Transmission of planetary wave effects to the upper atmosphere by

Transmission of Planetary Wave Effects to the Upper Atmosphere by Modula=on of Turbulent Mixing Vu A. Nguyen1 and Sco1 E. Palo1 (1)  Department of Aerospace Engineering Sciences, University of Colorado, Boulder, Colorado, USA Thursday, June 27, 2013 – CEDAR Workshop 1
Planetary Waves •  Resonant responses of the atmosphere at mulF-­‐day periods (2-­‐day, 10-­‐day, 16-­‐
day etc.) •  Seen as global oscillaFons in wind, temperature, density, etc. •  Forced in the troposphere and stratosphere •  Waves typically dissipate in the MLT (mesosphere-­‐
lower thermosphere) but effects sFll be seen at higher aStudes 16-­‐day planetary wave modulaFon of ionospheric total electron content at ~350 km and 22:00 local Fme. Data obtained from the CHAllenging Minisatellite Payload (CHAMP) satellite. Figure adapted from Pedatella and Forbes, 2009. Thursday, June 27, 2013 – CEDAR Workshop 2
Possible Mechanisms of Planetary Transmission 1.  ModulaFon of upward propagaFng gravity waves (Meyer, 1999) and atmospheric Fdes through nonlinear interacFons (Forbes, 1996) 2.  Direct propagaFon: More common for shorter period waves 3.  In-­‐situ generaFon of planetary waves by EUV/Joule heaFng in the lower thermosphere (Meyer and Forbes, 1997) 4.  Filtering of gravity waves driving the E-­‐region dynamo 5.  Modifica=on of turbulent mixing in the MLT region (Forbes, 1996) Thursday, June 27, 2013 – CEDAR Workshop 3
Modifica=on of Turbulent Mixing Lower Atmosphere MLT Planetary waves modulate the amount of verFcally propagaFng gravity waves through wave filtering Gravity wave/Fdal breaking determines the amount turbulent (eddy) mixing in the MLT region Upper Atmosphere Turbulent (eddy) mixing causes different neutral species to follow mean molecular scale height Gravity Wave Filtering Thursday, June 27, 2013 – CEDAR Workshop 4
Research Objec=ve and Procedure Research Objec=ve •  Understand how the modulaFon of eddy diffusion at planetary wave periods can affect upper atmospheric density •  QuanFfy the effects on the upper atmospheric density at different modulaFon periods Procedure •  Use the NaFonal Center for Atmospheric Research (NCAR) Thermosphere-­‐
Ionosphere-­‐Electrodynamics General CirculaFon Model (TIE-­‐GCM) •  Modulate the eddy diffusion coefficient (20% of the mean value) at a specified period at the model lower boundary (~97 km). •  Compute globally averaged quanFFes and percent change from the control run •  Repeat for different modulaFon periods (4-­‐day, 8-­‐day, 16-­‐day, 32-­‐day) Thursday, June 27, 2013 – CEDAR Workshop 5
Neutral Density at Constant Pressure Level •  Neutral density response is determined by the diffusion of minor species •  Black line shows relaFve eddy diffusion value over the model run •  Percent change in neutral density at constant pressure level is directly propor7onal to the eddy diffusion coefficient Percent Change in N2 Density
Altitude [km]
400
Percent Change in Neutral Density at Constant Pressure
5
300
0
200
−5
400
3
100
0
350
2
400
5
10
15
20
Days Since Start Date
25
1
Altitude [km]
300
5
300
0
200
−5
250
0
100
0
200
−1
400
5
10
15
20
Days Since Start Date
25
Percent Change in O
150
−2
Altitude [km]
Approximate Pressure Altitude [km]
Percent Change in O2 Density
5
300
0
200
−5
100
0
5
10
15
20
Days Since Start Date
25
−3
100
0
5
Thursday, June 27, 2013 – CEDAR Workshop 10
15
20
Days Since Start Date
25
6
Neutral Density at Constant Al=tude Percent Change in N2 Density
400
Altitude [km]
