Here comes the CME. Solar activity update

7 03 2012

The CME that I talked about in Fireworks from the Sun, originated from the X class solar flare of the 5th of March, is hitting the Earth right now. The increasing proton flux has produced an increase of particle flux in the ISS that is being measured by ALTEA. Here is the particle flux detected by ALTEA and the proton flux as detected by GOES satellites.

SPE 7 Marzo ALTEA

I remember that you can observe the real time flux as measured by ALTEA with the Integrated Space Weather Analysis System web app.

Let me conclude this flash post with a great infographic on Solar Flares. And stay tuned because a new CME could be arriving in the next days.

See how different types of solar flares stack up in this SPACE.com infographic.
Source: SPACE.com: All about our solar system, outer space and exploration

Advertisements




Fireworks from the Sun

7 03 2012

The intense activity of the sun recorded in late February is going on. On 7th of March 2012, the sun unleashed an X5.4-class flare at 00:28 UT coming from Active Region 1429. As described in what is a solar storm? this flare is associated to a large coronal mass ejection (CME) that is not yet known how will impact Earth. After a while a second X5.1 flare happened on the same spot.

An image of the flare as seen by NASA’s Solar Dynamics Observatory (AIA 304)

Below a short video of the double flare.

Download a full sun video of the double flare (ESA HSO movie).

On the same day a CME relative to the 5.1 flare happened on the 5th of March is impacting Earth. On the image below there is the X-Ray flux as measured by GOES satellites where it is possible to see both events.

image

This is the proton flux as measured by GOES. The sudden increase of flux on the 7th of March is relative to CME related to the flare of March 5th.

image

And what is the situation of the particle flux inside the ISS? At the moment ALTEA is not seeing any increase of the flux, but I recall you that ALTEA is not very sensitive to protons that are the main component of this kind of events. We will see in next hours since the flux is still increasing. For sure the sun is in a very active period.

Versione italiana: Attività solare. Doppia flare X

Sources:

http://www.universetoday.com/94018/sun-releases-a-powerful-x5-flare/

https://alteaspace.wordpress.com/2012/02/10/what-is-a-solar-storm/

iNtegrated Space Weater Analysis System web app





What is a solar storm?

10 02 2012

During the end of January the Sun went through a period of intense activity. The sunspot group 1402 has issued a solar flare with an associated CME that reached the Earth. As we have seen in solar particles these events cause the so-called solar particle events (SPEs). I was invited to speak about the nature of these events and their potential effects on safety for astronauts during the Italian podcast named AstronautiCAST (you can download the episode here). I would like to deepen the topic even here on the blog. We already talked about the solar cycle, sunspots, flares and CME, but how are they correlated and what are their differences?

Let’s start from the structure of the Sun. The Sun is a main sequence star with a mass of 2 × 1030 kg (representing alone 99.8% of the mass of the solar system) essentially made of hydrogen (74%) and helium (25%). Since the Sun doesn’t have a solid surface, but it is in a plasma state, it is subjected to a differential rotation: it rotates faster at the Equator than it does at the poles. The rotation period varies between 25 days of the Equator and 35 of the poles.

The differential rotation of the Sun is at the base of the solar cycle. The solar magnetic field (strongly coupled with the plasma of the photosphere) is warped by the differential rotation and while the solar cycle progresses it is increasingly twisted around the star. During solar minimum the magnetic field configuration is described by phase 1 of the figure, while during solar maximum the magnetic field looks like phase 3.

image

In this configuration, in which the field is heavily twisted, the field itself can form loops above the photosphere. At the points where the field emerges from the surface it inhibits the heat flow and it produces sunspots, which are colder than normal and are observed in pairs. This process continues until the magnetic dipole is totally destroyed and the polarity of the magnetic field is reversed. For this reason it is more correct to say that the solar cycle lasts 22 years (rather than 11) because this is the time that the magnetic field takes to return to the initial configuration with the Poles not reversed.

This behavior is evident in the following images of quiet Sun and active Sun (false-color image of the radio emission from the Sun’s Very Large Array radio telescope). The most intense points correspond to sunspots (source: NRAO solar radio emission).

