ast 301, solar lecture · 5 nov. 2024. will swoop to within 4 million miles of sun’s surface on...

AST 301, Solar Lecture

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

April 15, 2019

Cosmic Catastrophes

[email protected]

James Lattimer AST 301, Solar Lecture

Could The Sun Be Warming?

In the past, globaltemperatures have beencorrelated with solarinsolation changes causedby the Earth’s orbit andinclination, and these occurover thousands of years.

Solar output also changesover time, most notably inthe 11-year sunspot cycle.

But the average solaroutput has not changed indecades.


Solar Effects

Hannes Grobe, Wegener Institute for Polar and Marine Research


Ice AgesI Anomalous boulders led to the idea that giant ice sheets (glaciers)

once covered Europe.I The trigger for an ice age was proposed by Adehmar as due to

changes in solar insolation from precession. If winter began whenEarth was at aphelion, an ice age could result.

I Croll extended the idea, using data that suggested the Earth’sorbital eccentricity changes.

I Using calculations of Pilgrim, Milankovitch furthered the correlationof solar insolation and past Earth temperatures.

I From Milankovitch’s work, Koppen suggested glacial melting wascontrolled by summer insolation, not winter insolation.

I This work was later combined with data from geomagnetic reversalsin the 1970’s that showed there are four major cycles of insolation:

I Earth’s orbital eccentricity (100,000 years)I Earth’s axial tilt, oblliquity (41,000 years)I Precession (major variation 23,000 years)I Precession (minor variation 19,000 years)

I There have been a few other major climate changes: 250-350 Myrs,410 Myr, and 440 Myr which require a different trigger.

I The most likely trigger is continental drift, first proposed by Wegner.James Lattimer AST 301, Solar Lecture

Solar Insolation And Milankovitch Cycles

The Serbian geophysicist MilutinMilankovic proposed thatvariations in the Earth’s orbitaleccentricity and the axial tilt andprecession of Earth’s spin axisproduce a collective effect onEarth’s climate. Models show thestrongest correlation is tosummer insolation in northernhemisphere where most land is.

The 18O/16O ratio in CaCO3 ofplanktonic foraminifera traces T .


Sunspot Cycle

I 11-year sunspot cycle

I Equator-ward drift of theactive latitude

I 22-year magnetic cycle

I Tilt of sunspot groups

I Reversal of polar fieldnear cycle maximum

Joy’s Law

Lea

der

spot

Butterflydiagram


Babcock αω EffectI Initial poloidal field

located benearth thesurface at tachocline,the boundary betweensolid and differentialrotation.

I Submerged lines drawnout by differentialrotation, amplified andconverted totoroidal fields.

I Buoyancy andconvection cause fieldsto rise.

I Rising fields aretwisted by Corioliseffect, producing Joy’sLaw.

I Meridional circulationcarries reverse poloidalfields to pole andsubmerges them totachocline.


The Solar Cycle


The Solar Cycle and Recessions


The Sun As A Threat to Life

The Sun is the biggest extraterrestrialthreat to life on the Earth.

The solar wind has already eradicatedMars’ atmosphere, when that planetlost its magnetic field.

The Earth’s atmosphere and magneto-sphere protects us from harmful solarradiation; cosmic rays (including highenergy solar wind protons), UV,X-rays and γ-radiation.

The primary defense against high-energy particles from normal solaractivity and from giant storms and flares is the Earth’s magnetic field.

The greatest threat comes from coronal mass ejections (CME’s), violentejections of solar plasma and electromagnetic radiation, involving > 1010

tons of matter and energies of billions of H-bombs (enough to powerhumanity for 2 Myrs). These are accelerated to 107 mph and reach Earthin 1–3 days; they extend billions of miles in space (100 AU).


Preservation of Atmosphere

Atmosphere can be lost

I thermal escape

I giant impacts

I solar wind e.g. Mars

Requirements for planetarymagnetic field

I abundant Fe

I molten interior

I convection

I rapid rotation


Coronal Mass Ejections

The most powerful CME’s are thousands of times larger than the Earth(up to 1/2 AU) when they reach the Earth.

A CME is produced every few days on average, and 30 hit the Earth eachyear, but few hit the Earth directly. The frequency of CME’s correlateswith the sunspot cycle (a few per day to once a week).

The largest CME’s directly hit the Earth about once every hundred years.They have the potential to set technology back to the pre-IndustrialRevolution era.

The ’bright’ side is that we would be forced to rely heavily on solarenergy and would eliminate most fossil fuel use. In fact, if solar energywas our primary energy source, a CME would allow us to return to solarenergy within a day.

The Earth’s magnetic field is currently weakening, however, making usmost susceptible. The field will not regain strength until after the nextgeomagnetic reversal in 1–2 thousand years.


Observations of CME’s

Best observed with a whitelight coronograph locatedoutside the Earth’satmosphere.

First such observations werewith Skylab in early 70’s.

SOLWIND and the SOLARMAXIMUM MISSION(SMS) were used in late70’s and early 80’s.

The SOHO spacecraft(1995) has a large scalecoronograph and discoveredover 3000 comets.

Today, the STEREO-A andSTEREO-B spacecraft(2006) provide completecoverage of the Sun.

Comet Kudo-Fujikawa


Parker Solar Probe

Launched 12 Aug. 2018.

Venus flybys:3 Oct. 2018,26 Dec. 2019,11 July 2020,16 Oct. 2021,Aug. 21 2023,5 Nov. 2024.

Will swoop to within 4million miles of Sun’ssurface on 24 Dec. 2024.

Named after EugeneParker who predicted thesolar wind and explainedthe superheated corona.


