What are polar lows?
– Cyclones forming over the open sea in polar regions
WHERE DO POLAR LOWS FORM? Over the open sea in polar regions
– Several hundred kilometers in diameter
– Last a day or two
– Sometimes called “Arctic hurricanes” due to well defined “eye”
– Winds must be gale force
- Poleward of the polar front, the division between cold, polar air and warm, tropical
air, storms can form. These are referred to as polar lows. Sometimes, due to some
POLAR LOWS ARE REFFERED TO : the division between , warm tropical air and cold polar air (mT and cP)
similarities to hurricanes, they have been called polar hurricanes or Arctic hurricanes.
HOW DO THEY FORM?
They form when cold Arctic air forms over sea or ice or continental land surface, moves over to much
warmer ocean water
- This change is surface properties is reffered to as WHAT? The ARCTIC FRONT
- There is a strong temperature gradient between the air mass , and the ocean current beneath
(around 20 to 40 degrees) , and this difference is greater than what is seen in a midlatitude
- SO, the air mass receives substantial heating from the ocean current below, and this is the
MAJOR DRIVER or influence for the storm to occur
This, in turn, induces vertical motion by convection, followed by surface convergence and a
counterclockwise vortex. The ocean also provides moisture
- to the air mass and towering cumulus clouds form as the air rises.
Continental cold arctic air (cP or cA) moves over open sea water (relatively warm)
Heat source (sensible and latent) of the open sea fuels the storm
– In many ways similar to hurricanes
• Sea surface temperatures (SSTs) as energy source
• Eye formation
• Warm core
• Dissipate over land
POLAR LOWS FORMATION AND DURATION
- How long do polar lows tend to last? Polar lows form quickly reaching maximum intensity within
12 to 24 hours
- Dissipate quickly Most last less than 12 hours
The contrast in temperature between the air mass and the ocean surface beneath is quite large. By
tropical standards, the polar ocean is quite cold, perhaps only a few degrees above
freezing. Nevertheless, the ocean waters can be 20 to 40C warmer than the Arctic air
mass, a stronger temperature difference than experienced by tropical cyclones. Thus the
air mass receives substantial sensible heating from the ocean surface below and this is the
major driver of the storm. This, in turn, induces vertical motion by convection, followed by surface
convergence and a counterclockwise vortex. The ocean also provides moisture
to the air mass and towering cumulus clouds form as the air rises. As the air diverges at
the upper level, cirrus clouds form giving the storm its characteristic hurricane-like
appearance. This provides a second source of energy to the storm, latent heat. Most polar
lows extend to the tropopause, roughly 8 km above the surface in polar regions. Polar
lows can achieve central low pressures of 980 mb, typical of hurricanes and strong
midlatitude cyclones. Winds can be gale force, which are winds that exceed 62 km/h.
These storms produce heavy frozen precipitation, hail and snow.
The polar low is often a tight circular storm resembling a tropical cyclone. It can
be similar to a tropical cyclone in other ways as well. It often has a clear central core, an
eye. The core is warm relative to its surroundings; like a hurricane but not like a
midlatitude cyclone. Unlike a tropical cyclone, polar lows fully develop within 24 hours
and dissipate within a couple of days. They move quickly compared to other storms,
often exceeding 50 km/h. When polar lows move over land they quickly dissipate as they
are cutoff from their main energy source, the sensible heat flux from the ocean.
Where do polar lows form?
Where do they form? Polar regions over open sea – WHY ? relative warmth is energy source
• Northern Hemisphere
» Atlantic Ocean
» Pacific Ocean
» Canadian Seas
• Limited by sea ice conditions , WHAT KIND OF CONDITIONS ARE NECESSARY? open water a necessary
condition, without it , polar lows will not form
This type of storm is smaller than both midlatitude cyclones and tropical storms,
ranging in size from 200 to 1000 km in diameter. They typically form from November to
March in the North Pacific, North Atlantic, especially east of Greenland. They
occasionally form east of Greenland and in the Beaufort Sea of the Arctic Ocean. They
have been observed on the Southern Hemisphere, particularly in the Tasman Sea near
WHERE DO POLAR LOWS OCCUR IN CANADA?
Most polar lows occur in the Labrador Sea
• Hudson Bay and Baffin
Bay are limited by annual sea ice cycle –polar lows occur in the fall until the sea ice forms
- What is a firestorm? A firestorm is a self-sustaining convective cell that forms from an intense
- Can form pyrocumulus cloud
- How are firestorms caused? These storms are caused naturally in forest fires as well as by
human actions such as a targeted explosion.
Cyclones forming over the open sea in polar regions. Sometimes called arctic hurricanes due to well defined eye . Poleward of the polar front, the division between cold, polar air and warm, tropical air, storms can form. Polar lows are reffered to : the division between , warm tropical air and cold polar air (mt and cp) similarities to hurricanes, they have been called polar hurricanes or arctic hurricanes. They form when cold arctic air forms over sea or ice or continental land surface, moves over to much warmer ocean water. There is a strong temperature gradient between the air mass , and the ocean current beneath (around 20 to 40 degrees) , and this difference is greater than what is seen in a midlatitude cyclone. So, the air mass receives substantial heating from the ocean current below, and this is the. Major driver or influence for the storm to occur.