Fabry–Perot Interferometer Winds Research Articles

Effect of Polar Cap Patches on the High‐Latitude Upper Thermospheric Winds

AbstractThis study focuses on the poorly known effect of polar cap patches (PCPs) on the ion‐neutral coupling in the F‐region. The PCPs were identified by total electron content measurements from the Global Navigation Satellite System (GNSS) and the ionospheric parameters from the Defense Meteorological Satellite Program spacecraft. The EISCAT incoherent scatter radars on Svalbard and at Tromsø, Norway observed that PCPs entered the nightside auroral oval from the polar cap and became plasma blobs. The ionospheric convection further transported the plasma blobs to the duskside. Simultaneously, long‐lasting strong upper thermospheric winds were detected in the duskside auroral oval by a Fabry‐Perot Interferometer (FPI) at Tromsø and in the polar cap by the Gravity Recovery and Climate Experiment satellite. Using EISCAT ion velocities and plasma parameters as well as FPI winds, the ion drag acting on neutrals and the time constant for the ion drag could be estimated. Due to the arrival of PCPs/blobs and the accompanied increase in the F‐region electron densities, the ion drag is enhanced between about 220 and 500 km altitudes. At the F peak altitudes near 300 km, the median ion drag acceleration affecting neutrals more than doubled and the associated median e‐folding time decreased from 4.4 to 2 hr. The strong neutral wind was found to be driven primarily by the ion drag force due to large‐scale ionospheric convection. Our results provide a new insight into ionosphere‐thermosphere coupling in the presence of PCPs/blobs.

Spectral Contamination of the 6300 Å Emission in Single‐Etalon Fabry‐Perot Interferometers

AbstractThe spectral line profile of the atomic oxygen O1D2—3P2 transition near 6300 Å in the airglow has been used for more than 50 years to extract neutral wind and temperature information from the F‐region ionosphere. A new spectral model and recent samples of this airglow emission in the presence of the nearby lambda‐doubled OH Meinel (9‐3) P2(2.5) emission lines underscores earlier cautions that OH can significantly distort the OI line center position and line width observed using a single‐etalon Fabry‐Perot interferometer (FPI). The consequence of these profile distortions in terms of the emission profile line width and Doppler position is a strong function of the selected etalon plate spacing. Single‐etalon Fabry‐Perot interferometers placed in the field for thermospheric measurements have widely varying etalon spacings, so that systematic wind biases caused by the OH line positions differ between instruments, complicating comparisons between sites. Based on the best current determinations of the OH and O1D line positions, the ideal gap for a single‐etalon FPI wind measurements places the OH emissions in the wings of the O1D spectral line profile. Optical systems that can accommodate prefilters with square passbands less than ∼3 Å in the optical beam can effectively block the OH contamination. When that is not possible, a method to fit for OH contamination and remove it in the spectral background of an active Fabry‐Perot system is evaluated.

A Comparison of Fabry–Perot Interferometer and Meteor Radar Wind Measurements Near the Polar Mesopause Region

AbstractThe neutral winds in the Mesosphere and Lower Thermosphere (MLT) region have been observed at King Sejong Station, Antarctica using a meteor radar (MR) and a Fabry–Perot interferometer (FPI) simultaneously. These two independent MLT wind measurements are compared to each other to identify the characteristics of FPI measurement. Instead of using a fixed emission height for FPI winds, for the first time, we consider the temporal variations of airglow emission layer in association with corresponding meteor height distributions for more accurate comparison between the FPI and MR winds. The temporal variations of the airglow emission layers are examined from the inverse relationship between the height integrated emission rate and the peak emission height derived from the TIMED/SABER observations. It is found that FPI winds are consistently smaller than MR winds and the discrepancy becomes larger for OI emission at higher altitude, which may be related to large wind shear in the MLT region and variabilities of the emission layers. Finally, we found that the FPI can provide reliable height‐averaged winds in the MLT region where existing a strong wind shear from this simultaneous MR wind measurements.

