09155183 d essay

The Hong Kong Polytechnic University
Department of Land Surveying and Geo-Informatics
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As a GIT consultant, you are instructed by Hong Kong Observatory to
review their homepage on weather for the public. Please critically review
the strength and limitations of the technologies employed and suggest
improvements in GIT aspect.

A. Background
Weather informationsuch as temperature, rainfall, humidity, air pressure, wind
speed and direction, are highly correlated with spatial and temporal data. To
store, analysis and present these data,Geographic Information System (GIS) is an
efficient and reliable platform.

Hong Kong Observatory (HKO) has been adoptingGeographic Information System
(GIS)to processing meteorological and other geophysical data spatially, and
presenting them ongeographical displays for both internal analysis and external
service delivery(Lee, 2007) from 1980s.Therefore, the public weather services
such as weather warnings and forecasts can be enhanced by making use of GIS
technologies. As a result, the public can get a better understanding of the
current weather situation through the homepage of Hong Kong Observatory.

B. Introduction of technologies employed by HKO
Numerical Weather Prediction (NWP)
Since 1980s, the Hong Kong Observatory has been using numerical weather
prediction (NWP) to forecast weather. For the numerical weather prediction
(NWP), a set of equations of a numerical model that describes the evolution of
the atmosphere is solved by a high-speed computer.The meteorological
parameters considered by the numerical model include temperature, wind,
pressure and moisture content.(HKO, 2010)

The numerical model represents the atmosphere by a three-dimensional grid set
up by systemically arranged points with the values of the meteorological
parameters. The larger the set of grid points, the finer the model resolution and
more details in the future state of the atmosphere can be describe, but the
computational demand is also higher.(HKO, 2010)

For forecasting large-scale weather systems such as surges of the winter
monsoon, the Hong Kong Observatory adopted the numerical weather prediction

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models of the European Centre for Medium Range Weather Forecasts and the
United Kingdom Meteorological Office received in the form of grid point values
via the Global Telecommunication System, as well as the numerical weather
prediction products from the Japan Meteorological Agency (JMA). (HKO, 2011)

For short-range forecast, the Hong Kong Observatory runs an Operational
Regional Spectral Model (ORSM) from the Japan Meteorological Agency (JMA) on
a high speed computer. This spectral model has a resolution of 20 km and
produces forecasts up to 48 hours. (HKO, 2010)

Since 2010, the Non-Hydrostatic Model (NHM) implemented by the Hong Kong
Observatory (HKO)has been running by a high-speed computer cluster, the NWP
Integrated Computing Environment (NICE) to coverthe lower end of the
mesoscale weather systems. And mesoscale weather systems refer to weather
systems with horizontal scales ranging from a few to several hundred
kilometers.The Non-Hydrostatic Model (NHM) has horizontal resolutions of 2 km
for inner domainand 10 km for outer domain.(HKO, 2010)

C. Strengths of technologies employed by HKO
With increased computer speed and memory resources, a fine resolution of 2 km
by 2 km grids with a short analysis time can be provided by the Non-Hydrostatic
Model (NHM) implemented by the Hong Kong Observatory (HKO). Such a small
grid size can allow a higher resolution and more details model. Moreover, the
accuracy of the model can be enhanced. The 10-km NHM is run eight times a day
to generate 72 hour forecasts and the 2-km NHM is run every hour to generate
15 hour forecasts. Prognostic weather charts and other post-processed products
are made available to forecasters as early as 1 hour and 3 hours after analysis
time for 2-km NHM and 10-km NHM respectively.Therefore, more timely and
detailed objective guidance for formulating weather forecasts and time-critical
warnings of inclement weather can be provided.(HKO, 2010)

With the data supported by the analysis of the non-hydrostatic model, the Hong
Kong Observatory has implemented a spatial weather information service called
“Digital Weather Forecast”. It presents weather forecast in fine spatial and
temporal resolution.(TONG, 2011)

There are two types of forecast products, forecast map and time series provided

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by the Digital Weather Forecast. For the forecast time series, the forecast time
charts of a specific region of a grid size 10 km x 10 km in Hong Kong can be
produced. It can show the time variation of various weather elements such as
temperature, wind and relative humidity within three days.For the forecast map,
the data in each grid box, about 10 km x 10 km in size, on the map shows the
general weather situation over the region as forecast by the model.It can show
the variation of various weather elements such as temperature, wind and relative
humidity within three days graphically.Both of the two products are updated
twice a day, hence, a updated graphical representation of weather forecast can
be reviewed by the public through the homepage of the Hong Kong Observatory
easily.

D. Limitations of technologies employed by HKO
Firstly, for the products of “Digital Weather Forecast” implemented by the Hong
Kong Observatory, the smallest grid size for data analysis is 10 km X 10 km. The
value of various weather elements such as temperature, wind and relative
humidity in each grid on the map shows the general weather situation over the
region as forecast by the model.

However, as each grid box is relatively large which is about 10 km X 10 km, it may
comprise a wide range of geographic characteristics such as land mass, sea
surface, hill and valley. Therefore, the weather conditions described by the
products may be not fine in resolution and different from those recorded at
individual weather stations within the grid box and the weather forecasts issued
by the Observatory.(HKO, 2011)

For that reason, as limited by the resolution of the numerical model, the “Digital
Weather Forecast”is only suitable for overviewing the general weather condition
of a relatively large area, but not accurate to preview the weather of a specific
place or a relatively small area, for example, a housing estate.Therefore, it might
not useful for the user to find the weather condition of his current position by
using the “Digital Weather Forecast”.

