الأخ الغشياء، كما وعدتك سابقاً بخصوص ظاهرة ثنائية قطب المحيط الهندي
Indian Ocean Dipole ،
فقد صدر اليوم 14 سبتمبر أخر تحديث لهذه الظاهرة من المركز الاسترالي
و لله الحمد يبشر بالخير
وهو يشير إلى تطور هذه الظاهرة إلى إيجابية .
Pacific approaches La Niña. Positive Indian Ocean dipole develops.
Issued on Wednesday 14 September
Steady cooling of the central Pacific Ocean since early winter has increased the chance of La Niña returning during the last quarter of 2011. Current ENSO indicators are approaching values typically associated with La Niña events.
However, ocean temperatures are yet to reach critical thresholds, while climate model guidance about their future trends is mixed. Some models predict only modest cooling resulting in a borderline-La Niña event, but others predict stronger cooling beyond La Niña thresholds during the southern spring. A minority predict little or no cooling. Taken as a whole, there is an expectation that the trend towards La Niña will continue.
If a La Niña does form, current indicators are that it will be weaker than the strong 2010-11 event. La Niña events raise the odds of above average rainfall across the north and east of the country, but don't guarantee it. The Bureau's National Climate Centre will monitor the situation closely and issue regular updates via this summary.
The latest observations from the Indian Ocean show the development of a positive dipole event, as predicted over the last few months by climate models, including the Bureau's POAMA. Typically peaking in spring, positive dipole modes increase the chance of below average rainfall over southeastern and central Australia.
شرح ظاهرة IOD :
About the Indian Ocean Dipole
The Indian Ocean Dipole (IOD) is a coupled ocean and atmosphere phenomenon in the equatorial Indian Ocean that affects the climate of Australia and other countries that surround the Indian Ocean basin (Saji et al. 1999).
The IOD is commonly measured by an index that is the difference between sea surface temperature (SST) in the western (50°E to 70°E and 10°S to 10°N) and eastern (90°E to 110°E and 10°S to 0°S) equatorial Indian Ocean. The index is called the Dipole Mode Index (DMI). The map below shows the east and west poles of the IOD for November 1997; a positive IOD year.
A positive IOD period is characterised by cooler than normal water in the tropical eastern Indian Ocean and warmer than normal water in the tropical western Indian Ocean (see map below for an example of a typical positive IOD SST pattern). A positive IOD SST pattern has been shown to be associated with a decrease in rainfall over parts of central and southern Australia. For more information about Australian rainfall patterns during positive IOD years. Conversely, a negative IOD period is characterised by warmer than normal water in the tropical eastern Indian Ocean and cooler than normal water in the tropical western Indian Ocean. A negative IOD SST pattern has been shown to be associated with an increase in rainfall over parts of southern Australia. For more information about Australian rainfall patterns during negative IOD years
هي ظاهرة غريبة مرتبطة مابين المحيط الهندي والغلاف الجوي في منطقة خط الاستواء في المحيط الهندي، وتؤثر على مناخ الدول المطلة على هذا المحيط بما فيها استراليا.
تقاس تلك الظاهرة بالفرق مابين درجة الحرارة في منطقة غرب المحيط الهندي وشرقه (كما هو موضح بالخريطة ) ، فعندما تكون حرارة مياااااه المحيط في شرقه (غرب الجزر الاندنوسية) أبرد من غربه فيقال عنها إيجابية، والعكس صحيح فعندما تكون الحرارة في غربه أبرد من شرقه فيقال عنها سلبية.
Some positive
IOD events, but not all, occur during the same year as an El Nino.
In 2007 a positive
IOD occurred in the same year as a La nina. This is the only clear occurance of a positive
IOD event coinciding with a La Niña; 1967 showed a weak La Niña like pattern in the Pacific Ocean after August, but was clearly neutral in the atmosphere.
تعتبر علاقة ظاهرة ثنائية القطب بظاهرتي اللانينا والنينو معقد جداً، ففي بعض السنوات وكما حدث في عام 2007 فقد كانت لانينا وثنائية القطب موجبة ،
09-13-2011, 07:23 PM
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