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Millstone Hill Observations: Jan 7 - 10, 1997 ISTP/MLTCS Event

Enhanced Mid-Latitude Electron Temperature during Storm Onset

Millstone Hill observed a sharp increase in local electron temperature, without a corresponding signature in the electron density or the local plasma velocities, in conjunction with the disturbance onset near 08 UT on January 10, 1997. Electron temperature was greatly increased, while ion temperature was largely uneffected, resulting in a strong enhancement of the temperature ratio. Te/Ti exceeded 6 near the F-region peak altitude. Large temperature ratio can lead to plasma instabilities and the growth of ion-acoustic lines of the incoherent scatter spectrum as has been described by Foster et al [GRL, vol 15, 1988].

Analysis of radar fixed-position data taken to the north and south of Millstone Hill, at high elevation angle, has been used to investigate the spatial/temporal evolution of the ionospheric heating event. Data averaged for all altitudes between 300 km and 500 km and over 20 minutes for positions to the north (57 deg invariant) and south (51 deg invariant) indicate an equatorward motion of temperature enhancement during the event. The heating event begins poleward of 54 deg around 06:30 UT, peaks locally (54 deg) between 08 Ut and 09 UT, and persists until ~10 UT at the most equatorward location.

DMSP-F13 overflight of the region near 08:00 UT observed enhanced electron temperature over a 5-8 deg extent with peak values > 5000 K immediately poleward of the plasmapause, at 54 deg maglat (the latitude being sampled by the Millstone Hill zenith-antenna radar observations). Electron temperature/altitude profile for this time indicated that the DMSP value at 850 km is consistent with the heating near the F-region peak altitude, which extended down to ~300 km at this time. Data for an undisturbed night, January 8, 1997 at the same UT, are shown (Xs) for comparison.

The variation of electron temperature observed near 350 km altitude overhead at Millstone Hill during the Jan 10th storm greatly exceeds that observed on the preceding quiet night. Electron temperatures increased to >2500K during the early phases of the disturbance (03 - 06 UT) and then began a more-pronounced increase at ~0630 UT, reaching ~4000K in the postmidnight MLT sector between 08 and 09 UT. No corresponding enhancement in the ion temperature was observed and the local convection electric field was not perturbed. F-region peak electron density remained essentially constant at ~2.5E10 m-3. The radar operating mode sampled the mid-latitude ionosphere over a limited range of latitudes (51 - 56 INVL) and observations made to the north and south of the site permit a characterization of the spatial and temporal evolution of the ionospheric heating event. These data clearly indicate that the region of elevated ionospheric temperature was of limited latitude extent (~5 deg) and progressed equatorward through the radar field of view between 0630 UT and ~1000 UT. The elevated heating was first observed near 57 INVL at ~0700 UT, maximizes near 54 INVL at 0830 UT, and moves equatorward of 51 INVL after ~0930 UT. Two overflights of the DMSP F13 satellite near the Millstone longitude observed a similar spatial extent and equatorward progression of the region of enhanced temperature.

The electron temperature enhancements observed by Millstone Hill and DMSP F-13 have the characteristics of an intense SAR arc located at the plasmapause/ plasmasheet/ring current boundary as it recedes equatorward during the expansion phase of the storm. No optical observations of the expected 630.0 nm emissions were obtained from Millstone Hill, due to overcast-sky conditions.

Millstone Zenith Electron Density Profiles Jan 9 & 10, 1997

Arecibo Zenith Parameters @ 380 km Atitude

Zenith data are compared for the nighttime intervals from January 8-10, 1997. January 9 appears to represent the undisturbed nighttime conditions, while a perturbation (best seen in the vertical velocity data) occurs on the 8th and 10th. Electron temperature is enhanced during the period 08:30-09:30 UT on the 10th.
The downward vertical velocity observed between 07:00 UT and 09:00 UT appears to be the effect of an eastward electric field, which can destabalize the low and mid-latitude ionosphere, resulting in ionospheric depletions with the characteristics of 'equatorial plasma bubbles.' Arecibo vertical density profiles observed such a feature, a spatially discrete density depletion near 08:30 UT. The depleted region was observed at steadily decreasing altitude (invariant latitude) of the depleted flux tube.

Storm Perturbations (ISTP EVENT) Jan 7 - 10, 1997

Millstone MLTCS F Region Observations of Basic Plasma Parameters Jan 7 - 10, 1997


Millstone MLTCS E Region Observations of Basic Plasma Parameters Jan 7 - 10, 1997

http://www.haystack.edu/~jcf/jan97.htm -- Revised: February 26, 1999
E-mail: jcf@haystack.mit.edu
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