Cuaca
From Wikipedia
| Sains atmosferik [kat.] |
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Meteorologi [cat.]
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| Klimatologi [kat.] |
Cuaca adalah istilah yang digunakan untuk menghuraikan semua fenomena yang banyak dan pelbagai yang boleh berlaku dalam atmosfera planet. Istilah ini biasanya digunakan untuk memaksudkan aktiviti fenomena ini selama tempoh masa yang pendek, biasanya tidak lebih dari beberapa hari panjangnya. Purata keadaan atmosfera untuk tempoh yang lebih panjang dikenali sebagai iklim. Penggunaan dua istilah ini selalu bertindih dan konsep ini jelas berhubungkait rapat.
Jadual isi kandungan |
[Sunting] Mekanisma asas
Fenomena cuaca terhasil akibat dari perbezaan suhu seluruh dunia, yang timbul sebahagian besarnya kerana kawasan yang lebih dekat kepada tropika, di sekitar khatulistiwa, menerima lebih tenaga dari Matahari berbanding bahagian utara dan selatan, lebih dekat kepada kutub Bumi.
Sebab kedua perbezaan suhu pada Bumi adalah kelainan permukaan tempat (seperti air lautan, tanah berhutan, dan kepingan ais) mempunyai kebolehpantulan berbeza (albedo), dan dengan itu menyerap dan menyinarkan kadar berbeza tenaga suria yang diterima.
Perbezaan suhu permukaan mengakibatkan arus angin menegak. Permukaan panas akan memanaskan udara di atasnya, menyebabkan ia mengembang dan naik ke atas, menurunkan tekanan udara dan menarik udara yang lebih sejuk ke tempat tersebut. Udara panas yang mengembang dan naik itu akan kehilangan haba dan menyejuk, yang menyebabkannya mengecut dan turun ke bawah, meningkatkan tekanan udara dan menggantikan udara yang berada di bawahnya.
Arus angin melintang terbentuk di sempadan kawasan yang berbeza kepanasan dan boleh menjadi-jadi jika terdapat permukaan cerun. Sistem ringkas ini boleh menimbulkan tingkah laku yang menghasilkan sistem yang lebih rumit dan demikian semua fenomena cuaca. Contoh skala besar proses ini boleh dilihat di sel Hadley dan bentuk lain peredaran atmosfera. Contoh kecilan pula dalah seperti bayu laut.
Kesan Coriolis penting dalam menjadi punca putaran besar asing yang dikenali sebagai siklon.
Jadi punca asas cuaca adalah suhu permukaan, dan boleh juga ketinggian.
Oleh kerana paksi Bumi miring sedikit (tidak berserenjang dengan satah orbitnya), cahaya matahari sampai pada sudut yang berbeza pada waktu yang berbeza dalam setahun. Semasa Jun, Hemisfera Utara condong ke arah matahari, jadi pada mana-mana latitud cahaya matahari akan jatuh lebih menegak berbanding pada Disember (lihat kesan sudut matahari pada iklim). Ini menghasilkan musim. Sebarang liukan dalam orbit planet akan mengubah jumlah tenaga yang diterima di suatu tempat sepanjang tahun dam mungkin mempengaruhi pola cuaca jangka panjang. Lihat kitaran Milankovitch.
[Sunting] Cuaca bumi
Di Bumi, fenomena cuaca yang sering berlaku termasuklah angin, awan, hujan, salji, kabus dan ribut pasir. Perkara lain yang lebih jarang termasuklah bencana alam seperti puting beliung, ribut taufan dan ribut ais. Hampir semua fenomena cuaca di Bumi terjadi di troposfera (bahagian bawah atmosfera). Ada juga yang berlaku di stratosfera dan empengaruhi cuaca di troposfera, namun mekanismanya masih belum difahami [1].
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The Earth's atmosphere is one large chaotic system so small changes to one part can have large effects elsewhere. This makes it very difficult to accurately predict short term weather changes more than a few days in advance, though weather forecasters are continually working to extend this limit through the science of the study of weather, Meteorology.
Chaos theory explains that there are an infinite number of variables which affect the weather. The slightest variation in the motion of any molecule in the air influences the atmospheric situation. The slightest difference could affect the troposphere sufficiently to lead to utterly different conditions. Thus it will never be possible to forecast perfectly.
[Sunting] Shaping the planet
Along with plate tectonics and ocean circulation, weather is one of the fundamental processes that have shaped the Earth since its creation and will continue to do so as long as it exists. The process of weathering breaks down rocks and soils into smaller fragments and then into their constituent substances. These are then free to take part in chemical reactions that can affect the surface further (e.g. acid rain) or are reformed into other rocks and soils. Weather also plays a major, if indirect, role in erosion of the surface, moving surface constituents around.