Carrington And Other Events

On Sep. 1, 1859, the largest recorded solar storm propelled a CMEdirectly at the Earth, creating the most prolific auroras ever seen; theyextended as far south as Cuba and as far north as Queensland, Australia.They were brighter than the full moon.

The flare was observed by R.C. Carrington and R. Hodgson stemmingfrom a sunspot group, and visible on solar screen projections. This eventknocked out Earth’s leading technology: the global telegraph system. Itgave operators shocks and set fire to some equipment. The reasons werenot understood as X-rays were responsible but weren’t discovered until1895 by Roentgen. This event occurred before electricity-producingutilities were established 20 years later.

A Carrington-scale event occurred in May 1921, causing auroras inSamoa and telegraph fires in Sweden.

A great storm on Sep. 18 1941 led to U-boat damage to a convoybecause auroras were so bright.

A nuclear war was almost started by an event on 23 May 1967; itjammed radar and radio communications. But observations of a giantflare on 18 May had led to predictions of radio disruptions by the SolarForecasting Center, which alerted NORAD. This even precipitatedincreased funding to monitor space weather.


July 23, 2012 Event

Other events were recorded on 17 November, 1882 (auroras), ageomagnetic storm in January 1938, a solar storm in August 1972, aMarch 1989 geomagnetic storm, and the Bastille Day Event in 2000.

Large events occurred on 9 March 1989, which caused power failures inQuebec, and in October 2003 (Halloween Storm), due to a solar flare,which caused blackouts in Sweden and a loss of many transformers inSouth Africa.

The most powerful recent event occurred on July 23, 2012; a CME wassent directly through Earth’s orbit in just 19 hours, but missed a directimpact by 9 days (2.5% of Earth’s orbital circumference). It wasCarrington-scale.

Another large event occurred shortly after on 31 August 2012.

It is now thought that 14C and 10Be can be used as markers for extremesolar events in ice cores, which pinpoints AD 775 and AD 993-4 strongevents.

Although CME’s are correlated with the sunspot cycle, the events of1859 and 2012 occurred during solar minima.


Simple Model of a CME

As a CME moves away from the Sunit expands. Observations show

V ∼ r2.

The magnetic field is frozen in theCME and carried along:

B ∼ 1/V 1/2 ∼ 1/r


Major Destructive Effects

I Power grid disruptions due to geomagntically induced currents(GIC’s). About 4% of disruptions occuring between 1992 and 2010were due to geomagnetic activity, usually causing voltage instabilityand transformer damage.

I GIC’s cause changes in pipe to soil voltage that drives enhancedcorrosion. Aeromagnetic surveys and precision drilling are affected.

I Mobile network performance is affected, as is short-wave radio usedby shipping, aviation and the military. Power structures needed forrepeater stations in optical fiber networks are at risk.

I Ground transportation such as trams, subways and railroads, anddriverless cars, can be affected.

I Satellites are at risk due to damage to solar panels and computers.During the 2003 Halloween solar storms, 47 out of 450 satellitesreported anomalies, one was lost and 10 lost operational service formore than a day. Satellites are designed to tolerate high doses.

I Signal distortion in the ionosphere puts the GPS system at risk.I Solar storms enhance cosmic-ray-generated damage at high altitude,

although a CME can block galactic cosmic rays which balanceseffects. Nevertheless, enhanced radiation puts flight crews at risk.Aviation communication will be affected, especially on polar routes.


Risks As Calculated By Insurance Companies

Zurich Insurance did a study of 11,242claims related to electric or electronicfailures between 2000 and 2010; it hasabout an 8% market share.

I Zurich paid out $175M for these losses, with average 10%deductible, so nationwide losses would be $2.3B.

I The average electrical claim was about $20,000.I Statistically, geomagnetic activity accounts for 4% of all claim costs.I But other losses stem from power failures: productivity, loss of

materials, cost of resumption of production, etc. These areestimated to be $200B per year in the US. A similar amount isfound for the EU since 2007. If 4% is related to space weather, thatamounts to $8B per year in the US.

I The total is then $10B per year in the US.

But if an insurance company required users to buy protective equipment,customers would move on to another insurance company that did nothave such a requirement.

So governmental regulations will be necessary to ensure protection forour power grid.


Comparison Of Activities Of Sun and Solar-Type Stars

Three major studies include:

I Maehara et al. (2015) “Statistical properties of superflares onsolar-type stars based on 1-min cadence data”Observed 365 superflares on 148 stars in 120 days.

I Shibeyama et al. (2013) “Superflares on solar-type stars observedwith Kepler. I. Statistical properties of superflares”Observed 1547 flares on 279 G-stars in 550 days, 1150 of which wereon rapidly-rotating stars (P < 10 d).

I Karoff et al. (2016) “Observational evidence for enhanced magneticactivity of superflare stars”Observed 5648 solar-like stars including 48 superflare stars withLAMOST (China) telescope with 4000 optical fibers.

Estimates indicate that a flare with E > 1035 erg needs a sunspotcovering more than 30% of solar surface, unlikely in case of Sun. Themagnetic energy of the Sun may preclude events E > 3 · 1032 erg.


Measures Of Stellar Activity

All studies: flare frequency is highly correlatedwith stellar activity and short rotation periods.

Stellar activity is highly correlated withchromospheric emission, notably the Ca II H &K lines (S-Index), and with stellar brightnessvariations (i.e., sunspot coverage).

young, active

old, less active


Relative Flare Frequency By Energy

inferred for AD 775/994 events

There are apparently breaks in the flare activity ratearound 3 · 1032 erg and 1034 erg for solar-like stars.


ast 301, solar lecture · 5 nov. 2024. will swoop to within 4 million miles of sun’s surface on...

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