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今年的平均最冷一天怎么能在冬至前?

有部分的美国,平均而言,12月21日之前,是今年最冷的一天。(源]

今年最冷的一天

这怎么可能?为什么温度再次上升尽管天仍在增长短?

(我认为每天的温度,一般来说,总是落后于日常日晒,某种形式的磁滞关系。)

回答

我已经创建了复合地块从再分析数据的日期作为图像分割的问题。我使用了[NARR][1]数据集,涵盖1979年至2014年,所以我有几年比上图中包含的数据。在很大程度上可以看到冬季气候意味着什么。持久的副热带高压在加州海岸和持续低位在北太平洋和大西洋。变化是什么意思的北极空气陷入美国像春天冬天进展和撤退的方法。# # #复合NARR MSLP 1979 - 2014和500 - 1000 hPa厚度(!(enter image description here][2]][3] ![enter image description here][4] <sub>**Figure 1**. From left to right, top to bottom the dates composited are *Dec 1-15, 16-20, 21-25, 26-31, Jan 1-5, 6-10, 11-15, 16-20, 21-25, 26-31, Feb 1-15, 16-28, Mar 1-15 and 16-31*. MSLP is contoured every 4 hPa. Thickness is shaded at intervals of 10 dm. Click the plot for a larger version.</sub> The signal I can pick out of this is the approaching and retreating cold (using the proxy of 1000-500 mb thickness) that seems to correlate well with the latest dates of cold in the eastern US, particularly in the great lakes and northeast. What I'm seeing in the west is that initially the subtropical high is broad and surface flowing westerlies impinging on the west coast would originate initially at higher latitudes than the do later in the winter. By January the subtropical high and the low in the north Pacific have re-oriented so the surface flow is coming from around Hawaii. The western US will also be subject the reduced seasonal temperature fluctuates from its proximity to the Pacific. Once the area has cooled and equilibrated with the Pacific, temperatures will be stable. As the continental landmass would lose more energy and cool, the westerlies coming off the Pacific (now relatively warm) counteract this tendency. Conversely the east with mostly continental air flows experiences large seasonality and has a long-lasted source of very cold air from our neighbors to the north. ###Summary The west ceases to cool once it equilibrates with the Pacific, which looks like it happens early in winter (because even though the Pacific is cold, it isn't *that* cold). Westerlies from the ocean heep the west warm. East of the rockies there is no influence from large bodies of water and a constant source of cold arctic air and so the east continues to cool throughout the winter, until the pattern changes toward spring (and all the snow melts...). For a smaller scale example of how water can have this influence, take a look at during the next extreme cold event in the midwest and great lakes, particularly when air is flowing westerly across Wisconsin and into Michigan. You will observe a large temperature gradient across Lake Michigan, which keeps Michigan warmer (sometimes much warmer) than Wisconsin. Later in the winter when the lake is frozen, that benefit is lost and so Michigan tends to be cooler later in winter as it is no longer "shielded" by the lakes. ###Data Data was downloaded from NOAA's North American Regional Reanalysis, accessed 17 Feb 2015. Files accessed include: - ftp://ftp.cdc.noaa.gov/Datasets/NARR/Dailies/monolevel/prmsl*nc - ftp://ftp.cdc.noaa.gov/Datasets/NARR/Derived/pressure/hgt.day.ltm.nc [1]: http://www.esrl.noaa.gov/psd/data/gridded/data.narr.html [2]: http://i.stack.imgur.com/5jWto.jpg [3]: http://i.stack.imgur.com/5jWto.jpg [4]: http://i.stack.imgur.com/CCPVI.png

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\ begingroup美元它可能更有助于重新计算复合的冬季和计算上述复合材料作为完整的异常想看到更多微妙的变化在冬季。也许当我有更多的时间.... \ endgroup美元
- - - - - -凯西
2015年2月17日21:37
2

\ begingroup美元高兴看到实际工作写出答案。 \ endgroup美元
- - - - - -gansub
2015年2月18日,在收窄
\ begingroup美元 @casey我建议面板图,如果你想显示很多图片相同的域。也通常更少的图片就好了。 \ endgroup美元
- - - - - -f.thorpe ♦
2015年2月18日在三点半结束
\ begingroup美元 @farrenthorpe图像更新 \ endgroup美元
- - - - - -凯西
2015年2月18日在十八22
\ begingroup美元 @casey太棒了!现在更digestable。 \ endgroup美元
- - - - - -f.thorpe ♦
2015年2月18日19:58

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