A study on the relationship among visibility, atmospheric suspended particulate concentration and meteorological conditions in Hong Kong, Y.K. Leung, M.C. Wu & K.K. Yeung. Bull. HK. Met. Soc., 66(3), p461-469, June 2008, HKO Reprint No. 784 (June 2008, in Chinese only)
Possible Meteorological Influence on the Severe Acute Respiatory Syndrome (SARS) Community Outbreak at Amoy Gardens, Hong Kong, K.M. Yip, W.L. Chang, K.H. Yeung & T.S. Yu*, J. Environmental Health, 70(3), October 2007, 39-46. HKO Reprint No. 732 (October 2007)
Climatic Influence on the Prevalence of Noncutaneous Disease Flare in Systemic Lupus Erythematosus in Hong Kong, C.C. Szeto*, H.Y. Mok, K.M. Chow*, T.C. Lee, Y.K. Leung, K.M. Li*, K.C. Tsui*, Samuel Yu*, L.S. Tam*, Journal of Rheumatology, 1031-1037, 35(6), June 2008. HKO Reprint No. 842 (June 2008).
Relationship between thermal index and mortality in Hong Kong, Y.K. Leung, K.M. Yip & K.H. Yeung, Meteorological Applications, 399-409, 15(3), September 2008, HKO Reprint No. 785 (September 2008).
Seasonal influenza activity in Hong Kong and its association with meteorological variations, Paul K.S. Chan*, H.Y. Mok, T.C. Lee, Ida M.T. Chu*, W.Y. Lam*, Joseph J.Y. Sung*, Journal of Medical Virology, 1797-1806, 81(10), October 2009. HKO Reprint No. 841 (October 2009).
Vertical Profile and Origin of Wintertime Tropospheric Ozone over China During the PEACE-A Period, C.Y. Chan* et al., E.W.L Ginn & Y.K. Leung, J. Geophy. Res., 109, 2004, HKO Reprint No. 585 (2004)
An analysis on Abnormally Low Ozone in the Upper Troposphere over Subtropical East Asia in Spring 2004, C.Y. Chan* et al., Y.K. Leung & M.C. Wu, Atmospheric Environment41(17), p3556-3564, June 2007, HKO Reprint No. 721 (June 2007)
This Educational Package represents an efforts by the Hong Kong Observatory to promote public awareness of climate change. It is intended to help people appreciate what climate change is and understand its serious impacts.
Hopefully people would be motivated to act as responsible individuals, helping to reduce carbon dioxide emission by all available means, so as to give the Earth a chance to recover. In this endeavour, the Observatory would be happy to work alongside the education sector and non-government organizations to defend our beautiful Earth which we call home, for the sake of the people of Hong Kong as well as all mankind.
The Thermohaline Circulation (also called Great Ocean Conveyor belt) is a large-scale density-driven circulation in the ocean, caused by differences in temperature (thermo) and salinity (haline), but despite what its name suggests, it is also driven by mechanical forces such as winds and tides. A more accurate scientific term would be the Meridional Overturning Circulation (MOC). In the North Atlantic the thermohaline circulation or MOC consists of warm surface water flowing northward and cold deep water flowing southward, resulting in a net poleward transport of heat, thereby moderating the tropics and warming the high latitudes of Europe. The surface water sinks in highly restricted sinking regions located in high latitudes.
According to IPCC (Climate Change 2007: Working Group I: Physical Science basis), it is very likely that the Atlantic Ocean MOC will slow down during the 21st century. However it is very unlikely that the MOC will undergo a large abrupt transition during the 21st century. At this stage, it is too early to assess the likelihood of an abrupt charge of the MOC beyond the end of the 21st century but the possibility cannot be excluded.
Simpified illustration of the Great ocean conveyor belt
(Source: Climate change 2001 - Synthesis report,
Intergovernmental Panel on Climate Change)
El Nino-Southern Oscillation ENSO
El Nino is a local warming of surface waters which takes place in the entire equatorial zone of the central and eastern Pacific Ocean off the Peruvian coast and which affects the atmospheric circulation world-wide. El Nino usually peaks around Christmas, hence the name of the phenomenon (Spanish for "the little boy" or "the Christ Child"). It occurs on average every two to four years, lasting 12 months or so.
La Nina, "the little girl" in Spanish, is characterized by below-normal sea surface temperatures in the eastern equatorial Pacific. In general, La Nina occurs less frequently but lasts longer compared with El Nino.
The Southern Oscillation is an east-west balancing movement of air masses between the Pacific and the Indo-Australian areas. It is roughly synchronized and associated with typical wind patterns and El Nino, and measured by the Southern Oscillation Index (SOI), the difference between sea level atmospheric pressures at Tahiti and Darwin.
El Nino is the oceanic component, while the Southern Oscillation is the atmospheric one. This combination gives rise to the term ENSO. In general, negative values of the SOI are associated with warm events.
ENSO conditions are commonly defined with reference to the sea surface temperatures in the Nino regions (see figure below). Latest conditions of ENSO can be found at http://www.weather.gov.hk/lrf/enso/enso.htm.
Graphical depiction of the four Nino regions and
the location of Tahiti and Darwin for SOI
The local impacts of ENSO can be found in the following references prepared by HKO staff:
The Pacific Decadal Oscillation (PDO) is the predominant source of inter-decadal climate variability in the Pacific Northwest. Like ENSO, PDO is characterized by changes in sea surface temperature, sea level pressure, and wind patterns. The PDO is described as being in one of two phases: a warm phase and a cool phase.
The warm phase of PDO favors anomalously warm sea surface temperatures near the equator and along the coast of North America, and anomalously cool sea surface temperatures in the central North Pacific. The cool phase for PDO has the opposite pattern of SST anomalies. Each PDO phase typically lasts for 20-30 years.
Typical wintertime Sea Surface Temperature (colors), Sea Level Pressure (contours) and surface windstress (arrows) anomaly patterns during warm and cool phases of PDO (Source: University of Washington)
The Arctic Oscillation (AO) refers to variations in the difference in the atmospheric pressure patterns between northern mid-latitudes (about 45 degrees North) and the Arctic. It is an important Arctic climate index with positive and negative phases representing the state of atmospheric circulation over the Arctic.
Low pressure systems usually dominate over the Arctic while high pressure systems sit over the mid-latitudes. In the positive phase of the AO, the pressure difference of the systems is stronger than normal, confining the southward extension of cold Arctic air. In the negative phase, the pressure difference is weaker than normal, allowing easier outbreaks of frigid air to the south. (See the figures below)
