Transcript Weather forecasting - Department of Applied Physics

The Hong Kong Polytechnic University
Department of Applied Physics
GE Subject : Climate and Our Environment
Weather Monitoring & Forecasting in Hong Kong
29 September 2008
What is WEATHER FORECASTING ?
Predict the future weather
z
12
at
in
9
3
x
6
y
3D
a complex and difficult job
a risky business too !
1D
= 4D problem
Forecasting Range
Forecasting range
Lead time
Nowcasting
~ several hours
Very short range
~ 12 hours
Short range
~ a few days
Medium range
~ one week
Long range
over 10 days
Seasonal
a month to a year
Length
Scale of Weather Systems & Atmospheric Motion
10 000 km
planetary, seasonal
scale
Sub-tropical
ridge,
Monsoon,
5 000 km
synoptic
scale
2 000 km
High / Low s
on weather
map,
ITCZ
Cold / Warm
fronts
200 km
Tropical
cyclones
mesoscale
20 km
2 km
microscale
200 m
2m
Land / Sea
Breeze
Squall lines
Thunderstorms
Tornadoes
Waterspouts
Turbulent
eddies
s to min min to hrs
Time
hrs to days
days to weeks, months …
Weather Forecasting Procedures
Meteorological
Information
Forecasting
Methods/Analysis
Forecast
Products/Warnings
Procedures of Weather Forecasting
Meteorological observations
Data analysis
Forecasting methods and techniques
Forecast and warning dissemination
Observation and Monitoring
Surface Observations :Automatic Weather Stations (AWS)
Telemetering Rain Gauges
Weather Buoys
Visibility Meters
Upper Air Observations :Radiosonde and Wind Profiler
Remote Sensing :Doppler Weather Radars
Weather Satellites
Lightning Location Networks
Meteorological Observations
Surface observations over land
Stevenson Screen:
Temperature,
Dew point
Pressure
Wind mask:
wind speed and direction
Human observation
Telemetering rain gauge
Surface observations over the ocean
Voluntary Observing Ship (VOS) Program
Temperature, Dew point, Sea surface
temperature, wind direction/speed, pressure, sea
wave, swell, weather observations, etc.
Weather Buoy
Automatic Weather Station and Sea surface
temperature
Visibility Meter
Traditionally, visibility monitoring of
Victoria Harbour has been carried out by
trained observers at the Observatory
Headquarters.
With the increasing number of high rise
buildings obscuring the visibility
observations, there is a need to devise a
new method to maintain the long-term
visibility monitoring in Victoria Harbour.
To this end, an automatic visibility meter
has been installed at Central to provide
visibility readings.
Data Coverage (Asia) - surface
Station circle
Each station is represented by a “station circle” and the observational
data are plotted around this circle in standard positions so that the
meteorologist can see at a glance all the parameters at every station.
From : Dr P. M. Inness
Wind barbs (1knot ~ 2km/hr)
Weather Chart
Upper Air Observations
Radiosonde
• To measure upper-air temperature, dew point, pressure,
wind speed and direction
• 2 times per day (00, 12 UTC), where 00 UTC = 0800 HKT
Wind Profiler
Uses radar to detect the wind speed and direction at various elevations
above the ground.
Upper air observations – Tephigram
The Tephigram is a
thermodynamic diagram
designed to aid in the
interpretation of the temperature
and humidity structure of the
atmosphere and used widely
throughout the world
meteorological community.
Allows a radiosonde profile to
be analysed for stability
Upper air observations – Upper air charts
Remote Sensing Observations
Weather Radar Systems
•
大老山多普勒天氣雷達 (Tates' Cairn Doppler Weather Radar
System) since 1994
•
大帽山多普勒天氣雷達 (Tai Mo Shan Doppler Weather Radar
System) since 1999
•
機場多普勒天氣雷達 (Terminal Doppler Weather Radar System)
since 1996
Tates' Cairn Radar Station
(TCR Radar)
Tai Mo Shan Radar Station
(TMS Radar)
Radar Images
Meteorological Satellites
Two major types of meteorological satellites characterized by
their orbits:
N
35,800 km
Polar-orbiting satellites
Geostationary satellites
S
Satellite Antenna
圖片顯示 Image Display
1966
1999
地球靜止衛星 - Geostationary satellites
紅外線
Infrared
水氣圖
Water vapour
可見光
Visible
極軌衛星 – Polar Orbiting Satellite
Special Senor Microwave / Imager
(SSM/I)
QuikSCAT
Lightning sensor stations
The network comprises six stations jointly established by the Hong Kong
Observatory, the Guangdong Meteorological Bureau and the Macao Meteorological
and Geophysical Bureau. The stations are located at Chung Hom Kok, Tsim Bei
Tsui, Sha Tau Kok, Taipa in Macao, Sanshui and Huidong in Guangdong.
