MF Radar Data Research Articles

Mesosphere summer echoes observed with the SuperDARN Hokkaido HF radar at Rikubetsu, Japan (43.5°N)

Using the SuperDARN Hokkaido HF radar located at Rikubetsu in Hokkaido, Japan (43.5°N), we present first oblique-incidence observations of midlatitude mesosphere summer echoes (MSE) at the HF band (HF-MSE). Three HF-MSE events in June 2009 are case-studied. Analyses of HF-MSE data together with VHF and MF radar data obtained at Wakkanai, 260 km northwest of Rikubetsu, indicate the following: (1) in two events HF-MSE were accompanied by MSE at VHF (VHF-MSE), and in one event only HF-MSE were observed. (2) In accordance with southward neutral winds observed with the MF radar, HF-MSE exhibited high Doppler velocities with a maximum of about 60 m/s toward the south, and also HF-MSE regions moved southward with time, suggesting that irregularities and/or cold ice particles responsible for the radar wave scattering might be advected southward from higher latitudes.

Evidence of gravity wave ducting in the mesopause region from airglow network observations

AbstractWe present observational evidence of gravity wave ducting and show, for the first time, that the ducting occurs over large horizontal distances in the mesopause region. An optical network of four all‐sky imagers in Japan identified two‐dimensional patterns of small‐scale gravity wave bands in OH airglow images on 13 June 2004. The wave signatures clearly showed northward propagation of more than 1800 km over a wide range of latitudes. The horizontal wavelength, horizontal phase speed, and wave period were estimated from the airglow data as 33.4 km, 42.8 m s−1, and 13.4 min, respectively. The wave structure lasted for the whole 5‐h airglow observation period. Simultaneous MF radar wind data and TIMED/SABER measurements suggested that the wave was trapped and ducted at the airglow height. The ducting likely contributed to the remarkable coherence of the wave as it propagated northward.

Polar mesosphere and lower thermosphere dynamics: 2. Response to sudden stratospheric warmings

The dynamical response of the polar mesosphere and lower thermosphere (MLT) to sudden stratospheric warmings is investigated using MF radars at Davis (69°S, 78°E), Syowa (69°S, 40°E) and Rothera (68°S, 68°W) in the Antarctic and Poker Flat (65°N, 147°W) and Andenes (69°N, 16°E) in the Arctic. Mean winds, gravity waves and planetary waves are investigated during sudden stratospheric warmings, and comparisons are made with climatological means. The available MF radar data set includes six major sudden stratospheric warmings in the Northern Hemisphere and the unprecedented 2002 Southern Hemisphere major stratospheric warming. Three of the six northern events are relatively weak and could almost be classed as minor warmings, while the larger three have similar characteristics to the event in the Southern Hemisphere. Zonal wind reversals associated with the major warmings in both hemispheres are generally weaker and earlier by several days in the mesosphere than in the stratosphere. There are, however, significant differences between locations in their response to stratospheric warmings. The zonal winds are remarkably weaker than average during both winter and spring around the time of the southern major warming of 2002, but these effects are not observed for the Northern Hemisphere events. Gravity wave activity is found to vary significantly between individual stratospheric warming events and also between individual locations.

Seasonal variation of diurnal perturbations in mesopause region temperature, zonal, and meridional winds above Fort Collins, Colorado (40.6°N, 105°W)

