High-resolution Mesoscale Modeling and Diagnosing of a
Severe Fog Event
ZUOHAO CAO1*, ISMAIL GULTEPE2, Amin Erfani3, and Patrick King2
1Meteorological
Service of Canada, Burlington, Ontario, Canada
2Meteorological Service of Canada, Downsview, Ontario, Canada
3Canadian Meteorological Centre, Dorval, Quebec, Canada
*Contact: Phone: 905-336-6006 E-mail: zuohao.cao@ec.gc.ca
Fog has significant impacts on Canadian society, especially on road transportation.
On average, about 53 fatal vehicle accidents in which fog is a contributing factor
occur each year on Canadian highways. Due to its small-scale nature, fog is a
localized short-lived phenomenon and it is therefore difficult to detect and predict.
To improve operational fog detection and prediction in Canada, a project has been
implemented through the collaboration between scientific and operational
community. As one of the studies of this project, we have investigated a severe fog
event that occurred near Barrie, Ontario, on March 17, 2003. This event resulted in
an accident involved more than 200 vehicles and two-dozen personal injuries. The
dense fog event is simulated using the Canadian Operational Global Environmental
Multiscale Model (GEM). The structure and evolution of the fog event is further
resolved using the very high-resolution GEM Limited Area Model (GEM-LAM) by
employing a nesting technique. The numerical simulations are verified and
supported by both satellite observations and surface observations. Diagnoses are
also performed to understand the physical processes responsible for the dense fog
event.
Introduction
-Fog impacts range from delays in aviation, marine, and surface transportation and
deliveries to serious accidents caused in part by poor visibility.
- Although efforts have been made on observational aspects of fog phenomena
(e.g., Duynkerke 1991; Guedalia and Bergot 1994), using numerical weather
prediction models (NWP) to forecast fog formation, evolution, and dispersion as well
as its areal extent, vertical depth, and intensity is still one of the most challenges
confronting with our meteorological community (Ballard et al. 1991; Bergot and
Guedalia 1994; Pagowski et al. 2004).
- The difficulties are mainly due to fog forecasting requirements of an adequate
representation of the nocturnal boundary layer, a high-resolution vertical grid close
to the surface, a parameterization of soil-atmosphere interactions, and small-scale
surface heterogeneities.
- In this study, we will employ the 3-D very high-resolution GEM Limited Area Model
(GEM-LAM) to simulate a dense fog event, which caused two-dozen personal
injuries and more than 200 vehicle damages, and to examine physical processes
contributing to this severe fog event.
The fog event
(a). A fog-related accident on Highway 400 near Barrie, Ontario, Canada
Bill Stanford, Toronto Star
- March 17, 200
- “More than 60 separate pile-ups kept rescue worker busy along Highway 400 all day
yesterday.”
- “One man was flown to hospital in Toronto in critical condition and a paramedic said
the fog-shrouded scene looked like a war zone.”
- Over 200 vehicles, two dozen injuries
Results
(b). Overview of the event
a. GEM
b. GEM-LAM
- CMC analysis at 12 UTC 17 March 2003 - Surface map at 12 UTC 17 March 2003
- low wind speed (in blue arrow)
- post ridge and weak front
- low dew-point depression (in red)
- fog
Visibility (km)
Abstract
Fig. 1 Liquid water content (at an interval of 5x10-5 kg/kg) on 10 UTC 17 March 2003
at a sigma level of 0.9606 obtained from (a) GEM and (b) GEM-LAM.
16
14
12
10
8
6
4
2
0
a. GEM-LAM Control
b. GEM-LAM Control + Kain-Fritsch
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Local Time
- Hourly visibility observations at Barrie,
Ontario, Canada on 17 March 2003
- the GOES image at 13:15 UTC 17 March
- green color indicating fog areas
Numerical models
(a). Canadian operational global environmental multiscale model (GEM)
- 15 km resolution in horizontal; 58 levels in vertical
- initial conditions obtained from Canadian Meteorological Centre analyses
- physical processes: land surface process ISBA; PBL; Kain-Fritsch convection;
new Sundqvist explicit scheme; radiation scheme
(b). GEM – Limited Area Model (GEM-LAM)
- 2.5 km resolution in horizontal; 58 levels in vertical
- initial and boundary conditions obtained from GEM outputs using a self-nesting
technique
- physical processes: ISBA; PBL; Kong-Yau explicit microphysics scheme
Fig. 2 Same as Fig. 1 except GEM-LAM at a sigma level of 0.9151.
a. GEM-LAM Control
b. GEM-LAM + Force restore
Experiment design
- Control: ISBA surface scheme and Kong-Yau explicit microphysics scheme
- Experiment 1: Force restore surface scheme and Kong-Yau explicit microphysics
scheme to examine the effects of surface processes on liquid water
content (LWC)
- Experiment 2: ISBA surface scheme, Kong-Yau explicit microphysics scheme and
Kain-Fritsch convection scheme to examine the effects of subgrid convection
on LWC
- Experiment 3: Force restore surface scheme, Kong-Yau explicit microphysics scheme
and Kain-Fritsch convection scheme to examine the combined effects of
surface processes and subgrid convection on LWC
Acknowledgments
The numerical simulations were performed on the IBM supercomputer of
Environment Canada.
Fig. 3 Same as Fig. 2 except on 14 UTC 17 March 2003 at a sigma level of 0.8571.
Concluding remarks
-LWC is well simulated using the high-resolution GEM-LAM in the area of interest
where LWC is not captured by the coarse-resolution GEM.
- Convective process play important roles in fog formation. Results show that with
inclusion of Kain-Fritsch convective parameterization scheme, the vertical depth of fog
is thicker than the one without the convective parameterization scheme.
- Fog development is sensitive to land surface process schemes. The simulation with
ISBA scheme leads to more intensive fog than the one with force restore scheme,
particularly during the late stage of fog development.