Moreton wave

{{Short description|Large-scale chromospheric perturbation}}

Image:MoretonWaveAnimation200612.gif

File:Solar tsunami.jpg

A Moreton wave, Solar Tsunami, or Moreton-Ramsey wave is the chromospheric signature of a large-scale solar corona shock wave. Described as a kind of solar "tsunami",{{cite web |last=Phillips |first=Tony |title=Monster Waves on the Sun are Real |url=https://science.nasa.gov/science-news/science-at-nasa/2009/24nov_solartsunami/ |publisher=NASA |access-date=16 July 2010 |date=November 24, 2009 }} they are generated by solar flares. They are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank, and Harry E. Ramsey, an observer who spotted them in 1959 at The Sacramento Peak Observatory.{{Cite journal |last=Moreton |first=G. E. |title=Hα Observations of Flare-Initiated Disturbances with Velocities ~1000 km/sec |journal=Astronomical Journal |volume=65 |pages=494 |year=1960 |doi=10.1086/108346 |bibcode=1960AJ.....65U.494M}}{{Cite journal |last1=Moreton |first1=G. E. |name-list-style=amp |last2=Ramsey |first2=H. E. |title=Recent Observations of Dynamical Phenomena Associated with Solar Flares |journal=Publications of the Astronomical Society of the Pacific |volume=72 |issue=428 |pages=357 |year=1960 |doi=10.1086/127549 |bibcode=1960PASP...72..357M|doi-access=free }}{{Cite journal |first1=R. Grant |last1=Athay |first2=Gail E. |last2=Moreton |title=Impulsive Phenomena of the Solar Atmosphere. I. Some Optical Events Associated with Flares Showing Explosive Phase |journal=Astrophysical Journal |year=1961 |volume=133 |pages=935 |doi=10.1086/147098 |bibcode=1961ApJ...133..935A|doi-access=free }} He discovered them in time-lapse photography of the chromosphere in the light of the Balmer alpha transition.

There were few follow-up studies for decades. Then the 1995 launch of the Solar and Heliospheric Observatory (SOHO) led to observation of coronal waves, which cause Moreton waves. Moreton waves were a research topic again. (SOHO's EIT instrument discovered another, different wave type called "EIT waves".){{Cite journal |url=http://solar.physics.montana.edu/nuggets/2002/020208/020208.html |title=SOHO/EIT observations of an Earth-directed coronal mass ejection on May 12, 1997 |journal=Geophysical Research Letters |volume=25 |issue= 14|pages=2465–2468 |year=1998 |bibcode = 1998GeoRL..25.2465T|doi = 10.1029/98GL50429 |last1=Thompson |first1=B. |last2=Plunkett |first2=S. P. |last3=Gurman |first3=J. B.|last4=Newmark |first4=J.S.|last5=St. Cyr |first5=O.C. |last6=Michels |first6=D.J. |s2cid=120367644 |doi-access=free }} The reality of Moreton waves (also known as fast-mode MHD waves) has also been confirmed by the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. They observed a 100,000-km-high wave of hot plasma and magnetism, moving at 250 km/s, in conjunction with a big coronal mass ejection in February 2009.{{cite web|last=Atkins|first=William|title=STEREO spacecraft finds gigantic tsunami on Sun|url=http://www.itwire.com/science-news/space/29658-stereo-spacecraft-finds-gigantic-tsunami-on-sun|publisher=iTWire|access-date=16 July 2010|date=26 November 2009}}{{cite web|title=Mystery of the Solar Tsunami -- Solved|url=http://www.physorg.com/news177872248.html|publisher=PhysOrg.com|access-date=16 July 2010|author=JPL/NASA|date=19 November 2009}}

Moreton measured the waves propagating at a speed of 500–1500 km/s. Yutaka Uchida interpreted Moreton waves as MHD fast mode shock waves propagating in the corona.{{cite web|last=Sakurai|first=Takashi|title=SolarNews Newsletter|url=http://spd.aas.org/SolarNews/archive/news.2002/19.sep|publisher=Solar Physics Division, American Astronomical Society|access-date=15 June 2011|date=3 September 2002|archive-url=https://web.archive.org/web/20110827174504/http://spd.aas.org/SolarNews/archive/news.2002/19.sep|archive-date=27 August 2011|url-status=dead}} He links them to type II radio bursts, which are radio-wave discharges created when coronal mass ejections accelerate shocks.{{cite web|last=Layton|first=Laura|title=STEREO Spies First Major Activity of Solar Cycle 24|url=http://www.nasa.gov/mission_pages/stereo/news/solarcycle24.html|publisher=NASA|access-date=15 June 2011|date=May 15, 2009}}

Moreton waves can be observed primarily in the Hα band.{{cite journal |first1=N. |last1=Narukage |last2=Eto |year=2004 |first2=Shigeru |last3=Kadota |first3=Miwako |last4=Kitai |first4=Reizaburo |last5=Kurokawa |first5=Hiroki |last6=Shibata |first6=Kazunari |title=Moreton waves observed at Hida Observatory|journal = Proceedings IAU Symposium |issue = 223 |pages = 367–370 |doi=10.1017/S1743921304006143 |volume = 2004|bibcode=2004IAUS..223..367N |doi-access=free }}