Climatology of Nighttime Upper Thermospheric Winds From Fabry‐Perot Interferometer 2011–2019 Measurements Over Kelan (38.7°N, 111.6°E), China: Local Time, Seasonal, Solar Cycle, and Geomagnetic Activity Dependence

AbstractFor the first time, we develop a local time and day of year dependent climatological model in different geomagnetic activity based on 630.0 nm Fabry‐Perot Interferometer (FPI) measurements over Kelan (38.7°N, 111.6°E) during 2011–2019. With this model, we analyze the regional climatological characteristics of nighttime thermospheric neutral winds, and a comparison is made with two recent versions of the Horizontal Wind Model series (HWMs), HWM07 and HWM14. Due to the location of Kelan far from the northern magnetic pole longitude at middle latitude, the statistical characterizations of meridional and zonal winds show some unique local time, seasonal, solar cycle and geomagnetic activity dependence. There are predominantly annual variations of horizontal winds characterized by rapid transitions from eastward December winds to westward or less eastward June winds and largest equatorward meridional winds during summer months. To some degree, the wind patterns show casual solar activity dependence especially for the zonal component. The maximum southward winds show negative relationship with increasing solar activity in summer months, while the maximum eastward winds present negative trend in winter months. The Kp dependencies are characterized by larger westward perturbation winds for all night and enhanced northward winds in the premidnight sector and equatorward surges in the postmidnight sector during strongly active conditions. With increasing solar flux, the westward perturbation winds become weaker at nights. Results also reveal that HWM14 predictions are in better agreement with Kelan FPI winds in the shape and magnitude than HWM07, and the consistency improves with increasing Kp.

First Comparison of Mesospheric Winds Measured with a Fabry-Perot Interferometer and Meteor Radar at the King Sejong Station (62.2°S, 58.8°W)

A Fabry-Perot interferometer (FPI) for mesospheric observations was installed at King Sejong Station (62.2°S, 58.9° W) in Antarctica in 2017. For the initial validation of the FPI measurements, we compare neutral wind data recorded with the FPI with those from a Meteor Radar (MR) located nearby. The overall characteristics of the FPI and MR winds of both OH 892.0 nm (87 km) and OI 557.7 nm (97 km) airglow layers are similar. The FPI winds of both layers generally match the MR winds well on the observed days, with a few exceptions. The correlation analysis of the FPI and MR wind data shows that the correlation coefficients for the zonal winds at 87 and 97 km are 0.28 and 0.54, respectively, and those for the meridional winds are 0.36 and 0.54, respectively. Based on the assumption that the distribution of the airglow emissions has a Gaussian function with respect to the altitude, we calculated the weighted mean winds from the MR wind profile and compared them with the FPI winds. By adjusting the peak height and full width at half maximum of the Gaussian function, we determined the change of the correlation between the two winds. The best correlation for the OH and OI airglow layers was obtained at a peak height of 88–89 km and 97–98 km, respectively.

Polar Thermospheric Winds and Temperature Observed by Fabry‐Perot Interferometer at Jang Bogo Station, Antarctica

AbstractUpper atmospheric neutral winds and temperature have been observed by the Fabry‐Perot interferometer (FPI) which was installed at Jang Bogo Station (JBS), Antarctica, in 2014. Since JBS is mostly located within the polar cap region, the observed thermospheric winds at 250 km show strong diurnal variations with notable antisunward motions due to the effects of plasma convection. The winds at 87 km, on the other hand, show semidiurnal variations due to the lower atmospheric tidal effects. We found that the winds from green line emission show largely diurnal variations, unlike the other independent observations, which might be due to the auroral contamination. The horizontal wind model 2014 winds at 250 km show reasonable agreement with FPI winds, while large discrepancies exist at 87 km in terms of seasonal variations. There is a distinctive asymmetric seasonal variation of the thermospheric zonal wind in the dusk and dawn sectors. FPI temperatures at 250 km show a fairly close correlation with Kp index, especially in 2015 when the geomagnetic activity is stronger. However, the temperatures at 87 km are mostly independent on Kp index. Finally, during the intense geomagnetic storm, thermospheric winds and temperature are significantly disturbed and Thermosphere Ionosphere Electrodynamics General Circulation Model simulations are in surprisingly good agreement with observation for winds but the temperatures are significantly underestimated during the whole storm period.