On the basis of lidar observations from May 2002 through April 2003, covering both day and night, we performed a harmonic analysis to extract the diurnal perturbations in mesopause region temperature, zonal and meridional winds over Fort Collins, Colorado (40.6°N, 105°W), binned every 2 months. The results were compared to predictions of the 2000 and 2002 versions of Global‐Scale Wave Model (GSWM00 and GSWM02). The diurnal tidal period oscillations showed a mixture of propagating and evanescent (trapped) modes, but the propagating modes dominated for most of the year. The agreement in temperature diurnal phases between observation and GSWM prediction is marginal. On the other hand, other than July‐August meridional winds, the observed diurnal phases in both wind components are in good agreement with GSWM predictions for most of the altitude range reported. The diurnal amplitude predictions of GSWM00 were reasonably close to lidar observations, while other than January‐February, the GSWM02 amplitude prediction overestimated the observations, typically by a factor of two. We also conducted comparisons on tidal perturbations in zonal wind between radar campaigns and our lidar observations. The lidar data agreed reasonably well with the MF radar data from 2000 to 2001 at nearby Platteville, Colorado (40.2°N, 104.7°W), but showed considerable differences with the data from other midlatitude stations from 1992 to 1993. The dominance of the evanescent mode in the temperature diurnal tidal oscillation during the early winter (November and December), which reached a peak value at midnight, was interesting and anomalous. By invoking the more recent data (November and December in 2003), as well as the diurnal temperature observations from December 1998, we report that the evanescent (trapped) diurnal tidal perturbations were robust and persisted from one year to the next.

Three‐field photometer observations of short‐period gravity wave intrinsic parameters in the 80 to 100 km height region

A three‐field photometer (3FP) for making observations of airglow in the Mesosphere Lower Thermosphere (MLT) region has been operated at the center of the large MF aerial array located near Adelaide (138°E, 35°S) since 1993. Observations of the 557.7 nm airglow intensity emitted by atomic oxygen (OI) at heights near 97 km and the 730.0 nm airglow intensity emitted by hydroxyl (OH) near 87 km have been made simultaneously with MF spaced antenna observations of wind velocities in the 80–100 km height region. The 3FP measures the intensity of the 557.7 nm airglow in three fields separated by about 13 km at heights near 97 km, and then the intensity of the 730 nm airglow in three fields separated by about 12 km at heights near 87 km, on a 60 s cycle. These data have been analyzed to yield gravity wave observed phase speeds and horizontal wavelengths. Simultaneous MF radar data have been analyzed to yield measurements of the neutral wind velocity in 2 km height steps in the 80–100 km height interval every 2 min, and these have been used together with the observed wave parameters to calculate intrinsic gravity wave parameters. This paper presents a very brief overview of the system, the motivation for the work, and preliminary analysis of the data from 1995 until 2000.

Planetary wave coupling in the middle atmosphere (20-90km): A CUJO study involving TOMS, MetO and MF radar data

Abstract. The atmospheric coupling due to Planetary Waves (PW) in the middle atmosphere (20-90km) has been studied using TOMS, MetO and MFR data. The wavelet and wave number analyses have been applied to all parameters at five CUJO (Canada US Japan Opportunity) locations. The CUJO network covers latitudes of 31-52° N and longitudes from 81° W to 142° E, and allows for the assessment of longitudinal variability. The results of temporal and spectral comparisons show that the total ozone (TOMS) and MetO temperatures at low stratospheric heights (typically 100mbar) have high values of correlation as well as similar spectral content. The eastward motions dominate at low stratospheric heights (100mbar), while westward motions became comparable or even stronger in the upper stratosphere (0.46mbar). During the summer months a reduction of PW activity has been observed in the stratosphere, especially at its upper heights, and in the upper middle atmosphere. The MetO (0.32mbar, 55km) and MFR winds (circa 60km) are in good general agreement, especially for the zonal component. Several examples of planetary wave activity at different atmospheric levels throughout the middle atmosphere have been presented. These examples include an eastward propagating 15-day disturbance with wave number 6, that has been observed only at low stratospheric heights; long-period (20-30 days) oscillations with wave number ~1 that have been detected in a wide height range (20-90km); and an oscillation with period near 16 days that was found only at mesospheric heights.

