Those DARN Radars: New Directions for the Super Dual Auroral Radar Network

Transcription

1 Those DARN Radars: New Directions for the Super Dual Auroral Radar Network Joseph B. H. Baker 1, J. M. Ruohoniemi 1, S. G. Shepherd 2, K. A. McWilliams 3, R. A. Greenwald 1, W. A. Bristow 4 1 Bradley Department of Electrical and Computer Engineering, Virginia Tech 2 Thayer School of Engineering, Dartmouth College 3 Department of Physics and Engineering Physics, University of Saskatchewan 4 Geophysical Institute, University of Alaska With Acknowledgements to our International SuperDARN Collaborators

2 Presentation Outline What is SuperDARN? Recent Developments: New Antenna Design PolarDARN and StormDARN Collaborations with NASA THEMIS Future Directions

3 What is SuperDARN? The Super Dual Auroral Radar Network (SuperDARN) of high-frequency (HF) radars was developed to study ionospheric convection at auroral latitudes. The principle backscatter targets are decameter-scale plasma irregularities. At the present time there are 14 radars in the northern hemisphere and 7 radars in the southern hemisphere. Each SuperDARN radar has the following characteristics: Transmits and receives between 9-18 MHz Uses electronic phasing to steer in 16 (or more) look directions Uses multipulse sequences to determine range and Doppler information Maximum range is km; range resolution is typically 45 km Operates continuously with a typical temporal resolution of 1-2 minutes All SuperDARN radars produce identical data products that are routinely combined to produce hemispheric characterizations of ionospheric convection.

4 SuperDARN PI Institutions Johns Hopkins University Applied Physics Laboratory (1983) British Antarctic Survey (1988) University of Saskatchewan, Canada (1993) National Center for Scientific Research, France (1994) National Institute for Polar Research, Japan (1995) University of Leicester, England (1995) University of KwaZulu-Natal, South Africa (1997) University of Alaska (2000) Communications Research Laboratory, Japan (2001) La Trobe University, Australia (2001) Nagoya University, Japan (2006) Virginia Tech (2008)

5 Northern Hemisphere Radars King Salmon, AK (Japan) Saskatoon, Sask. (Canada) Stokkseyri, Iceland (France) Kodiak, AK (USA) Kapuskasing, Ont. (USA) Goose Bay, Lab. (USA) Pykkvibaer, Iceland (UK) Prince George, B.C. (Canada) Hankasalmi, Finland (UK)

6 SuperDARN Achievements Hemispheric structure and dynamics of ionospheric convection. Mesoscale signatures of magnetosphere-ionosphere coupling: Convection vortices associated with field-aligned currents. Ionospheric flow bursts associated with dayside reconnection events or FTEs. Convection associated with auroral activations (e.g. substorms). Inter-hemispheric (i.e. north-south) conjugacy of ionospheric convection. Ionospheric irregularities and high latitude plasma structures (i.e. patches). Electromagnetic waves: MHD, ULF, Magnetic Field Line Resonances. Neutral atmosphere: Gravity waves, mesospheric winds, planetary waves. More generally, SuperDARN convection patterns have been widely used to aid the interpretation of localized features identified in other ground and space-based datasets.

7 Hemispheric Convection Pattern

8 New Antenna Design First generation SuperDARN radars used Sabre log-periodic antennas. Sabre antennas are sturdy and reliable but they have become an increasingly larger portion of the overall cost of building a SuperDARN radar. In 2004 a considerable modeling effort was directed toward identifying a simple and inexpensive alternative. The result is a twin-terminated folded dipole antenna: Easy to construct. Significant reduction in cost.

9 New SuperDARN Antenna Front View Side View The antennas are strung between 55-foot traffic poles using Kevlar cable (dashed lines). The feed point is a 25:1 balun at the center of a plate mounted on the pole at 30 feet. The termination is in two 100-ohm resistors at each end of the plate. Behind the antennas is a corner reflector constructed from 24 wires running the length of the array.

10 Wallops Radar (May 2005)

11 Antenna Performance VSWR Values: Blackstone Main Array 4 3 VSWR Frequency (MHz) Ant 1 Ant 2 Ant 3 Ant 4 Ant 5 Ant 6 Ant 7 Ant 8 Ant 9 Ant 10 Ant 11 Ant 12 Ant 13 Ant 14 Ant 15 Ant 16 Model Wallops

12 PolarDARN: High Latitude SuperDARN Two polar cap radars operational since May 2006 (Rankin Inlet) and November 2007 (Inuvik). PI: Jean-Pierre St Maurice (University of Saskatchewan). The PolarDARN radars have been obtaining better scatter statistics than other SuperDARN radars during the quiet solar wind conditions at the end of Solar Cycle 23. For more information see PolarDARN investigations of the high latitude ionosphere by St Maurice et al., at 16:00 UT this afternoon (G05b.7).

