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Friday, 9th July 2010

Lake Baikal

Located in Siberia just north of present-day Mongolia, Lake Baikal is the second most voluminous freshwater lake in the world, after the Caspian Sea. Its biodiversity features a large number of species of plants and animals, most of which are unique to the area. In the past, many Russians respectfully referred to it as the "Baikal Sea".

Figure 1     Map showing location of Lake Baikal
Figure 1      Map showing location of Lake Baikal


Figure 2     Lake Baikal (southwest shore) in summer  (Courtesy :Wikipedia Commons)
Figure 2      Lake Baikal (southwest
shore) in summer (Courtesy :
Wikipedia Commons)


The lake is geographically familiar to forecasters in Hong Kong. In the 1970s two Observatory colleagues, Messrs Gordon Bell (then the Director) and Edmund Chu, noticed that the passage of a trough at mid-atmosphere (about 5500 metres aloft) over the lake was usually followed by a surge of winter monsoon at Hong Kong two days later.

Despite the advent of numerical weather prediction, forecasters nowadays still find this 'rule of thumb' useful when formulating the weather forecast for the next few days during winter and spring time. An example of trough passage is given in Figure 3. On that occasion, Hong Kong experienced a fall of 5 degrees Celsius 48 hours after the trough passed over the lake.

Figure 3     An example of the passage of mid-atmosphere trough (dotted line) through Lake Baikal
Figure 3      An example of the passage of mid-atmosphere trough (dotted line)
through Lake Baikal (Courtesy of European Centre
of Medium-range Forecast, 19 January 2010)


Not many people here are aware that intense winter monsoon can influence the weather in southeast Asia, as far south as Singapore and Malaysia. These places are characterized by a wetter monsoon season --- from around November to January, when the monthly rainfall is higher than those in the hotter months. An abrupt rise in Hong Kong's air pressure during winter or spring time may be followed by an outburst of severe weather there. A case in point was early March of 1967, when sudden strengthening of northerly winds over the South China Sea brought more than 300 millimetres of rain in 24 hours to the Malaysia Peninsula a few days later. Figure 4 shows how Singapore's rainfall contrasts that of Hong Kong.

Air blowing from the distant Siberia could bring heavy rain to the tropics. Truly, weather knows no boundaries.

Figure 4     Diagram showing how Singapore's rainfall contrasts that of Hong Kong
Figure 4      Diagram showing how Singapore's rainfall contrasts that of Hong Kong




B.Y. Lee


Reference:

Wikipedia


Last revision date: <17 Jan 2013>