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On the night of 2 June 2002, the sodium lidar in Fort Collins, CO (40.6 N,105 W) measured an extremely strong sporadic sodium layer lasting from 03:30 to05:00 UT with several weaker layers later in the night at 06:00 and 09:00 UT. There is adouble layer structure with peaks at 101 and 104 km. The peak sodium densitywas 21 000 atoms/cm3 with a column abundance of up to twice that of thenormal sodium layer. The peak density was 500 times greater than the typicaldensity at that altitude. The sporadic layer abundance and strength factorwere higher than any reported in the literature. The two lidar beams,separated by 70 km at this altitude, both measured 0.6 h periodicities inthe abundance, but out of phase with each other by 0.3 h. There is alsoevidence for strong wave activity in the lidar temperatures and winds. TheNOAA ionosonde in Boulder, CO (40.0 N, 105 W) measured a critical frequency(foEs) of 14.3 MHz at 03:00 UT on this night, the highest valueanytime during 2002. The high values of total ion density inferred meansthat Na+ fraction must have been only a few percent to explain theneutral Na layer abundances. The Bear Lake, Utah (41.9 N, 111.4 W) dynasondealso measured intense Es between 02:00 and 05:00 UT and again from 06:00 to 08:00 UTabout 700 km west of the lidar, with most of the ionograms during theseintervals measuring Es up to 12 MHz, the limit of the ionosonde sweep.Other ionosondes around North America on the NGDC database measured normalfoEs values that night, so it was a localized event within NorthAmerica. The peak of Es activity observed in Europe during the summerof 2002 occurred on 4 June. The observations are consistent with the currenttheories where a combination of wind shears and long period waves form andpush downward a concentrated layer of ions, which then chemically react andform a narrow layer of sodium atoms

Coincident extremely large sporadic sodium and sporadic E layers observed in the lower thermosphere over Colorado and Utah