Observations of dramatic enhancements to the mesopheric K layer

Highly concentrated layers of atomic K have been observed in the mesosphere above Yanqing near Beijing (40°N, 116°E). The K density in these narrow layers exceeds 1,100 cm−3 (at least 4 times higher than reported elsewhere), and the K/Na ratio is superchondritic by a factor of 3–4. A model with detailed metal ion chemistry, supported by ancillary measurements from a nearby ionosonde and meteor radar, is used to show that these sporadic K layers can be produced from a strong sporadic E layer (critical frequency > 11 MHz) that descends from above 100 km at a velocity of 1–2 km h−1. This allows most of the Na+ ions to be neutralized before the remaining ions are dumped around 90 km, where the higher pressures and colder temperatures facilitate the formation of K+.N2 and K+.CO2 cluster ions. These cluster ions then undergo dissociative recombination with electrons to form K.