Posted by: Anna Webb | June 6, 2009

Wind Wake and Hawaii’s Big Island


 

Mauna Kea

Mauna Kea

 

In researching my last blog article, I came upon an interesting phenomenon unique to the Big Island and the Hawaiian Islands in general that I thought I’d share with you. It’s a phenomenon called “wind wake” which is a zone of weak wind caused when trade winds are “split” by the highest mountains of Hawaii. Mauna Kea stands 13,796 feet above sea level, Mauna Loa 13,680 feet, Haleakala on Maui 10,023 feet and Hualalai 8,271 feet. All but one of these are found on the Big Island.

 

Mauna Loa from Volcanoes National Park

Mauna Loa view from Volcanoes National Park

 

As we read in my last article, the trade winds travel over approximately 2,600 miles of ocean before arriving at the Hawaiian Islands. Wind wake in Hawaii is created when the trade winds are split by the mountains then continue westward toward Asia. Aerodynamic theory states that wind wake should dissipate within a hundred or so miles since once the air is split, it weakens. However the wind wake, in splitting and saying “Aloha” to Hawaii, continues for approximately 1,900 miles further  which is found to be 10 times longer than any others observed.

Interesting, right? Hang ten with me for a little longer and let’s discover how this affects Pacific Ocean current and climate.

Oceanographers have observed an eastern ocean current which stretches thousands of miles from the coast of Asia to Hawaii, bringing with it warm waters. There was no definable explanation for the driving force of this “counter current” until the wind wake was observed from satellite observation. The anomaly is that the counter current runs against the wind wake whereas normal currents will flow in the direction of the wind. 

It makes sense to me that because the wind wake is split, the current runs between the two winds in the opposite direction. I’m not a scientist and it is just my simplistic way to view it, however, the wind wake could serve as a “channel” of sorts for the current. 

So how can what appears to be a small island chain have such a large impact on ocean current and climate? 

There are three reasons for explaining this phenomenon and all are listed in the attached article links below. What interested me from a physics perspective, it that the Hawaiian Islands sit perfectly within a 4 degree horizontal position to “break” the wind on its journey creating the wind wake and the counter current. Similar to small rocks in the ocean serving to break the momentum of waves pushing in with tremendous force, the islands break the tradewinds which have traveled 2,600 miles to get here. 

 

Waves beginning to break on small rock formations

Waves beginning to break on small rock formations

The ultimate result is that warm waters are brought via the counter current to the islands. I found this aspect to be unique, fascinating and a reminder that even the smallest influence can create a large positive result. Remember that the next time you believe that as an individual you are small and insignificant. Even the least among us can effect change.

http://earthobservatory.nasa.gov/Features/Wake/

Shang-Ping Xie published article in Science Magazine on the far reaching effects of the Hawaiian Islands on the Pacific Ocean-Atmosphere System. You may have to register (free) to read the article.

http://tinyurl.com/q3mje8

International Pacific Research Center

http://iprc.soest.hawaii.edu/

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Responses

  1. A few years ago I attended a meeting organised by the Mauna Kea Weather Center – the lead meteorologist had an interesting theory which he said he might publish, but I don’t think he ever did.

    The wake effect that you mention was the reason hurricane Iniki hit Kauai – that was the theory anyway. You may or may not know that most central Pacific hurricanes pass south of the islands, but there have been some that suddenly turn north after passing the Big Island.

    I can’t remember the science behind it, the meeting was some time ago, but I think it had something to do with a lack of trades west of the Big Island due to the shadow effect which allows storms to track north once they’re past the islands.

    I also remember him saying that no matter what people believe with respect to the mountains on the Big Island preventing us from getting a direct hit from a hurricane, it’s just a myth.

    Thanks for such an interesting post! There’s a lot there I had no idea about and will have to do some reading – although I’m an astronomer my real love was always oceanography!

    Tom

  2. Anna, did you ever teach? Your explanations of even some of the most complex situations are simple to understand. The information on how our island affects ‘wind wakes’ is fascinating. I had never heard the term before.

  3. Tom,
    It makes perfect sense for a hurricane to pass the islands, then get drawn back into them by the warm water counter current.
    The hurricane in 2007 that passed near the island was interesting to watch from my perspective down on the S/SE coast. My theory on that one was the the heat in the higher atmosphere by the volcano combined with the colder deep water somehow diffused it. It was interesting to percieve it as Pele vs. the Hurricane…Pele one.

    I don’t think the mountains would have anything to do with hurricanes not hitting the Big Island, it has to do with the deep colder waters and the hot air in its S/SE approach area.

    Very interesting indeed!
    Thanks for commenting.

  4. Hi Sonia,
    I come from a family of teacher going back for generations, but with the exception of a college communications course my teaching experience has been in sales and marketing training.

    There are many facets of science and technology that capture my interest and I have long researched many of them. I was employed in the technology field for many years.

    Now I just look at it as “raising awareness” with respect to subjects that are of interest to me. I sometimes think, “Well, if I wasn’t aware of this others may not be aware of it either”.

    Thanks for reading and commenting!


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