•  Increase/decrease in mean molecular mass at constant pressure level causes decrease/increase in atmospheric scale height •  As a result, percent change in neutral density at constant al7tude is inversely propor7onal to the eddy diffusion coefficient 3
2
1
250
5
−3
150
−4
5
10
15
20
Days Since Start Date
25
−5
25
300
0
200
−5
5
10
15
20
Days Since Start Date
25
Percent Change in O
400
−1
−2
10
15
20
Days Since Start Date
5
0
200
100
0
−5
100
0
Altitude [km]
Altitude [km]
300
200
Percent Change in O2 Density
Altitude [km]
350
0
400
5
4
300
100
0
Percent Change in Neutral Density
400
5
5
300
0
200
−5
100
0
5
Thursday, June 27, 2013 – CEDAR Workshop 10
15
20
Days Since Start Date
25
7
Electron Density at Constant Al=tude Percent Change in Neutral Species and Electron Density at 117.5 km
4
2
0
−1
−3
5
−4
0
4
350
1
−2
Percent Change in Electron Density
400
Electron
N2
O
O2
3
Percent Change
•  Electron density change follows the change in neutral species composiFon •  Different drivers are present in different alFtude regimes •  Below 180 km: Electron density is primarily driven by change in N2 and O2 •  Above 180 km: Electron density is driven by change in O 5
10
15
Days Since Start Date
20
25
3
Percent Change in Neutral Species and Electron Density at 400 km
2
6
1
4
250
0
−1
200
−2
−3
150
2
0
−2
−4
−6
−4
100
0
Percent Change
Altitude [km]
300
8
5
10
15
20
Days Since Start Date
25
−8
0
5
−5
Thursday, June 27, 2013 – CEDAR Workshop 10
15
Days Since Start Date
20
25
8
Electron Density at Constant Al=tude •  Experiment is repeated for different modulaFon periods (4-­‐days, 8-­‐day, 32-­‐day) to compare amplitude response •  Results show that the atmosphere acts like a low pass filter for this mechanism •  The amplitude of the response is larger for longer eddy diffusion modulaFon periods •  Cutoff period is determined by the lag of the response •  More response lag will result in a larger cutoff period Amplitude of Neutral Density Response
Amplitude of Electron Density Response
5
5
400 km
220 km
180 km
117.5 km
4.5
4
3.5
Amplitude [% Change]
Amplitude [% Change]
4
4.5
3
2.5
2
1.5
1
3.5
3
2.5
2
1.5
1
0.5
0
0
400 km
220 km
180 km
117.5 km
0.5
5
10
15
20
Period [Days]
25
30
35
0
0
5
10
Thursday, June 27, 2013 – CEDAR Workshop 15
20
Period [Days]
25
30
35
9
Conclusions/Future Work •  Conclusions –  Varying the eddy diffusion coefficient in the MLT has the potenFal to induce planetary wave oscillaFons in the upper atmosphere •  A 20% change in eddy diffusion causes a ~5% change in neutral and electron density at 400 km –  Results show this mechanism is more efficient for longer period waves •  Future Ques=ons –  How does gravity wave filtering by planetary waves actually modulate the eddy diffusion in the MLT region? –  How does this mechanism compare to other mechanisms for planetary transmission in the upper atmosphere? Thursday, June 27, 2013 – CEDAR Workshop 10 Acknowledgements •  This research was supported by NSF grant AGS-­‐0836518, part of the CEDAR program under Dr. Sco1 Palo. Thursday, June 27, 2013 – CEDAR Workshop 11 References •  Forbes, J. M., Planetary Waves in the Thermosphere-­‐
Ionosphere System, J. Geomag. Geoelec., 48 (1), 91-­‐98, 1996. •  Meyer, C. K., and J. M. Forbes, Natural resonance of the Ionosphere-­‐Thermosphere-­‐Mesosphere (ITM) system, J. Atmos. Sol. Terr. Phys., 59(17), 2185-­‐2202, 1997. •  Meyer, C. K., Gravity wave interacFons with mesospheric planetary waves: A mechanism for penetraFon into the thermosphere-­‐ionosphere system, J. Geophys. Res., 104, 28181-­‐28196, 1999. •  Pedatella, N. M., and J. M. Forbes, ModulaFon of the equatorial F-­‐region by the quasi-­‐16-­‐day planetary wave, Geophys. Res. Le1., 36, 2009. Thursday, June 27, 2013 – CEDAR Workshop 12