Cloud Physics and Dynamic Stratus
Forecasting
Content grade: 2.5/5
by
Erica J. Silva
Literature Review
Prepared For:
Prof. D.M. Sinton
Prof. R. D. Bornstein
28 September 2006
An analysis of the methodology and accuracy of fog and low stratus forecasting
will be presented. Use of observational sensing tools, such as radar, satellite, profilers,
soundings, and standard surface observations (METARS), will be discussed. Model
forecasting technique will be reviewed. An assessment will be given of the Climatology
in Fog/Stratus Forecasting (CFSF) project, which produces both local and regional
forecasts as a functional weather pattern.
Information from the SFO Marine Stratus Forecast Guidance website will be
summarized with respect to the following parameters: Approach Clear Message (no
clouds in approach zone), CWSU 15Z Forecast Display (GMT aircraft acceptance rate of
at least 45 planes every hour in a day), COBEL Model (1-D numerical model that
simulates evolution and burn-off of marine stratus), Local SFM and Regional SFM
(statistical regression to forecast stratus burn-off time in approach zone), Satellite SFM
(evolution of Bay Area cloudiness), Consensus (time stratus is expected to clear approach
zone to allow parallel aircraft approaches), and Probability of Clearing (likelihood
approach zone will be clear for double approaches).
The senior thesis will evaluate synoptic-scale influences that drive local
conditions to assess whether a fog or stratus event is possible. The thesis will explain how
synoptic situations each have physical and dynamic processes that contribute to fog
formation or dissipation.
Outline
I. Stratus Fog Influences
a. Synoptic
b. Cloud Physics
II. Stratus Fog Forecasting
a. General
b. Models
c. Forecast
III. SFO/SJSU Project
a. Surface Observations
b. SODAR Inversion Base
c. Solar Radiation
IV. Temperature Variations
V. Dynamics
wo types of fog that will be discussed are radiation fog and advection fog. Fog produced
by earth’s radiational cooling is radiation fog. Warm moist air moves over a cold surface
while cooling the air to its saturation point. Transfer of heat from the air to surface will
cool air to dew point producing fog if the surface is cooler than the air above. Four
actions must take pace for radiation fog to take place: Moist low-level conditions below
an inversion, Fast cooling of the lower boundary layer beneath the inversion, Presence of
a low-level anticyclone creatingcalm atmospheric conditions through the containment of
surface winds, drying the air aloft through subsidence (air slowly sinks over a large area),
and increasing radiative cooling at the surface. On the contrary, advective fog needs
subsidence and anticyclonic large-scale winds. This allows saturation of boundary layer
capped by an inversion.
Radiation fog and advection fog is very critical when it comes to the safety of air
planes. Because each airport is located at a different place on earth, it is important to
realize different factors which differ in the atmosphere. Another scenario where radiation
fog is critical is for boats and ships. Visibility is all the more time dependent when
visibility factors like fog are concerned.
Fog is found especially in San Francisco. On any given day of the year, fog is no
surprise for the inhabitants of San Francisco, California. Fog is seen in Los Angeles,
California at a very small fraction at a time during the year. When the fog does take place
a lot of precaution comes into part for traffic. In addition to the fog Los Angeles s gets at
different times of the year, the pollution and smog from cars and factories adds to the
thickness of the air leading to problems that affect the population individually in different
forms.
Looking at the advantages of fog, it helps moisten the land and agriculture. It
gives it a rest from very hot dry days when the most adiabatic lapse rate is very low. Fog
comes in handy when the dew point and relative humidity temperatures are low. Fog
allows the amount of pollution in the air to decrease by absorbing it in a sense when it
begins to disappear while the sun comes out. The sun burns off the fog and allows the air
to become breathable again. When the air is not breathable during the time of fog
(especially of smog and pollution add on to it), the human skin that take them out of
balance and cause them to function incorrectly.
There is no one type of fog that is good or bad. Fog has advantages and
disadvantages. Fog adds moisture to plants when needed and causes problems of
visibility to plane air traffic and ship/boat sea traffic as well as car traffic in the everyday
life. San Francisco, Ca is a place of more than normal fog distribution. Los Angeles, Ca is
another place of fog distribution with a lot of pollution and smog added. The best way to
decrease problems with traffic visibility due to fog is to first know the leading factors
which contribute to fog in specific areas. It is god to know weather patterns for different
locations. Topography is critical because it broadens the scope of knowing which winds
to expect, what type of weather to expect given a specific time of year. Forecasts help one
to determine what the future may hold in order to cease visibility problem in traffic for
planes, cars, boats ships, and the commercial life in general. Researchers are presently
trying to come up with a solution to help better forecast for weather conditions.
References
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