Solar Outbursts Provide 'Perfect Storms' For Haystack Space Weather Watchers

News Office
Massachusetts Institute of Technology
Cambridge, Massachusetts

NOVEMBER 14, 2003

Solar outbursts provide "perfect storms" for Haystack space weather watchers
By Carolyn Collins Petersen

On the morning of October 28, 2003 a gigantic solar flare sent a powerful burst
of energy and matter racing out into space. It was the third most powerful ever
measured and astronomers classified it as an X17.2 flare (on a scale of x-ray
intensity ranging from 1 to 20). The coronal mass ejection associated with it
unleashed a flood of charged particles directly toward Earth and triggered
auroral displays seen as far south as Texas. During the next few days, two more
giant eruptions of the Sun also sent their energy hurtling towards Earth.

During the next few days, two more giant eruptions also sent their energy
hurtling towards Earth.

For the atmospheric scientists at MIT's Haystack Observatory who track dynamic
interactions between the sun and Earth, these outbursts were the perfect storms:
strong, fast-moving solar winds and streams of plasma interacting with Earth's
magnetic field, creating magnetic disturbances and circulating electrical
currents in the upper atmosphere. While satellite operators, pipeline companies
and grid owners rushed to shut down and safeguard their equipment, Haystack
space weather watchers swung into action, measuring the activity with the
Westford, Mass.-based Millstone Hill Radar, a Global Positioning Satellite
receiver tied into a worldwide network of more than 900 GPS sites and a series
of optical instruments.

The observatory's radars, supported by the National Science Foundation, charted
changes in the ionosphere (a region of the Earth's atmosphere extending from
about 100 to 1,000 kilometers above the Earth's surface), measured the thickness
of the ionosphere and tracked auroral displays as they danced overhead.

Now, more than two weeks after the events, the data gathered at Haystack and its
associated facilities are just starting to be analyzed. Preliminary indications
show incredible changes in Earth's upper atmosphere during late October,
resulting from disturbances characterized by John Foster, the observatory's
associate director and leader of the Atmospheric Sciences Group at Haystack, as
the most violent in years. "These powerful storms were the biggest in this solar
cycle and in this decade," he said. "The effects we've observed, such as the
redistribution of the ionosphere, are the most pronounced of any we've seen to
this date."

While the upper atmosphere is constantly changing during storms, Foster noted
that the ionospheric redistribution during the latest events gave Haystack
observers plenty of data to analyze over the coming months. "We are doing
leading-edge research here at Haystack in this area," he said. "In particular,
the mid-latitude geomagnetic storm response is something that we've been doing
fundamental work on for the past couple of years."

Foster's team will use their data to quantify the size and effects of
perturbations of the upper atmosphere, and integrate that into what's already
known about space weather. And, since the sunspot group that birthed these
outbursts will soon rotate Earthward, the science teams are getting ready for
another round of severe space weather around Thanksgiving. "This group is large
and active," Foster said. "It will come back and point at the Earth again, and
when it does, we'll be ready for it. We're planning to have our full monitoring
system in place to catch all the changes in Earth's ionosphere as they occur."

The sun and Earth: electrical ties that bind

These geomagnetic storms are powerful evidence of the electrical ties coupling
Earth and the sun, particularly when they stir up activity in the near-Earth
environment. Space weather-induced disturbances, plus the effects from more
humdrum solar activity, have been a research focus of the Haystack group for
more than 30 years. Yet it is only recently that the full story of sun-Earth
interactions has started to unfold, and space weather plays a huge role.

The sun-Earth connection is an intricate one. Earth floats along cocooned inside
a thick atmosphere, protected by a magnetic field (its magnetosphere), warmed by
sunlight but also buffeted by the solar wind and stronger outbursts from the
sun. The sun, in turn, has its own complex magnetic field structure. The most
obvious manifestations of that structure show up as sunspots (where intense
magnetic lines of force break through the surface), prominences (which are
supported and pervaded by magnetic fields), and streamers and loops that are
shaped by magnetic lines of force.

Outbursts from the sun are pervaded by magnetic fields, and when these hit
Earth's magnetosphere, we get space weather. Solar ultraviolet radiation and
X-rays interact with the top of our atmosphere to create the ionosphere, and
radiation strips electrons of atoms of atmospheric gas, creating a region of
positively charged ions and free negative electrons, usually pervaded by an
electrical current. This ionospheric soup bends or reflects radio and radar
signals and allows them to bounce around the planet. Changes in the composition,
temperature and location of the ionosphere show up as perturbations in the
propagation of radio signals, and those perturbations can be used as diagnostics
of the ionosphere and the space weather that affects it.

Space weather originates with solar activity that arrives at Earth in stages,
and during storms like those unleashed in late October, the magnetosphere really
takes a beating. A snowstorm of energetic particles from an outburst starts to
arrive about 20 minutes after the outburst and poses hazards to spacecraft
electronics and any astronauts on orbit. Plasmas (with entrained magnetic
fields) arrive a day or so after the flare. They set off geomagnetic storms,
cause currents to flow in the magnetosphere, heat the ionosphere and energize
particles, which in turn increases drag on orbiting satellites. The electrons in
the ionosphere collide with molecules, causing auroral displays and raising the
risk of electrostatic discharges that can damage spacecraft hardware.