An alternative explanation of PMSE-like scatter in MF radar data

Abstract. There have been reports in the literature that spaced-antenna MF radars may provide a source of data on Polar Mesospheric Summer Echoes (PMSE). Even though the expected scatter from PMSE at MF frequencies is very much weaker than at VHF, the wide distribution of sites and long duration of data sets for MF radar systems could provide valuable information about the occurrence of PMSE. This paper tests whether there is any evidence of PMSE in the profiles derived using the MF radar at Rothera, Antarctica, one of the few such radars at high southern latitudes. Over a year of data during 1997/1998 has been analysed for the occurrence of persistent features around midday in the altitude range 60-95km. Criteria were chosen to test the likelihood that some of the narrow peaks in the power profiles were manifestations of electron density structures associated with PMSE. Although a small number of persistent features were seen at altitudes of 80-85km that are typically associated with PMSE, there was no seasonality in their occurrence. A detailed analysis of specific days showed that two peaks were often seen with altitude separations consistent with the vertical wavelength of the diurnal tide. Persistent features were also detected at altitudes of 70km and 90km during the winter months, thus showing a quite different seasonality to that of PMSE. An estimate of the turbulence caused by the breaking of gravity waves that have propagated up from the lower atmosphere shows that at Rothera significant energy is deposited near 80km during summer, and near 70 and 90km during winter. This seasonal variability is driven by the screening effect of stratospheric winds, and it appears that breaking gravity wave dynamics, rather than PMSE phenomena, can explain many of the localised altitude features in the MF radar data.

Remote sensing of mesospheric electric fields using MF radars

Large mesospheric electric fields can play an essential role in middle atmospheric electrodynamics (see, e.g., Goldberg, R. A., Middle Atmospheric Electrodynamics during MAP, Adv. Space Res. 10 (10) (1990) 209). The V/m electric fields of atmospheric origin can be the possible cause of large variations in the electron collision frequency at mesospheric altitudes, and this provides a unique opportunity to take measurements of electric fields in the lower ionosphere by using remote sensing instruments employing radiowave techniques. A technique has been proposed for making estimates of large mesospheric electric field intensities on the lower edge of the ionosphere by using MF radar data and the inherent effective electron collision frequency. To do this, data collected in Canada and Ukraine were utilized. The developed technique permits the changes in mesospheric electric field intensities to be derived from MF radar data in real time. The statistical analysis of data consistent with large mesospheric electric field intensities in the 60– 67 km region resulted in the following inferences. There are at least two mechanisms for the generation of large mesospheric electric fields in the mesosphere. The most likely mechanism, with a probability of 60–70%, is the summation of random fields from a large number of elementary small-scale mesospheric generators, which results in a one-parameter Rayleigh distribution of the total large mesospheric electric field intensity E with a mean value of approximately 0.7– 0.9 V/m in the 60– 67 km altitude region, or in the corresponding one-parameter exponential distribution of the intensity squared E 2 of large mesospheric electric fields. The second mechanism of unknown nature, with 5–15% probability, gives rise to the sporadic appearance of large mesospheric electric field intensities E>2.5 V/m with a mean of 4 V/m . Statistically significant seasonal differences in the averaged large mesospheric electric field parameters have not been revealed. The probability of the absence of local large mesospheric electric fields amounts to approximately 25% for Ukraine and approximately 30% for Canada. A comparison of the Ukrainian and Canadian data indicates the possible existence of a latitudinal dependence in mean large mesospheric electric field features. Hence, the large electric fields are an additional source of electron heating that must be taken into account in studying a disturbed lower ionosphere and radio wave propagation within it.

Further evidence of hemispheric differences in the MLT mean wind climatology: Simultaneous MF radar observations at Poker Flat (65°N, 147°W) and Davis (69°S, 78°E)

Results of a comparative study of the wind fields in the mesosphere and lower thermosphere over Poker Flat (65°N, 147°W) and Davis (69°S, 78°E) are presented. The study utilized the MF radar wind data collected simultaneously during the period 1999–2000. Mean winds during this period are examined to study the hemispheric features. Emphasis has been given to the climatological variations over these two high‐latitude stations. The results suggest large hemispheric differences in the mean circulation. Further, the observed mean wind characteristics are compared with results obtained from other high‐latitude stations.

