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Mesoscale Modelling of Optical Turbulence in the Atmosphere:
Quantifying the Impact of Ultra-High Vertical Resolution
COAT – December 2nd, 2019
Sukanta Basu
Associate Professor
Faculty of Civil Engineering and Geosciences
s.basu@tudelft.nl
Acknowledgement: Ping He
Optical Turbulence Forecasting
2 Source: Trinquet and Vernin (2009)
All Roads Lead to Rome
Cn2 Parameterization
Higher-order Closure Approach Regression (ANN) Approach
DNS/LES Approach Scaling Approach
Estimation
(e.g., Radiosonde)
Forecasting
(Mesoscale Model)
3
Radiation
Planetary
Boundary
Layer
Land Surface
Microphysics
Convection
Mesoscale Modeling
4
Modeling Framework
Mesoscale Atmospheric
Modeling
Global Reanalysis
(~30 km Resolution)
Pressure(lat,lon,z,t)
Temperature(lat,lon,z,t)
Moisture(lat,lon,z,t)
Turbulent Diagnostics
Refractive
Index(lat,lon,z,t)
Static Geographic Data
(e.g., Terrain, Landuse)
Geometric Optics-
Based Ray Tracing
Realistic Long-Range
Optical Ray Trajectories
Ray Origin(lat,lon,z,t)
Ray Propagation
Azimuth
Ray Elevation Angle
Parameterized
Cn2 (lat,lon,z,t)
5
Objective
Intermittent Optical Turbulence in Free Atmosphere
7
May 26, 2006; Masciadri et al. (2008)
ORM: Roque de los Muchachos on the island of La Palma
OT: El Teide on the island of Tenerife
Both observatories are on the Canary Islands and about 160 km from each other
Time-Height Plot of Cn2 from G-SCIDARs
Intermittent Optical Turbulence in Free Atmosphere (Cont.)
8 Dome C, Antarctic Cerro Tololo, Chile
Challenge
Vertical Grids in Mesoscale Models
10 Source: Alligo et al. (2009)
Relevant Literature
11
Effects of Vertical Resolution on Eddy Viscosity
12
Source: Skamarock et al. (2019)
Methodology
Higher-order Closure (HOC) Approach
14
HOC Approach (Cont.)
15
HOC Approach (Cont.)
16
Case Study:
Hawaii 2002 Thermosonde Campaign
Hawaii 2002
Large-Scale Behavior of Ascent Rate
19 Source: McHugh et al. (2008)
Computational Domain (9/3/1 km)
20
Vertical Grids in WRF Runs
21
Dec 11-12, 2002
Mean Temperature Profiles
23
Mean Wind Speed Profiles
24
𝐶𝑛2 Profiles
25
Simulated 𝐶𝑛2 over Hawaii and Pacific Ocean
26
# vertical grid points: 51
Simulated 𝐶𝑛2 over Hawaii and Pacific Ocean (Cont.)
27
# vertical grid points: 101
Simulated 𝐶𝑛2 over Hawaii and Pacific Ocean (Cont.)
28
# vertical grid points: 286 (uniform grid spacing of 100 m)
Simulated “Seeing” (Total)
30
Source: McHugh et al. (2008)
Simulated “Seeing” (Ground Layer)
31
Simulated “Seeing” (Upper Layer)
32
Dec 12-13, 2002
Mean Temperature Profiles
34
Mean Wind Speed Profiles
35
𝐶𝑛2 Profiles
36
Simulated 𝐶𝑛2 over Hawaii and Pacific Ocean
37
# vertical grid points: 51
Simulated 𝐶𝑛2 over Hawaii and Pacific Ocean (Cont.)
38
# vertical grid points: 101
Simulated “Seeing” (Total)
39
Source: McHugh et al. (2008)
Horizontal Cross-Sections
Island Wakes
41 Source: NASA
Flow Structures around Big Island
42
Source: Smith and Grubišic (1993)
Spatial Distribution of 𝐶𝑛2 (# Vertical Grid Points = 286; 1 km MSL)
43 2 UTC, Dec 12 7 UTC, Dec 12
Spatial Distribution of 𝐶𝑛2 (# Vertical Grid Points = 286; 10 km MSL)
44 2 UTC, Dec 12 7 UTC, Dec 12
Case Study:
Paranal 2017
Observed 𝐶𝑛2 over Paranal
46 Courtesy: James Osborn
Simulated 𝐶𝑛2 over Paranal
47
# vertical grid points: 201
Simulated 𝐶𝑛2 over Paranal (Cont.)
48
# vertical grid points: 286 (uniform grid spacing of 100 m)
To be continued…
Richardson (1922)
50
“Perhaps some day in the dim future it will be possible to advance the computations faster than the
weather advances and at a cost less than the saving to mankind due to the information gained. But
that is a dream.”
Richardson’s
forecast factory
Source: Bengtsson
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