Retrieval of middle and upper atmospheric wind based on non-full circular fringe recorded by Fabry-Perot Inteferometer

Fabry-Perot Interferometer (FPI) has been used widely for wind measurements of the middle and upper atmosphere. To date, most of FPIs have been based on full-closed circular fringe, which needs 15–25 min to obtain a group of wind velocity (zonal and meridional). However, it is hard to improve the temporal resolution because full-closed circular fringe in several directions cannot be easily imaged onto the same Charge-Coupled Device (CCD) with enough airglow intensity. In this paper, a data processing method is proposed for non-full circular fringe of FPI, which can support CCD with enough area of observations in several directions simultaneously. The method is focused on the center determination of non-full fringe. It includes radial cross-section, peak coordinate determination, and center calculation. Based on the calculated center, the fringe is annular summed. Then its radius is determined subsequently using Gaussian fitting. Finally, the wind is retrieved from the fringe radius. For validation, fringes from two ground-based FPIs were used, which are deployed in Kelan (38.71°N, 111.58°E) and Xinglong (40.40°N, 117.59°E) in China. The results retrieved from non-full fringes of FPIs were compared with that from full-closed circular fringe. The averaged wind deviation between them demonstrates reasonable difference with 5.38 m s−1 for 892.0 nm airglow emission, 5.81 m s−1 for 630.0 nm emission, and 3.03 m s−1 for 557.7 nm emission. Besides, wind results of Xinglong FPI are compared roughly with measurements of meteor radar which is deployed in Ming Tombs of Beijing (40.3°N, 116.2°E). Good agreement demonstrates that this method is robust enough for FPI wind retrieval of mesosphere and thermosphere.

Peak height of OH airglow derived from simultaneous observations a Fabry‐Perot interferometer and a meteor radar

AbstractA new method for estimating daily averaged peak height of the OH airglow layer from a ground‐based meteor radar (MR) and a Fabry‐Perot interferometer (FPI) is presented. The first results are derived from 4 year simultaneous measurements of winds by a MR and a FPI at two adjacent stations over center China and are compared with observations from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. The OH airglow peak heights, which are derived by using correlation analysis between winds of the FPI and MR, are found to generally peak at an altitude of 87 km and frequently varied between 80 km and 90 km day to day. In comparison with SABER OH 1.6 μm observations, reasonable similarity of airglow peak heights is found, and rapid day‐to‐day variations are also pronounced. Lomb‐Scargle analysis is used to determine cycles of temporal variations of airglow peak heights, and there are obvious periodic variations both in our airglow peak heights and in the satellite observations. In addition to the annual, semiannual, monthly, and three monthly variations, the shorter time variations, e.g., day‐to‐day and several days' variations, are also conspicuous. The day‐to‐day variations of airglow height obviously could reduce observation accuracy and lead to some deviations in FPI measurements. These FPI wind deviations arising from airglow height variations are also estimated to be about 3–5 m/s from 2011 to 2015, with strong positive correlation with airglow peak height variation. More attention should be paid to the wind deviations associated with airglow height variation when using and interpreting winds measured by FPI.

Properties of the Long-Term Oscillations in the Middle Atmosphere Based on Observations from TIMED/SABER Instrument and FPI over Kelan

The properties of the long-term oscillations in the middle atmosphere have been investigated using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data and Fabry–Perot interferometer (FPI) data. Results for SABER temperature show that the semiannual oscillation (SAO) has three amplitude maxima at altitudes of 45, 75, and 85 km, respectively, and shows prominent seasonal asymmetries there. The SAOs in the upper mesosphere (75 km) are out of phase with those in the mesopause (85 km) in the tropical regions, which can generate an enhancement of 11 K on average at each equinox, contributing to the lower mesospheric inversion layer (MIL). It is shown that stronger enhancement can be found at the spring equinox than at the autumn equinox. The triennial oscillation (TO) is significant in the tropical region. The spectral peak of the TO is probably a sub-peak of the quasi-biennial oscillation (QBO) and is due to modulation of QBO. In addition, there may be potential interaction of the TO with SAO at 85 km at the equator. The relation between ENSO and TO has also been discussed. The ENSO signal may modulate the amplitude of the TO, mainly in the lower stratosphere. The annual oscillation (AO) and SAO are analyzed over Kelan by FPI data. Generally, the amplitudes of FPI wind are smaller than those of the Horizontal Wind Model (HWM07). The comparison between FPI and TIMED Doppler Interferometer (TIDI) winds shows relatively large discrepancy. This may be due to the tidal aliasing in the nighttime results derived from the FPI data. Results also show that the algorithm to derive FPI temperature needs improvements.

