Presentation is loading. Please wait.

Presentation is loading. Please wait.

Orographic Processes Andrew Orr. Turner et al., 2009 Baines and Fraedrich, 1989 Mean JJA 700hPa height Experiment simulating westerly flow Large scale.

Similar presentations


Presentation on theme: "Orographic Processes Andrew Orr. Turner et al., 2009 Baines and Fraedrich, 1989 Mean JJA 700hPa height Experiment simulating westerly flow Large scale."— Presentation transcript:

1 Orographic Processes Andrew Orr

2 Turner et al., 2009 Baines and Fraedrich, 1989 Mean JJA 700hPa height Experiment simulating westerly flow Large scale flow response Antarctica

3 Orr et al., 2005 Petersen et al., 2003 Large scale flow response Greenland Surface wind speed Mean sea level pressure

4 Powers et al., 2003 High horizontal resolution required to represent complex orography and associated processes Complex orography Spiers et al., 2010

5 Smith et al., 2006 Mean orography UK Met Office Unified Model (UM)

6 Rontu, 2007 Topographic map of Carpathian mountains Sensitivity to resolution Streamlines over the Carpathian profile with different resolutions: orography smoothed to 32, 10, and 3.3 km

7 Nh/U=0.5 Nh/U=1 Olafsson and Bougeault, 1996 Nh/U=1.4 Nh/U=2.2 Basic flow response to isolated mountain

8 Petersen et al, 2003 Sensitivity to the Coriolis force

9 Horizontal and vertical wind Unified Model, 12km res Blocking conditions, 29 Jan 2002Flow-over conditions, 21 Feb 2002 Orr et al., 2007 Antarctic Peninsula

10 Potential temperature Unified Model, 12km res Blocking conditions, 29 Jan 2002Flow-over conditions, 21 Feb 2002

11 Aircraft observations Flight 19: Jan 2006, ascent from Rothera and descent over the Larsen Ice Shelf

12 Marshall et al., 2006 Eastern Peninsula summer warming of 2oC over 40 years Difference in ERA40 10 m winds and surface temperature between years with strongly positive and strongly negative summer Southern Annular Model (SAM)

13 Comparison of observations and AMPS Flight 19: Jan 2006, perturbations in vertical velocity and temperature, ascent from Rothera and descent over the Larsen Ice Shelf against Polar MM5, 10 km res

14 1)Modified parametrization for the prediction of ice cloud fraction 2)Improved cloud-radiation interactions 3)An optimal stable boundary layer treatment 4)Improved calculation of heat transfer through snow and ice surfaces 5)The addition of fractional sea ice surface type Polar MM5 Is further optimization required? Is higher horizontal or vertical resolution required? Bromwich et al., 2001

15 Is a higher resolution required? Comparison of observations and COAMPS 1.7 km resolution simulation on 29 Jan 1997 over Greenland Doyle et al., 2005

16 Comparison of observations and AMPS: impact of cold pool Spiers et al., 2010 Polar MM5 at 2.2km resolution on a grid encompassing the Ross Island Area

17 Lilly and Kennedy, 1973 Down-slope wind storms Observations over Rocky mountains Wave reflection, hydraulic jump, trapped lee waves

18 Evaluation of AMPS May Ross Island severe wind storm case study simulated by AMPS (Polar MM5) at 3.3 km, res Steinhoff et al., Formation of barrier jet + Interacts with pre-existing near-surface radiation inversion over Ross Ice Shelf +Resulting conditions favourable for development of large- amplitude mountain waves + Leads to down slope windstorm in Ross Island Area + Underestimation of wind speed due to misplacement of hydraulic jump + Originates from inaccuracies in storm track + Migration to WRF and 3dVar assimilation might lead to improvement

19 Mobbs et al., 2005 Rotors Sheridan and Vosper, 2006 Wind component simulated by Met Office model BLASIUS at 200 m resolution

20 Barrier jet Olson et al., 2007 Comparison of winds and temperatures (dashed) at 150 m from observations and 4km MM5 simulation on 26 Sep 2004

21 Cross section: winds, terrain- parallel wind (solid line), potential temperature (dashed line)

22 Hybrid gap-barrier jet 13 Oct 2003

23 Doyle and Shapiro, 1999 Tip-jets Comparison of observations and COAMPS simulated surface wind greater than 30 m/s on 18 Feb 1997

24 Parish and Bromwich, 2007 Katabatic winds Mean wintertime streamlines over the surface of the Antarctic

25 Mean AMPS surface wind speed from June 2003 – May 2004

26 Comparison of observations and forecast over Greenland Brmowich et al., 2001 Polar MM5, 40 km res reproduce the observed atmospheric state with a high degree of realism

27 Strong wind events Turner et al, 2009

28 Case study: ERA40 MSLP at 0600 GMT 25 July 2004 when Mawson experienced a hurricane force wind of 37.5 m/s Interaction between katabtic pressure gradient force and synoptic pressure gradient force

29 ERA40 UM 12 km Wind speed at Mawson Observed: 37 m/s ERA40: 20 m/s UM 12 km: 22 m/s Comparison of ERA40 and UM 12 km simulation 10 m winds and MSLP Minimum MSLP ERA40: 944 hPa UM 12km: 936 hPa UM captures synoptic forcing and simulates stronger katabatic winds

30 Observed: 37 m/s UM 12 km: 22 m/s UM 4 km: 24 m/s Comparison of UM 12 and 4 km simulations Is higher resolution required to capture local topographical conditions? Is optimization of model required ?

31 Bromwich et al., 2005 Evaluation of AMPS Polar MM5 at 30 km resolution from Sep 2001 to Aug 2003, h Reduced surface wind speed correlation at coast line reflecting complex topography

32 Coastal jets (4 km res) Very sharp gradients in velocity across coastline ~30 m/s ~20 m/s

33 Mechanism 1)Offshore winds cross coastline 2)Accelerate due to reduced drag 3)Turn to the left in the Southern Hemisphere 4)If coast is on the left of the wind results in horizontal convergence 5)Associated with this is the inversion height rising offshore, due to conservation of mass 6)Coriolis force induces a wind jet parallel to coastline (see Hunt et al., 2004) 7)Temperature falls offshore encouraging condensation and more cloud Land Sea convergence Orr et al., 2005

34 Laboratory investigation

35 UM simulation at 12 and 2 km

36 Orographic rain Smith

37 Webster et al., 2008 Case study over New Zealand Qualitative agreement at 12km resolution and quantitative agreement at <4 km resolution

38 Summary + Polar regions marked by complex orography. Requires a high resolution to resolve. + Some processes forecast well at medium resolution, such as barrier jets, katabatic winds + Some processes dependent on resolution (for example, gravity waves, rotors, precipitation, coastal jets) + Some processes dependent on boundary layer, etc, and complex interactions (for example, fohn winds) + Initial conditions important, both upstream and downstream


Download ppt "Orographic Processes Andrew Orr. Turner et al., 2009 Baines and Fraedrich, 1989 Mean JJA 700hPa height Experiment simulating westerly flow Large scale."

Similar presentations


Ads by Google