Monsoon 合集: 一次了解多個地方既季候風
Monsoon: a seasonal prevailing wind in the region.
Monsoons are large-scale wind systems caused by differences in the temperatures of land and sea over the seasons.
HONG KONG 香港
Also Reference:Strong Monsoon Signal｜Hong Kong Observatory(HKO)｜Details of Warnings
Key knowledge from this clip:
- Winter in Hong Kong : North to East (North-East) monsoon
- Summer in Hong Kong : Southwest monsoon
Winter
In winter, the continental land mass cools off rapidly, resulting in very low temperatures over central Asia. As cold air accumulates, pressure rises and a huge continental anticyclone develops over Siberia with the Tibetan Plateau forming an effective barrier blocking the southward spread of cold air from the anticyclone. From time to time, under the influence of upper air disturbances, cold air from this anticyclone plunges southward through China and brings outbursts of cold air to the south China coastal areas. Depending on the time of the season, and the juxtaposition of various weather systems, these surges will arrive in Hong Kong as northerlies, northeasterlies or easterlies.
在冬天，亞洲大陸迅速冷卻，導致其中部十分寒冷。當冷空氣集結，氣壓上升，一股巨大的大陸性反氣旋便在西伯利亞形成。青藏高原則構成一個有效的天然屏障，阻礙這股反氣旋內的冷空氣向南伸展。有時，在高空擾動氣流影響下，冷空氣會南下橫過中國。這些冬季季候風寒潮，最後為華南沿岸帶來一陣陣的冷空氣。在冬季不同時間，隨著各天氣系統的配合，寒潮可從北面、東北面或東面抵達香港。
Summer
In summer, intense solar heating leads to scorching temperatures over the Asian land masses. As a result, the overlying air heats up, expands and rises upwards. This leads to the formation of a semi-permanent low pressure area near the heart of the continent. Warm and moist air from the Indian Ocean and the South China Sea flowing into this low pressure area is experienced as the summer monsoon over south and southeast Asia.
在夏天，亞洲大陸受到太陽的強烈照射，地面溫度升高，其上的空氣受熱，於是膨脹和上升，一個長期維持的低壓區便在亞洲中部形成。當溫暖潮濕的空氣從印度洋及南海吹向這個低壓區時，亞洲南部及東南部便受到夏季季候風的影響。
Monsoons v.s Tropical cyclones
Winds associated with the monsoons are generally more persistent than those brought by tropical cyclones and may last for days. In intense surges of the winter monsoon, northeasterlies of up to gale force are not uncommon over the south China coastal waters. However, the full impact of these winds is not always felt in Hong Kong, particularly in heavily built-up areas or where nearby terrain provides some sheltering.
Occasionally, in winter, tropical cyclones traversing the South China Sea pass to the south of Hong Kong just when a monsoon is affecting the coastal areas of south China. Winds in Hong Kong are greatly enhanced due to the very large pressure difference between the continental anticyclone and the centre of the tropical cyclone.
與熱帶氣旋比較，季候風一般較為持久，往往會延續多天。在較強的冬季季候風寒潮影響下，華南沿岸海域常會出現烈風程度的東北風。但香港境內不一定會受到這些烈風的影響，尤其是在大廈林立的市區或在受到地形遮擋的地方。
在冬季季候風影響著華南沿岸的時候，間中會有熱帶氣旋橫過南海，並於香港以南掠過。這時候，大陸性反氣旋和熱帶氣旋間的巨大氣壓差距，會導致香港的風力更為增強。
The Strong Monsoon Signal
The Strong Monsoon Signal is issued when winds associated with the summer or winter monsoon are blowing in excess of or are expected to exceed 40 kilometres per hour near sea level anywhere in Hong Kong. Winter monsoon normally blows from the north or from the east while summer monsoon typically blows from the southwest. In very exposed places, monsoon winds may exceed 70 kilometres per hour.
Phoenix, Arizona
Monsoon in Arizona – Tommy’s Diaries (tommykwan.com)
Australia
Ref About Australian Climate (bom.gov.au)
- Northern Australia, the prevailing wind is from the east or southeast (E/SE) for most of the year
- Nov to Apr (11-4) : active monsoon periods = southern summer – winds shift to become northwesterly (NW) at the surface as the Australian summer approaches, the continent heats up
The monsoon can be in either an “ active” or an “inactive” phase.
Active phase is usually associated with broad areas of cloud and rain, with sustained moderate to fresh northwesterly winds on the north side of the trough. Widespread heavy rainfall can result if the trough is close to, or over, land.
Inactive or “break” period occurs when the monsoon trough temporarily weakens or retreats north of Australia. It is characterised by light winds and isolated shower and thunderstorm activity, sometimes with gusty squall lines. Transitions from active to inactive monsoon phases may be associated with the Madden-Julian Oscillation, a large-scale slow-moving band of increased cloudiness that travels eastwards in the tropics.
Key knowledge from this clip:
- Dry season in Australia (southern winter) : May to Sept
- Wet season in Australia (southern summer) : Oct to Apr
- Southern summer period, the sun heat up nothern part of continental in Australia at a higher rate than the surrounding oceans, which sets up sea breeze and draws in moisture to the land, where has a low pressure system
Note: The effect of monsson is also subject to other climate drivers:
