PHYSICS AND ENGINEERING PHYSICS

PolarDARN

The New SuperDARN Polar Cap radar pair

George Sofko, Jean-Pierre St.Maurice, Sasha Koustov, Kathryn McWilliams and Glenn Hussey

AMISR Workshop, Pacific Grove, Oct. 12-14, 2006

University of University of SaskatchewanSaskatchewan

The Driven Magnetosphere The magnetosphere is separated from the sheath by a boundary layer consisting of the LLBL and the “magnetotail boundary layer”. This boundary region separates open and closed flux. CONVECTION IS MOST LIKELY DRIVEN BY PROCESSES IN THIS BOUNDARY REGION.

The PolarDARN echoes show VERY DYNAMIC, CONTINUOUS activity at MLAT ~78 – 83° , i.e. near the nominal edge of the polar cap. This is the region that should map to the LLBL and magnetotail bdy layer.

University of University of SaskatchewanSaskatchewan

Crooker: Imbedded open flux tubes and “viscous interaction” in the LLBL (Physics of Magnetic Flux

Ropes, AGU Monograph 58)

The open flux tubes resulting from successive FTEs are driven antisunward. The trapped closed flux between the open flux regions is therefore also pulled antisunward. Crooker claimed that this explained “viscous” driving. In effect, RECONNECTION in the form of successive FTE events explains everything!!

University of University of SaskatchewanSaskatchewan

Southward IMF – merging a subsolar locations

IMF soutward & toward dawn – antiparallel merging will occur on dawnside

IMF northward and dawnward

View from the sun

Ionospheric footprints – shading is open polar cap

Crooker, N. U. JGR, July 1990, Figs. 3, 4

University of University of SaskatchewanSaskatchewan

SuperDARN Lobe Cell observations in the PolarCap - November 11, 1998

Huang et al. JGR, Dec. 2000. View of pattern at high latitudes using SD radars from T (Saskatoon) eastward to F (Finland). The two lobe cells are seen virtually in their entirety, a measurement that is unique to the SuperDARN radars.

University of University of SaskatchewanSaskatchewan

PolarDARN Coverage at High Latitudes

The PolarDARN radars at Rankin and Inuvik would complement the AMISR ISRs at Poker Flat and Resolute and the Sondre Stromfjord ISR. The other SuperDARN radars at Kodiak, Prince George, Saskatoon and Kapuskasing extend the coverage down into the auroral zone.

University of University of SaskatchewanSaskatchewan

Main “new” feature – wire antennaThe main array of 16 twin-terminated double-folded dipole wire antennas is shown . A special 21-wire reflecting fence suppresses backlobe echoes. This antenna saves over $200 k.

University of University of SaskatchewanSaskatchewan

Interferometer array with reflecting fence

The interferometer array has only 4 antennas, and is used to measure the elevation angle of received rays. The 21-wire reflecting fence is clearly seen.

University of University of SaskatchewanSaskatchewan

The PolarDARN-AMISR Geometry

PolarDARN (& SuperDARN) and AMISR will form a powerful combination of coherent and incoherent scatter radars to study “polar cap” science and high-latitude space weather.

University of University of SaskatchewanSaskatchewan

Sample of Rankin Observations• The Rankin radar has been operating since May

11/06, during the minimum of Solar Cycle 23. As such, HF propagation conditions are at their worst (they are best at solar maximum).

• Scatter has been virtually continuous, 24 hours a day, near the equatorward edge of the polar cap/poleward edge of the auroral zone. The boundary between these regions is the ionospheric projection of the LLBL.

• Summer conditions have prevailed during the first 4 months, with full sunlight in the polar cap region.

• Beam 7 is pointed toward the AACGM pole, Beam 5 toward Resolute Bay (range is ~1360 km for scatter from altitude 200 km).

University of University of SaskatchewanSaskatchewan

Raytracing: Solar min summer at noon (~18 UT) for 12 MHz

Uses only the IRI Ne profile for Rankin Inlet instead of latitudinally varying Ne

Hatched regions are within 2 deg of perfect aspect sensitivity. Echo pattern that is predicted: (a) F-region echoes from near range (900-1700 km) (b) ground-scatter echoes (2100-2500 km); (c) no F-region echoes from central polar cap (1700-3200 km).

University of University of SaskatchewanSaskatchewan

ACE SWEPAM data for May 16,17,18, 2006

Note the very quiet conditions on May 16. In spite of this, the radar echo activity was strong and dynamic.

On May 17, there was an increase in Bx and By starting about 12 UT, then a density increase starting about 17 UT. The latter has a strong effect - the radar echoes spread to over 3000 km in range!

University of University of SaskatchewanSaskatchewan

May 16/06 –first Rankin full day – one of the quietest days of Solar Cycle 23

In spite of the very quiet IMF and solar wind conditions (low density, low speed), there were good echoes at the low-lat side of the polar cap, near and south of Resolute Bay (range ~1360 km).

University of University of SaskatchewanSaskatchewan

One-minute scan near Mag noon – “throat” flow is prominent

Note the 3 features predicted by the raytracing: (1) F-region echoes at near ranges from about 1000 – 1500 km (Res Bay ~ 1360 km); (2) ground scatter poleward of the ionospheric echoes; (3) not much over the central polar cap.

