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

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Thermospheric K Chemistry

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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

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Ionosonde measurements, 7 UT

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4 MHzPlasma Frequency

Altit

ude

The ionogram indicates the presence of a fairly strong Es layer. 4 MHz [e-] ~ 2×105/cc

2

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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?

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K Integrated Column above 110 km

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StatisticalNoise

A hint at an enhancement at 04 UT (local midnight), 6-h wave?

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Wave modulation of K densities below 100 km

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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.

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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