Comparison of D-region Doppler drift winds measured by the SuperDARN Finland HF radar over an annual cycle using the Kiruna VHF meteor radar

Abstract

Abstract. The SuperDARN chain of oblique HF radars has provided an opportunity to generate a unique climatology of horizontal winds near the mesopause at a number of high latitude locations, via the Doppler shifted echoes from sources of ionisation in the D-region. Ablating meteor trails form the bulk of these targets, but other phenomena also contribute to the observations. Due to the poor vertical resolution of the radars, care must be taken to reduce possible biases from sporadic-E layers and Polar Mesospheric Summer echoes that can affect the effective altitude of the geophysical parameters being observed. Second, there is strong theoretical and observational evidence to suggest that the radars are picking up echoes from the backward looking direction that will tend to reduce the measured wind strengths. The effect is strongly frequency dependent, resulting in a 20% reduction at 12 MHz and a 50% reduction at 10 MHz.A comparison of the climatologies observed by the Super-DARN Finland radar between September 1999 and September 2000 and that obtained from the adjacent VHF meteor radar located at Kiruna is also presented. The agreement between the two instruments was very good. Extending the analysis to the SuperDARN Iceland East radar indicated that the principles outlined above could be applied successfully to the rest of the SuperDARN network.

Finland HF and Esrange MST radar observations of polar mesosphere summer echoes

“…7 where the following is observed: (1) powers decrease with increasing frequency, (2) velocities are mostly within ± 20 m/s, (3) widths are less than 60 m s −1 , which is characteristic of the widths of meteor echoes to derive neutral winds (e.g. Arnold et al, 2001Arnold et al, , 2003, when the power is strong, (4) the power, velocity and width fluctuate with periods of several to 20 min and (5) no particular correlation among three parameters exists. It is noted that the echoes are often contaminated with sporadic meteor echoes so that the short period fluctuations (less than, say, 5 min) of the three parameters do not always represent the PMSE-related fluctuations.…”

“…At 8 MHz, the sensitivity maximizes at an elevation angle (EL) of 35 • whereas, at 20 MHz, this EL decreases to 15 • . This means that the Finland HF radar has a maximum gain at about EL = 33 • at 9 MHz and EL = 23 • at 15 MHz (Arnold et al, 2003). The sensitivity at EL's larger than 60 • is believed to Finland Echo Power (9,11,13,15 MHz) August 8, 1999…”

“…Also, the echoes beyond 140 km in the 13 and 15 MHz plots are meteor echoes. It is noted that the interferometer is accurate to a few degrees, meaning that, for a range resolution of 15 km, it is impossible to determine echo altitude with a resolution better than about 10 km (Arnold et al, 2003). EL's shown in Fig.…”

“…Beam 5 looks toward Esrange, about 650 km from Hankasalmi, where the ESRAD radar is located. On 8 August 1999, the Finland radar was operated in a special mode to investigate detailed meteor echo characteristics and neutral winds (Arnold et al, 2003); that is, the radar emitted sequentially four frequencies close to 9, 11, 13 and 15 MHz. At each frequency, the radar beam was scanned from beam 15 to 0 for about 35 s with a range resolution of 15 km and the first range gate of 60 km.…”

“…The Super Dual Auroral Radar Network (SuperDARN) HF radars at northern and southern high latitudes use oblique multiple beams to investigate the high latitude E-and F-region ionosphere (Greenwald Correspondence to: T. Ogawa (ogawa@stelab.nagoya-u.ac.jp) et al, 1995). These radars are also capable of measuring neutral winds in the upper mesosphere and lower thermosphere (80-100 km) by detecting meteor echoes (Hall et al, 1997;Jenkins and Jarvis, 1999;Arnold et al, 2003).…”