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مباحث عمومی هواشناسی

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A

arashz

مدیر بخش هواشناسی
Amir Mohsen گفت:
What is it? Think of the [HIGHLIGHT]EPO sort of like a Pacific cousin of the NAO.[/HIGHLIGHT] The EPO is a good[HIGHLIGHT] measure of what the upper wind flow is doing and tends to correlate well to downstream impacts.[/HIGHLIGHT][HIGHLIGHT] When the EPO is in a positive phase, you typically see troughing or zonal winds on the West Coast, which translates to the Lower 48 being "flooded" by Pacific air[/HIGHLIGHT]. Anyone who is a weather enthusiast, especially with regard to winter, knows that this does not bode well for snow and cold. These sorts of patterns are dominated by fast flow, often some weather systems get embedded in the flow and it can be almost a "dirty" type pattern, with cloud cover and mild temps. Alternatively, you can occasionally get fair weather in that sort of pattern this time of year, but I tend to view it as more of a cloudy, mild to occasionally warm sort of pattern. [HIGHLIGHT]When the EPO shifts to a negative phase, this can lead to a ridge in the Gulf of Alaska, which is generally good for a trough downstream somewhere, specifically in the Eastern US, and as a result, cold air[/HIGHLIGHT].

Why does it matter? [HIGHLIGHT]A lot of people tend to neglect the EPO as a major consideration in forecasting[/HIGHLIGHT], as [HIGHLIGHT]much laboring will be done over the AO or NAO...the more discussed and relatable correlations to Eastern US cold[/HIGHLIGHT].
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کلیک کنید تا باز شود...

تا جایی که من متوجه شدم این در خصوص شاخص هم مثل بیشتر شاخص ها برای ایران و منطقه ما کار بخصوصی انجام نشده و تاثیراتش رو در منطقه خودشون بررسی کردن.
 
A

Amir Mohsen

متخصص بخش هواشناسی
[h=4]EPO versus NAO:
As important as the progress of El Niño will be the evolution of the North Atlantic Oscillation (NAO) and the Eastern Pacific Oscillation (EPO). The NAO, basically, is the dominant upper wind flow pattern over the North Atlantic influenced by the ocean. While in a negative phase, the NAO sometimes tends to act as a block (or dam) to the upper wind flow over the eastern half of North America. This blocking effect, in turn, tends to deliver the polar/arctic air into the eastern half of the country and Great Lakes more readily.
The Eastern Pacific Oscillation (EPO) is the upper wind flow over the Eastern Pacific influenced by the ocean. When in a positive phase, the EPO generally is reflected by dominant stronger zonal flow and/or troughing along the West Coast of the U.S. This combination, in turn, tends to funnel milder Pacific air well inland into the country and thus, limits arctic outbreaks by holding them at bay up in Canada. When the EPO is dominated by a negative phase (as with the NAO), more ridging develops along the West Coast as higher pressure extends from the Gulf of Alaska south along the West Coast of Canada (opposite of the positive phase). This, in turn, encourages a northwesterly flow from Canada into the middle and eastern sections of the US and thus, the delivery of polar or arctic air.
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A

Amir Mohsen

متخصص بخش هواشناسی
Amir Mohsen گفت:
EPO versus NAO:

As important as the progress of El Niño will be the evolution of the North Atlantic Oscillation (NAO) and the Eastern Pacific Oscillation (EPO). The NAO, basically, is the dominant upper wind flow pattern over the North Atlantic influenced by the ocean. While in a negative phase, the NAO sometimes tends to act as a block (or dam) to the upper wind flow over the eastern half of North America. This blocking effect, in turn, tends to deliver the polar/arctic air into the eastern half of the country and Great Lakes more readily.
The Eastern Pacific Oscillation (EPO) is the upper wind flow over the Eastern Pacific influenced by the ocean. When in a positive phase, the EPO generally is reflected by dominant stronger zonal flow and/or troughing along the West Coast of the U.S. This combination, in turn, tends to funnel milder Pacific air well inland into the country and thus, limits arctic outbreaks by holding them at bay up in Canada. [HIGHLIGHT]When the EPO is dominated by a negative phase (as with the NAO), more ridging develops along the West Coast as higher pressure extends from the Gulf of Alaska south along the West Coast of Canada (opposite of the positive phase). This, in turn, encourages a northwesterly flow from Canada into the middle and eastern sections of the US and thus, the delivery of polar or arctic air[/HIGHLIGHT].
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کلیک کنید تا باز شود...