The quasi 2‐day wave observed in the polar mesosphere

Using MF radar data obtained at Tromsø (69.6°N, 19.2°E) for ∼37 months between 1 November 1998 and 8 December 2001, we have examined characteristics of the quasi 2‐day wave (Q2DW) in the polar mesosphere in the height range from 70 to 91 km. The activity of the Q2DW is higher in winter months (November–February) than in summer months (May–August) over this height region. The maximum values of the amplitude are ∼25 m s−1 in winter and ∼15 m s−1 in summer. Between 70 and 82 km, the amplitude appears to maximize near winter solstice over the 3 years. The average ratio of meridional to zonal amplitudes is ∼1.1–1.2 over the height region. Thus, there is no significant preference towards either components. The variations of the periods of maximum amplitude are also examined, and periods with 45.2 and 54.9 hours occur more frequently than those with 48.0 and 51.2 hours. However, no clear seasonal trend of the variation of the period is found. In addition, the amplitude is modulated at 4–10 day rate. With simultaneous observational data from the MF radar and the EISCAT UHF radar colocated in Tromsø, we have examined whether or not the Q2DW was able to penetrate to the lower thermosphere for the period of 1–9 July 1999. It is found that the amplitude of the Q2DW with period of 51.2 hours maximized at 95 km height with values of ∼25 m s−1 in both meridional and zonal components. The Q2DW was attenuated above 95 km, but it appears to survive up to 108 km height in the meridional component. Between 85 and 95 km for the meridional component during this 8‐day interval, the Q2DW and semidiurnal tide were the strongest among the periodic components.

Airglow observations of dynamical (wind shear‐induced) instabilities over Adelaide, Australia, associated with atmospheric gravity waves

While several observations have been made in recent years of instability features in airglow images of atmospheric gravity waves (AGWs), such measurements are still rare. To date, these features are characterized by appearing to be aligned perpendicular to the AGW wave fronts. Multi‐instrument observations confirm the theoretical prediction that such features are caused by convective instabilities where the AGW‐induced temperature variation causes the total lapse rate to exceed the adiabatic lapse rate. In February 2000, airglow observations were obtained at Buckland Park, Australia, which showed instability features with a different characteristic. These images showed small‐scale (less than 10 km horizontal wavelength) features aligned parallel to the larger scale AGW wave fronts. These features were only seen in OH images, not in O2A images, indicating that they originate below 90 km altitude. Simultaneous MF radar wind data reveal the presence of a mean wind shear which, during the period of the small‐scale features, was aligned nearly in the direction of AGW propagation. In addition, the larger scale AGW approached a critical level near 90 km altitude. While the wind shear itself is not large enough to cause an instability, an analysis of the data suggests that the small‐scale features are the result of a dynamic (wind shear‐induced) instability in the 87–90 km altitude region. The instability was due to a combination of the background wind shear and the large shear induced by the passage of the larger scale AGW as it approached the critical level.

Climatology and modeling of quasi‐monochromatic atmospheric gravity waves observed over Urbana Illinois

From analyzing nine months of airglow imaging observations of atmospheric gravity waves (AGWs) over Adelaide, Australia (35°S) [Walterscheid et al., 1999] have proposed that many of the quasi‐monochromatic waves seen in the images were primarily thermally ducted. Here are presented 15 months of observations, from February 1996 to May 1997, for AGW frequency and propagation direction from a northern latitude site, Urbana Illinois (40°N). As Adelaide, Urbana is geographically distant from large orographic features. Similar to what was found in Adelaide, the AGWs seem to originate from a preferred location during the time period around summer solstice. In conjunction with these airglow data there exists MF radar data to provide winds in the 90 km region and near‐simultaneous lidar data which provide a temperature climatology. The temperature data have previously been analyzed by States and Gardner [2000]. The temperature and wind data are used here in a full wave model analysis to determine the characteristics of the wave ducting and wave reflection during the 15 month observation period. This model analysis is applied to this and another existing data set recently described by Nakamura et al. [1999]. It is shown that the existence of a thermal duct around summer solstice can plausibly account for our observations. However, the characteristics of the thermal duct and the ability of waves to be ducted is also greatly dependent on the characteristics of the background wind. A simple model is constructed to simulate the trapping of these waves by such a duct. It is suggested that the waves seen over Urbana originate no more than a few thousand kilometers from the observation site.

