INVESTIGATING ISOLATED SUNSPOTS AS

SOURCES OF SLOW SOLAR WIND

[Photo G.Gaigals]

ARTURS

VRUBLEVSKIS

Solar Physics Group

(B. Ryabov, D. Bezrukov)

Ventspils International

Radio Astronomy Centre

(VIRAC)

Ventspils University of

Applied Sciences

Latvia

Uppsala, Sweden

October 2018

Ventspils International Radio Astronomy Centre (VIRAC)

Top: RT-32 antena (photo G.Rozenfelds)

Bottom left: Solar radio observations (D.Bezrukovs)

Bottom right: LOFAR Sweden (Onsala Space Observatory /

Västkustflyg )

32 m / 16 m / (LOFAR)

Ventspils International Radio Astronomy Centre (VIRAC)

VIRAC part of EVN

and JIV-ERIC

Previous Work→ fundamental plasma physics research – laboratory investigations of magnetic

reconnection

Previous Work→ fundamental plasma physics research – experimental investigations of magnetic

reconnection

Previous Work→ fundamental plasma physics research – experimental investigations of magnetic

reconnection

[from movie «Spider-Man 2»]

ERDF Postdoctoral research aid project No. 1.1.1.2/16/1/001 research application No.

1.1.1.2/VIAA/1/16/079 «Understanding Solar Magnetic Atmosphere» (USMA).

[Ventspils University of Applied Sciences]

INVESTIGATING ISOLATED SUNSPOTS AS SOURCES OF SLOW

SOLAR WIND

Motivation: Space Weather

[NASA/STEREO]

“...considered by scientists to be as

powerful as the iconic Carrington

Event of Sept. 1859...”

“A similar storm today could have a

catastrophic effect. According to a

study by the National Academy of

Sciences, the total economic impact

could exceed $2 trillion or 20 times

greater than the costs of a Hurricane

Katrina. Multi-ton transformers

damaged by such a storm might take

years to repair.”

“It turns out that the active region

responsible for producing the July

2012 storm didn't launch just one

CME into space, but many. Some of

those CMEs "plowed the road" for

the superstorm.”

STEREO – July 23, 2012 - CME

[Science@NASA]

Solar WindPhotographer

rsackett00@yahoo.com

Email

rsackett00@yahoo.com

Location of photo

Cape Girardeau, MO

Date/Time of photo

August 21, 2017 at 1:21 pm CDT

Equipment

Stellarvue 60mm f/5.5 refractor and Canon 60D camera

Description

High dynamic range composite processed to bring out coronal streamers and earthshine on moon.

[Sky&Telescope]

Open question 1: Solar wind sources

– fast wind: > 700 km/s – originates in polar coronal holes

– slow wind: ~ 400 km/s – source unclear, possibly:

• helmet streamers,

• “blobs” disconnecting from helmet streamer cusps,

• equatorial coronal holes,

• active regions,

• active region boundaries,

• edges of active regions,

• chromospheric jets,

• “Narrow open-field corridors that connect coronal holes of the same polarity”.

[Brooks et al., 2015]

[Antiochos et al., 2011]

Open question 1: Solar wind sources

[Abbo et al., 2016; Wang et al., 2007]

Open question 2: Sunspot atmosphere

• What is the temperature structure of the chromosphere above sunspot umbrae?

• What heating mechanism produces the temperature structure?

[Loukitcheva et al., 2014, 2017]

Isolated sunspots with “dark lane”

[Ryabov and Shibasaki, 2016]

The NOAA 8535 in white-light (a),

magnetogram (b), and high-temperature

coronal emission - soft X-ray (c) and the

EUV line at 284 Å (d)) The arrow shows

the direction of the dark lane S1.

Some isolated sunspot observations

include a dark lane in the coronal and

microwave emission.

Overall Goals

• Investigate structure of sunspot atmosphere and determine consistency with

plasma outflows

• Determine global magnetic field structure (including open field and QSLs)

originating at the sunspot

• Look for outflows related to the sunspot

– In situ observations – PSP, Solar Orbiter

– Must establish connectivity – LOFAR?

– Doppler shifts

Potential for reconnection research!

Observations: SOHO / MDI

[Ryabov and Shibasaki, 2016]

The NOAA 8535 on May 12, 1999

Left: in white-light (NSO/KP)

Right: Longitudinal magnetogram (SOHO/MDI)[SOHO (ESA & NASA)]

Derived Magnetic Fields - PFSSPFSS = Potential-Field Source-Surface

Assumes:

- no currents

- field completely radial at RSun and at some source-surface (typically RSS = 2.5 RSun)

Input: radial magnetic field (e.g. from SOHO / MDI magnetogram)Use: IDL – SolarSoft – pfss (Schrijver and DeRosa, 2003)

PFSS modeling:

(a) open field lines under RSS=2.5×RSun in CP1 and

rSS=1.8×RSun in CP2

(b) contours comprising the footprints of the two

open field regions

(c) closed field lines of the magnetic arcades.

Observations: VLA

[Photo J.Fowler]

Observations: VLA

[Brosius and White, 2004]The NOAA 8535 VLA observations at 5, 8, and 15 [GHz]

(contours) superposed on O V 629.7 Å SOHO / CDS EUV data

Thermal Radio PhysicsIn thermal between electrons and radiation have: I = Bν(T) and for most frequencies and temperatures:

Solution to radiative transfer equation:

For homongeneous source and in thermal equilibrium:

Two basic therma radio emission mechanisms:

1) free-free a.k.a. thermal bremsstrahlung – electron «collisions» with ions:

2) gyroresonance

[Gary and Hurford in Gary and Keller, 2004]

Gyroresonance emission properties

- Significant only in regions where frequency matches local Larmor frequency

- Angular dependence

- Two modes – o and x with different absorption

[White in Gary and Keller, 2004]

Thermal Radio as a Diagnostic[Gary and Hurford, 1994; Bong et al., 2003; Tun, Gary and Georgoulis, 2011]

1) Read off coronal temperature Te

2) For thermal bremsstrahlung estimate emission

measure:

3) For thermal gyro resonance estimate peak magnetic

field

Results of Tun et al.

"The implication of these results and the one presented in this paper is that the field lines reach apeak temperature that depends on the footpoint location within the sunspot region, with temperatures varying greatly between very closely spaced footpoint locations, even within the umbra."

Observations: VLA

[Brosius and White, 2004]The NOAA 8535 VLA observations at 5, 8, and 15 [GHz]

(contours) superposed on O V 629.7 Å SOHO / CDS EUV data

Region of top VLA Brightness spectrum

1) Read off coronal temperature Te – 2.7e6 [K]

IDL – SolarSoft – gx_simulator[Nita et al. 2015, 2018]

Atmosphere modeling[Reimers, 1971a, 1971b - Borovik et al., 1990 – Ryabov et al. 1999]

Atmosphere modeling

Atmosphere modeling

1) Read off coronal temperature

Te = 2.7e6 [K]

2) Read off coronal temperature

Te = 9.6e5 [K]

Atmosphere modeling – two

components

Atmosphere modeling – two

components

Future and Immediate Work

• Deal with low frequencies:

– another data point at 1.41 [GHz]

– model atmosphere to larger heights (presently 90 000 [km])

– use polarization data

• Identify open field line regions

• Proper optimization

• Look for outflows related to the sunspot

– In situ observations – PSP, Solar Orbiter

– Must establish connectivity – LOFAR?

– Doppler shifts

Potential for reconnection research!