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DR WHO

کاربر ويژه
عاليه

طوفان خورشيدى باعث افزايش دماى آب اقيانوس ها و افزايش تبخير و افزايش تشكيل شدن ابر مى شود

طبق گفته هواشناسى كرمونشاه افزايش فعاليت خورشيد = افزايش بارشها
 

Amir Mohsen

متخصص بخش هواشناسی
عاليه

طوفان خورشيدى باعث افزايش دماى آب اقيانوس ها و افزايش تبخير و افزايش تشكيل شدن ابر مى شود

طبق گفته هواشناسى كرمونشاه افزايش فعاليت خورشيد = افزايش بارشها

امیر کوروش جان
شما اصولا مطلب رو میخونی یا همینطوری اظهار نظر میکنی! چون اینجا نوشته فعالیتهای خورشیدی در سیکل 24 که باید شدید باشه در پایین ترین سطحه و اگه به لطف گرمایش جهانی نبود ما وارد یک عصر یخبندان کوچک می شدیم

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Amir Mohsen

متخصص بخش هواشناسی
Unusually cold spring in Europe and the Southeast U.S. due to the Arctic Oscillation
By: JeffMasters, 2:52 PM GMT on April 25, 2013+39

During March 2013, residents of Europe and the Southeast U.S. must have wondered what happened to global warming. Repeated bitter blasts of bitter cold air invaded from the Arctic, bringing one of the coldest and snowiest Marches on record for much of northern Europe. In the U.K., only one March since 1910 was colder (1962), and parts of Eastern Europe had their coldest March since 1952. A series of exceptional snowstorms struck many European locations, including the remarkable blizzard of March 11 - 12, which dumped up to 25 cm (10”) of snow on the Channel Islands of Guernsey and Jersey in the U.K., and in the northern French provinces of Manche and Calvados. The entire Southeast U.S. experienced a top-ten coldest March on record, with several states experiencing a colder month than in January 2013. Despite all these remarkable cold weather events, global temperatures during March 2013 were the 9th warmest since 1880, said NASA. How, then, did such cold extremes occur in a month that was in the top 8% of warmest Marches in Earth's recorded history? The answer lies in the behavior of the jet stream. This band of strong high-altitude winds marks the boundary between cold, polar air and warm, subtropical air. The jet stream, on average, blows west to east. But there are always large ripples in the jet, called planetary waves (or Rossby waves.) In the Northern Hemisphere, cold air from the polar regions spills southward into the U-shaped troughs of these ripples, and warm air is drawn northwards into the upside-down U-shaped ridges. If these ripples attain unusually high amplitude, a large amount of cold polar air will spill southwards into the mid-latitudes, causing unusual cold extremes. This was the case in Europe and the Eastern U.S. in March 2013. These cold extremes were offset by unusually warm conditions where the jet stream bulged northwards--over the Atlantic, the Western U.S., and in China during March 2013. In fact, the amplitude of the ripples in the jet stream reached their most extreme value ever recorded in any March during 2013, as measured by an index called the Arctic Oscillation (AO).

ao-march2013.png

Figure 1. The monthly Arctic Oscillation (AO) index from 1950 - March 2013 shows that three of the six most extreme negative cases have occurred since 2009. Note that all of the six most negative AO indices on record were associated with historic cold waves and blizzards over Europe or the Eastern U.S. Image created using data from NOAA's Climate Prediction Center.

Measuring the jet stream's contortions: the Arctic Oscillation (AO)
One measure of how extreme the ripples in the jet stream are is by measuring the difference in pressure between the Icelandic Low and the Azores High. An index based in this pressure difference is called the North Atlantic Oscillation (NAO). When this index is strongly negative, it means that the pressure difference between the Icelandic Low and the Azores High is low. This results in a weaker jet stream, allowing it to take large, meandering loops. These loops allow cold air to spill far to the south from the Arctic into the mid-latitudes. A more general index that looks at pressure patterns over the entire Arctic, not just the North Atlantic, is called the Arctic Oscillation (AO). The AO and NAO are closely related about 90% of the time. According to a 2010 paper by L'Heureux et al., a strongly negative AO pattern that allows cold air to spill southwards into the mid-latitudes does nothing to the average temperature of the planet. Fluctuations in the jet stream as measured by the AO simply act to redistribute heat. It's kind of like turning off your refrigerator and leaving the refrigerator door open--the cold air from the refrigerator spills out into the room, but is replaced inside the refrigerator by warm room air. No net change in heat occurs. During March 2013, the AO index hit -3.2. Not only was this the most extreme negative March value of the AO since record keeping began in 1950, it was also the sixth lowest AO index ever measured. It was also the first time the AO index had been that extremely negative in a non-winter month (because the circulation patterns are stronger in the winter, we tend to see more extreme values of the AO index in December, January, and February.) This unusual contortion of the jet stream in March 2013 allowed Europe to have exceptional cold weather in a month when the global average temperature was among the warmest 8% of Marches on record. Why did the AO index get so extreme in March 2013? Part of the blame goes to the sudden stratospheric warming event that began in January (wunderblogger Lee Grenci has a detailed post on this event.) Sudden stratospheric warming events tend to push the atmosphere into a more negative AO configuration. Another major factor was the very active Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. When the area of increased thunderstorms associated with the MJO is located in the Pacific Ocean, as occurred during much of March 2013, this tends to create negative AO conditions. Finally, wintertime Arctic sea ice loss has been tied to more negative AO patterns, and sea ice was well blow average again during March.

