F region

<p>The F region of the <a href="/facts/Ionosphere/mT9tTBE5">ionosphere</a> is home to the F layer of ionization, also called the Appleton–Barnett layer, after the English physicist <a href="/facts/Edward_Victor_Appleton/7FfJIqz5">Edward Appleton</a> and New Zealand physicist and meteorologist <a href="/facts/Miles_Aylmer_Fulton_Barnett/pKAtX3X1">Miles Barnett</a>. As with other ionospheric sectors, 'layer' implies a concentration of <a href="/facts/Plasma_(physics)/1d3btMVU">plasma</a>, while 'region' is the volume that contains the said layer. The F region contains ionized gases at a height of around 150–800 km (93–497 mi) above sea level, placing it in the Earth's <a href="/facts/Thermosphere/uhG50e2V">thermosphere</a>, a hot region in the upper <a href="/facts/Atmosphere/oUpLaGRF">atmosphere</a>, and also in the <a href="/facts/Heterosphere/HJAl2C18">heterosphere</a>, where chemical composition varies with height. Generally speaking, the F region has the highest concentration of free <a href="/facts/Electrons/L0KBo5cW">electrons</a> and <a href="/facts/Ions/fXGhgbFc">ions</a> anywhere in the atmosphere. It may be thought of as comprising two layers, the F1 and F2 layers.
</p><p>The F-region is located directly above the <a href="/facts/E_region/KTaSSGeP">E region</a> (formerly the Kennelly-Heaviside layer) and below the <a href="/facts/Protonosphere/Iuc6bNqa">protonosphere</a>. It acts as a dependable reflector of HF radio signals as it is not affected by atmospheric conditions, although its ionic composition varies with the sunspot cycle. It reflects normal-incident frequencies at or below the <a href="/facts/Critical_frequency/6Kc5xFTj">critical frequency</a> (approximately 10 MHz) and partially absorbs waves of higher frequency.
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F region open-in-new

F region