New possibilities for mesospheric electricity diagnostics

Abstract A possible cause of large variations in the electron collision frequency could be the effect of strong external electric fields of atmospheric origin. This provides a new opportunity to take measurements of electric fields in the lower ionosphere using remote sensing instruments employing radio wave techniques. It has been proposed the technique for making estimates of strong mesospheric electric field intensities on the lower edge of the ionosphere using MF radar data on the effective electron collision frequency, and the data has been presented. The technique described permits a real-time derivation from MF radar data of changes in mesospheric electric field intensities, and estimates of electric current densities. Our results give proof that the source of strong mesospheric electricity is very likely to be a current source.

A comparison of northern hemisphere winds using SuperDARN meteor trail and MF radar wind measurements

The main purpose of the Super Dual Auroral Radar Network (Super‐DARN) is to use paired radars to deduce the F‐region convection from Doppler measurements of backscatter seen at large ranges, typically beyond ∼900 km. Nearer to each HF radar, the nearest ranges at ∼165–400 km are dominated by meteor trail echoes. Once formed, the motion of these meteor trails is normally controlled by neutral winds in the 80–110 km altitude range. By combining the line‐of‐sight velocities from all 16 receiver beams (∼52° in azimuth) of a given SuperDARN radar, it is possible to determine the full horizontal wind vector field over the meteor trail height range. Elevation angles are also measured using an interferometer mode and as such height information can, in principle, be obtained from the combined range and elevation angle data. A comparison with neutral wind measurements from a colocated (Saskatoon, Canada) MF wind radar indicates good agreement between the two radar systems at heights of ∼95 km. Based on these detailed comparisons, a simple common method for determining two‐dimensional winds for all SuperDARN radars, which have extensive longitudinal coverage, was developed. Comparisons with other systems used for dynamical studies of tides and planetary waves are desirable and prove to be essential to obtain a good SuperDARN neutral wind motion analysis. The MF radars at Saskatoon and Tromsø, Norway, are located near the western and eastern ends of the Northern Hemisphere network of six SuperDARN radars. Comparisons between the two types of radars for two seasonal intervals (September and December) show that the SuperDARN radars provide good longitudinal coverage of tides in support of the more detailed MF radar data. The two systems complement each other effectively.

On the radar estimation of turbulence parameters in a stably stratified atmosphere

Four estimators of the rate of dissipation of turbulent energy based on the velocity structure function, rms turbulent velocities, Brunt‐Väisälä frequencies, and ground diffraction pattern fading rates are discussed and compared using Arecibo Initiative on the Dynamics of the Atmosphere MF radar data in both the imaging Doppler interferometry (IDI) and spaced antenna modes. A consistent set of empirical equations is developed which define and describe the relationships between the turbulent velocity, the Brunt‐Väisälä frequency, the buoyancy length scale, the rate of dissipation of turbulent energy, the eddy diffusivity, and the time constant of the gravity wave generated, intermittent, decaying, coherent structures responsible for the scatterers detected by the IDI technique. It should be noted that the constants of proportionality are significantly different from the currently accepted values.

Coordinated radar observations of atmospheric diurnal tides in equatorial regions

The long-term behavior of atmospheric tides in the mesosphere and lower thermosphere has been observed with the meteor wind radar (MWR) in Jakarta, Indonesia (6°S, 107°E) from November 1992 to August 1997. The amplitudes and phases of the diurnal tides show systematic seasonal variations, particularly distinct in the meridional component. In addition, substantial interannual variability is evident, characterized by a biennial periodicity of tidal parameters, and considerably small tidal amplitudes exclusively seen in 1996. The MWR results are compared with the Global Scale Wave Model (GSWM) as well as MF radar data collected in two equatorial sites in Pontianak (0.03°N, 109°E) and Christmas Island (2°N, 158°W) for November 1995–July 1997 and January 1996–October 1997, respectively. Comparison studies of these radar data have revealed the detailed latitudinal structure of the diurnal tide near the equator. The GSWM has successfully described the general characteristics of the radar results, although some discrepancies are recognized. In 1996 when radar data are available at all the three sites, the monthly mean values of tidal amplitudes at 90 km agreed very well between Jakarta and Pontianak, while significant discrepancy was found for Christmas Island, suggesting the existence of geographical effects such as non-migrating tides.

