Kelvin Waves

1
Kelvin Waves as Observed by the SABER Instrument
on the TIMED Spacecraft
Jeffrey M. Forbes, Xiaoli Zhang, Saburo Miyahara,
Scott E. Palo, James Russell, Christopher J.
Mertens and Martin Mlynczak

• This Paper
• Main Focus on Equatorial Temperatures, 20-120
  km
• Wavenumber vs. Period Spectra as a Function of
  Height
• Ultra-Fast Kelvin Waves (UFKW), Periods 2.5-4.5
  days
• Intraseasonal Oscillation (ISO) of UFKW and
• Zonal Mean Temperatures

2

• Data processing
• Sliding 60-day window, 1 day at a time, covering
  all local times and longitudes
• Extract zonal mean, diurnal semidiurnal solar
  lunar tides,
• stationary planetary waves
• Analyze residuals from above fit

Raw Temperature Residuals at Equator
3

• Data processing sliding fits performed
• zonal wavenumbers s -6 (eastward) to s 6
  (westward)
• periods 2 to 20 days in increments of 0.5 days
• window length 3 x wave period
• all data during 2002-2006

4
Dominant Kelvin waves (s -1, s -2) transition
from long-periods (5-10 days) and
short-wavelengths (9-13 km) in the stratosphere,
to shorter periods (2-3 days) and longer
wavelengths (35-45 km) in the MLT
35-42
47
21
14
155
58
30
18
10
Zonal phase speed ms-1
116
38
5
In Addition to Kelvin Waves, Other Parts of the
Spectrum also Vary with Height, e.g., s 0
6
Results similar to the previous were obtained by
examining the symmetric component of the
temperature residuals No notable results were
obtained when the anti-symmetric component of the
temperature residuals was examined.

• We now concentrate on
• MLT Kelvin waves, periods 2.5-4.5 days, i.e.,
  UFKW
• Characterizing IS variability of MLT UFKW, and
  possible connections with IS variability of the
  zonal mean state

7
Ultra-Fast Kelvin Waves (UFKW), Diurnal Tides
(DT) and Intraseasonal Oscillations (ISO) in the
MLT

• In the context of a full-atmosphere GCM,
  Miyoshi and Fujiwara (2006) established
  connections between EPFD due to DT and UFKW, and
  20-60 day ISO in zonal mean winds.
• Variations in DT and UFKW are connected with
  established troposphere ISOs at 20-25 days
  (Hartmann et al., 1992) and 40-60 days (Madden
  and Julian, 1994) manifested in tropical
  convection, e.g., latent heating rates.
• Existence of UFKW are well-established in the
  tropical MLT
• Lieberman and Riggin (1997), Riggin et al.
  (1997), Yoshida et al. (1999)
• Previous similar suggestions and supportive
  observations relating waves and ISO in the MLT
  provided by Eckerman et al. (1997), Isoda et al.
  (2004), Lieberman et al. (1998).

The SABER data provide the first look at the
above that extends continuously from 20-120 km,
-50o to 50o latitude, 2002 to 2006
8
ISO of 2.5-4.5 day Wave Amplitudes, 90 km,
Eastward s -1
9
UFKW and Zonal Mean Variability at the Equator,
2003
3.3 km day-1
Filtered zonal mean 20-60 days 2-4K
10
Spectra show some similarities, but not close
correspondence. However, the UFKW omits the
effects of longer-period and s ? -1 KW DT
UFKW
Zonal Mean
11
SUMMARY CONCLUSIONS

• SABER temperature data provide the first
  opportunity to see vertical coupling from the
  lower stratosphere to lower thermosphere in the
  equatorial region vis-à-vis vertically-propagating
  waves with periods gt 2 days.
• The dominant waves responsible for this
  coupling are symmetric eastward-propagating
  waves, i.e., Kelvin waves.
• Dominant Kelvin waves transition from
  long-periods (5-10 days) and short-wavelengths
  (9-13 km) in the stratosphere, to shorter periods
  (2-3 days) and longer wavelengths (35-45 km) in
  the MLT.
• UFKW (periods 2.5-4.5 days) intermittently
  exist at similar amplitudes (3-10 K, 80-120 km)
  during all months of the year, with variability
  in the 20-60 day range.
• An ISO of zonal mean temperatures also exists
  with periods 20-60 days that may be driven by
  EPFD due, at least in part, to UFKW.
• The zonal mean ISO preferentially exists above
  70 km, consistent with in-situ generation at
  these altitudes.
• Possible F-region effects of UFKW vis-à-vis
  dynamo, similar to DE3?
• (see Takahashi et al. Paper 4.2-10)