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

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

ascending

descending

30 km

October-November, 2005

30 km: ~10-day eastward-propagating structures (Kelvin waves) clearly visible

ascending

descending

90 km

October-November, 2005

90 km: Larger amplitudes, but no clear patterns. Kelvin waves probably masked by day-to- day variability of tides, gravity waves, etc.

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

“Background spectrum” due to various sources ofvariability, e.g., tides, gravity waves

3.0-3.5 day Ultra-fast Kelvin Wave

6-7 day oscillation ~16-day normal mode

ISO, possiblydriven by UFKW &diurnal tide EPFD (e.g.,Miyoshi & Fujiwara,GRL, 2006)

Multi-Year Mean Spectrum

λz =2π

N

λ xT

− u⎛⎝⎜

⎞⎠⎟

λz = vertical wavelength

λx = zonal wavelength

T = wave period

N = buoyancy frequency

ubar = zonal mean u (= 0)

e.g. Holton et al. (2001)

35-42 47

21 14

30

18 10

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

Zonal phase speed ms-1116 38

155 58

13

9

9

3730

Slow Kelvinwaves

Ultra fast Kelvin waves

21

1714

35-42

In Addition to Kelvin Waves, Other Parts of the Spectrum also Vary with Height, e.g., s = 0

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

• 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 ISO’s 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).

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

The SABER data provide the first look at the above that extends continuously from 20-120 km, -50o to +50o

latitude, 2002 to 2006

ISO of 2.5-4.5 day Wave Amplitudes, 90 km, Eastward s = -1

3.3 km day-1

Filtered zonal mean 20-60 days ~± 2-4K

UFKW and Zonal Mean Variability at the Equator, 2003

UFKW

Zonal Mean

Spectra show some similarities, but not close correspondence. However, the “UFKW” omits the effects of longer-period and s -1 KW & DT

• 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 > 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)

SUMMARY & CONCLUSIONS