Monitoring of turbulence profile at Cerro Tololo continues throughout June and July 2002. It was rewarded by a discovery of a period of exceptionally calm upper atmosphere on June 19-22, four nights in a row! The seeing as measured by DIMMs (at Tololo, La Silla and Paranal) was good, but not exceptional; without a profiler, one would never know that something special was happening.
On the night of June 19-20, most of the seeing was generated within the first few hundred meters over the ground. MASS actually detects the top of this turbulence in the 0.5km slab. The remaining turbulence in the free atmosphere was located at the top of troposphere and was very stable. Only a small turbulent "packet" at 9:20 UT spoils the calm atmosphere.
Such stably good free-atmosphere seeing was never known to exist before and supercedes any "lucky observer" models made in the past on the basis of occasional balloon turbulence soundings. If ground turbulence were compensated by adaptive optics, an excellent seeing over wide field would be achieved. What was the seeing at Cerro Pachon which is 500m higher than Cerro Tololo? Helas, there was no DIMM there to tell us.
Still more amazing, these conditions last for 3 more nights and degrade only on June 23rd. MASS and DIMM data were acquired continuously for the period of June 10 to 28 which was mostly clear.