These are other pictures where you can clearly see how sunspots show the underlying structure of the magnetic field.

imageimage

This mosaic of images from NASA’s SOHO footage in extreme ultraviolet (source: http://www.astronet.ru/db/xware/msg/1224916) shows the connection between solar cycles and sunspot number.

The increased intensity of the solar wind during periods of maximum solar also reduces the flow of galactic cosmic rays with energies below 1 GeV/n.

After seeing what sunspots are, let’s describe the solar flares. The solar flares are huge explosions occurring in the solar atmosphere. The effect of flares is a sudden acceleration of particles, plasma heating up to tens of millions of degrees and the expulsion of huge quantities of solar mass. The flares are classified as A, B, C, M or X depending on their x-ray brightness near the Earth, measured in Watts/m². Each class is ten times more powerful than the previous one, with X (the largest) equal to 1012 W/m² and is divided by 1 to 9 linearly, and then a X2 is four times more powerful than an M5. Solar activity is normally between classes A and C.

There are two main types of flares: impulsive flares and gradual flares.
The impulsive flares mainly accelerate electrons with small amount of protons. Their duration ranges from a few minutes up to a few hours, and the majority comes from regions near the equator.
The gradual flares accelerate protons and nuclei up to speed the coming of light. They occur mainly in regions near the poles.

Below there is the video of the recent January 22 activity. It is very interesting to note how in the region concerned by the flare the magnetic field structure that emerges from the photosphere is clearly visible. In this video, as in other photos, the loops leaving the solar surface are due to the emission of particles of plasma that spiral along the lines of the field, making it visible.

imageimage

The particles accelerated by flares end up in solar cosmic rays, also known as SEP (solar energetic particles). Solar particle events (SPEs) are defined by the number of protons. Important events show a total proton fluence over 30 MeV greater than 106/cm2. There are about 50 events of this intensity for each solar cycle. Major events have a fluency of protons over 10 MeV greater than 1010/cm2. There are about one or two events of this type for each cycle. Solar particle events associated with flares have up to 30 degree spatial extension.

The CME (coronal mass ejection) are, as the name implies, massive emissions of coronal mass that consists mostly of plasma of protons and electrons. The plasma transported along the magnetic field in the interplanetary space is going to interfere with the planetary magnetic fields encountered along the way. As we already saw, Earth’s magnetic field is deformed by this interaction and a CME can distort it and lower its ability to deflect the cosmic rays (technically, the geomagnetic cutoff is lowered). The energetic particles are also channeled along the field lines reaching low altitudes to form Aurora Borealis. The angular extent of a CME can reach up to 180 degrees sweeping practically half of the plane of the solar system. The speed of propagation of particles of this latest CME was estimated to be 2200 Km/s.

In the following video you can see, at 7th second, the recent CME observed with a coronagraph. Look at the extension of the phenomenon as well as the first relativistic particles that arrive on the sensor of the coronagraph displayed as white streaks.

In the following video, from 00:33 time, a graphical representation of the propagation of a CME in interplanetary space is shown.

 

Recent studies show that solar flares and CMEs might have a common origin from the phenomenon of magnetic reconnection. Magnetic reconnection is the rearrangement of field lines when two opposing magnetic fields are placed in contact. This rearrangement is accompanied by the sudden release of the energy stored into the two opposing fields.
In the Sun the magnetic field loops that protrude from sunspots can extend over to the point where the lines are reconnected in lower height loops, leaving a magnetic field bubble disconnected from the rest of the loop. The sudden release of energy causes the blasting while the magnetic field and the plasma of protons and electrons contained in the projected bubble expands outwards violently giving rise to CME.

imageimage image

After describing the various physical phenomena that lie behind those commonly known as solar storms, let’s see whether and how these events may be hazardous to the safety of astronauts. While the geomagnetic field protects space crews in LEO orbit from solar events, this protection is not available during an interplanetary trip outside the magnetosphere. The flow of protons during a trip to the Moon or to Mars would be similar to the one measured by geostationary satellites of the GOES series. One of the largest SPE recorded in August 1972 occurred between two missions, Apollo 16 and Apollo 17. If there was an Apollo capsule in a journey to the Moon during this event the astronauts would go through a potentially lethal acute radiation syndrome. During the solar event in October 1989, the Shuttle mission STS-34 was in a slightly tilted (34°) orbit to launch the Galileo spacecraft to Jupiter. Due to the low inclination of the orbit, the protection of the geomagnetic field was enough not to measure any increase in dose during this mission. Meanwhile, aboard the MIR space station, the dosimeter R-16 measured 40 mGy during the events of September and October 1989, equivalent to 100 days of normal exposure on MIR.