AO.jpg

Figure 2. The Arctic Oscillation (AO) is a pattern of varying pressure and winds over the Northern Hemisphere that can strongly influence mid-latitude weather patterns. When the AO is in its positive phase, jet stream winds are strong and the jet stream tends to blow mostly west to east, with low-amplitude waves (troughs and ridges.) Since the jet stream marks the boundary between cold Arctic air to the north and warm subtropical air to the south, cold air stays bottled up in the Arctic. When the AO is in its negative phase, the winds of the jet stream slow down, allowing the jet to take on more wavy pattern with high-amplitude troughs and ridges. High amplitude troughs typically set up over the Eastern U.S. and Western Europe during negative AO episodes, allowing cold air to spill southwards in those regions and create unusually cold weather.

Are jet stream patterns getting more extreme?
We've had some wildly variable jet stream patterns in recent years in the Northern Hemisphere. Just last year, we had a strongly positive AO in March, when our ridiculous "Summer in March" heat wave brought the warmest March on record to the U.S. The first day of spring in Chicago, IL on March 20, 2013 had a high temperature of just 25°F--a 60 degree difference from last year's high of 85°F on March 20! During the past five years, we've set new monthly records for extreme negative AO index for six of the twelve months of the year:

-4.3: February 2010
-3.4: December 2009
-3.2: March 2013
-1.5: October 2009, 2012
-1.4: June 2009
-1.4: July 2009

Note that four of these months with an extremely negative AO occurred in one year--2009. This unusual event was "unprecedented in the 60-year record", according to L'Heureux et al. (2010.) Despite the unusually large negative AO in 2009, the authors found that the AO index between 1950 - 2009 had actually trended to be more positive, in both the winter and annual mean. This is in agreement with what many climate models predict: the AO index should get increasingly positive, due to increasing levels of CO2 in the atmosphere, since this tends to make the stratosphere cool and increase the strength of high altitude winds over the Arctic. However, a number of papers have been published since 2009 theorizing that the record loss of Arctic sea ice in recent years may be significantly altering Northern Hemisphere jet stream patterns (I list eleven of these papers below.) Many of these studies show a link between Arctic sea ice loss and an increasingly negative AO and NAO index in winter. Dr. Jennifer Francis of Rutgers has authored several of these papers, and wrote a very readable explanation of the theory linking Arctic sea ice loss to extreme weather in the mid-latitudes for our Earth Day 2013 microsite. Her post was called, "The Changing Face of Mother Nature." The most recent technical paper connecting Arctic sea ice loss to extreme weather was a March 2013 paper by Tang et al., "Cold winter extremes in northern continents linked to Arctic sea ice loss". The paper argued that unusual jet stream contortions in winter have become increasingly common in recent years. The scientists found a mathematical relationship between wintertime Arctic sea ice loss and the increase in unusual jet stream patterns capable of bringing cold, snowy weather to the Eastern U.S., Western Europe, and East Asia, typical of what one sees during a strongly negative Arctic Oscillation. They theorized that sea ice loss in the Arctic promotes more evaporation, resulting in earlier snowfall in Siberia and other Arctic lands. The earlier snow insulates the soil, allowing the land to cool more rapidly. This results in a southwards shift of the jet stream and builds higher atmospheric pressures farther to the south, which increases the odds of cold spells and blocking high pressure systems that can cause extended periods of unusually cold and snowy weather in the mid-latitudes. The research linking climate change impacts in the Arctic to more extreme jet stream patterns is still very new, and we need several more years of data and additional research before we can be confident that this is occurring. But if the new research is correct, the crazy winter weather we've been seeing since 2009 may be the new normal in a world with rapid warming occurring in the Arctic.
 