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A

Amir Mohsen

متخصص بخش هواشناسی
[h=4]Sunspot Cycle and Autumn Trends:
Along with the aforementioned factors, other considerations are taken into account for this winter outlook. First are the weather trends of the last year and how well they relate to the weather trends proceeding the 13 winters in the study. Second, is a check of the solar activity during the years of the past winters studied. It is known that sunspot activity has an impact on climatic trends and patterns over the earth. The current sunspot cycle is then compared with sunspot cycles (timing/peak/intensity) of past winters in the study.
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During the winter of 2002-03, sunspot maxima continued to wane from the peaks attained during the past few years and this trend was compared to the past winters in the study. Though a similar sunspot waning trend was noted in some of the researched winters, the end result was more variable than other factors researched and mentioned above. A bit more weight, however, was given to the overall weather pattern of the proceeding summer and autumn time periods.
While the majority of winters in the study proved to proved mild with normal to below normal snow, there were important exceptions. Perhaps no trend of some of Autumns was more noteworthy than the abrupt change in the upper wind pattern to a dominant northwesterly flow beginning in October. Interestingly, this trend also was a foreboding of things to come and was picked up on in the research and then, noted in the original outlook under "Contrary Indicators".
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A

Amir Mohsen

متخصص بخش هواشناسی
[h=4]Contrary Indicators: Perhaps none of the winters challenged the prevalent below normal snowfall trend (and above normal temperatures when looking at 1977-78) more than the winters of 1885-86, 1972-73 and 1977-78 when snowfall was significantly above normal at most locations. While the detailed EPO and NAO trends were not available for 1885-86, they were for the winters of 1972-73 and 1977-78. Also, in addition to the being snowy, why was the winter of 1977-78 so much colder than the rest in the study? Reviewing the earlier archives of the EPO and NAO, along with the 500 MB upper wind pattern, may help understand the differences between the harder winters of 1972-73, 1977-78 and the dominant milder ones. Is there some trend to watch for in the EPO and NAO and upper air pattern this fall that occurred in 1972 and 1977

An important change came in October (and again, one of the few cool Octobers in the study) when abnormally cold air surged into the region mid month. While the timing of the polar blast duplicated most in the study its strength and dominance was atypical. The monthly average temperature for October 1977 was a cool 47.9 degrees /normal 51.9/ at Detroit. Curiously, this same pattern was noted in the fall of 1972 and again, this abrupt change surfaced in October. October of 1972 not only turned out to average well below normal, but with nearly the same average temperature as October 1977 with 47.3 degrees.
While October 2002 remained warm until mid October, the recent abrupt change to a deep 500 MB trough over the eastern half of the country resulting in much colder weather bears watching, especially if it represents an intermediate trend change to the past several months. In addition, the near-term projections of the EPO and NAO both indicate, at least short term, negative phases and this too bears watching for any overall, longer term trend change.




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A

AFSORDE

کاربر ويژه
ماه های نا به هنجار و تاریخ ساز اینجا از نظر دمایی از آغاز سال 1390 تا حالا....

اسفند 90 - بهمن 91 - دی 92
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D

Dr.ben

کاربر ويژه
سلام دوستان.
نمی دونم اسم این درختچه چیه ولی در شرایط نرمال با شروع فروردین ماه شروع می کرد به گل دادن و برگ های سبزش نمایان می شد. اما هوای بهاری هفته های اخیر باعث شده از خواب بسیار کوتاه زمستونی بیدار بشه:

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A

alirezamousavi

New member
ولی بازم به غیر از ما شمال شرقی ها و جنوب شرقی ها کمی هم از شمال غرب تا 192 ساعت اینده هیچ بارشی ندارند
 
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