There are currently two NOAA hurricane hunters in the air tracking Irene. NOA42 is a P3 Orion that generally stays at or below 10,000 ft, while NOA49 is a Gulfstream IV that works well above 40,000 ft. The “track log & graphs” link gives information that is usually pretty boring for the average airline flight, but these graphs do tell a story!
It sure takes a strong stomach to fly those routes. Not to mention some good IFR skills. I hadn’t realized those flights last as long as they do. They really go all over the area of the hurricane. I had the idea they just flew to the eye, gathered data, then flew back.
Interesting to note in the image with the flags and the storm names, all of the storms indicate counter-clockwise rotation, except for two in the top row. I can’t make out any of the storm names in the image, but it appears to be the same storm investigated twice. The clockwise rotation would indicate a storm south of the equator! This got me thinkin’ - what would happen to a storm that formed south of the equator with clockwise rotation if it traveled north and crossed the line into the north? Would it just break up or somethin’? Or maybe some phenomenon simply keeps storms that form in the south in the south, and storms that form in the north to the north? At any rate, what were they doing investigating a storm with clockwise rotation???
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Interesting to note in the image with the flags and the storm names, all of the storms indicate counter-clockwise rotation, except for two in the top row. I can’t make out any of the storm names in the image, but it appears to be the same storm investigated twice. The clockwise rotation would indicate a storm south of the equator! This got me thinkin’ - what would happen to a storm that formed south of the equator with clockwise rotation if it traveled north and crossed the line into the north? Would it just break up or somethin’? Or maybe some phenomenon simply keeps storms that form in the south in the south, and storms that form in the north to the north? At any rate, what were they doing investigating a storm with clockwise rotation???
Needle, I talked to the crew about the same thing. From what i remember 3/4 of the hurricanes follow the expected clockwise/counterclockwise direction. 1/4 rotate contrary to the expectation. The hurricane hunter pictured has traveled north and south of the equator over the years. This link should give you a slightly larger photo with the hurricane names visible:
It’s not possible for a storm to cross the equator.
If Coriolis force drives weather systems in one direction in the northern hemisphere and another in the southern does this mean that hurricanes and other weather systems cannot cross the Equator?
Worried about hurricanes crossing the equator ? The Coriolis force is what we call an apparent force - it handles the problem that the earth is spinning and thus a point on the globe is always changing direction or always accelerating.
You may also view Coriolis as a consequence of the conservation of angular momentum. At the equator you have a great deal as you are rotating about 25,000 miles in a day while someone on the poles is not moving anywhere in the same period. From your and my perspective air, rockets, and aircraft, are all deflected to the right in the northern hemisphere and to the left in the southern. (Yes, they correct for Coriolis when they shoot artillery shells!) The Coriolis “force” is a maximum at the poles and zero at the equator.
Observations show that no hurricanes form within 5 degrees latitude of the equator. People argue that the Coriolis force is too weak there to get air to rotate around a low pressure rather than flow from high to low pressure, which it does initially. If you can’t get the air to rotate you can’t get a storm. This is a reason why genesis does not occur at low latitudes but it does not explain why a developed hurricane does not cross the equator…
Could a hurricane cross ? Yes, because a well developed storm has plenty of spin that would dominate the weak Coriolis force near there. If it crossed the Coriolis force would be working against the initial direction of the spin, but it would be dominated by what we call the relative vorticity of the storm. Have we seen this happen ? Hurricanes can move south and get close to the equator but I cannot find an example of one crossing in the Atlantic or eastern Pacific. In the Indian Ocean some come closer to pulling off this trick. Why don’t they cross ? The variation in Coriolis with latitude - called the Beta effect - actually will move a hurricane to the NW in the northern hemisphere even if there is no large scale wind pushing the storm along ! So, Coriolis not onlyseems to be a necessary ingredient to make a storm, but it may also pull them away from the equator making the crossing event a tough one to pull off.
Gary Barnes, Professor of Meteorology
Department of Meteorology
University of Hawaii, Honolulu HI 96822
They were flying through two storms off the coast of Australia.
The Coriolis effect generally keeps storms spinning in the proper direction for their hemisphere and also serves as an effective prevention against migration across the equator. The normal path of a cyclonic storm over the oceans is from the equatorial zone towards the respective pole, regardless of which hemisphere it is in. E.g. Atlantic hurricanes head for the North Pole and South Pacific Hurricanes head for the South Pole.
I’ve never heard of a cyclonic storm transiting from one hemisphere to the other.
