Eugene N. Parker, the astrophysicist who theorized the existence of solar wind and became the first person to witness the launch of a spacecraft bearing his name, died March 15 at a retirement community in Chicago. He was 94.
Without a doubt, Dr. Parker was perhaps the most illustrious pioneer in the specialty field of solar physics (my field) and many of his solar insights drove my own work, especially into the structure and role of sunspots as proximate solar flare triggers, e.g.
http://adsabs.harvard.edu/full/1983JRASC..77..203S
And:
1987SoPh..112..387S Page 387 (harvard.edu)
It was while Dr. Parker was still a budding young
astrophysicist at the University of Chicago that he wrote a seminal paper in
1958 about the solar wind and its association with the interplanetary magnetic
field. (Parker, E.N. : Dynamics of the interplanetary gas and magnetic
fields,” 128, 664, Astrophys. J., 1958.) The paper can be
accessed at the link below for those interested:
http://adsabs.harvard.edu/full/1958ApJ...128..664P
Fast forward some 21 years, to ca. 1979. Measurements over decades of the so
-called Evershed effect showed the plasma motions to be radial and
inwards. There did not appear to be any 'escape hatch' for the rising
gas columns represented by the umbral dots. This being the case sunspots ought
to heat up and reach equilibrium with the surrounding photosphere after a few
days, and yet spots with umbral dots were observed to last weeks.
And so the "multiple flux tube" model of Eugene Parker was born
(cf. Astrophys. J., 230, 905-13). In the diagram shown below
note the geometry of the field lines extending from beneath the photosphere (in
the convective zone) to far above it. The 'flaring field' on top is buoyant for
reasons that have to do with the stratification of the solar atmosphere. The
Wilson depression is shown as the indentations at the umbral surface on either
side.
Parker in his paper (ibid.)
showed that the downdraft velocity ( v d ) needed to
remove heat from beneath a sunspot (at a depth of 2500- 5000 km) is on
the order of the Alfven velocity e.g.
v A = Bo
/ [m o r o] 1/ 2
for this region, where Bo is the equilibrium magnetic field, m o is the magnetic permeability of free space,
and r o is the plasma density. This leads to v A = about 2 kilometers per second. This then is adequate to
provide the observed umbral energy flux of 0.2 F o where F o denotes the normal photospheric flux.
The full paper can be accessed here:
http://articles.adsabs.harvard.edu//full/1979ApJ...230..905P/0000905.000.html
A key fact relevant here is that heat flux
and magnetic field strength are independent
of sunspot area. The parameter that best helps to explain this is
the vertical distance 'x' which the model predicts is characteristic of
all sunspots whether they be 4,000 km or 40,000 km across. Calculations by
Parker show x = 1150 km approximately. It is the limiting distance below which
an instability would occur in a single flux tube.
All Parker's earlier work has now been amplified and built upon thanks to groundbreaking images of the Sun captured by solar physicists at Big Bear Solar Observatory (BBSO) which have provided us the first-ever detailed view of the interior structure of umbrae.
From all these points of
view, the adoption of Eugene Parker's name for the Parker Solar probe (see top
graphic) - a one of a kind solar craft - - is welcome and quite
understandable. Indeed, the mission is a culmination of Prof. Parker's research
in the fields of solar physics and heliophysics (the latter distinguished from
the former on the basis of the extent of the solar wind, e.g. into the
heliosphere - or the magnetically affected region that extends beyond Pluto's
orbit). A few of the features which make the Parker probe noteworthy include:
1) A component experiment for
'Integrated Science Investigation of the Sun' which is designed to detect solar
particles across a wide range of energies. This will allow solar
physicists to decipher how the Sun accelerates the solar wind. One
detector will search for low energy particles, while a different one will
search for high energy ones.
2) A component designated WISPR (Wide -field Imager
for Solar Probe) will take images of the solar corona, solar wind, shocks and
solar flares. These images will help scientists properly interpret data
from the other instruments.
3) The craft features two solar panels mounted on a movable
joint to control how much sun light (radiant energy) the panels absorb.
In close passes to the Sun - such as last November- the panels will fold
behind the heat shield, leaving only a last row of solar cells to absorb
energy.
A hundred years hence, and assuming humanity is still around and hasn't blown itself to bits in nuclear war, Eugene Parker will be remembered for his monumental solar contributions. Contributions which drove the most fundamental astrophysics, that of our nearest star, which supports all life on this fragile world.
See Also:
Eugene Parker, groundbreaking solar physicist, dies at 94 | Astronomy.com
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