by George Denniston
A number of attempts to encircle the globe in a balloon have tried to use the Sub-tropical Jet Stream. Among recent attempts were Per Lindstrand and Richard Branson's takeoff from Morocco early this year, and Steve Fossett's flight from St Louis, which resulted in a trip half way around the world. Balloon Life interviewed Bob Rice, whose knowledge of balloons and weather has been instrumental to the success of many record flights over several decades. Bob answers questions about the Sub-tropical Jet Stream, and reviews aspects of world weather relevant to the upcoming attempts to circle the globe this winter.
Balloon Life: Tell us about the Sub-tropical Jet Stream.
Bob Rice: This major eastward-flowing jet stream does not exist during the summer months. In fact, over North Africa, in summer, there are strong winds in the opposite direction - to the west. The Sub-tropical Jet Stream probably forms over the Tibetan Plateau, which is the only major plateau in the world at the 500 millibar level. In the fall in Tibet, the winds are light and variable. But with the monsoons, and with winter, the plateau cools off, creating a huge radiation surface.
The classic model of the Sub-tropical Jet Stream was first advanced by a student as his college thesis. At the time there was very little data available over the oceans. So he took the data over land, and extrapolated, creating a model that depicted an unbroken band around the earth. This strong stream of air passes over southern Morocco, Egypt, India just south of the Himalayas, Shanghai, southern Japan (Kyushu), northern Baja Mexico, over Florida and back to Morocco.
BL: What is the problem for balloons that want to use this system?
Rice: With this model as a basis, commercial jets began to fill in the details. Over time, pilot reports discovered two gaping holes and large meanders in the Sub-tropical Jet Stream. These occurred over the eastern portion of the two major oceans. One was west of Baja; the other was west of Morocco. When a balloon gets to one of these meanders, there is no way that it is going to continue eastward. The lower winds are usually not going in the same direction. For example, when Per Lindstrand and Richard Branson reached Hawaii during their crossing of the Pacific in a hot air balloon, they faced a meander that petered out before it reached the west coast. So we dropped them down to 18,000 feet. They drifted north and caught the impinging Polar Jet Stream, which took them to the Alaskan Panhandle and on into the Yukon.
Also, with the DaVinci balloon in 1979, we shifted it from one jet stream to another. From these experiences, we have learned that one can make rather dramatic latitude changes by going down, then up.
BL: Since there are these big breaks, why do you bother to use the Sub-tropical Jet Stream?
Rice: In 1981, when we launched Maxie Anderson from Luxor, Egypt on an around the world attempt, we did so because we did not have overflight clearance from Russia. At that time, the USSR occupied eleven of the 24 time zones, and covered a lot of latitude in the northern hemisphere as well. We would have preferred to be further north.
BL: Why do you think the Polar Jet Stream is better?
Rice: In the first place, it covers a shorter distance while circumnavigating.
Secondly, while there may be breaks in the jet stream, a balloon can usually get across. The stream may even come to an end, because of arrangements in the pressure, but the lower winds are still going where you want to go, even though you may experience a sharp deceleration. If you are in the Sub-tropical Jet Stream, there is a much higher risk of being absorbed into some big flat pressure feature that you just cannot get out of.
Third, major thunderstorm outbreaks occur in the path of the Sub-tropical Jet Stream. There is a big area of cyclogenesis off Japan, just as there is off Cape Hatteras, North Carolina. In both cases, there is warm water to the east, and cold land to the west. Around Japan, especially, huge thunderstorms arise and tilt eastward in the strong flow. This tends to generate super volt lightning in the tops.
The Polar Jet Stream flows out of Mongolia, across
northern Japan (Honshu), where the two streams can get pretty close. Then
it flows across the Pacific to the Pacific Northwest, across the United
States, the Atlantic, Europe and Russia.
BL: So in general, you would recommend the Polar Jet Stream.
Rice: Yes. If you will recall, Steve Fossett gave serious consideration to a more northerly route.
BL: What other factors will you take into consideration this winter?
Rice: The big unknown this winter is El Niño. The cycle of rain and drought that shifts back and forth from Peru to Australia is clearly El Niño. As you radiate out from that, it becomes less clear what is and what is not El Niño. Weather has so much "noise," it is impossible to say whether or not something would have happened anyway. But you cannot jack up surface water temperatures 8-10 degrees F. over large areas of the Pacific without doing something major.
Right now, in mid October, 1997, we have an extraordinary amplitude going over North America, and it is even more pronounced over the Atlantic. Travelling east, a balloon would follow a zigzag course. If this pattern were to persist into the winter, there would be a lot of soul-searching as to go or no go.
Here is what may happen this winter. A split in the Sub-tropical Jet Stream may show up. The northern branch will flow east along the Canadian border, trapping cold air in Canada, and making for a milder winter across the United States - except for one thing. The southern branch will travel across the southern states in the vicinity of California to the Texas Gulf Coast and northern Florida. Underneath it are a series of low pressure storm tracks, bringing cooler weather and rains during the winter.
We already have what appears to be the strongest El Niño since 1982-83, when rain and storms were thrown into California. We shall have to wait until April to see if this scenario is what actually happens this winter.
For the winter of 1997-98, we have the relatively
unknown factor of El Niño affecting the Sub-tropical Jet Stream.
The Polar Jet Stream is preferable for an around the world attempt.
BL: This decision will affect where you launch, will it not?
Rice: Yes it will. But there are a lot of factors other than weather pushing the location of a launch site. There are financial constraints, and public relation constraints. You need a good site to inflate the balloon. Incidentally, Akron, Ohio is not one of those places.
The weather should be a major factor in picking the site. We launched Double Eagle I from Marshfield, Massachusetts. The logistics were good but it was too far south. As we readied to launch Double Eagle II, Ben Abruzzo came to me and asked me where we should go. I suggested Caribou or Presque Isle in northern Maine.
Ben countered, "How about Bar Harbor (150 miles further south)? If I place 100% chance of success on Presque Isle, what chance of success do we have if we launch from Bar Harbor?"
I replied, pulling a figure out of the air, "Ninety-five percent."
"O.K. then, we will go to Presque Isle!" - and the rest is history.
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