A comparison of mesospheric and low‐thermospheric winds measured by Fabry‐Perot interferometer and meteor radar over central China

AbstractWind data observed by a Fabry‐Perot interferometer (FPI) and a meteor radar (MR) deployed in two stations, which are 430 km apart in ground distance, are used to study wind climatology in mesosphere/lower thermosphere over central China and compare between the measurements. A general morphologic similarity of the FPI winds and MR winds is identified with 4 year data since November 2011. At 87 km, the wind vector plots show that the FPI and MR winds agree with each other very well in all months. The zonal winds of both instruments have an apparent semiannual variation with a maximal strength of −20 m/s at around 18:00 UT in equinoctial months, and the meridional winds from both instruments have an apparent annual variation with a maximal strength of −40 m/s at around 15:00 UT in summer months. The correlation coefficients between the measurements of the two instruments are about 0.95 for meridional wind and 0.90 for zonal wind. At 97 km, the wind vector plots show that FPI and MR winds agree with each other from May to October and are obviously different in the rest months. There are very weak semiannual variations at around 18:00 UT for both zonal winds and pronounced annual variation at around 13:00 UT for both meridional winds. The correlation coefficients between the FPI and MR winds are 0.73 for zonal wind and 0.86 for meridional wind, which are overall smaller than that at 87 km. A Gaussian distribution of airglow profile is used to investigate the deviations associated with peak height and full width at half maximum (FWHM) of airglow layer. It is found that the variation of peak height could lead to about 20% variation of correlation coefficients between measurements at the height of 87 km and about 14.8% at the height of 97 km on average. The variation of FWHM could lead to a correlation coefficient variation of about 2.4% and 3.5% at the height of 87 km and 97 km, respectively. Some other reasons, such as the influence of geomagnetic field on meteor trail and the propagation of gravity waves, could also contribute to these differences between measurements.

Ionosonde and optical determinations of thermospheric neutral winds over the Antarctic Peninsula

Ionosonde observations have been made at Great Wall station (62.22°S; 58.97°W), King George Island, and at further south Vernadsky station (65.25°S; 64.27°W), Argentine Islands, for many years. For several days at the two locations the magnetic meridional component of the thermospheric neutral wind has also been derived using three different algorithms with ionosonde data input. At King Sejong station (62.22°S; 58.78°W), close to Great Wall, almost simultaneous thermospheric winds were measured with a Fabry–Perot Interferometer (FPI) during a few days in 1997. All days correspond to intervals of low solar and geomagnetic activity levels and for different seasons. Here, the geographic meridional FPI winds measured at the geographic south pointing location are compared with the magnetic meridional component of the wind derived from ionosonde observations at Vernadsky. Also, the magnetic meridian FPI winds measured using all four cardinal pointing locations are compared with the magnetic meridional component of the wind derived from ionosonde observations at Great Wall. The patterns of the diurnal variations of the magnetic meridional component of ionosonde derived winds using the three different techniques are similar in most cases. However, the amplitudes of these variations and some individual values can differ by more than 150m/s depending on season, particularly during daytime. Comparison of the autumn FPI with the ionosonde winds for Vernadsky and Great Wall shows that they coincide within observation uncertainties. Results for other seasons are not so good. Some of the discrepancies are discussed in relation to the hour-to-hour variability of ionosonde based winds and the latitudinal gradients of ionospheric characteristics. Other discrepancies need to be further explained. Recently reported FPI mean winds for tens of days in different seasons for Palmer (64.77°S; 64.05°W), Anvers Island, are found to be particularly close to ionosonde derived mean winds for Argentine Islands station (former Vernadsky), albeit observations are for different time intervals. Unless comprehensive FPI winds for the Antarctic Peninsula longitude sector become available, ionosonde based winds seem to be reliable enough for several purposes.

