Editing Ionosphere (section)

==History of discovery==
As early as 1839, the German mathematician and physicist [[Carl Friedrich Gauss]] postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field.<ref>{{cite book |last1=Gauss |first1=Carl Friedrich |editor1-last=Gauss |editor1-first=Carl Friedrich |editor2-last=Weber |editor2-first=Wilhelm |title=Resultate aus den Beobachtungen des Magnetischen Vereins im Jahre 1838 |trans-title=Findings from the Observations of the Magnetic Society in the Year 1838 |date=1839 |publisher=Weidmanns' Bookshop |location=Leipzig, (Germany) |pages=1–57 |url=https://books.google.com/books?id=TYI5AAAAcAAJ&pg=PA50 |language=German |chapter=Allgemeine Theorie des Erdmagnetismus [General theory of terrestrial magnetism]}} Gauss speculated that magnetic forces might be generated not only by electrical currents flowing through the Earth's interior but also by some sort of electrical current(s) flowing through the atmosphere. From p. 50:  ''"§ 36. Ein anderer Theil unserer Theorie, über welchen ein Zweifel Statt finden kann, ist die Voraussetzung, … zu untersuchen, wie die aus denselben hervorgehende magnetische Wirkung auf der Erdoberfläche sich gestalten würde."''  (Another part of our theory about which doubt may arise is the assumption that the agents of terrestrial magnetic force have their source exclusively in the interior of the Earth.   If the immediate causes [of terrestrial magnetism] should be sought entirely or in part outside [the Earth's interior], then we can — in so far as we exclude baseless fantasies and we want to restrict ourselves to the scientifically known [facts] — consider only galvanic currents. Atmospheric air is not a conductor of such currents; empty space also is not: thus our knowledge fails us when we seek a carrier for galvanic currents in the upper regions [of the atmosphere]. Only the enigmatic phenomena of the northern lights — in which by all appearances electricity in motion plays a major role — prohibits us from simply denying the possibility of such currents just on account of that ignorance, and in any case it remains interesting to investigate how the magnetic effect resulting from [those currents] would manifest itself on the Earth's surface.)  
*  English translation: {{cite book |last1=Gauss |first1=Carl Friedrich |last2=Sabine |first2=Elizabeth Juliana, trans. |editor1-last=Taylor |editor1-first=Richard |title=Scientific Memoirs, Selected from the Transactions of Foreign Academies of Science and Learned Societies, and from Foreign Journals |date=1841 |publisher=Richard and John E. Taylor |location=London, England |pages=184–251 |chapter-url=https://books.google.com/books?id=Nn9HAQAAMAAJ&pg=PA229 |chapter=General theory of terrestrial magnetism}} See p. 229.
*  English translation: {{cite journal |last1=Glassmeier |first1=K.-H |last2=Tsurutani |first2=B. T. |title=Carl Friedrich Gauss – General Theory of Terrestrial Magnetism – a revised translation of the German text |journal=History of Geo- and Space Sciences |date=2014 |volume=5 |issue=1 |pages=11–62|doi=10.5194/hgss-5-11-2014 |bibcode=2014HGSS....5...11G |doi-access=free }}</ref> Sixty years later, [[Guglielmo Marconi]] received the first trans-Atlantic radio signal on December 12, 1901, in [[St. John's, Newfoundland]] (now in [[Canada]]) using a {{convert|152.4|m|ft|abbr=on}} kite-supported antenna for reception.<ref>{{Cite journal |last=Marconi |first=Guglielmo |date=January 2002 |title=Wireless telegraphic communication |url=http://dx.doi.org/10.1007/bf02836176 |journal=Resonance |volume=7 |issue=1 |pages=95–101 |doi=10.1007/bf02836176 |issn=0971-8044}}</ref> The transmitting station in [[Poldhu]], Cornwall, used a [[spark-gap transmitter]] to produce a signal with a [[frequency]] of approximately 500&nbsp;[[Kilohertz|kHz]] and a power of 100 times more than any radio signal previously produced. The message received was three dits, the [[Morse code]] for the letter '''S'''. To reach Newfoundland the signal would have to bounce off the ionosphere twice. Dr. [[Jack Belrose]] has contested this, however, based on theoretical and experimental work.<ref>John S. Belrose, "[http://www.ieee.ca/millennium/radio/radio_differences.html Fessenden and Marconi: Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century] {{webarchive|url=https://web.archive.org/web/20090123214652/http://www.ieee.ca/millennium/radio/radio_differences.html |date=2009-01-23 }}". International Conference on 100 Years of Radio, 5–7 September 1995.</ref> However, Marconi did achieve transatlantic wireless communications in [[Glace Bay, Nova Scotia]], one year later.<ref>{{Cite journal|title=Marconi and the History of Radio|journal=IEEE Antennas and Propagation Magazine|volume=46}}</ref>

