Kelvin Waves and the QBO

Rolando Garcia

2 Colorado Research Associates, Boulder, CO

1

HIRDLS JAN 08 2

Synoptic mapping of long asynoptic data sequences• Example using TIMED/SABER temperature data

• Salby’s Fast-Fourier Synoptic Mapping

• Extension to arbitrarily long data sequences

Compare with models• WACCM3 with different convective parameterizations

• Compare wave forcing in model vs. observational estimates

HIRDLS data• Higher vertical resolution

• Ozone and water vapor (?)

HIRDLS JAN 08 3

SABER observations are asynoptic:

• Salby (1982) has shown that one can obtain a synoptic spectrum from the spectra of asynoptic observations referred to an “s-coordinate”:

(which is a hybrid of longitude and UT)

• Salby’s technique requires a regular observation sequence (which SABER–and HIRDLS–can provide)

• Fourier analysis of asynoptic data yields an asynoptic spectrum that corresponds closely to the synoptic one

• The technique has usually been applied to observations made in a single satellite “yaw cycle”

• But the technique can be extended to data sequences of arbitrary length

€

s =c0 λ − t

1+ c02

HIRDLS JAN 08 4

Interpolation to common s-coordinates

• At yaw maneuvers, the value of the s-coordinate shifts slightly, as shown on the right

• To analyze data sequences longer than one yaw cycle, the observations are interpolated to common ascending and descending s-coordinates

• The data are interpolated across gaps associated with yaw maneuvers

• The analysis then proceeds as usual; but it can be extended to arbitrarily long sequences of data. Here we will show results for 1-year sequences.

this shows the common s-cordinates for an

entire year’s sequence (>5000 orbits), referred to common sasc so the

entire sequence can be viewed clearly

absolute values of s

s relative to common sasc

yaw maneuver

sasc

sdesc

common sasc

common sdesc

common sasc

common sdesc

sasc

sdesc

HIRDLS JAN 08 5

Equatorial waves: Equatorial Spectra(z,) for m = 1

1. high-frequency Kevin waves2. low-frequency Kelvin waves3. diurnal tide4. non-sun-synchronous tide

Note sign convention: • positive frequencies <=> westward• negative frequencies <=> eastwardfrequencies are given in cycles/day (cpd)

2

stratosphere and mesosphere stratosphere

1 4 3

2

HIRDLS JAN 08 6

Examples of Kelvin wave structures1. m=1 Kelvin wave structure, ~12 d 2. m=1 Kelvin wave structure, ~3 d

0.5 K

2.5 K

These wave structures are obtained via Hayashi (1971) coherence analysis. Only locations with significance level > 1 are plotted. Note different latitude scales.

These waves are presumed to play a role in forcing

the QBO

HIRDLS JAN 08 7

Low-frequency m=1 Kelvin waves ( ~ 20 days) and the QBO

0402

03 05

06

2003

2002

~ 0.05 cpd => ~ 20 d i.e., c ~ 20 ms-1 for m=1

Spectra (z,), m=1, Equator

HIRDLS JAN 08 8

QBO West QBO East

2002

20052004

2003

Amplitude(t,z) of m=1 Kelvin waves at the Equator

note the clear relationship between wave amplitude and QBO phase at z ~ 2 – 5.5 s.h.

amplitude in frequency range –0.08 to –0.025 cpd, or  ~ 12–40 days

eastward

HIRDLS JAN 08 9

Work with WACCM highlights the importance of the parameterization

of convection

HIRDLS JAN 08 10

Model calculations vs. SABER observations of temperature at

10 mb in the Tropics

• Spectra in WACCM and SABER observations are remarkably similar overall• But relative amplitude of east- vs. west-propagating (arrows) waves appears smaller in SABER compared to WACCM• Vertical resolution too coarse in SABER? Can HIRDLS data help here?

WACCM + Tietdke

HIRDLS JAN 08 11

Possible Applications of HIRDLS data

• Confirm SABER results for equatorial waves

• Does higher vertical resolution in SABER enhance the detectability of westward-propagating waves (inertia-gravity, Rossby gravity)?

• Use HIRDLS and SABER data to quantify wave driving; compare with model results

• Can ozone and water vapor data be used to look for the signature of the QBO in minor constituents?