Effects of Dynamical Variability in the Mesosphere and Lower Thermosphere on Energetics and Constituents

Transcription

1 Effects of Dynamical Variability in the Mesosphere and Lower Thermosphere on Energetics and Constituents William Ward Victor Fomichev, and Jian Du ISWA, Tokyo University, September 16, 2016

2 Overview How close are we to understanding the weather of the Mesosphere and Lower thermosphere? Is dynamical variability an essential component of the constituent and energy budgets? Introduction/context. M/LT dynamical variability. Consequences for energetics and constituents. ISWA, Tokyo University, September 16, 2016

3 Airglow Variability Hays et al., JGR, 2003 Taylor et al., 1997

4 Context The mesosphere/lower thermosphere ( km) is a transition region in the terrestrial atmosphere. Diabatic heating is driven by dynamics in this region. Below Above Well Mixed, homogeneous Inviscid, motion over many scales MLT is a sink for dynamical motions forced below. Diffusive equilibrium, heterogeneous Viscous, motions tend to be forced MLT is a sink for thermal energy absorbed above

5 Pre-UARS (~1990) Understanding K zz Calculations (Colgroveet al., 1965) Questions Homogeneous mesopause region. What is the atomic oxygen concentration profile? M/LT dynamics primarily from radar observations. Tidal investigations primarily of migrating components. Issues: differing K zz values (oxygen budget (~4e6 cm 2 /s), Ar/N 2 budget (~4e5 cm 2 /s), thermal budget (~0 cm 2 /s)). Physical process unclear (measurement interpretation ambiguous).

6 130 Mesosphere/Lower Thermosphere 120 Dissociation: CO 2, O 2 O 2 + h ν O + O Thermosphere 110 Molecular Diffusion Height (km) 100 CO 2 NLTE Processes Large Amplitude Wave Motion Tidal/Gravity Wave Breakdown Airglow: O( 1 S), OH, O 2 Recombination: CO, O O+O+M O 2 +M Chemical Heating Mesosphere Temperature (K)

7 Zonal Mean Constituent Profiles NH winter solstice - TIMEGCM

8 Energy Budget Globally averaged energy balance for June. Views of three regions of the atmosphere. Includes solar heating IR cooling molecular diffusion chemical heating (O+O+M) All other terms. Fomichev et al., 2002

9 Kinetic Energy Partitioning Shepherd and Koshyk, 2000 Because density decreases with height, the amplitude of waves which do not dissipate, increase with height.

10 Annual Cycle of Migrating Diurnal Tidal Temperature Amplitude

11 Diurnal Components

12 Dw1 Dw1 + De1 WN1+2+3 WN1+2

13 Temperature Gradient in March (CMAM) Comparison of superposition of wave 0 to 2 diurnal and semidiurnal tides along with stationary wave 1 and 2 and the background. Note the enhanced negative gradient associated with the combined field It appears that convective and dynamic instabilities occur in the net tidal field and not in individual components. Ward et al., GRL, 2005

14 Conditions for Instability The model fields are evaluated to determine whether the following conditions hold. g dθ 1 Ri = θ dz < Dynamical Instability 2 du 4 dz dθ < 0 Convective Instability dz

15 Reconstructed Fields The Richardson number is calculated as a function of time (672), height (22), latitude (32) and longitude (24) using the background fields, wave 1 and wave 2, eastward and westward diurnal and semidiurnal components, and the stationary wave component. These fields are calculated using a two day window stepped by two days using cubic splines to interpolate between the data points. The wind and potential temperature gradients are calculated using two point differences and then points where instability criteria are met are identified.

16 Altitude (km) Longitude Latitude Local Time ISWA, Tokyo University, September 16, 2016

17 Altitude (km) Longitude Latitude ISWA, Tokyo University, September 16, Local Time

18 Log of Power in GWD

19 Atomic oxygen is involved in both chemical heating and the cooling efficiency of CO2 (non-lte effects) in the mesopause region. From a Lagrangian perspective, parcels are driven through quasi-adiabatic cycles (of many scales) each of which results in changes in the energy of the parcel. Mixing events will also redistribute constituents and as a result their heating/cooling character. CONSEQUENCES FOR CONSTITUENTS AND ENERGETICS ISWA, Tokyo University, September 16, 2016

20 Exothermic Reactions of Importance Several of these reactions depend quadratically on the concentration of atomic oxygen. Hence variations in the oxygen concentration cause the chemical heating rate to vary non-linearly. Atomic oxygen also modulatesco2 cooling.

21 Atomic Oxygen: Role in Radiative cooling and chemical heating ISWA, Tokyo University, September 16, 2016 Ward and Fomichev, 1993, 1996 Fomichev et al., 1996

22 Conceptual Model of Periodic Adiabatic Vertical Motion Periodic Advection - Conceptual Model An observation at a fixed point samples air from a variety of locations. For quasi-periodic motion we may model this process as the periodic appearance of air parcels with equilibrium positions from other heights or latitudes. The figure at the right shows the range of latitudes or heights (+/- 2.5 units) sampled over 24 hours for a diurnal motion. Position (km or deg) δz (km) or δlat (deg) Local Time (Hrs) Obs Point Equilibrium Position of Parcel Appearing at Observation Point Ward,

23 Airglow Profile Variation with Vertical Motion 130 Emission profiles: Adiabatic expansion and contraction Height (km) VER O( 1 S)(ph/cm**3/s)

24 OH Airglow vs Temperature (SABER) Temperature Airglow Brightness Xu et al., GRL, 2010

25 Diurnal variation in chemical heating and atomic oxygen mixing ratio Smith et al., JGR, 2003 Smith, JGR, 2010, SABER data

26 Box Model of Chemistry during Trajectory In the figures which follow the variation in the atomic oxygen concentration following a sinusoidal trajectory with amplitudes ranging from 1-3 km and periods of 1 hr and 24 hours is compared to the concentration associated with a parcel which remains stationary. For these calculations simple oxygen/hydrogen chemistry is assumed and MSIS is used to set the initial concentrations. The motion enhances the loss of atomic oxygen. 26

27 This figure shows how [O] varies around a trajectory with a 3 km amplitude and 24 hr period compared to a stationary parcel and one with the same amplitude but 1 hr period. The two 24 hour curves are for trajectories differing in phase by 180 degrees. 4.5 x 1010 Variation of [O]: Diurnal Cycle at 85 km 4 3 Km Amplitude 3.5 Concentration (1/cm 3 ) hour period 1 hour period Stationary Time (hours) 27

28 In this figure the amplitude of the trajectories is varied through values of 0, 1, 2, and 3 km. The resulting variation in concentration shows that the motion accelerates the recombination of O and the diabatic heating of the parcel. 7 x 109 Variation of [O] at 82 km 6 1 Hour Period Concentration (cm -3 ) Stationary 1 km Amplitude 2 km 3 km Time (hours) 28

29 Conclusions The large scale dynamical fields in the M/LT structure this region: Regions (layers) of instability Parcel motions These motions drive the chemistry and energetics. We are now at the point that the weather of the MLT can be investigated and included to realize a physically based, internally consistent understanding of the momentum, constituent and energy budgets of this region.

30 Thanks for your attention ISWA, Tokyo University, September 16, 2016

31

32 Inversion Layer as a Mixing Event

33 The Mixing Process Mixing ratio will behave as potential temperature

34 Extended CMAM/UARS Zonal Winds Fomichev et al., 2002

35 Short Term Variability of Components T DW 1 DE3 U