Secondly, the forecast map generated by the “Digital Weather Forecast”only
contains the map with the outline of Hong Kong andlegend showing the value of
various weather elements such as temperature, wind and relative humidity. It is

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lack of the geographic information of the map, for examples, the road features
with their names, the building features with their names, the names of the
districts and location, and so on. Moreover, the scale of the map is fixed and
relatively small where the area of the map has also including the Pearl River
Delta.

However, the weather forecast of the Pearl River Delta may not necessary for the
majority of local users.The more detail in the map of Hong Kong maybe more
appreciated. Furthermore, for those map users who are not familiar with the
location of district and places in Hong Kong, they may have to spend more time
onreferring to a general map to find a specific location on the forecast map
produced by the “Digital Weather Forecast”.Therefore, the forecast map may not
be convenient and user-friendly for the intermediate map users.

The last but not least, the Numerical Weather Prediction model (NWP) adopted
by Hong Kong Observatory do not consider the 3-D urban model.However, urban
areas have many ‘roughness’ elements such as buildings, trees, masts, street
furniture andvehicles. As the wind blows over urban areas, the air interacts with
these roughness elements andresponds according to their size, shape, layout and
distribution. (Evans, 2009)These interactions have great impact on the weather
forecast, especially for the urban area like Hong Kong.

However, the Hong Kong Observatory does not take these urban elements into
account. Therefore, the analyzed result for the weather forecast maybe not
accurate and reliable and different from the weather information recorded at the
individual weather stations of the Hong Kong Observatory.

E. Suggested Improvements
In order to increase the detail of the map productfromthe “Digital Weather
Forecast”, the Hong Kong Observatory can utilize the existing Non-Hydrostatic
Model (NHM)of grid size 2 km X 2 km which is implemented by itself, instead of
the Non-Hydrostatic Model (NHM) of grid size 10 km X 10 km. If the grid size of
the numerical weather prediction model is decreased, the resolution of the
weather forecast map can be increased.

The area represented by one grid can be reduced greatly from 100 km sq. to 4 km

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sq. As less geographic characteristics such as land mass, sea surface, hill and
valley would be include in a smaller grid, the expected variation of weather
conditions such as temperature and relative humidity within a grid box would be
smaller and closer to the actual values. Therefore, the overall accuracy of
products from the “Digital Weather Forecast” can be enhanced and it is possible
to preview the weather of a specific place or a relatively small area.

Moreover, the “Digital Weather Forecast” can be associated with the geographic
information. The data of the “Digital Weather Forecast”is in the format of Open
GIS standard KML 2.0 where KML stands for Keyhole Markup Language. There are
a number of KML-supported GIS display software packages. Users can choose the
appropriate software such as Google Earth according to their own needs.
Through GIS display software, users can zoom in, zoom out, animate and overlay
other geographic information on the weather forecast maps to better appreciate
the weather conditions in their area of interest.(HKO, 2011)

As a result, the products from the “Digital Weather Forecast” can become a
multi-scale digital forecast map.The map user can search the information of
weather forecast and other geographical information of any point on map easily
in the homepage of the Hong Kong Observatory. The forecast map would be
more user-friendly.

To forecast weather accurately, the interaction between meteorology and the
urban environment can be modeled. The numerical weather prediction model
used by the Hong Kong Observatory is grid-based which is using a regular grid
with each cell resenting a value, such as temperature, air pressure and so-on.
And the 3-D city models are usually vector based. 3-D city model can be taken
and developed to create input data for a numerical weather prediction
model.(Evans, 2009)

Although constructing and maintaining a 3-D city model with fine details for Hong
Kong is costly and time-consuming, the detailed spatial analysis can be carried
out and the quality of the weather forecast can be ensured. In the data analysis,
the interaction between the urban environment and the numerical weather
prediction models can be took into account. Therefore, the analyzed result of the
weather forecasting would be more reliable than the conventional method of
Hong Kong Observatory that only considers the numerical weather prediction

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models.

F. Conclusion
The Hong Kong Observatory has provided many useful public services of issuing
weather warnings and forecasts by using the Geographic Information System (GIS)
technology on its homepage. It has been developed and enhanced spatial weather
information services such as “Digital Weather Forecast” for the public and special
users with a view to supporting their decision-making in relation to weather-sensitive
activities (TONG, 2011) .

However, there are some weak points in these services, for examples, the accuracy
and user-friendliness. As the “Digital Weather Forecast” provided is in beta-version,
it can look forward to the improvement on it, as well as other weather services which
are making use of GIS technologies, in the near future.

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Reference
Evans, S. (2009). 3D cities and numeriacal weather prediction models: A overview of
the methods used in the LUCID project. London: Centre for Advanced Spatial Analysis
University College.
HKO. (2011, 11 3). Digital Weather Forecast. Retrieved 11 3, 2011, from Hong Kong
Observatory: http://www.hko.gov.hk/dfs/main/dfs_tt_e.html
HKO. (2010, 9 30). Mesoscale Model. Retrieved 11 3, 2011, from Hong Kong
Observatory: http://www.hko.gov.hk/nhm/mesomodel_e.htm
HKO. (2011, 8 15). Numerical Weather Prediction Models. Retrieved 11 3, 2011, from
Hong Kong Observatory: http://www.hko.gov.hk/aviat/amt_e/nwp_e.htm
Lee, L. (2007). GIS and LBS Applications in the Delivery of Weather and Geophysical
Services in Hong Kong. Hong Kong: Hong Kong Observatory.
TONG, Y.-f. (2011). Recent Development of Location-based and Spatial Weather
Information Services by the Hong Kong Observatory. 7th Annual Seminar on Spatial
Information Science and Technology (p. 3). Hong Kong: Department of Land
Surveying and Geo-Informatics of the Hong Kong Polytechnic University.

09155183 d essay

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