The Response of the Thermosphere and Ionosphere to the Dissipation of Gravity Waves Generated from Deep Convection

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The Response of the Thermosphere and Ionosphere
to the Dissipation of Gravity Waves Generated
from Deep Convection
Sharon Vadas NorthWest Research
Associates/CoRA and Hanli Liu NCAR/High Altitude
Observatory
IAGA, II06, 0474 Equatorial
atmosphere-ionosphere interactive processes
vertical and latitudinal coupling and
magnetospheric forcing SAT, 29 August, 9AM, 2009
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Yucca Ridge OH imager, Colorado 8 Sept, 2005
Observations of concentric Gws Taylor and
Hapgood, 1988 Dewan etal, 1998 Sentman etal,
2003 Suzuki etal, 2006 Yue etal, 2009?
Overshooting convective plumes create concentric
rings of gravity waves
z87 km
(Coutesy of Jia Yue, Colorado State)?
Yue etal (2009)?
3
Modeled GWs excited by a deep convective plume in
Brazil on 01 October, 2005 density perturbations
z90 km (mesopause)?

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latitude
Many of these excited primary GWs propagate into
the mesosphere and thermosphere
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(Vadas and Liu, 2009)?
longitude
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Excited primary GWs with ?Hlt150 km dissipate in
the thermosphere at z120-200 km, creating
horizontal body forces
z250 km
These body forces Create medium and large-scale
secondary GWs which radiate outward and upward
(to zgt420 km) globally and Drive a mean flow in
the background neutral winds
latitude
longitude
altitude
latitude
Temperature perturbations are ?T? 20-30o Wind
perturbations are 100-400 m/s
z190 km
(Vadas and Liu, 2009)?
5
Large-scale travelling ionospheric disturbances
(TIDs) are created which follow the secondary
GWs globally
(Vadas and Liu, 2009)?
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NEW RESULTS
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Thermospheric response to 6 hours of deep
convection on 01 Oct, 2005, in Brazil during
SpreadFEx campaign 0 to 20oS and 45-65oW and
1822-2408 UT (LTUT-3)
Total of 272 convective objects (plumes,
clusters, etc) Input thermospheric
body forces into the TIME-GCM
Ray trace GWs with parameterized GW breaking
(Lindzen, 1981). This reduces the primary GW
amplitudes by a factor of 5-10
GW breaking in thermosphere at z110-140
km ?H?30-50 km, ?z??0-15 km
(Lund and Fritts)
Minimum scales of turbulence ?1 km
?z
?x
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Neutral density perturbations from TIME-GCM
These are the large-scale SECONDARY GRAVITY
WAVE perturbations!!
z250 km, 2230 UT
z270-300 km
At 730 PM LT, there is a neutral density
depletion of 10 over western-mid Brazil, and a
neutral density enhancement of 6 over eastern
Brazil
Vadas and Liu, in preparation
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Neutral Horizontal Wind Perturbations from
Secondary GWs at z250 km
Tidal winds are 20-40 m/s
DIFFERENCE neutral horizontal winds at z250 km
are large max(U,V) ???? m/s. Therefore, MUST ADD
THESE WINDS TO THE TIDAL WINDS prior to
calculating the growth rates for seeding ESF and
plasma bubbles
z250 km, 2230 UT
Vadas and Liu, in preparation
At 730 PM LT, there are 80 m/s eastward and
SEward neutral wind perturbations over mid Brazil
at seeding altitudes
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Neutral Horizontal Wind Perturbations from
Secondary GWs at z250 km
Vadas and Liu, in preparation
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Neutral Horizontal Wind Perturbations from
Secondary GWs at z400 km
DIFFERENCE neutral horizontal winds at z375 km
are max(U,V) ???? m/s.
z375 km, 2230 UT
These are the wind perturbations from SECONDARY
GRAVITY WAVES!!
Vadas and Liu, in preparation
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Neutral Zonal Wind Perturbations from Secondary
GWs at 14o S
Secondary wave perturbations propagate to the top
of the TIME-GCM, at zgt400 km

2230 UT
ALTITUDE

LONGITUDE
Secondary waves can propagate to higher altitudes
than primary waves because smaller wave periods
are obtainable (for the same ?H) where H is
larger in the thermosphere
Vadas and Liu, in preparation
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Spectra of secondary GWs detected at Wallops
Island at the bottomside of the F layer using the
TIDDBIT ionospheric sounder
Distribution looks similar to number of plasma
bubbles as a function of horizontal spacing as
presented yesterday by J. Makela. If seeded by
GWs, those waves with lHgt300 km likely must be
secondary waves!
The peak of the secondary GW spectrum overlaps
with the peak of the primary GW spectrum at the
same altitudes.
(Vadas and Crowley, in preparation)
(peaks at 200 km

