Notice the "knee" that occurs at 18,000 feet. Initially the stack's ascent
rate is a little faster just after liftoff. Also notice that a second "knee"
occurs at 30,000 feet, as the stack begins rising a little faster. The first knee
has been seen before, however this is the first time I recall seeing the
second knee.
The cause of the change in ascent rate has not been determined to my satisfaction. Some believe the change in ascent rate occurs as the balloon pushes its way into the stratosphere, where the temperature profile changes. However temperature data collected on this flight indicates the stratosphere begins at 45,000 feet. Well, it just goes to show that there are still mysteries for amateurs to explore in near space. I love this hobby.
The GPGGA sentence also contains a time stamp. Using the change in time and change
in altitude between sucessive GPGGA sentences, we can determine the ascent and
descent rate of the capsule (actually, the GPS antenna, which is firmly
attached to the capsule - or one hopes).
Because of the "spikes" in the data, it's difficult to clearly identify the "knees" in the ascent rate. I'm not sure the spikes are primarily the result of GPS errors, induced by the ionosphere. The spikes translate to accelerations on the order of 200 feet per minute, per five minutes. This reduces to forty feet per minute squared, or 0.11 feet per second squared, which is 3/1000 of a G.
The burst of the balloon sticks out like a sore thumb. Notice initially the ascent rate approaches 4000 feet per minute. As the atmospheric density increases, the descent rate decreases. This is a good thing as lithobraking, using the ground to stop a descent, is rather hard on equipment and private property.
The balloon should find it impossible to travel against the wind. Therefore
the GPS reported direction of travel should be the wind's direction of
travel. The graph above shows the wind at the surface is from the east,
that is, it blows the balloon west. There's a gradual shift to winds from
the north that push the balloon south by the time it reaches 30,000 feet.
Above 70,000 feet the winds again are from the north. This shift in wind
direction at different altitudes is typical. Winds at the Earth's surface
are influenced by friction from the ground. If it wasn't for the Earth's
surface, the winds would have probably been from the north at launch.
Again, since the balloon can't travel against the winds, the balloon's speed
of travel should also be the wind speed aloft. from the graph above we can
see that the winds at launch were close to zero knots, the best speeds to
launch a balloon in. The winds gradually pick up speed as the balloon
rises to higher altitude until the balloon passes through the jet stream
at an altitude of 40,000 feet where the winds reach 66 mph. The jet
stream occurs below the stratosphere (as I believe it always does), but close
to the level of the stratosphere.
Once in the stratosphere the winds remain quite pleasant, and prevent chase crews from having to travel into neighboring states to recover the capsule. Although high level jets have been detected in other near space flights.