13 StormDARN: Mid-Latitude SuperDARN Hokkaido The first generation SuperDARN radars were sited near 60 degrees magnetic latitude and have been very successful at monitoring ionospheric convection during weak to moderate geomagnetic activity. Blackstone Wallops However, during magnetic storms the rate of SuperDARN data capture is reduced: (1) Equatorward motion of aurora (2) Increased HF absorption To overcome these shortcomings it was decided to build a second chain of radars at middle latitudes: Wallops Island, VA (2005) Hokkaido, Japan (2006) Blackstone, VA (2008)

14 Wallops Measurements: SAPS/SAIDs Beam UT June 12,2005 June 13, 2005 Oksavik et al., [2006] Two-Dimensional Image of Sub Auroral Ion Drifts (SAID) within the Sub Auroral Polarization Stream (SAPS).

15 Wallops Measurements: Impact on Statistical Patterns Φ=61kV Φ=76kV Disturbed Conditions (Kp > 3): Two-cell convection pattern expands equatorward of 60 degrees. Average cross polar potential increased by 25%. Φ=40kV Φ=36kV Quiet Conditions (Kp < 3): The two-cell convection pattern at high latitudes is fed from lower latitudes on the evening side and drained on the morning side. Baker et al., [2007]

16 Hokkaido Measurements: TIDs Daytime TIDs (Sea Scatter) Nighttime TIDs (Ionospheric Scatter) The second mid-latitude SuperDARN radar became operational at Rikubetsu, Hokkaido, in December, The Hokkaido radar is being used to monitor the equatorward propagation of Traveling Ionospheric Disturbances (TIDs) generated at higher latitudes. By combining Hokkaido radar data with ground-based 630nm all-sky imaging and GPS TEC measurements it is possible to continuously monitor the propagation of wave fronts over a scale length of 6000km. Figures courtesy of T. Ogawa, STE Lab, Nagoya University

17 The Blackstone Radar The third mid-latitude SuperDARN radar became operational at Blackstone, VA, on February 2 nd, The Blackstone radar is a collaboration between: Virginia Tech Johns Hopkins University Applied Physics Laboratory University of Leicester Construction schedule for Blackstone was accelerated so that the radar would be taking measurements during the first NASA THEMIS tail conjunctions.

18 The NASA THEMIS Mission The NASA THEMIS (Time History of Events and Macroscale Interactions during Sustorms) mission was designed to unambiguously measure the relative timing of events in the magnetotail during the onset of the expansion phase of magnetospheric substorms. Periodically, the 5 spacecraft come into alignment along the Sun-Earth line under new Moon conditions so that the relative timing of mid-tail and near-tail processes can be resolved. THEMIS also has a robust ground-based component of All-sky Imagers and magnetometers that are being used to identify the onset time and location within the nightside ionosphere. The Blackstone radar is ideally located to contribute useful data for THEMIS events.

19 SuperDARN THEMIS Mode During THEMIS tail conjunctions SuperDARN radars are running a special THEMIS mode to increase temporal resolution during substorms: Dwell time reduced from 7 to 4 seconds. The radar returns to a designated campingbeam between each successive beam. The THEMIS mode simultaneously provides: Hemispheric spatial coverage every 2 mins. Higher temporal resolution on one camped beam per radar (8 secs). THEMIS mode camping beams (Blue) The THEMIS mode provides an increased capability to measure ULF waves.

20 THEMIS Substorm: Feb 22 nd 2008 Beam-8: normal scan data (2-minutes) Beam-7: camping beam data (8-second) 0430 UT 0440 UT 0450 UT Substorm expansion phase onset at approximately 0437 UT on February 22 nd 2008: THEMIS spacecraft measure two bursts of Earthward convection in the tail. Ground-based magnetometers measure the onset of Pi2 oscillations. Blackstone Radar Measurements: Pi2 oscillations measured on camped beam-7. Neighboring beam-8 sees no evidence of oscillations. These measurements were obtained near the plasmapause (Alfven Waves?).

21 Future Development Plans Proposal to build 8 new radars at middle latitudes has been submitted to the NSF MSI opportunity. Partners: Virginia Tech, JHU/APL, University of Alaska, Dartmouth College.

22 Other Development Plans Discussions are under way for: Second mid-latitude radar at Hokkaido. Third PolarDARN radar in Greenland. Several (6) radars at mid- and high latitudes in Eastern Europe. An Australian mid-latitude radar. A South African mid-latitude radar. Radars under Development: US Antarctic radar at McMurdo. A Chinese radar at Zhongshan, Antarctica. Two radars at the French-Italian base at Dome C, Antarctica.