آخرین ویرایش:

Amir Mohsen

متخصص بخش هواشناسی
[h=3]Capital Weather Gang Inside the patterns that may govern our winter weather and snow
  • [h=6]By Wes Junker
  • [h=6]November 15 at 12:07 pm


cwg_Junker.jpg
With neither an El Niño nor a La Niña in place, the winter forecast is unusually difficult. In our winter outlook, we touch on some of the other weather patterns that might impact our weather this year. In this article, I’ll discuss two of the most important and how they typically affect our temperatures while also playing a major role in determining how much snow we get. These patterns are the Pacific North American Pattern (PNA) and the Arctic Oscillation (AO). Both can sometimes lead to a southern displacement of the jet stream that forces storms to track to our south – in a favorable position for snow – depending on which phase of the patterns are present.
The Pacific North American Pattern (PNA)
This pattern has two general phases.
The positive phase (on the left below) has the ridge or northward bulge in the jet stream over western North America. That keeps the eastern half of the U.S. in a trough or dip in the jet stream. This dip in the jet usually holds the storm track to our south which pulls cold air to the East while also keeping a storm track near the coast. Snow lovers need to pull for this phase of the PNA pattern this winter.
pna2.jpg
Phases of the PNA pattern (N.C. State)

The negative or reverse phase of the PNA pattern (on right above) has the ridge or northward bulge in the jet stream well off the Pacific coast which helps force a trough in the western U.S. and a ridge of high pressure over the East. This ridge helps nudge the storm track to our north. The flow around storms (low pressure systems) is counterclockwise so any storm passing to our north produces a period of southerly winds out ahead it which ends up warming us up and usually leads to a period of above normal temperatures. The negative PNA pattern generally keeps us warmer than normal (sometimes well above normal) and sometimes drier than normal. It is not a good pattern for snow lovers.
The Arctic Oscillation (AO)
The difference in pressure and winds at higher latitudes (the Arctic) versus mid-latitudes, indicated by the AO, plays a huge role in winter temperature and precipitation distribution across the U.S.
The AO is defined to be in its positive phase when the belt of winds around the Arctic is circulating in a counterclockwise direction and the pressures are lower than normal. Over the mid-latitudes, conversely, pressures are above normal. On the figure below (top left), note how the 500mb heights (or pressures) are below normal (blue) across Canada, Greenland, and Iceland and above normal (orange) to the south of the Great Lakes revealing a strong positive AO. Such a configuration enhances the upper level winds across Canada and the northern U.S. while also bottling up the cold air. When the AO is positive, temperatures east of the Rocky Mountains are typically above normal (see figure top right). If the PNA pattern is negative at the same time (causing a bulge in the jet stream in the East), temperatures can really torch and end up being well above normal. That is a true snow lovers’ nightmare.
ao-wes.jpg
(Left) Average upper level heights (or pressures) when the AO is positive (top) and negative (bottom). (Right) Temperature difference from average when the AO is positive (top) and negative (bottom). (NOAA)

When the AO is in its negative phase, pressures and heights are higher across the north and lower to the south (bottom left). Since air moves from areas of higher to lower pressure, that pressure differential helps force cold air southward into out region. Plus, the storm track is usually forced to our south. The National Weather Service’s Climate Prediction Center provides an index of both the Arctic Oscillation and its close cousin the North Atlantic Oscillation (NAO). Snow lovers want both indices to be negative. Personally, I tend to track the AO more closely since it is more predictive of four inch or greater snowfall events in the D.C. area.
Questions you may have about these patterns
Can we get snow when the AO is positive and the PNA is negative?
Yes, but such a combination is not very favorable for getting even a modest snowstorm in the District. Below is a scatter diagram showing all four inch or greater events at Reagan National Airport between 1950 and 2010. Only 11 percent were observed when both the AO and PNA were in this unfavorable combination. 89 percent occurred when the PNA was in the positive phase or the AO was negative.
ao-pna.jpg

What is the best combination of AO and PNA for snow lovers?
By far the most common combination for substantial snow events has been a positive PNA and negative AO. That combination is most likely to place the storm track to our south while also providing us with enough cold air for snow.
What about the really big storms? The scatter diagram below illustrates the importance of having either a negative AO or positive PNA for getting an 8 inch or greater snowstorm in the District. All but one of these events occurred with either a positive PNA pattern or a negative AO. The only exception occurred when the AO and PNA were essentially neutral. No major snowstorms have occurred in the District when the PNA was strongly negative at the same time that the AO was positive. The vast majority of snowstorms were associated with a positive PNA index and a negative AO. All our big snowstorms in 2009-2010 had that combination.
bigs-pna-nao.jpg