The lightning location information service
Internet lightning alert service to
provide lightning information
according to individual needs in an
interactive way.
People can choose their location of
interest, either from the popular
places listed on the webpage or
entering the name of a building,
estate or street. The user can also
click directly on the lightning map to
specify the place of concern.
An alert will be provided
automatically when there is lightning
within a 15km range of the specified
location.
http://www.weather.gov.hk/wxinfo/llis/index.htm
Weather Forecasting Procedures
 Met. Information -> forecasting methods  forecast products
Weather Forecasting Methods
• Subjective:
– human experience
• Statistical:
– Analogue, persistence, trend analysis
• Dynamical:
– Chart analysis
• Numerical weather forecast
In the old days Forecasting methods :
mainly statistical or climatological +
human experience
Modern days –
Numerical Weather Prediction
• NWP = Using physical equations to simulate the
evolution of the atmospheric motions
• Methods:
– integration of the evolution equations, based on the initial and
boundary conditions
• Applicable Scale:
– mesoscale (Tropical cyclone) to synoptic scale (cloud front)
• Valid time:
– 1 - 48 hr (short-range)
– 24 - 196 hr (medium range)
– > 10days (long-range)
Numerical Weather Predictions
Equations
+
Conceptual Models
+
High Performance Computers
Major Weather Systems affecting Hong Kong
Air masses affecting us
Summer Monsoon Rain
Tropical Cyclones
Winter Monsoon
Air masses affecting us
Summer Monsoon Rain
What is a trough ?
A trough of low pressure is an extension of an area of low pressure.
It is called a trough because the atmospheric pressure over the
region is lower than its two adjacent sides.
Tropical Cyclones
Classification of Tropical Cyclones
Max 10-min mean wind near the centre
Tropical Depression
up to 62 km/h
Tropical Storm
63 to 87 km/h
Severe Tropical Storm
88 to 117 km/h
Typhoon
118 km/h or more
Locations of tropical cyclone formation
Winter Monsoon
H
What is an anticyclone or high pressure area ?
When the atmospheric pressure over a region is higher than its
surrounding, it is called an anticyclone or an area of high pressure. The air
mass surrounding an anticyclone will move clockwise in the northern
hemisphere. The weather under an area of high pressure is generally
stable.
Rule of Thumb for Forecasting Weather in Hong Kong
 Wind (air mass theory):
 Northerly winds- dry and cold (in winter)
NW – hazy and dry
 Southerly winds - warm and humid
SW – unstable
SE – misty in spring
 Easterly winds – tricky !
High pressure area : Stable weather
Low pressure area : Unstable weather
Some examples of severe weather
Rainstorms
•Rainstorms more
frequent in summertime
•Can cause widespread
flooding and landslips
•Can also accompanied
with hail and tornado (not
frequent in Hong Kong)
A Black rainstorm (2000/04/23)
A hail storm (1998/02/18)
Hailstorms
© Hong Kong Observatory
a hail storm with
"hook" signature
© Hong Kong Observatory
Squall lines and “Shi Hu Feng (石湖風) ”
A squall line is a cluster of several severe thunderstorm cells along a line.
Squall lines travel quickly and are destructive.
