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|1375 - RPK - Poker Flat Alaska MF Radar|
Instrument Type: Instrument > Radar > MiddleAtmosphereRadar > MFRadar
Observation Site: RPK - Poker Flat Alaska MF Radar
Instrument Page: RPKDescription:
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  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.