High-resolution simulations of mountain weather improved with observations from small unmanned aircraft

Transcription

1 High-resolution simulations of mountain weather improved with observations from small unmanned aircraft Hálfdán Ágústsson, Haraldur Ólafsson, Marius O. Johannessen, Joachim Reuder, Dubravka Rasol and Ólafur Rögnvaldsson

2 Video footage from national TV news SumoFrett.avi

3 The observations Approx. 10 days of with the SUMO (Small Unmanned Meteorological Observer) in Southwest-Iceland in In addition, surface based observations were available at a high temporal and spatial resolution.

4 The SUMO observes winds, temperature, humidity, pressure Up to ca. 3 km.

5 The weather on 15 July 2009 at 12 UTC Observations Weak winds with a northeasterly background flow. Mean sea level pressure. Keflavík

6 The weather on 15 July 2009 at 12 UTC Weak easterly winds in the lower troposphere. Keflavík (no. 4180)

7 Time of flights on 15 July 2009 Mount Esja (900 m) N 12:15 3 Kollafjörður bay 13:27 13: km x Álfsnes 11:19 11:47 12:57 14:18

8 Wind Photos from location 2 Mt. Esja Looking north Wind Mt. Esja Looking east

9 Observations on 15 July 2009 Mountain Location 3 at 12:15 UTC Gusty surface winds Wind speed 3 Wind direction Weak NE and E winds Strong N winds Ascending Descending 1 2

10 Observations on 15 July 2009 Mountain Location 2 at 12:57 UTC Gusty northerly surface winds Wind speed 3 Wind direction Weaker winds with height and turning from N to E Ascending Descending 1 2

11 Observations on 15 July 2009 Mountain Location 1 at 13:27 UTC Northerly surface winds Wind speed 3 Wind direction Weak N winds "Strong" N winds weaken and deepen Ascending Descending 1 2

12 Schematics of observed winds Gravity wave activity is presumably accelerating winds down the leeside slopes of Mt. Esja with a maximum in wind speed near the surface close to Mt. Esja. The wind maximum weakens and thickens further away from Mt. Esja.

13 Surface obs. of winds North Mountain Wind direction 9 m/s Wind speed Pure westerly winds NOT observed in the afternoon!

14 Simulated and observed surface winds on 15 July 2009 at 13 UTC WRF at a resolution of 500 m forced with ECMWF-data on model levels. Observed surface winds in red A Mt. Esja

15 The SUMO-data is incorporated into the WRF-simulation, via obs-nudging SUMO-data obs-nudging Run WRF-model Input Preprocessing Postprocessing

16 Simulated flow in section across mountain With in-situ obs. with a model aircraft. Better! A major difference in flow pattern extending far above mountain top level No extra observations Wrong! 23 km Wind speed, ranging from 0 to 12 m/s

17 Simulated and observed wind direction Reykjavík No SUMO First SUMO profile With SUMO

18 Mountain Height [m] Simulated wind profile Wind speed SUMO - Better No SUMO Wind dir.

19 One forecasting perspective Wind mills in complex terrain Encarta Encyclopedie Winkler Prins, Porterfield Chickering/Photo Researchers, Inc.

20 Gravity waves are important for the wind climate! Mean easterly winds [m/s], downscaled at 3 km See poster by Marius O. Jonassen et al.

21 Main conclusions We improve high-resolution atmospheric simulations using unique observations from aloft. The observations reveal unexpected winds in the boundary layer and lower troposphere. Indications of accelerated lee-side flow in spite of weak mountain top and boundary layer winds. Input of realtime in-situ SUMO-observations into operational WRF-simulations is under way. Further work includes: Investigate the dynamics of the flow, Increase resolution of grid, use 3D turbulence calc., More field experiments with the SUMO.

22 Observations on 15 July 2009 Mountain Location 2 at 14:18 UTC Gusty northerly surface winds Wind speed 3 Wind direction Weak E og NE winds "Strong" N and NE winds Ascending Descending 1 2

23 Simulated and observed surface winds at Kjalarnes, south of and near Esja Non-zero surface friction Wind direction Wind speed Simulated Wrong Observed Observed Simulated

24 Simulated and observed surface winds on 15 July 2009 at 13 UTC WRF at a resolution of 500 m forced with ECMWF-data on model levels. No surface friction Mostly correct Surface friction Mostly wrong A Mt. Esja Loc. 2 Mt. Esja

25 Are the gravity waves important for the wind climate? Mean annual wind speed at 8 km resolution with MM5 Rögnvaldsson and Ólafsson

26 Wind and isentropes in section across mt. Examples from an Icelandic glacier Glacier small z0 Control simulation Strong Glacier large z0 Weak No glacier small z0 Strong No glacier large z0 Weak

27 Simulated wind and isentropes in section A across Mt. Esja Non-zero surface friction At 13 UTC ESJAN Wrong wind direction

28 Simulated wind and isentropes in section A across Mt. Esja Zero surface friction At 13 UTC Wave activity ESJAN ESJAN

29 Simulated wind and isentropes in section A across Mt. Esja Zero surface friction At 15 UTC Wave activity ESJAN

30 Forecasting perspective Windstorms Wind Lee wave Rotor Ágústsson and Ólafsson, 2009