In 1902, [[Oliver Heaviside]] proposed the existence of the [[Kennelly–Heaviside layer]] of the ionosphere which bears his name.<ref>{{cite encyclopedia  | last = Heaviside  | first = Oliver | title = Telegraphy |encyclopedia= Encyclopaedia Britannica |year=1902 | edition = 10th | volume = 33 | pages = 213–235 | url = https://digital.nls.uk/encyclopaedia-britannica/archive/193470565#?c=0&m=0&s=0&cv=238&xywh=2459%2C398%2C2561%2C2108 }} Speaking of wireless telegraphy, Heaviside speculated about the propagation of Hertzian (radio) waves through the atmosphere. From p. 215:  "There may possibly be a sufficiently conducting layer in the upper air. If so, the waves will, so to speak, catch on to it more or less. Then the guidance will be the sea on one side and the upper layer on the other."</ref> Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Also in 1902, [[Arthur Edwin Kennelly]] discovered some of the ionosphere's radio-electrical properties.<ref>{{cite journal |last1=Kennelly |first1=A.E. |title=On the elevation of the electrically conducting strata of the earth's atmosphere |journal=The Electrical World and Engineer |date=15 March 1902 |volume=39 |issue=11 |page=473 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015048964426&view=1up&seq=497&skin=2021}}</ref>

In 1912, the [[U.S. Congress]] imposed the [[Radio Act of 1912]] on [[amateur radio operators]], limiting their operations to frequencies above 1.5&nbsp;MHz (wavelength 200 meters or smaller). The government thought those frequencies were useless. This led to the discovery of HF radio propagation via the ionosphere in 1923.<ref>[https://worldradiohistory.com/BOOKSHELF-ARH/On-The-Short-Waves.pdf worldradiohistory.com: Broadcast listening in the pioneer days of radio on the short waves, 1923 1945 Jerome S. Berg] Quote: "...In addition to having to obtain licenses - a constraint to which they adapted only slowly - the amateurs were, with some exceptions, restricted to the range below 200 meters (that is, above 1500 kc.), bands that were largely unexplored and thought to be of little value. The navy attributed most interference to the amateurs, and was happy to see them on the road to a hoped - for extinction. From the amateurs' point of view, their development of the shortwave spectrum began less as a love affair than a shotgun marriage. However, all that would change...It took several years before experimenters ventured above 2-3 mc. and started to understand such things as shortwave propagation and directionality. The short waves, as they were called, were surrounded with mystery...Also in 1928 Radio News publisher Hugo Gernsback began shortwave broadcasting on 9700 kc. from his station, WRNY, New York, using the call W2XAL. "A reader in New South Wales, Aus- tralia," reported Gernsback, "writes us that while he was writing his letter he was listening to WRNY's short-wave transmitter, 2XAL, on a three-tube set; and had to turn down the volume, otherwise he would wake up his family. All this at a distance of some 10,000 miles! Yet 2XAL ...uses less than 500 watts; a quite negligible amount of power. "6...The 1930s were the golden age of shortwave broadcasting...Shortwave also facilitated communication with people in remote areas. Amateur radio became a basic ingredient of all expeditions...The term shortwave was generally taken to refer to anything above 1.5 mc., without upper limit...", [https://web.archive.org/web/20210703104647/https://worldradiohistory.com/BOOKSHELF-ARH/On-The-Short-Waves.pdf backup]</ref>