Climatological modeling of horizontal winds in the mesosphere and lower thermosphere over a mid-latitude station in China

In this study, we employed the non-uniform rational B-splines surface technique to develop a provisional horizontal wind model of the mesosphere and lower thermosphere at altitudes of 87, 97, and 250km over Kelan (38.7°N, 111.6°E) in China using Fabry–Perot interferometer (FPI) observations for the period between January 2012 and May 2014. We compared the meridional and zonal winds derived from the Kelan FPI wind model with those based on Meteor Radar wind observations at Beijing (39.92°N, 116.39°E), and those calculated from horizontal wind models, i.e., HWM93 and HWM07, at Kelan. Our analysis showed the following. (1) At 87 and 97km, the Kelan FPI wind patterns exhibited strong annual variation in the meridional wind and semiannual variation in the zonal wind, as well as diurnal variation, which was dominated by a semidiurnal tidal variation in the meridional and zonal winds during May and September with a diurnal phase difference. The Kelan FPI wind patterns agreed well with the Meteor Radar winds and the HWM07 model results, but less well with the HWM93 model. (2) At 250km, the FPI wind patterns agreed fairly well with the HWM93 results, where both indicated annual/diurnal variation in the meridional and zonal winds, and weak semidiurnal tidal variation. There were large discrepancies between the Kelan FPI winds and the HWM07 model results, which were mainly due to differences in the annual variation in the nighttime meridional wind. (3) The magnitude of the FPI winds was comparable to the HWM93 results but they were nearly 40–50% lower than the other winds, which is attributable to the inherent limitations of airglow measurement. Thus, this local empirical wind model could be used to investigate the climatological features of local ionospheric spatial–temporal variations.

Error calculation and analysis for an improved wind retrieval method based on the ground-based Fabry–Perot interferometer measurements

A ground-based Fabry–Perot interferometer (FPI) fabricated by American National Center for Atmospheric Research (A-NCAR) was deployed in Kelan (111.6°E, 38.7°N), in middle of China, to observe OH 892.0nm, OI 630.0nm, and OI 557.7nm airglow emissions for wind retrieval of mesospheric and thermospheric atmosphere using a method based on the convolution of the source profile and instrumental function. Based on the instrument, wind velocities were retrieved using another retrieval method but improved in both noise reduction and choice of interference fringes, which can reduce the disturbance of bad fringes and advance the retrieval precision. The retrieval results were subsequently compared with the FPI wind products, and good agreement was found between them. The averaged deviations of wind velocities between the two retrieval methods depend on airglow intensity with 5.7m/s for 892.0nm emission, 6.18m/s for 630.0nm emission, and 3.66m/s for 557.7nm emission, respectively. Then, a new method was proposed for error calculation by considering the influence of airglow intensity, CCD dark noise, background emissions, and data processing, which can steadily evaluate the precision and reliability of wind retrieval. The relationships between errors derived from the two retrieval methods and airglow intensity were compared and analyzed. It is found that the variation of errors is inversely correlated with the variation of airglow intensity.

FPI observations of nighttime mesospheric and thermospheric winds in China and their comparisons with HWM07

Abstract. We analyzed the nighttime horizontal neutral winds in the middle atmosphere (~ 87 and ~ 98 km) and thermosphere (~ 250 km) derived from a Fabry–Perot interferometer (FPI), which was installed at Xinglong station (40.2° N, 117.4° E) in central China. The wind data covered the period from April 2010 to July 2012. We studied the annual, semiannual and terannual variations of the midnight winds at ~ 87 km, ~ 98 km and ~ 250 km for the first time and compared them with Horizontal Wind Model 2007 (HWM07). Our results show the following: (1) at ~ 87 km, both the observed and model zonal winds have similar phases in the annual and semiannual variations. However, the HWM07 amplitudes are much larger. (2) At ~ 98 km, the model shows strong eastward wind in the summer solstice, resulting in a large annual variation, while the observed strongest component is semiannual. The observation and model midnight meridional winds agree well. Both are equatorward throughout the year and have small amplitudes in the annual and semiannual variations. (3) There are large discrepancies between the observed and HWM07 winds at ~ 250 km. This discrepancy is largely due to the strong semiannual zonal wind in the model and the phase difference in the annual variation of the meridional wind. The FPI annual variation coincides with the results from Arecibo, which has similar geomagnetic latitude as Xinglong station. In General, the consistency of FPI winds with model winds is better at ~ 87 and ~ 98 km than that at ~ 250 km. We also studied the seasonally and monthly averaged nighttime winds. The most salient features include the following: (1) the seasonally averaged zonal winds at ~ 87 and ~ 98 km typically have small variations throughout the night. (2) The model zonal and meridional nighttime wind variations are typically much larger than those of observations at ~ 87 km and ~ 98 km. (3) At ~ 250 km, model zonal wind compares well with the observation in the winter. For spring and autumn, the model wind is more eastward before ~ 03:00 LT but more westward after. The observed nighttime zonal and meridional winds on average are close to zero in the summer and autumn, which indicates a lack of strong stable tides. The consistency of FPI zonal wind with model wind at ~ 250 km is better than the meridional wind.