23 Summary SuperDARN is an international collaborative network of HF radars that is used to study the Earth s upper atmosphere, ionosphere, and connection into Geospace. The primary data product is Doppler measurements of ionospheric convection. Much of the success of SuperDARN can be attributed to a unique capability for specifying a hemispheric state of geomagnetic activity via ionospheric convection patterns. The development of a new low-cost antenna design has jump started construction of a second generation of SuperDARN radars: (1) PolarDARN radars (Rankin Inlet and Inuvik) are providing new information about convection in the highest latitudes of the polar cap (see G05b.7 this afternoon). (2) StormDARN radars (Wallops, Hokkaido and Blackstone) are providing new information about convection at middle latitudes during quiet and disturbed conditions. During NASA THEMIS conjunctions SuperDARN radars are running a special high temporal resolution mode that is providing new information about ULF waves during substorms. Plans to expand SuperDARN include several initiatives to build new radars at high and middle latitudes in both hemispheres. New partners include the Chinese and eastern Europeans. A proposal to build 8 mid-latitude radars across the North American sector is under review.

24 SuperDARN-related Acronyms Pre-SuperDARN: STARE (Scandinavian Twin Auroral Radar Experiment) SABRE (Sweden and Britain Radar Experiment) BARS (Bistatic Auroral Radar System) SAFARI (Scandinavian and French Auroral Radar Investigation) SHERPA (Systeme HF d Etudes Radar Polaires et Aurorales) DARN (Dual Auroral Radar Network) SuperDARN: PACE (Polar Anglo-American Conjugate Experiment) CUTLASS (Collaborative UK Twin-located Auroral Sounding System) SHARE (Southern Hemisphere Auroral Radar Experiment) TIGER (Tasman International Geospace Environment Radars) PolarDARN StormDARN

25 Four TTFD Antennas with Corner Reflector (26 Wires to 58 ) Element height=32 Pole Height=56 14 MHz 75 ohm loads 3.4 db 9 MHz, MHz Selected Design for Blackstone

26 Selected Design for Blackstone

27 SuperDARN Multi-Pulse Sequences A Original Goose Bay sequence τ = 2.4 ms B SuperDARN sequence τ = 2.4 ms C Experimental sequence 2002 τ = 1.2 ms Sequence A has all lags through 16; Lag 13 is repeated and not used. Sequence B uses first pulse to get unambiguous power profile. First missing lag is 16. Sequence C is Sequence B with τ set to 1.2 ms and additional pulse at beginning to provide unambiguous power profile. First missing lag is 16.

28 Access to SuperDARN Data Products All SuperDARN data for both hemispheres is available through the JHU/APL SuperDARN webpage: Registered users can download: Plots Data files Plotting software There are also real-time displays for the northern hemisphere radars.

29 Range-Time Plot: Kapuskasing (Beam 4) UT on January 11, 2001

30 Doppler Velocity Map: Kapuskasing January 11, :10:00 01:11:47 UT

31 Average Convection Patterns Binned by IMF Orientation in Y-Z GSM Plane The dominant driver for high latitude convection is merging between the geomagnetic field and the interplanetary magnetic field (IMF) in the solar wind. Two-cell convection is strongest when the IMF is southward (Z-component negative). When the IMF is northward the convection is much weaker and multiple cells develop. When the IMF points toward dusk (dawn) the dusk (dawn) cell is larger. Ruohoniemi and Greenwald, 2005

32 Multi-Radar Doppler Measurements SUN

33 Substorm Event : February 22 nd 2008 Small enhancement in AL index at approximately UT is the first sign of geomagnetic activity on this particular day. At ~0437 UT the THEMIS spacecraft measured two bursts of earthward convection.

34 Substorm Event: Ground Magnetometers Cross-phase calculations of the magnetometer data estimate the Plasmapause is located at L- shell ~ (54-58Λ) (Courtesy of Zoe Kale)

35 Substorm Onset Event SWNO Ground Mag Bx By Bz THEMIS-D ESA (-10.9,2.3,-3.4) Re Vx THEMIS-E ESA (-10.1,3.1,-3.5) Re Vy Vz THEMIS-D FGM Bx By THEMIS-E FGM Bz 0400UT 0600 UT

36 Substorm Event : Shear Alfven Waves? Bx Pinawa Magnetometer By Bz Blackstone Beam UT 0450 UT The similarity between features of the oscillations seen by the Blackstone radar and the ground magnetometers suggest that the oscillations may be associated with shear Alfven waves.