1. March 31, 2016
Characterization of High- to Medium-Frequency
Gravity Waves in the Mesosphere Lower
Thermosphere Region using WACCM
Alan Sánchez
Chu Research Group
Cooperative Institute for Research in Environmental Sciences

2. Atmospheric Gravity Waves
Initial disturbance
Airflow over mountains
Tropospheric jet streams
Buoyancy force in atmosphere due to
vertically varying density
Attempts to restore equilibrium in air, resulting in wave
Carry large amounts of energy/momentum
Affect mean circulation
Affect mean temperature and winds antarctica.gov.au
nasa.gov
2

3. Mesoscale Gravity Waves
Defined as GWs with:
1-4 hr period
Horizontal wavelength 50-500 km
Typically created by lower atmosphere
activities
Propagate upwards and affect MLT activities,
weather systems, and space weather
Scarcely studied because of instrumental
limitations
ucar.edu
nasa.gov
3

4. Instrumental Limitations
There exists no single technique to completely obtain a GW’s parameters
Requires coordinated study with multiple instruments
Airglow imagers - λx, λy
LIDAR - λz
Radar - λz
LIDAR systems are limited to range of ~ 80-110 km
Much left to be discovered on origins and behavior in upper atmosphere
4

5. Whole Atmosphere Community Climate Model (WACCM)
Comprehensive numerical model spanning the range of altitude from Earth’s surface
to the thermosphere
15 minute temporal resolution
¼ degree spatial resolution (~20 km)
Given 8 days of data from February 04-11, 2015
Latitude: ~39 to ~41°N
Longitude: 100 to 120 °W
Geopotential Height: ~80km to ~110km
Zonal wind (U), Meridional wind (V), Temperature (T), Vertical wind (W) 5

6. Initial Process
1. Analyze entire 8 day span from February 04-11 in search of high- to medium-
frequency GWs
2. Analyze data wrt time and one other dimension (i.e. time vs z)
a. Raw data
b. Raw data - perturbation (mean at each altitude)
c. Filtered data
i. Butterworth filter, high pass was used for initial investigation (up to 4hr period)
d. “Smoothed”
i. Subtract (smooth(U_pert(j,:),8)) from perturbation 6

7. Raw fields - Not particularly useful (besides in W)
7

8. Perturbation fields - Subtracting the mean at each altitude
8

9. Applying high-pass filter extracts waves with desired periods
9

10. Wavelet analysis confirms February 8 as a good candidate
10

11. Continued the study focusing on February 8
Choose wave(s) to characterize
Period
Phase
Vertical wavelength
Horizontal Wavelength
Searching for GW near Boulder region at ~98 km with period of ~ 2 hr
11

12. Decent results, but GW not clear enough/long enough to analyze.
Opted to check other latitudes/longitudes where this wave may be at a lower
altitude because it seems to be propagating upwards
Still looking for roughly 2 hr period wave around hr 13 of February 8, 2015
12

13. 13
Promising GW found passing through 40.6641 N, 113.4375 W

14. 14
Wavelet analysis confirms: GW with ~1.02 hr period
1.012
1.0121.026
0.6629

15. With a period of 1.02 hr identified, one can narrow down
bandpass filter substantially
15UT 11.5 - 16

16. 16
Bandpass filtered data during time of wave event

17. Characterizing a 3-dimensional, time-variant wave
Make wave a function of time and one other parameter
Obtain wave characteristics in wrt that dimension only
17

18. Wave event fit to the proper form
Place appropriate limits on wave parameters
Fit all U, V, T, and W data in time and Z to this wave
equation
Derive amplitude (average)
Derive phase (average)
Derive λz
Obtain plots of fitted parameters
1818

19. 19
Fitted data (1D Fitting)

20. Amplitude and phase in all four parameters
20

21. Slope of linear fit to wave phase used to
derive λz (average)
21
Derive wavelength

22. Parameters fitted using 2D Fitting
22

23. Results (to be continued)
23
T [hr] 1.02 ± 0.10
λz [km] 13.63 ± 0.021

24. Conclusions, Broader Impacts, and Future Work
Preliminary results match well with experimental observations
First validation of newly refined WACCM
Enables an unprecedented study of source of GWs,as well as behavior in upper
atmosphere, by eliminating instrumental limitations,
Request lower altitude/higher altitude data from NCAR
Continue studying this GW
Expand study to other GWs
24

25. March 31, 2016
Questions?