I want to end this post with a video responding to various fantasies of conspiracy involving this increased solar activity and the Mayan prophecies about the end of the world in 2012. There are even rumors that NASA has admitted these correlations and has foreseen that during 2012 super solar storms will blow technological civilization away from the face of the Earth. NASA would have also sent an email to employees saying to stay ready.

Here is what NASA thinks: "This solar cycle that will culminate in 2014 isn’t going to be significantly different from the next one, and the next one and the previous one. We always have solar flares. Some times we have big ones, some times we have small ones. Even the most powerful solar event of the last 10000 years could not damage the atmosphere (and the geomagnetic field) so that we are no longer protected. CMEs are happening on the sun all the time and they hit the Earth once or twice a week and in general the effects are minimal. Very powerful ones produce very intense auroras and can have effects on satellites and power grids, but these are the kind of things that people who run these systems know about. And we have warning, since these CMEs can take 2 or 3 days to reach the ground, and we can therefore take appropriate measures to prepare for them. We understand the Sun quite well and we have many spacecrafts that are monitoring it 24 hours a day, 7 days a week, to know that this super storm that is going to wipe out the Earth simply isn’t going to happen."

 

Sources and further reading:
NASA’S Cosmicopia – Solar activity
http://helios.gsfc.nasa.gov/cme.html
http://it.wikipedia.org/wiki/Sole
Solar Flares and Magnetic Reconnection (ppt)
Observations on Current Sheet and Magnetic Reconnection (ppt)
Space radiation dosimetry in low-Earth orbit and beyond (Benton, 2001)





Solar Particles

2 12 2011

Solar particles are the components of the solar wind. They are mainly composed by low energy protons and electrons ejected by the outer shells of the Sun (the Chromosphere) and they have speed near 400 km/s or energies of some KeVs. This condition is called quiet Sun. Solar wind comes directly from the solar Corona, that is a shell of ionized gas (plasma) with temperatures of about 10 millions degree. In the 50’s scientist understood that gravity is not able to keep this plasma bound to the Sun and that it should be in a continuous state of supersonic expansion filling all the solar system.

image

Solar Corona observed during a solar eclipse (February 26 1998, Guadeloupe, Christian Viladrich, SAF http://www2.saf-lastronomie.com/accueil.html). The irregular shape of the Corona is due to the interaction of the plasma with the solar wind itself.

The trajectory of solar particles is determined by the rotation of the Sun. Like a rotating pump, the trajectory follows an Archimedean (or Parker) spiral. It’s interesting that magnetic field lines are aligned with these trajectories. As shown in the figure, magnetic field lines connect the Earth with a point on the solar surface located on the right side of the Sun.

image

Solar particles usually does not represents an hazard for astronauts safety, but occasionally events associated with solar flares or coronal mass ejections (CME) could cause a sudden flux increase that can eventually harm astronauts. These events are called generically Solar Particle Events (SPE) and particles have energies of some MeVs (usually under 100 MeV).

A solar flare implies a large energy release in the form of electromagnetic radiation and charged particles that are originated from solar spots. In particular, EM radiation increases in the extreme ultraviolet (EUV), in the X-ray and in radio waves. But also in the gamma ray region, where the Sun is usually not active.

Flare

Animated image of a solar flare (click for animation)

CMEs are the most spectacular expressions of eruptive solar activity. The series of frames below were taken by the LASCO coronagraph onboard the Solar and Heliospheric Observatory spacecraft (SoHO; ESA/NASA).  In a coronagraph the solar disk is hidden, so that the faint corona is visible as during an eclipse.

image

The first frame shows the corona before the mass ejection event. The emerging structure on the lower right over the disk is called streamer, and it is a shape commonly seen during an eclipse. In the following frame the gas is pushed towards the outer corona confined by magnetic field lines, At the end the gas leaves the Sun and propagates through the heliosphere. Here the gas shows the structure of the magnetic field. The coronal magnetic field is ejected from the Sun, taking the gas along with it. It’s worth noting that the Sun is the white circle in the center of the coronagraph disk.