University of University of SaskatchewanSaskatchewan

Pc5 Pulsations near dusk? Is the quiet polar cap mostly on closed field lines?

Over the 5-minute period 1615-1620 MLT, the flow changes from toward to away from the radar over the echo region, which extends north of Rankin Inlet.

University of University of SaskatchewanSaskatchewan

A little later, more Pc5-like oscillations

Over a 9- minute period 1650-1659 MLT, the flow changes from away to toward the radar. It would seem that, if the Pc5 is on closed field lines, they extend to at least 85° MLAT.

University of University of SaskatchewanSaskatchewan

May 17/06 – Activity increases about 18 UT, leading to extension of echo range

Echoes on radar beam 0 (western beam) are shown. At about 18 UT (11 MLT ) when the solar wind density increased, the echo region expanded to nearly 3000 km!

University of University of SaskatchewanSaskatchewan

May 17/06 - One-minute scan at 1950 UT=>Echoes on west beams near equatorward edge of polar cap

The echoes are seen coming antisunward all the way from the European sector. Those echoes hug the equatorward part of the polar cap /LLBL /poleward part of auroral oval.

NOTE: There are few echoes seen over the CENTRAL polar cap. This simply could be because propagation is not getting there.

University of University of SaskatchewanSaskatchewan

Rankin Inlet – July 12/06 / 0–12 UT

Note the intense flows (bright blue) toward the radar (out of the polar cap) just after magnetic midnght (MLT = UT - 7). This should be near the reconnection region.

University of University of SaskatchewanSaskatchewan

Rankin Inlet July 12/06 12-24 UTNote the intense flows at ~16 UT (0930 MLT) away from the radar - normally these would be seen near noon MLT (19 UT). Has the throat been displaced to the AM side?

University of University of SaskatchewanSaskatchewan

Gravity waves – Will we see a PolarDARN or AMISR signature corresponding to

SuperDARN observations?

Joule heating in the auroral zone (ranges ~ 2300 km) leads to AGWs seen later at lower latitudes near range 1200 km. Will we see AGWs at higher latitudes in the polar cap too?

University of University of SaskatchewanSaskatchewan

Gravity Wave Pairs generated by Joule heating in the auroral zone – Sofko and Huang, JGR, Feb. 2000

Top panel shows the velocity in scatter bursts in the auroral zone. These are associated with enhanced electric fields that cause Joule heating. From each burst, a pair of gravity waves propagate south.

University of University of SaskatchewanSaskatchewan

Cycling dense ionospheric plasma through the polar cap – plumes & SED events

Elphic, Weiss, Thomsen, McComas & Moldwin, GRL, 2189, 1996 (Aug. 15) .

Evolution of original plasmaspheric material (on corotating streamlines) to the PM merging cell when the plasmapause suddenly moves inward. The premidnight “filled” flux tubes suddenly are on the PM merging cell streamlines and flow westward => SED, plume formation

University of University of SaskatchewanSaskatchewan

SED event – Foster et al. GRL 2002

Here the plasmapause has moved far inward and the filled flux tubes that have been displaced to just beyond the plasmapause start to drift sunward and poleward in the PM convection cell, forming a “plume” outlined by the red lines.

University of University of SaskatchewanSaskatchewan

SED flux tubes move to noon merging region => then empty across the polar cap

Sequence of stages of convection of the original plasmaspheric flux tube as it it recycles through the PM merging cell. Merging takes place near noon, and then the flux tube returns over the polar cap, where it rapidly empties out. Originally (1) the density was about 100 cm-3, but after merging (2) it decreases across the polar cap (3,4,5), going down to ~1 cm-3 in CPS (6)

(Elphic, Thomsen, Borovsky, GRL, Feb.15, 1997)

University of University of SaskatchewanSaskatchewan

Use of PolarDARN & AMISR to detect SED remnants in Polar Cap

• After the SED region (plasmaspheric drainage plume) goes through the noon merging region and then across the polar cap, it should readily be detected by AMISR and PolarDARN.

• There also will likely be polar patches seen as the SED remnant crosses the polar cap (Su, Thomsen, Borovsky, Foster GRL, Jan. 2001)

University of University of SaskatchewanSaskatchewan

Main Conclusions – First Results

• Convection near the equatorward edge of the polar cap (or poleward edge of the auroral oval) is DYNAMIC AND VIRTUALLY CONTINUOUS 24 HOURS A DAY, EVEN UNDER “VERY QUIET” CONDITIONS.

• Clearly, processes in the LLBL and magnetotail boundary layer play critical roles in driving the convection pattern.

• The “throat” flow and flow out of the polar cap at midnight are particularly evident most days

University of University of SaskatchewanSaskatchewan

First Results – cont’d

• Pc5 activity extends to high latitudes (>85° MLAT) during “quiet days”. This may indicate a nearly-closed polar cap.

• After a quiet period, a solar wind speed and density increase (May 17/06) resulted in a dramatic increase in echo range out to 3000 km, but again seen best by the beams (0 to 2) near the equatorward edge of the polar cap, all the way to the European sector.