forecast a warming soon on the Pacific side of the Arctic Ocean.
Maybe so but those beautiful "cloud streets" in the Barents (associated with cold winds of a meandering central anti-cyclonic high) will continue out to March 25th and beyond, per GFS.
Twitter can confuse these with with blowing Antarctic ice needles or katabatic Greenland winds but Zach notes correctly today these are parallel bands of cumulus clouds that form as cold winds from the north blow off the ice edge onto warmer ocean waters.
OK, but why now, why cumulus mediocris, and what causes the street banding?
The temperature differential between cold air blowing off the ice and the sea surface water, either open leads or more commonly beyond the ice edge, can easily exceed 20ºC in March. Thermal columns of moist heated air rise off the sea surface until they hit a denser warmer lid of air (provided a temperature inversion is present).
As the thermals are advected downwind and sink or rise according to ambient density differences, they form parallel pairs of counter-rotating cylinders of air. On the upper surface of rising air, water vapor cools and condenses into flat-bottomed, fluffy-topped clouds (ie cumulus:
https://en.wikipedia.org/wiki/Cumulus_cloud). On the downdrafts, condensates evaporate giving clear skies on the sides of the clouds, the banding.
Surprisingly, the alignment of vortices alone does not reliably indicate wind direction. Stably stratified environments have lines 30° off CCW to the left; only an unstably stratified (ie convective) situation has bands parallel to mean wind.
Cloud streets are technically called horizontal convective rolls. The most favorable conditions for them occur when the lowermost layer of air is unstable, driven by a moderate wind and capped by a stable inversion, a common situation when upper air is subsiding, such as under recently prevailing anticyclonic conditions.
https://en.wikipedia.org/wiki/Horizontal_convective_rolls turbulent momentum flux in PBL
Cloud Streets over sea can be seen during synoptic scale outbreaks of cold, dry air from continents over a neighboring relatively warm ocean. This flow often occurs behind a Cold front. As the cold air leaves the land or ice surface it is modified by vertical transfer of heat and moisture from the underlying water surface. An inversion will be formed the base of which rises with the distance from shore. The formation of the inversion is, in many cases, stimulated by NVA and subsequent sinking motion in the stream upwind of the 500 hPa trough-axis. The transformation of the air mass eventually leads to the formation of clouds which, under certain circumstances, take the form of Cloud Streets, and develop roughly parallel to the wind direction. Further downwind from the outbreak, the unstable layer becomes deeper, the flow becomes more cyclonic and the streets develop into three-dimensional open cells. Near the upper-trough the convection is enhanced by PVA, resulting in the formation of enhanced cumulus and comma.
http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?/docu/Manual/SatManu/CMs/ClStr/backgr.htm
North Atlantic islands like Jan Mayen disrupt the flow of the wind and create spiral eddies patterns in the cloud streets called von Karman vortex streets. These have not been seen this March with SZ or FJL islands, presumably because they are less disruptive to air flow.
http://en.es-static.us/upl/2013/05/von-karman-vortex-clouds-nasa-24feb2009-540.jpgWe've also been seeing "comma clouds" which are vortices or mesoscale eddies that occur when warm humid air wraps counterclockwise around the cold air, forming clouds as these air masses rise. Comma clouds are a leading indicator of a small-scale low-pressure system forming. In the absence of an inversion, polar lows can grow into strong but small-scale cyclones. March is a big month for both cloud streets and polar lows.
http://polarportal.dk/fileadmin/polarportal/sea/Map_IST_LA_EN_20180319.pnghttps://earth.nullschool.net/#2018/03/[cal]/1200Z/wind/isobaric/1000hPa/overlay=off/orthographic=-45.00,82,1250/loc=2.5,83.00
https://earthobservatory.nasa.gov/IOTD/view.php?id=87749 nice example
New areas of polar lows over the Arctic as a result of the decrease in sea ice extent
E Zabolotskikh et al.
https://link.springer.com/article/10.1134/S0001433815090200
Mesocyclones can arise when new areas of open water appear. Polar lows don’t form over sea ice, so as the sea ice retreats, new ocean areas with relatively warm water are exposed to cold air outbreaks, the favored environment for polar low formation, the Kara Sea being a prime example. Zahn and von Storch 2013) predict the decrease in both number of polar lows in the Arctic and their
intensity in the future due to the faster air temperature increase relative to water temperature and therefore higher stability of the boundary atmospheric layer.
Street clouds represent very cold and dry air from above the sea ice transported out over the open ocean, ie cold air outbreaks. It's not uncommon to see 3-4 polar lows over the Barents Sea in comma cloud cyclone category. These are baroclinic, meaning the low near the surface is linked to a trough higher up in the atmosphere, with these not located on top of each other. This vertical structure displacement allows the two lows to work together and to strengthen each other.
Most polar lows start out as baroclinic but many develop a warm core and go barotropic, meaning the and near-surface and lows aloft are locked in phase and no longer help each other grow. For the polar low to intensify at this stage, it needs to get its energy from the warm ocean surface, as with tropical cyclones (hurricanes) energetics. However the Arctic Ocean surface is far too cold to admit arctic hurricanes. (Adapted from
https://polarlows.wordpress.com/author/erikwkolstad/)