During heavy bouts of space weather, material in the upper ionosphere is
redistributed from Earth's lower latitudes to the mid-latitudes and ultimately
up to the rarefied atmosphere over the polar regions. This happens very quickly,
said Foster, who described charged plasmas in the ionosphere moving at speeds of
a kilometer per second. "This material moves from the equatorial regions and
South America up to the north slope of Alaska on about a 30-minute time scale,"
he said.

One effect that intrigues Foster's team is an apparent preferential perturbation
in the ionosphere over the North American continent during geomagnetic storms.
"This is an effect that is not well understood," he said. "It's an area where
we're doing groundbreaking research to figure out why this sort of asymmetry
exists."


Space weather watching at Haystack
by Carolyn Collins Petersen

Haystack Observatory's space weather-watching assets are impressive and
widespread. The largest single pieces are the Millstone Hill -- a 46-meter
steerable radar antenna and a 67-meter fixed zenith pointing antenna, operating
between 440.0 - 440.4 MHz. In addition, developments in data communication and
real-time analysis are receiving emphasis from the Haystack Atmospheric Sciences
Group. These capabilities are being applied to the analysis of ionospheric data
gathered through the use of a worldwide distributed array of more than 900 GPS
receivers that can supply close to real-time measurements. Finally, a series of
optical telescopes are used to observe aurorae and background sky emissions.
Also operating at Haystack are facilities from other institutions, including the
University of Massachusetts-Lowell Digisonde, the Applied Research Laboratory's
Coherent Ionospheric Doppler Receiver (CIDR) array, and various optical
detectors from Boston University and elsewhere.

The Millstone Hill radars utilize Thomson backscatter from the ionospheric
plasma to measure the plasma's drift velocities as the ionosphere bounces around
overhead, electron and ion temperatures, electron densities, ion composition,
and ion-neutral collision frequencies. Analysis of the returned signals also
gives the total electron content (TEC) of the ionosphere at any given time, as
well as changes in the size and opacity of the upper atmosphere. The incoherent
scatter technique provides observations of ionospheric characteristics over an
altitude range extending from less than 100 kilometers to a thousand kilometers
or more. The higher the electron count (especially during storm conditions), the
thicker and more perturbed the ionosphere.

In addition to the Millstone radars, Haystack's GPS receiver is part of an
international network of receivers that use global positioning signals to probe
the ionosphere. Combined data from all the GPS sites during the most recent
storms will give researchers a very good picture of the total electron content.
According to John Foster, the observatory's associate director and leader of the
Atmospheric Sciences Group at Haystack, the GPS datasets allowed measurements of
the ionosphere out to 20,000 kilometers from the surface of the Earth. "As the
total electron content increases, the more material you have between you and the
satellite," he said. "This really affects the signal. With 28 satellites and all
the receivers you can get close to real-time measurements of the ionosphere."

The effect of geomagnetic storms on GPS measurements can be quite severe.
Signals from the satellite transmitters to any of the hundreds of receivers in
the network are delayed by the dynamic changes in the ionosphere. The result can
be position errors of up to several tens of meters and loss of receiver signal
lock, further compromising the use of the GPS navigation system.

At a recent meeting of the GPS teams, held at Haystack Observatory, developers
used the most recent storms as case studies for development of more efficient
ways to use their far-flung network to monitor the Earth's ionosphere during the
next storm. The end results will dovetail nicely with Haystack Observatory's
longtime and ongoing contributions to the world's space weather detection and
monitoring efforts.

MORE INFORMATION:

* MIT Haystack Observatory
http://www.haystack.mit.edu/
* John C. Foster -- Group Leader, Atmospheric Sciences Group, MIT
http://www.haystack.mit.edu/%7Ejcf/

IMAGE CAPTIONS:

[Image 1:
http://web.mit.edu/newsoffice/nr/2003/flares.jpg (11KB)]
One of the largest solar flares ever observed by the Solar & Heliospheric
Observatory set off a strong high energy proton event and a fast-moving coronal
mass ejection that hit Earth early on the 29th of October. MIT's Haystack
Observatory atmospheric scientists utilized an array of detectors to track
changes to Earth's ionosphere as a result of this ejection. IMAGE / COURTESY
SOHO (ESA & NASA)

[Image 2:
http://web.mit.edu/newsoffice/nr/200...-chart-big.gif (60KB)]
The redistribution of ionospheric plasma is apparent in this map of total
electron content (TEC), which is displayed here on a linear scale from blue to
red, over a range of 0 - 200 TEC units. During normal periods, the values of TEC
over the United States are about 30 TEC units. The major geomagnetic disturbance
on October 30, 2003 produced a dramatic space weather storm front which spanned
the continental U.S., bringing TEC in excess of 150 TEC units, and large spatial
TEC gradients above the central United States. This material was carried rapidly
across Canada and into the polar latitude regime in the northern arctic. Work
performed by the Haystack group in the past year has shown that this
space-weather feature is due to the erosion of the Earth's plasmasphere (inner
magnetosphere) by storm-time disturbance electric fields. IMAGE / COURTESY JOHN
FOSTER, MIT HAYSTACK OBSERVATORY ATMOSPHERIC SCIENCES GROUP