In 1925, observations during [[Solar eclipse of January 24, 1925|a solar eclipse]] in New York by [[Alfred Norton Goldsmith|Dr. Alfred N. Goldsmith]] and his team demonstrated the influence of sunlight on radio wave propagation, revealing that short waves became weak or inaudible while long waves steadied during the eclipse, thus contributing to the understanding of the ionosphere's role in radio transmission.<ref>{{cite news |title=Sun Affects Radio, Observations Show |url=https://timesmachine.nytimes.com/timesmachine/1925/01/25/101635261.html |access-date=25 January 2024 |work=[[The New York Times]] |issue=24473  |date=25 January 1925 |pages=1, 4}}</ref>

In 1926, Scottish physicist [[Robert Watson-Watt]] introduced the term ''ionosphere'' in a letter published only in 1969 in ''[[Nature (journal)|Nature]]'':<ref>The letter, dated 8 November 1926, was addressed to the Secretary
of the Radio Research Board.
*  The letter was quoted in: {{cite journal |last1=Gardiner |first1=G. W. |title=Origin of the term Ionosphere |journal=Nature |date=13 December 1969 |volume=224 |issue=5224 |page=1096|doi=10.1038/2241096a0 |bibcode=1969Natur.224.1096G |s2cid=4296253 |doi-access=free }}
*  See also:  {{cite journal |last1=Ratcliffe |first1=J.A. |title=Robert Alexander Watson-Watt |journal=Biographical Memoirs of Fellows of the Royal Society |date=1975 |volume=21 |pages=549–568}} See p. 554.</ref>

{{Blockquote|We have in quite recent years seen the universal adoption of the term 'stratosphere'..and..the companion term 'troposphere'...&nbsp;The term 'ionosphere', for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series.}}

In the early 1930s, test transmissions of [[Radio Luxembourg]] inadvertently provided evidence of the first radio modification of the ionosphere; [[HAARP]] ran a series of experiments in 2017 using the eponymous [[Luxemburg–Gorky effect|Luxembourg Effect]].<ref name="Gakona HAARPoon 2017">{{cite web |url=https://sites.google.com/alaska.edu/gakonahaarpoon/operations-news |title=Gakona HAARPoon 2017 |date=2017-02-19 |url-status=live |archive-url=https://web.archive.org/web/20170220175950/https://sites.google.com/alaska.edu/gakonahaarpoon/operations-news |archive-date=2017-02-20 }}</ref>

[[Edward V. Appleton]] was awarded a [[Nobel Prize]] in 1947 for his confirmation in 1927 of the existence of the ionosphere. [[Lloyd Berkner]] first measured the height and density of the ionosphere. This permitted the first complete theory of short-wave radio propagation. [[Maurice V. Wilkes]] and [[J. A. Ratcliffe]] researched the topic of radio propagation of very long radio waves in the ionosphere. [[Vitaly Ginzburg]] has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere.

In 1962, the [[Canada|Canadian]] satellite [[Alouette 1]] was launched to study the ionosphere. Following its success were [[Alouette 2]] in 1965 and the two [[ISIS (satellite)|ISIS]] satellites in 1969 and 1971, further AEROS-A and -B in 1972 and 1975, all for measuring the ionosphere.

On July 26, 1963, the first operational geosynchronous satellite Syncom 2 was launched.<ref>{{cite web|url=http://harveycohen.net/crcss/history.html|title=Firsts in the Space Race. From an Australian perspective|website=harveycohen.net|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170911162138/http://harveycohen.net/crcss/history.html|archive-date=11 September 2017}}</ref> On board radio beacons on this satellite (and its successors) enabled – for the first time – the measurement of [[total electron content]] (TEC) variation along a radio beam from geostationary orbit to an earth receiver. (The rotation of the plane of polarization directly measures TEC along the path.)  Australian geophysicist [[Elizabeth Essex-Cohen]] from 1969 onwards was using this technique to monitor the atmosphere above Australia and Antarctica.<ref>{{cite web|url=http://harveycohen.net/essex|title=Elizabeth A. Essex-Cohen Ionospheric Physics Papers etc|website=harveycohen.net|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20170911205109/http://harveycohen.net/essex/|archive-date=11 September 2017}}</ref>