Momentum Budget Analysis of the Migra5ng Diurnal Tide in WACCM4: Seasonal Varia5on

Transcription

1 AGU Chapman Conference Momentum Budget Analysis of the Migrang Diurnal Tide in WACCM4: Seasonal Variaon Xian Lu, Han Li Liu 2, Alan Liu 3, Jia Yue 2, Steven Franke. University of Illinois at Urbana Champaign 2. HAO, NCAR 3. Embry Riddle Aeronaucal University Mar 2,

2 Outline The seasonal variaon of the diurnal de Observaons and WACCM4 The momentum budget for the migrang diurnal de WACCM4 The seasonal variaon of the dal heang and GW forcing WACCM4 Conclusions

3 Meteor Radar Observaon (2 7) Amplitude of the diurnal de (Maui, HI, 2 o N) (a) Zonal Amplitude (m/s) Month(2 7) (b) Meridional Amplitude (m/s) Month(2 7)

4 Semiannual Oscillaon (SAO) of dal amplitude (Maui, 2 o N) (a) Zonal Amplitude (m/s) (b) Meridional Amplitude (m/s) (c) Maximum Zonal Amplitudes (m/s) (d) Maximum Meridional Amplitudes (m/s) Amplitudes (m/s) Month Month

5 SAO of Tidal Amplitude Cerro Pachon, Chile ( o S) (a) Zonal Amplitude (m/s) (b) Meridional Amplitude (m/s) (c) Maximum Zonal Amplitudes (m/s) (d) Maximum Meridional Amplitudes (m/s) Amplitudes (m/s) Month Month SAO is most dominant for the seasonal varia8on of the 8dal amplitude. The strongest diurnal 8de occurs in March.

6 2 SAO of Tidal Amplitude (WACCM4) 3 WACCM WACCM WACCM Month WACCM Month WACCM4 captures the seasonality of the diurnal 8de de (km)

7 Amplitudes of the Migrang Diurnal Tide (March) W Amplitude in Zonal Wind (ms ) W Amplitude in Meridional Wind (ms ) W Amplitude in Temperature (K) Latitude (Deg) Latitude (Deg) Latitude (Deg) [Wu et al., 8] [Mukhtarov et al., 9]

8 Momentum Budget Analysis u t = fv Φ acosφ λ V u + uv a tanφ + F + F ' GW,x A B C Classical Tidal Theory Advecon Curvature Dissipaon [Chapman and Lindzen, 97] Advecon Term: Linear advecon Term: u = u + u' v = v + v' F LinAd,x = ( v' a w = w + w' V u = ( u u acosφ λ + v a u φ + w' u z ) ( u φ + w u z ) u u' acosφ λ + v a u' φ + w u' z )

9 WACCM Amplitude of Time Tendency (Zonal Wind) Zonal Time Tendency Amplitude (m/s/day) W Mar A 4 6 Zonal CF+PGF Tendency Amplitude (m/s/day) W Mar B Zonal Difference Amplitude (m/s/day) W Mar C Total Zonal Advection Forcing Amplitude (m/s/day) Total Zonal GW Forcing Amplitude (m/s/day) GW+Advection Zonal Forcing Amplitude (m/s/day) Advecon GW Sum

10 Amplitude of Time Tendency (Meridional Wind) Meridional Time Tendency Amplitude (m/s/day) W Mar Meridional CF+PGF Tendency Amplitude (m/s/day) W Mar Total Meridional Advection Forcing Amplitude (m/s/day) A Total Meridional GW Forcing Amplitude (m/s/day) Meridional Difference Amplitude (m/s/day) W Mar GW+Advection Meridional Forcing Amplitude (m/s/day) 7 Advect GW SUM 4 4 Advec8on and GW forcing are two most important terms contribu8ng to the momentum budget of the migra8ng diurnal 8de. For the zonal wind, they are comparable while for the meridional wind, advec8on term is more significant. B C

11 Which advecon is more dominant? Zonal (a) Linear Zonal Advection Amplitude (m/s/day) W (b) Nonlinear Zonal Advection Amplitude (m/s/day) W (c) Linear Meridional Advection Amplitude (m/s/day) W 4 4 (d) Nonlinear Meridional Advection Amplitude (m/s/day) W Meridional Linear 4 4 Nonlinear 4 4 Because the zonal mean zonal wind is strong, linear advec8on is 3 8mes larger than nonlinear advec8on in the zonal wind. It is the opposite for the meridional wind.