As a snow lover I’ll be rooting for the Pacific North American pattern to flip to positive and stay there. However, with the Pacific Decadal Oscillation (PDO) currently locked into a negative phase (see Matt Ross’ winter outlook for additional discussion of the PDO), a negative PNA pattern is probably more likely to be prevalent. I’ll also be rooting for a negative Arctic Oscillation: lots of high latitude blocking indicated by above normal surface pressures and 500 mb heights across Greenland, Baffin Island and into northeastern Canada with below normal heights (pressures) to the south. Most meteorologists feel the AO is only predictable out to a week or two so we can always hope it flips from its current very positive mode.
One caveat is that even if the PNA index averages positive and AO index averages negative for the winter, there are no guarantees we will get a ton of snow. The winter of 1952-1953 had that “golden” combination but only 8.3 inches of snow was observed for the season.
What does the lack of an El Niño or La Niña mean for snow prospects?
In short, given “neutral” conditions in the tropical Pacific – neither an El Niño or a La Niña – it is very important for the AO to be predominantly negative for the District to receive significant snow.
The scatter diagram below indicates whether each of our heavy snow years occurred during an El Niño, La Niña, or neither (neutral conditions).
nada-ao.jpg
Plot of 17 season since 1950 when more than 20 inches of snow was observed at Reagan National Airport (DCA) given the different El Nino, La Nina and neutral (“La Nada”) phases and the phase of the Arctic Oscillation.

The good news for snow lovers is that five of the 17 “big” (at least 20 inches) snow years were associated with neutral winters. However, during all 5 of those winters the AO was predominately negative. In fact, all the big snow years but one fall below the red line on the figure indicating that they occurred then the AO was predominately negative. The lone exception was 1982-1983. That year, even though the AO balanced out positive for the winter overall, almost all the snow fell in a February (most of it in a single snowstorm, one of D.C.’s heaviest) when the AO index was extremely negative. Bottom line: unless the AO averages negative this winter, our chances of having a big snow season are very small.

 

pokerface

متخصص هواشناسی
برای روشن شدن این موضوع و واضحتر شدن مطلب جستجو برای پاسخ این سوال بسیار کمک کننده هست: در این فریم،سیکلون مدیترانه ایجاد گشته که باعث شده ترکیه سراسر زیر پوشش ابر و بارش و ایران عزیز بدون بارش باشد..هر ۲ کشور در خاور میانه! nao فاز منفی‌ و ao هم منفی‌ برای ۲۷ نوامبر.آیا افزایش یافتن سیکلونزأی مدیترانه که به تغییر فاز این نوسان ۲ قطبی نسبت داده میشود باعث افزایش بارش در ایران شده؟افزایش بارش در خاور میانه شده؟یا افزایش بارش در ترکیه شده؟ آیا سیکلون زایی بیشتر مدیترانه و انحراف جریانات غربی به سمت مدیترانه به معنای بیشتر شدن بارش ایران ماست یا استناد به روشهای آماری روش منطقی‌ و صحیح است!قضاوت با دوستان!


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محمد بجنورد

کاربر ويژه
درود بر دوستان عزیز

درسام نسبتا سنگین شدن واسه همین کمتر میامو پست میذارم..شرمنده..:خجالت2:

هفته ی دوم مدل عددی جی اف اس واقعا خوبه...

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Amir Mohsen

متخصص بخش هواشناسی
درود بهزاد جان خسته نباشید

ارتفاع ژئوپتانسیل در تراز 500 میلی بار+ضخامت لایه 500-1000 میلی بار+ فشار سطح دریا در روز 27 نوامبر در هر دو نقطه مورد بحث:

اروپا:

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خاورمیانه و ایران:

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برای روشن شدن این موضوع و واضحتر شدن مطلب جستجو برای پاسخ این سوال بسیار کمک کننده هست: در این فریم،سیکلون مدیترانه ایجاد گشته که باعث شده ترکیه سراسر زیر پوشش ابر و بارش و ایران عزیز بدون بارش باشد..هر ۲ کشور در خاور میانه! nao فاز منفی‌ و ao هم منفی‌ برای ۲۷ نوامبر.آیا افزایش یافتن سیکلونزأی مدیترانه که به تغییر فاز این نوسان ۲ قطبی نسبت داده میشود باعث افزایش بارش در ایران شده؟افزایش بارش در خاور میانه شده؟یا افزایش بارش در ترکیه شده؟ آیا سیکلون زایی بیشتر مدیترانه و انحراف جریانات غربی به سمت مدیترانه به معنای بیشتر شدن بارش ایران ماست یا استناد به روشهای آماری روش منطقی‌ و صحیح است!قضاوت با دوستان!


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Amir Mohsen

متخصص بخش هواشناسی
در واقع شرایط اینطوری میشه

اروپا و ترکیه در دامنه فرود قرار میگیره و هوایی مرطوب و سرد رو تجربه میکنند و ما در ایران متاسفانه در دامنه فراز ، فرازی که هیچ وقت........


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