Observational evidence of quasi two‐day/gravity wave interaction using MF Radar

The gravity wave/quasi two‐day wave interaction is an example of gravity wave/large‐scale flow interaction, a subject of great interest but insufficient understanding. Here we present evidence, from MF radar data, for the quasi two‐day wave modulation of gravity wave activity in the summer mesosphere over Urbana, Illinois (40° 10′ 10″ N, 88° 09′ 36″ W). A composite analysis of two‐day wave events, identified using the meridional winds at 84 km, is performed on the four‐hour mean winds and four‐hour standard deviations about those means, the latter being representative of gravity wave activity. Our results show that quasi two‐day variations in the winds modulate gravity wave activity at higher altitudes.

On the reality of upper mesospheric/lower thermospheric turbulent “eddies”

The structure of atmospheric turbulence and its relationship to the refractive index discontinuities responsible for the scattering of radio waves are discussed. Emphasis is placed more on the nature of the intermittent scatterers observed at upper mesospheric/lower thermospheric altitudes than on volume scattering. The preferred model is of transient patches composed of vortex strings. An overview of the methods used to estimate the rate of dissipation of turbulent energy using MF radar data which emphasizes the advantages of imaging Doppler interferometry is presented, together with a review of pertinent laboratory investigations of coherent structures. An attempt is made to remove the contamination by gravity waves from imaging Doppler interferometry fluctuating velocity data. Emphasis is given to the fact that all radar measurements of turbulent intensity to date are upper estimates, not only because of the presence of gravity wave fluctuations contaminating the data, but also because the turbulence itself is not stationary and homogeneous but intermittent in both space and time. The intermittent nature of the turbulence, in which the refractive index discontinuities responsible for the radar backscatter are associated with decaying, homogeneous turbulent coherent structures, is in contrast to the theory of volume scattering, which assumes the radar pulse volume to be partially filled with stationary, homogeneous turbulence.

Short‐period fluctuations of the diurnal tide observed with low‐latitude MF and meteor radars during CADRE: Evidence for gravity wave/tidal interactions

MF and meteor radar data from four equatorial and subtropical sites (Hawaii, Christmas Island, Jakarta, and Adelaide) are used to examine diurnal tide amplitude and phase variability at mesosphere and lower thermosphere altitudes. All sites exhibit significant seasonal variability, with the largest amplitude fluctuations occurring at Hawaii and Adelaide. Shorter‐term variability is found to occur primarily on timescales of ∼5 to 30 days. Amplitude and phase fluctuations are well correlated among different sites on occasion, but in general, the amplitude and phase coherences are low and suggest significant local influences on the tidal structures. The temporal behavior of height variations of the diurnal tide amplitude and phase is also examined. Cross correlations and cross spectra of these tidal parameters, especially between the amplitude and phase, are examined closely. The tendency for phase maxima to lead amplitude maxima is consistent with tidal modulation of gravity wave propagation and momentum fluxes, with a corresponding feedback by the gravity wave momentum flux divergences on the observed tidal structures. These results substantially extend previous more limited studies of gravity wave/tidal interactions and provide a statistical basis for the possible importance of this interaction and its influences on the diurnal tidal structure.

A new approach to MF radar interferometry for estimating mean winds and momentum flux

New techniques are applied to measured Doppler velocity and angle of arrival to estimate horizontal wind vectors, variances, and momentum fluxes, from MF radar data. The approach used to estimate mean winds was first introduced as “time domain interferometry” (TDI) by Vandepeer and Reid [1995]. In the present paper, the algorithm is refined and used with data from the Urbana MF radar, which employs a single vertical antenna beam, to obtain a monthly mean wind climatology which is compared with the results from conventional spaced antenna full correlation analysis. The comparison validates the scattering model used in the development of the TDI technique and highlights instrumental and processing biases that differ between the two techniques. An extension of the TDI method that can provide estimates of the Reynolds stress tensor associated with propagating gravity waves is also proposed, and some preliminary results are presented.