• heavy downpour and active lightning,
• sudden change in surface wind direction and abrupt increase in wind speed
• severe gust associated with squall lines can exceed 100 kilometres per hour
• some of them are even embedded with hails and tornadoes
Time series of 1-minute maximum gust recorded at Kawi Chung
from 11:00 a.m. to 2:00 p.m. on 9 May 2005
150
1-minute Maximum Gust (km/hr)
135 km/h
100
50
0
11:00
12:00
13:00
Hong Kong Time
Tropical Cyclones
© Hong Kong Observatory
Rainbands
Typhoon
eye
Radar Reflectivity of Typhoon Yutu
© Hong Kong Observatory
Typhoon Zeb (1998)
The image was originally captured by the Geostationary Meteorological Satellite (GMS-5) of Japan Meteorological Agency (JMA). Anyone
wishing to further disseminate the satellite image should seek permission from JMA, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (Fax: +813-3211-2032).
Typhoon Lupit (2003)
The satellite imagery was originally captured with GOES-9, which backs up GMS-5 and is operated over the western Pacific by the joint
effort of JMA and US NOAA NESDIS. Anyone wishing to further disseminate these satellite images should seek permission from JMA,
1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (Fax: +81-3-3211-2032).
El Niño and La Niña
El Niño and La Niña
El Niño refers to the above-normal sea surface temperatures from the coasts of
Peru and Ecuador to the equatorial central Pacific. El Niño usually peaks around
Christmas, hence the name of the phenomenon (Spanish for "the little boy" or
"the Christ Child"). It occurs on average every three to five years, lasting 12 to 18
months.
La Niña, "the little girl" in Spanish, is characterized by below-normal sea surface
temperatures in the eastern equatorial Pacific. La Niña occurs less frequently
compared with El Niño. La Niña conditions typically last approximately 9 to 12
months.
El Niño and La Niña can cause a
disruption of the oceanatmosphere system in the tropical
Pacific and result in climate
impacts in different regions
El Niño Situation
More rain in South America, while tropical Australia, Papua
New-Guinea and Indonesia experience drought conditions.
http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html
La Niña Situation
Increased convection or cloudiness over tropical Australia,
Papua New-Guinea, and Indonesia
http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html
Sea Surface Temperature Status from 2005 to 2008
Effect of El Niño and La Niña on Hong Kong Climate
Rainfall
Wet springs in Hong Kong seem to be associated with El Niño activity in
the previous winter, such as the springs of 1983, 1992 and 1998.
Tropical cyclones
El Niño years tend to have fewer tropical cyclones affecting Hong Kong,
relating to the favoured location for the formation of tropical cyclones shifting
towards the eastern and central Pacific.
Hong Kong tends to have more tropical cyclones in years with strong La Niña
activity
Seasonal Forecasting
Seasonal Forecasting
•
Monthly, Three-Monthly, or Annual Forecast
•
Usually forecast anomaly (above normal, normal, or below normal)
•
Methods :
(i) Conceptual/Statistical :- based on climatology and conceptual model on the
effects of different climate system on local climate (e.g. El Nino, La Nina,
Winter Monsoon Strength, Snow Cover, etc.)
(ii) Dynamical Approaches :- based on outputs of computer model simulations
and post-processing methods
Seasonal Forecasting in Hong Kong
Annual outlook :- total rainfall and tropical cyclone activities of the year
http://www.weather.gov.hk/wxinfo/season/anlf.htm
A conceptual-statistical approach is used to formulate the annual outlook
Seasonal forecast :- total rainfall and mean temperature of the season
http://www.weather.gov.hk/wxinfo/season/season.htm
The Hong Kong Observatory adapted a Global-Regional Climate Model (G-RCM)
suite consists of a Global Spectral Model and the latest version of the regional
climate model to provide seasonal forecasts for Hong Kong on experimental basis
Detailed methods : http://www.weather.gov.hk/wxinfo/season/met.htm
Regional Climate Model Rainfall Forecast Chart
Summer 2008 (June to August 2008)
Regional Climate Model Temperature Forecast Chart
Summer 2008 (June to August 2008)
Notes :
Notes :
Blue: +ve anomaly (above normal rainfall)
Orange: -ve anomaly (below normal rainfall)
Unit expressed in standard deviation (σ)
±0.5σ being classified as near normal
Red: +ve anomaly (above normal temperature)
Blue: -ve anomaly (below normal temperature)
Unit expressed in standard deviation (σ)
±0.5σ being classified as near normal
Thank you
Please visit HKO home page @
www.weather.gov.hk