Instruments:rpk

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Poker Flat, Alaska, USA MF Radar

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Acknowledgments

The Poker Flat MF radar is operated by the National Institute of Information and Communications Technology, Japan, with collaboration with the Geophysical Institute of the University of Alaska at Fairbanks. It contributes data as part of the joint TIMED-CEDAR program of the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF).

Instrument/Model Description

The Poker Flat, Alaska (65.126 N, 147.495 W; alt 208 m) 2.43 MHz MF radar has been in operation since 1998. On day 359 of 2001 at 89 km altitude, the apex magnetic coordinates were (65.4, -95.5) degrees. The magnetic inclination and declination angles were 77.4 deg and 24.1 deg. The magnetic local time at 0 Universal Time (UT) is about 1233 MLT. The solar local time (SLT) is UT minus 9 hours and 50 minutes (-147.495/15.=-9.833).

The original data files are 30 min averages of the zonal, meridional and 'vertical' velocity in UT. The UT time is the midpoint UT, and is also listed as the midpoint SLT. Samples are taken every 3, 4 or 5 min, so 6 to 10 samples can be had between UT 23:45:00 and UT 00:15:00. To improve data quality, 'median screening' is applied inside a 1-h bin. If data points lie outside a threshold standard deviation (code 4152) of usually 1.5 inside a 1-hr bin, they are discarded. So the low qulity (jamped) data are rejected and then the remaining data are averaged over 30-min bins with a threshold of usually 30% (code 4151). The number of points used in each direction are in codes 422, 423 and 424.

The 'vertical' velocities (code 1432, 'contaminated neutral vertical geographic wind (+up)') are from the beam in the vertical direction. The antenna array in a triangle has a different beam width for different azimuth direction, resulting in beam widths about 20-30 deg wide. Hence, the 'vertical' velocity will be contaminated by horizontal wind times the sine of 10 to 15 degrees (.17 to .26). Since the horizontal winds are stronger than the vertical winds, even the sign could be incorrect. The standard deviations of the 'vertical' winds are also larger than the average values.

The MF operating frequency is 1.95550 MHz, with a peak transmitter power of 50 kW. The radar operates as a spaced-antenna system (Vincent, 1986), relying on coherent echo signals from middle atmosphere ionization. The inter-pulse period is 12.5 millisec during the day and 25 millisec during the night. There are 80 coherent integrations during the day and 40 at night, using 240 samples in the full correlation analysis (FCA) of Briggs [1984] with built-in rejection criteria. [ie, if want 240 sec or 4 min integration during day and night, then 12.5x10-3sec * 80 integ * 240 samples = 240 sec and 25x10-3sec * 40 integ * 240 samples = 240 sec.]

Data sampling is done every 2 km usually between 60-98 km for Yamagawa (60-108 km for Wakkanai, 44-108 km for Poker Flat). The height range of wind velocity data is variable accoding to atmospheric and radio conditions and is usually about 70-90 km at Yamagawa and Wakkanai during the day and 80-90 km at night (60-90 km/70-90 km for Poker Flat for day/night conditions).

The pulse width is 48 microsec (27 microsec before September 1996), giving a height resolution of approx. 7.2 km (4.1 km) assuming a simple rectangular wave pulse. For the 48-microsec case, the range of heights illuminated by the wave pulse = velocity of light * pulse-width / 2 = 3x10**8 m/s * 48x10-6s / 2 = 7.2 km. However, neutral velocities are given every 2 km.

Starting in 2001, the data are also contributed to the joint TIMED-CEDAR program of the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF). The original hourly velocities are converted to harmonic analyses in UT over sliding 4-day intervals. The Mesosphere-Lower Thermosphere Radars (MLTR) organized for the TIMED-CEDAR program provide horizontal and sometimes 'vertical' neutral winds to the processing center at the University of Colorado. Summary plots from several types of MLTRs in the TIMED-CEDAR program and references for the instruments, analyses using the radars, and comparisons with other satellite or ground-based instruments can be found here

The harmonic analyses are also available at that site, or from the University of Colorado at:
http://sisko.colorado.edu/TIMED/data/MLTR/

References

Briggs, B. H., The analysis of spaced sensor records by correlation techniques, MAP Handbook, Vol. 13, 166-186, 1984.
Murayama, Y., K. Igarashi, D. Rice, B. Watkins, R. Collins, K. Mizutani, Y. Saito and S. Kainuma, Medium frequency radars in Japan and Alaska, for upper atmosphere observations, IEICE Trans., E83-B, 1996-2003, 2000. (http://search.ieice.org/2000/pdf/e83-b_9_1996.pdf)
Vincent, R. A., Hardware requirements: A new generation partial reflection radar for studies of the equatorial mesosphere, MAP Handbook, Vol. 20, p 85, 1986.

Summary Plots of 30-min Winds for TIMED from Poker Flat, Alaska, USA MF Radar

The 'vertical' velocity which is corrupted by horizontal winds due to the large beam width is available, but not plotted except for a sample plot in the beginning.

-Revised 01 Sep 2004 by Barbara Emery