active night presented here, a period of 45 min saw wind speeds decrease by around 180 ms−1, and temperatures increase by approximately 100 K. Active-period winds were poorly modelled by HWM93 and CTIP, although observed median temperatures were in better agreement with NRLMSISE-00 during such periods. Average behavior was found to be generally consistent with previous studies of thermospheric winds above Mawson. The collected data set was representative of quiet geomagnetic and solar conditions. Geographic eastward winds in the afternoon/evening generally continued until around local midnight, when winds turned equatorward. Geographic meridional and zonal winds in the afternoon were approximately 50 ms−1 weaker than expected from HWM93, as was the transition to equatorward flow around midnight. There was also a negligible geographic zonal component to the post-midnight wind where HWM93 predicted strong westward flow. Average temperatures between 19:00 and 04:00 local solar time were around 60 K higher than predicted by NRLMSISE-00.

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Assessment of the ERA-Interim Winds Using High-Altitude Stratospheric Balloons

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0137.1 ◽

2017 ◽

Vol 74 (6) ◽

pp. 2065-2080 ◽

Cited By ~ 7

Author(s):

Fabrice Duruisseau ◽

Nathalie Huret ◽

Alice Andral ◽

Claude Camy-Peyret

Keyword(s):

Wind Speed ◽

High Altitude ◽

Middle Atmosphere ◽

Meridional Wind ◽

Horizontal Wind ◽

Quasi Biennial Oscillation ◽

Wind Variability ◽

Wind Measurements ◽

Biennial Oscillation ◽

Balloon Measurements

Abstract This study focuses on the ability of ERA-Interim to represent wind variability in the middle atmosphere. The originality of the proposed approach is that wind measurements are deduced from the trajectories of zero-pressure balloons that can reach high-stratospheric altitudes. These balloons are mainly used to carry large scientific payloads. The trajectories of balloons launched above Esrange, Sweden, and Teresina, Brazil, from 2000 to 2011 were used to deduce zonal and meridional wind components (by considering the balloon as a perfect tracer at high altitude). Collected data cover several dynamical conditions associated with the winter and summer polar seasons and west and east phases of the quasi-biennial oscillation at the equator. Systematic comparisons between measurements and ERA-Interim data were performed for the two horizontal wind components, as well as wind speed and wind direction in the [100, 2]-hPa pressure range to deduce biases between the model and balloon measurements as a function of altitude. Results show that whatever the location and the geophysical conditions considered, biases between ERA-Interim and balloon wind measurements increase as a function of altitude. The standard deviation of the model–observation wind differences can attain more than 5 m s−1 at high altitude (pressure P < 20 hPa). A systematic ERA-Interim underestimation of the wind speed is observed and large biases are highlighted, especially for equatorial flights.

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