.CME

Animated image of a CME (click for animation)

The solar cycle

The frequency of these spectacular events is correlated with the solar activity that follows a 11 year cycle. The solar activity is measured from the number of solar spots that are visible on the surface. They increase their number during active sun periods and almost disappear during quiet sun. Solar spots are regions of high magnetic field (0.3 T versus 10-4 T on the rest of the surface).

imageimage

In the graph the Wolf number (related to the number of spots) is shown together with particle flux measured during solar particle events. The correlation between number of spots and SPE is evident.

image

The solar activity modulates also the flux of galactic cosmic rays. The image below shows the inverse correlation of cosmic ray flux (blue line) and the number of solar spots (yellow).

image

The Sun is currently exiting a anomalous minimum period. The first intense flare since December 2006 happened on February 13 2010 (Biggest flare of the cycle)





Space Radiation in Earth Orbit

15 11 2011

The Light Flash phenomenon is only one effect that is caused by cosmic rays in Earth Orbit or in the Solar System. Our planet with its atmosphere and its magnetic field shields us from cosmic rays and their dangerous effects.

Earth magnetic field offers a partial protection from cosmic radiation to astronauts in Low Earth Orbit (LEO) during Shuttle or ISS missions, while exiting the magnetosphere (missions to the Moon or to Mars) would expose astronauts to higher radiation doses. Anyway during all space missions, even LEO ones, ionizing radiation levels are higher than on Earth surface.

The main radiation sources in LEO are galactic cosmic rays, solar particles and particles trapped in the Van Allen belts.

Galactic cosmic rays (GCR) are charged particles, mainly nuclei:

imageimage

Nuclei are mainly composed by protons (87%) and helium (12%), while heavy nuclei are mostly carbon, nitrogen and oxygen nuclei. Heavier nuclei up to uranium are present in smaller quantities

Cosmic rays kinetic energies range from some MeVs up to 1012 MeV (who does not like powers of ten would like to know that 1012 is equal to ten with twelve zeroes, that is 1.000.000.000.000). For energies higher than 2 GeV for nucleon (that is 2000 MeV for nucleon) these particles travel at speed near to speed of light: they come from our galaxy after being accelerated by supernovae explosions; particles of higher kinetic energy are of extragalactic origin and their acceleration mechanism is still under debate.

Solar particles compose the solar wind and are mainly composed by low energy protons and electrons (kinetic energy less than 100 MeV) coming from outer shells of the Sun (the chromosphere) at speed around 400 km/s. Usually solar particle are not of great hazard, but particle events associated with solar flares of coronal mass ejections could occasionally cause a sudden increase of particle flux with possible risks for astronauts safety.

image

Solar flare of 13 February 2011. Credit: NASA/SDO

These two components can be found even outside earth magnetosphere and must be taken into account when planning missions outside Earth orbit.

The third radiation component can be found only in Earth orbit. Charged particles are trapped by the magnetic field in the radiation belts (Van Allen belts): the inner belt is mainly composed by protons and the outer one is composed by electrons. The outer belt is crossed by geostationary satellite orbits used for telecommunications. Solar storms cause an increase of particle flux and could harm or damage these satellites. The inner belt is crossed by the orbit of the Space Shuttle of the space stations.

Near the Earth the cosmic rays are almost totally deflected by the magnetic field that acts as a shield. These particles could be channeled along the field lines near the poles originating the fascinating effect known as aurora. These auroras are visible also on other planets.

image

The orbit used for long term missions is the result of a compromise between a stable orbit (out of the atmosphere to avoid friction) and a safe environment for the astronauts (far away from the center of the inner radiation belt).

Previous posts:
Cosmic rays and human exploration of space
ALTEA- An Italian experiment onboard the International Space Station
The effects of cosmic rays on astronauts: the Light Flash phenomenon

Further readings and sources:
Raggi cosmici e missioni spaziali (in Italian)
A special thanks to Riccardo ‘Unreal’ Rossi for pictures suggestions (via Facebook)