primary GWs
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Conclusions
When deep convective plumes overshoot the
tropopause, primary GWs are excited with ??5 to
300 km. Some GWs with ??gt100 km (medium scales)
and high frequencies propagate up to z300 km,
and therefore may help seed ESF. Maximum density
perturbations are 20-30. Those GWs with ??lt150
km (small scales) dissipate at z120-190 km,
creating neutral thermospheric body forces that
last for 30-60 min/plume. Neutral winds and
secondary GWs are excited. These secondary GWs
have neutral density perturbations of up to
10-15 and propagate globally up to zgt400 km.
Because secondary GWs likely have spatial scales
as small as 100 km and periods of 15-25 min
(Vadas and Crowley), they may also be important
for seeding ESF. Neutral zonal wind
perturbations from the large-scale secondary GWs
are large at z250 km, with amplitudes of up to
U100-150 m/s. This can be SIGNIFICANTLY larger
than the background tidal winds, especially at
sunset when the winds are small in the F region.
Additionally, these neutral wind perturbations
are eastward, westward, northward, and southward,
with large horizontal variations. This effect is
likely important for seeding plasma bubbles,
since the Rayleigh Taylor instability growth
rates likely depend on horizontal location.
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Evidence in support of the existence of
secondary GWs 1) DE2 satellite measured O
long-wavelength perturbations of 2 at z300 km
near the equator during geomagnetically quiet
times (Hedin and Mayr, 1987)--agrees well with
our results 2) CHAMP satellite measured RMS
density perturbations of 4-6 at z400 km near
the equator during geomagnetically quiet times
during solar minimum---agrees well with our
results 3) The TIDDBIT ionospheric sounder
observed mostly NW/Nward propagating GWs at
Wallops Island at the bottomside of the F layer.
Using ray trace studies, 27 out of 33 of these
waves were identified as secondary GWs from
Tropical Storm Noel

GWs with ?Hlt235 km reverse ray trace to the
tropopause 500 km north of Noel. Therefore,
likely NOT primary GWs. Instead identified as
initially downward-propagating secondary GWs
which reflected off the ground before re-entering
the thermosphere.
2000 km to closest convective overshoot
(Vadas and Crowley, 2009, in preparationsee
poster in this session)
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Evidence in support of the existence of
thermospheric body forces 1) EISCAT case study
downward and upward propagating GWs originate
from z200 km at 6UT. Occured during and after
rapid deceleration of the geomagnetic meridional
winds from -80 m/s to zero in 1-1.5 hrs at 5 UT
(Shibata and Schlegel, 1993). 2) PFISR case
study SEward propagating GWs observed
simultaneously with large SEward accelerations in
the extracted neutral thermospheric winds at
z180-200 km. GWs likely excited by mountain
wave breaking (Vadas and Nicolls, 2009)
(Vadas and Nicolls, 2009?)
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GW breaking at z 110-140 km ?x 30-50 km,
?z 10-15 km, u c-U 50 m/s, ? N/3, Re
104
(Lund and Fritts)
Minimum scales of turbulence ?1 km
?z
?x
Convective GWs readily achieve large amplitudes
in LT ---Instability and turbulence extend to
high altitude turbopause is likely an artifact
of lack of recognition of ---larger-scale
turbulence structure in the LT
Slide courtesy of David Fritts
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Convective plume model and ray tracing
updraft of air is modelled as a vertical body
force neglect small-scale structure retain
large-scale envelope of updrafts
Spectrum of GWs excited from a convective plume
with a 15 km envelope
Convective plume
Vertical wavelengths
w'0
ground
image force for wave reflection
Vadas and Fritts (2009)?
Horizontal wavelengths
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Excited GWs with ?Hlt150 km dissipate in the
thermosphere at z120-200 km, creating horizontal
body forces
Convective plume
Body force in this case is southward because the
winds are Nward in the lower thermosphere.
Maximum amplitude is 1 m/s2 at z?180 km.
Duration is 40 min
(Vadas and Liu, 2009)?
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Dissipation altitudes for white noise
GWs Dissipative filtering causes ?z (for the
gravity waves remaining in the spectrum) to
increase nearly exponentially with altitude ?H
also increases rapidly with altitude, and the
wave periods asymptote to 10 - 60 minutes
GWs with ?H 100-600 km, ?z100-125 km and
??20-60 minutes propagate well into the F region
to z250 km before dissipating
(Vadas, JGR,2007)?
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Single deep convective plume on 01 Oct, 2005, in
Brazil
Large scale secondary GWs propagate globally to
the south and north poles in 4-6 hours on the
nightside
Wave amplitudes get smaller with distance from
the body force due to geometric attenuation
Vadas and Liu (2009, under review)?
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Single deep convective plume on 01 Oct, 2005, in
Brazil
Relative O perturbations also propagate
globally, with maximum values of 1.5
Vadas and Liu (2009, under review)?
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