[Sunting] Human history
Weather has played a large, and sometimes direct, part in human history. Aside from climatic changes that have caused the gradual drift of populations (for example the desertification of the Middle East, and Ice ages in Northern Europe), extreme weather events have caused smaller scale population movements and intruded directly on the course of human history. One such event that is celebrated is the saving of Japan from invasion by the Mongol fleet of Kublai Khan by the Kamikaze winds in 1281. The Little Ice Age of the 14th to 18th centuries had wide ranging effects in the northern hemisphere, including decimating the fledgling Viking colonies of Greenland, catalysing the formation of leagues among the Native American groups in North America, and forcing the change of patterns of agriculture across Europe to accommodate the shortened growing season. A series of great storms throughout the 13th century caused the powerful English Cinque Ports to be silted up and hence lose their influence. More recently, Hurricane Katrina forced the temporary abandonment of the entire city of New Orleans in 2005.
Because of the large effect that weather has on day-to-day life and due to the impossibility of any type of forecasting before the advent of modern technology, a large body of folklore aimed at trying to explain the weather has grown up, some of which is fairly accurate, most less so. A well known example is the Groundhog Day celebrated near the end of winter in parts of the United States.
The effect of seasons on the life of primitive peoples also caused them to observe and celebrate certain events during the calendar, some of which, in adulterated form, are still observed today. Christmas, for example, is the Yule of the pagans, celebrated around the winter solstice, the shortest day of the year (in the Northern Hemisphere, the summer solstice in the Southern Hemisphere).
[Sunting] In the future
It is the goal of some scientists to control the weather. Experiments have been carried out for many years, but the results are usually ambiguous. On a grander scale, science fiction authors have long posited the idea of terraforming other planets in order to make them habitable by human beings. While this may be possible in the distant future, this is far beyond current technology.
[Sunting] Weather records
The coldest air temperature ever recorded on Earth is -88.8ºC (-127.8ºF), and that was at Vostok, Antarctica on July 21, 1983. The hottest air temperature ever recorded on earth was 57.7ºC (135.9º F), which accured in Al 'Aziziyah, Libya, on September 13, 1922. The highest recorded average annual temperature was 34.4ºC (94ºF) at Dallol, Ethiopia. The coldest recorded average annual temperature is -50.6ºC (-59ºF) at Vostok, Antarctica. And the coldest average annual temperature in an permanently inhabited location is at Resolute, Nunavut, in Canada.
[Sunting] Extra-terrestrial weather
Weather phenomena and systems on other planets are thought to be similar to those on Earth, but often occur on a much bigger scale or involve different substances to those familiar to Earth dwellers. The Cassini-Huygens mission to Titan, for example, discovered clouds formed from methane or ethane which deposit rain composed of liquid methane and other organic compounds.
Extra-terrestrial weather systems can be extremely stable; one of the most famous landmarks in the solar system, Jupiter's Great Red Spot is an anticyclonic storm known to have existed for at least 300 years. On other gas giants, the lack of a surface allows the wind to reach enormous speeds: gusts of up to 400 metres per second (900 mph) have been measured on the planet Neptune. This has created a puzzle for planetary scientists: The weather is created by the differential action of the Sun's energy on different places and the amount of energy received by Neptune is very, very small, relative to the Earth, yet the strength and magnitude of weather phenomena on Neptune is far, far greater than on Earth. This mystery is still to be solved [2].
Earth's weather appears to behave based on about a half-dozen latitudinal weather zones. Jupiter's banded appearance shows over a dozen such zones, while Venus appears to have no zones at all. Studying how the weather works on other planets has been seen as helpful in understanding how it works on Earth. [3]
[Sunting] Extra-planetary weather
Cuaca tidak terhad kepada dalaman planet sahaja. Korona bintang sering dilepaskan ke ankasa dan menghasilkan sesuatu seakan-akan atmosfera tipis dalam sistem suria, yang dikenali sebagai angin solar.
Angin yang tidak tetap dan proses yang berlaku di permukaan bintang, seperti pancuran jisim korona,membentuk satu sistem yang mempunyai persamaan dengan sistem cuaca konvensional (seperti tekanan dan angin) dan walaupun bukan cuaca sebenar, ia dikenali sebagai cuaca angkasa. Aktiviti sistem tersebut boleh memberi kesan kepada atmosfera planet dan permukaannya juga. Pertembungan angin solar dengan atmosfera boleh menghasilkan aurorae, tetapi boleh bertindak lebih dahsyat dengan mengganggu dan memusnahkan sistem yang peka kepada elektrik seperti grid kuasa elekrik, signal radio dan telekomunikasi.
[Sunting] Rujukan
- ↑ http://www.gsfc.nasa.gov/topstory/20011018windsurface.html
- ↑ http://hubblesite.org/newscenter/newsdesk/archive/releases/1998/34/text/
- ↑ http://www.space.com/scienceastronomy/solarsystem/solar_system_weather_010306-1.html
[Sunting] Lihat juga
| Carilah maklumat lanjut di Weather melalui projek-projek kembar Wikipedia:
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- Iklim
- Meteorologi
- Awan
- Senarai lagu mengenai cuaca