12 GW sources Frontogenesis > Convecon> Orography Total Zonal GW Forcing (m/s/day) W Mar UTGWORO (m/s/day) W Mar Total Oro BUTGWSPEC (m/s/day) W Mar UTGWSPEC (m/s/day) W Mar Convecon Front

13 Equivalent Rayleigh Fricon [Miyahara and Forbes, 99] u' t = F' u'= u ˆ (t)e i(ωt sλ ) = a(t)e i( ϕ(t )) e i(ωt sλ ) i(ωt sλ ϕ(t )) = a(t)e F'= F ˆ i(ωt sλ ) u (t)e Define the Equivalent Rayleigh Fricon as: F u ERF = ˆ u ˆ = a(t) t a(t) ϕ(t) i(ω ) t Real Part of ERF determines the amplitude change and imaginary part determines the phase change. real(erf) > : Amplitude imag(erf) < : Phase Decrease Advance

14 GW Real ERF U mar( s ) WACCM GW Real ERF V mar( s ) GSWM The structure of GW ERF is similar to that of the GSWM with strongest GW effect near o. But the magnitude in WACCM is one order in magnitude larger than the GSWM. [Hagan et al., 99]

15 Gravity Wave GW Real ERF U mar( 6 s ) ERF Real Part (Zonal Wind) Nonlinear Advecon NlinAd Real ERF U mar( 6 s ) Linear Advecon LinAd Real ERF U mar( 6 s ) Total Real ERF U mar( 6 s ) Total GW drag is a most important term and it always damps the 8de. Ver8cal advec8on of the zonal mean zonal wind plays a role near the equator. Contribu8on by nonlinear advec8on is rela8vely weak.

16 Gravity Wave GW Imag ERF U mar ( 6 s ) Nonlinear Advecon NlinAd Imag ERF U mar ( 6 s ) ERF Imaginary Part (Zonal Wind) Ad Imag ERF U mar ( 6 s ) Linear Advecon Total Imag ERF U mar ( 6 s ) Total GW drag advances the phase. Linear advec8on it the most important term and it is largely determined by Total Imag ERF V mar ( 6 s ) the meridional advec8on of zonal mean wind. 4 Contribu8on by nonlinear advec8on is rela8vely weak.

17 ERF Real Part (Meridional Wind) Gravity Wave GW Real ERF V mar( 6 s ) LinAd Real ERF V mar( 6 s ) 4 Linear Advecon 4 4 Nonlinear Advecon Total NlinAd Real ERF V mar( 6 s ) 4 Total Real ERF V mar( 6 s )

18 GW Imag ERF V mar ( 6 s ) ERF Imaginary Part (Meridional Wind) Gravity Wave 4 Linear Advecon LinAd Imag ERF V mar ( 6 s ) Nonlinear Advecon NlinAd Imag ERF V mar ( 6 s ) Total Total Imag ERF V mar ( 6 s ) 4 4 The nonlinear advec8on is more important than GW forcing and linear advec8on for the meridional wind 4 4

19 Seasonal Variaon of the GW Drag Frontogenesis GW drag to mean flow Jan Feb Mar Apr May 4 4 Jun 4 4 Jul 4 4 Aug Sep 4 4 Oct 4 4 Nov 4 4 Dec

20 Seasonal Variaon of GW Drag Convecon GW drag to mean flow Jan Feb Units: m/s/day Mar Apr 4 4 May 4 4 Jun 4 4 Jul 4 4 Aug Sep 4 4 Oct 4 4 Nov 4 4 Dec The GW drag to mean flow is stronger at sols8ce and weaker at equinox.

21 Seasonal Variaon of the GW Drag Frontogenesis GW drag to the migrang diurnal de jan feb mar apr may 4 4 jun 4 4 jul 4 4 aug sep 4 4 oct 4 4 nov 4 4 dec

22 jan Seasonal Variaon of the GW Drag Convecon GW drag to the migrang diurnal de feb mar apr may 4 4 jun 4 4 jul 4 4 aug sep 4 4 oct 4 4 nov 4 4 dec The GW drag to the migra8ng diurnal 8de is stronger at equinox and weaker at sols8ce, which is different from the GW drag to mean flow.

23 .7.8 Seasonal Variaon of Tidal Heang and Temperature.8. Diurnal, S=, mode= (K/day) Month Diurnal, T Amp Diurnal, S=, mode=2 S=, mode= (K/day)(K) The seasonality of the 8dal hea8ng due to the absorp8on of solar radia8on by H 2 O for Hough mode (,) is consistent with that of the temperature and horizontal winds. The 8dal hea8ng is likely to cause the seasonal varia8on of the amplitude of the migra8ng diurnal 8de Month

24 Conclusions Advecon and GW drag are two most important terms to account for the momentum budget of the migrang diurnal de. GW drag always damps the de and advances its phase. For the zonal wind, GW is responsible to change the amplitude and linear advecon is to change the dal phase. For the meridional wind, nonlinear advecon is the most significant factor to change both amplitude and phase of the de. The seasonal variaon of GW forcing is more like a feedback to the dal modulaon, rather than a cause. Instead, dal heang is likely to cause the seasonal variaon of the dal amplitude.

25 Thank you!