A comparison of mesospheric winds measured by FPI and meteor radar located at 40N

In this paper, winds derived from OH Meinel 892.0 nm detection by an FPI (Fabry-Perot Interferometer) are compared with the simultaneous wind measurements from a meteor radar during April–May of 2010. The peak height of OH Meinel 892.0 nm is about 87 km. The variations of FPI wind at 87 km mostly have the similar track to meteor radar wind at 87 km, and the data values of FPI wind mainly fall into the range of meteor radar wind. However, there are still quantitative differences between the observations of the two systems. The best cross-correlation occurs in meridional winds from two systems in April of 2010. An obvious wave signal with 0.2 cycle/d frequency is found in meridional winds observed by both FPI and meteor radar.

Comparison of winds measured by MU radar and Fabry–Perot interferometer and effect of OI5577 airglow height variations

We have compared wind velocities around mesopause height measured by the middle and upper atmosphere (MU) radar (meteor mode) and OI (5577) airglow observation by an Fabry–Perot Interferometer (FPI), at Shigaraki (34.8° N, 136.1° E) , Japan, on November 13/14, 1999. When we assume the airglow height is constant throughout the night, it was difficult to find a single height exhibiting small r.m.s. differences between the two methods for both eastward and northward wind velocities. However, in the case we introduce a time variation of the airglow height due to a large-scale gravity wave activity, we have found very small r.m.s. wind difference: The assumptions are of the airglow height variation with an amplitude of 1.5 km , a period of 5.7 h and a linear trend of −0.19 km/h having the average height of 92.8 km . Further analysis of time and height variations of the winds and diffusion coefficients measured by the MU radar indicated that a gravity wave with a very similar structure predicted in the above comparison between the FPI and meteor winds has been detected as a dominant wave component. Thus, we conclude that the existence of a gravity wave which can change the airglow height will lead to differences in wind velocities observed with FPI and radar techniques.

Dynamics of the lower thermosphere at Saskatoon (52°N, 107°W) during 1988/1989: Comparisons of measurements by a medium frequency radar and a Fabry-Perot interferometer

The Saskatoon medium frequency radar and Fabry-Perot interferometer (FPI) were operated continuously from September 1988 to February 1989. The radar data are from the new phase-coherent system which provides winds from 55/75 to 100/110 km during daylight/night hours. The yield at the airglow layer's height near 97 km is much improved, and regularly provides hourly mean winds even on quiet nights when electron precipitation associated with auroral activity is minimal. Observations of the green atomic oxygen OI 557.7 nm emission provide Doppler winds from the airglow layer, on the relatively few nights per month (2–5) when there is no contamination due to clouds, moon or aurorae. These data are supplemented with winds from the F-region's red atomic oxygen OI 630.0 nm emission, which are referred to on disturbed nights. Comparisons are made between the wind vectors from both systems on individual days (mainly quiet ones), and the resulting tidal profiles/points from the radar/FPI systems. Generally the agreement is excellent, with solar tides dominating the wind field of both instruments. However, on disturbed nights, while the radar winds show little or no change compared to the quiet neighbouring days, the FPI winds (558 nm) demonstrate non-tidal motions quite similar to those obtained from the 630-nm emission.