SA41C-03 1
Metal atoms observed in the thermosphere over Arecibo
Jonathan S. Friedman (SRI-AO)Xinzhao Chu (UCB–CIRES)Christiano Brum (SRI-AO)
Steven M. Smith (BU)Jia Yue (NCAR)
(and many others)
AGU Fall Meeting 2011
SA41C-03 2
AO K Lidar – 12 March 2005
AGU Fall Meeting 2011
(Note the log scale)
Layer descent rate is ~ 20 km/hr, or ~ 6 m/s
SA41C-03 3
Thermospheric K Chemistry
AGU Fall Meeting 2011
recombination rate ≈ 10-11 cm3/sK+ lifetime is ~240 hrs in a 2×105 e-/cc Es
for O2 k = 5.6 × 10-9 cm3/sfor NO k = 4 × 10-9 cm3/s
Neutralization production of K
Ionization loss of K
K lifetime is ~140 hrs at 135 km.K production exceeds loss by 25x
d[K]/dt = 5×10-5/s [e-] ~ 2×104/cc and
Ionosonde echoes [e-] ~ 2×105/cc
SA41C-03 4
Ionosonde measurements, 7 UT
AGU Fall Meeting 2011
4 MHzPlasma Frequency
Altit
ude
The ionogram indicates the presence of a fairly strong Es layer. 4 MHz [e-] ~ 2×105/cc
2
SA41C-03 5
TIL-like properties of the layer• TIL a wavefront, and a 20 km/hr (6 m/s)
wave would be consistent with a semidiurnal tide or gravity wave.(Chu et al. (GRL 2011 & SA44A-03) observed periodicity in the thermosphere over McMurdo and thus were able to establish the wave parameters related to the layer.)
• TIL Periodicity in the thermosphere.Upper mesosphere?
AGU Fall Meeting 2011
SA41C-03 6
K Integrated Column above 110 km
AGU Fall Meeting 2011
StatisticalNoise
A hint at an enhancement at 04 UT (local midnight), 6-h wave?
SA41C-03 7
Wave modulation of K densities below 100 km
AGU Fall Meeting 2011
10-10
- An upward-propagating GW of period ca. 115 min is seen to reflect after 4 UT.- Discontinuity in the profile centroid at 6:40 UT.
SA41C-03 8
Thermospheric Neutral Atom Layer Summary
• The characteristics of the layer are similar to those of a tidal ion layer: Phase velocity, morphology, concentration.
• There is a strong Es layer prior to the appearance of the thermospheric K layer.
• Neutral K production and loss rates are reasonable.
• The descent rate of ~6 m/s is slower than a typical tidal ion layer (~30 m/s). Does this allow time for the neutralization?
Note: Geomagnetic activity: Kp ≤ 1, low TEC.AGU Fall Meeting 2011
SA41C-03 9
Conclusions• We have presented what is, to our knowledge, the
first observation of a neutral metal (K) atom layer extending above 150 km into the thermosphere.
• It is likely the source of the K atoms is through radiative recombination of K+ within an Es layer.
• The evidence indicates the occurrence of a strong, localized sporadic E layer with sufficient K+ content over a long enough lifetime to produce detectable K through radiative recombination, although the altitude of the Es is unknown.
• After many hundreds of nights, 1000s of hours over 12 years observing this event is unique. Why?
AGU Fall Meeting 2011