1. Influences of Large-Scale Moist Convection on Turbulence in Clear Air (CAT) Stan Trier NCAR, Boulder Outline: 1)Observations and High Resolution Simulations of a Cold-Season Case Midlatitude cold front/upper trough case (9-10 March 2006) 2) Observations and High Resolution Simulations of a Warm-Season Case Central U.S. MCS case (16-17 June 2005) 3) Discussion of Common Roles of Organized Deep Convection Collaborators: Bob Sharman (NCAR), Todd Lane (Univ of Melbourne), Rob Fovell (UCLA) Workshop on Aviation Turbulence, 28 August 2013, NCAR, Boulder, CO

2. Reference: Trier, S.B., R.D. Sharman, and T.P. Lane 2012: Influences of moist convection on a cold-season outbreak of clear-air turbulence (CAT), Mon. Wea. Rev., 140, 2477-2496. Over 200 reports of moderate or greater turbulence from 1500 UTC 9 March to 0300 UTC 10 March CAT Outbreak within a Midlatitude Cyclone (9-10 March 2006)

3. Location of Turbulence Relative to Large-Scale Flow Features ABCD West – East Distance (km) 0000 UTC RUC Analysis and 2300-0100 UTC Time-Space Corrected Turbulence Reports 2 PVU

4. Experimental Design ARW-WRF Simulations with 4 interactive nests (with  = 30, 10, 3.333, and 0.667-km) Simulations: CRTL (full physics, uses D1, D2, D3) NOMP (cloud microphysics deactivated, uses D1, D2, D3) HRES (like CTRL, but  = 0.667 nest D4 activated between 2300 and 0100 UTC) - D3 and D4 have fully explicit convection (no cumulus parameterization)

5. 24-h Forecast (CTRL) over Domain 3 at 0000 UTC 10 March Observations over Region at 0000 UTC 10 March model derived reflectivity surface winds surface  (2-K contour intervals) NOWRAD reflectivity surface winds surface  (2-K contour intervals)

6. Line-Averaged Cross Section of Cloud (colorfill), , Winds, TKE (green), Nm (red) CTRL 24-h Forecast (0000 UTC 10 March 2006) Layer of reported turbulence

7. Wintertime Clear-Air Turbulence (CAT) Associated with Deep Convection Potential Temperature, Vertical Velocity and Total Cloud Condensate Horizontal Distance (km) Turbulence mechanisms at different locations on the fine-scale grid (  = 667 m) Breaking Gravity Waves Above StormsKelvin-Helmholtz Instability

8. Radial (Transverse) Cirrus Bands in MCS Anvils A recent example (13 August 2013) 1632 UTC 13 Aug 2013 1656 UTC 13 Aug 2013 Moderate Turbulence

9. Radial (Transverse) Cirrus Bands in MCS Anvils A recent example (13 August 2013) 1632 UTC 13 Aug 2013 1656 UTC 13 Aug 2013 Moderate Turbulence

10. 16 – 17 June 2005 Case Study 37 N 40 N 43 N 0905 UTC 16 June 0745 UTC 17 June

11. Simulation of Radial Outflow Bands in 17 June 2005 MCS Model Parameterizations - Thompson Bulk Microphysics - Noah LSM - PBL Scheme (MYJ) - Dudhia Longwave Radiation - RRTM Shortwave Radiation Simulations with ARW-WRF V2.2 Explicit Deep Convection Initial and Boundary Conditions from  = 13 km 3-hourly RUC Analyses Large Single Domain Run with  = 3 km Simulation with D2 nest of  = 600 m started at t = 7h of Large Domain Run 0800 UTC Simulated Reflectivity and 12.5-km MSL Winds

12. Simulated Cloud Top Temperature (0950 UTC, t = 5.8 h ) Observed Turbulence @ 37 Kft (0936-0957 UTC) L=light, M=Moderate IR Satellite at 0950 UTC 17 June 2005 Turbulence UA 776 Observations and WRF-Simulations of the 17 June 2005 MCS Case Trier and Sharman (2009, Mon. Wea. Rev.) Observations and MCS-Scale Simulations Trier et al. (2010, J. Atmos. Sci.) High-Resolution Simulation and Analysis of Radial Bands

13. m 4-hour Loop of Brightness Temperature, 12-km Moist Static Instability N < 0 and 11.5-13-km Vertical Shear from 07-11 UTC 17 June with  t = 10 min 2 Anvil bands originate within zones of moist static instability Bands are aligned along the anvil vertical shear vector Similar to horizontal convective rolls in boundary layer arising from thermal instability TbTb East North

14. Control Simulation (Full Physics) No Cloud-Radiative Feedback Simulation 0930 UTC Brightness Temperature and Moist Static Stability TbTb

15. Simulated TKE typically occurs where Ri number is reduced m At typical commercial aircraft cruising altitudes (z = 10-12 km) m ee ~ 150-km Line Average Stability Budget Equation Tendency Differential Horizontal Advection Differential Vertical Advection Subgrid Source Term

16. Red = Upward Motion Blue = Downward Motion

17. 17 June 2005 Turbulence Measurements Near Transverse (Radial) MCS Outflow Bands radial bands Turbulence intensities from in situ EDR: Green = Smooth Yellow = Light Orange = Moderate Red = Severe

20. Summary Near-cloud turbulence (NCT) can result from many different mechanisms - Many types of convective weather involved (isolated cells, MCSs, midlatitude cyclones) - Turbulence forecasting systems need to account for this non-traditional CAT Mesoscale circulations play an important role in producing NCT - Large-scale upper-level anticyclonic outflows enhance vertical shear supporting NCT - Many important effects of vertical shear Provides large-scale thermodynamic destabilization and organizes radial bands Promotes Kelvin-Helmholtz instability Gravity Waves play a role in many NCT situtations - Directly through wave breaking - Indirectly through local reductions in Ri where other instabilities are favored - Indirectly through their vertical motions, which perturb already unstable flow