Space Weather & Marine Navigation

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Tech Tips “average” or “quiet” ionosphere, using a model to calculate its
effect on the accuracy of the positioning information. But when
Space Weather and Marine the ionosphere is disturbed by a space weather event, the models
N: . ti are no longer accurate and the receivers are unable to calculate an
avigation accurate position based on the satellites overhead.
By Bill Whitney In calm conditions, GPS systems can provide position
All sailors are aware of the weather and its impact on information with an accuracy of 3 feet or less. During a severe
their comfort and safety. Terrestrial weather imposes limits on space weather storm, these errors can increase to 100 yards or
most of our nautical pursuits, and can, at its worst, pose a real more.
threat to our lives and property. However when studied by Since radio waves are affected by the presence of
knowledgeable meteorologists, its impact can be forecast and electrons, the more electrons in the path of the wave, the more the
action taken to mitigate whatever it may bring our way. radio signal will be affected. The change in the path and velocity
We live in the lower level of the atmosphere called the _ of radio waves in the ionosphere has a big impact on the accuracy
troposphere. Tropospheric weather is the weather that we can _ of satellite navigation systems.
watch develop. It’s up close and personal. It affects what we A geomagnetic storm is a major disturbance of Earth’s
wear, where we go, and our heating bill; even what we eat. magnetosphere that occurs when there is a very efficient exchange
However, there is another aspect of the weather that we give very of energy from the solar wind into the space environment
: little thought to, that is more important to our lives than we surrounding Earth. Geomagnetic storms create large disturbances
realize. As you probably guessed from the title above, I’m refer- in the ionosphere. The currents and energy introduced by the
ring to space weather, the cumulative sum of storms, calms and storm enhance the ionosphere and increase the total number of
other disturbances that occur on the sun and in the ionospheric _ ionospheric electrons. GPS systems cannot correctly model this
layers of the atmosphere above us, and which can impact our dynamic enhancement and errors are introduced into the position
electronic systems. calculations. This usually occurs at high latitudes, though major
Tonosphere storms can produce enhancements in the ionosphere large enough
The Ionosphere is part of Earth’s upper atmosphere, to impact mid-latitudes.
between approximately 50 and 400 miles above us, where During storms, the currents in the ionosphere, and the
extreme ultraviolet (EUV) and X-ray radiation from the sun energetic particles that precipitate into the ionosphere add energy
ionize the atoms and molecules in the high altitude gasses, creat- _ in the form of heat that can increase the density and distribution
ing an ion-rich layer of the atmosphere. The ionosphere is impor- of density in the upper atmosphere, causing extra drag on satel-
tant because it reflects and modifies radio waves used for commu- lites in low-earth orbit. The local heating also creates strong
nication and navigation. horizontal variations in the ionospheric density that can modify
The atmospheric atoms and molecules are impacted by _ the path of radio signals and create errors in the positioning infor-
the high energy the EUV and X-ray photons deliver from the sun. mation provided by GPS. While the storms can create beautiful
The amount of energy (photon flux) at EUV and X-ray aurora, they can also disrupt navigation systems and create
wavelengths varies by nearly a factor of ten over the 11 year solar harmful geomagnetic-induced currents in the power grid and
cycle. The density of the ionosphere changes accordingly. Other pipelines.
solar phenomena, such as solar flares (sunspots), changes in the Smaller scale electric field fluctuations that may cause
solar wind, and geomagnetic storms also effect the charging of _ GPS signal to waiver are called ionospheric scintillations, and are
the ionosphere. Since the largest amount of ionization is caused _ not associated with space weather storms, but are simply part of
by solar radiation, the night-side of the earth, and the pole pointed _ the natural day-night cycle of the equatorial ionosphere. Severe
away from the sun (depending on the season) have much less _ scintillation conditions can prevent a GPS receiver from locking
ionization than the day-side of the earth, and the pole pointing on to the signal and can make it impossible to calculate a
towards the sun. position. Less severe scintillation conditions can reduce the
This means that as the sun’s activity changes, so does accuracy and the confidence of positioning results. Scintillation
our ionosphere, and with these changes the performance of our _ is more prevalent at low and high latitudes; mid-latitudes, such as
electronic devices, which carry electronic data through the the United States, experience scintillation much less frequently.
. ionosphere, will change. Scintillation is a strong function of local time, season, geomag-
Space Weather and GPS Systems netic activity, and solar cycle.
The use of satellite radio navigation systems, like the The lesson here is that under “normal” atmospheric and
Global Positioning System (GPS), has grown dramatically in the solar conditions that have been studied and modeled for years,
last decade. GPS receivers are now in nearly every cell phone _ our electronic aids to navigation, such as GPS, will work reliably
and in many automobiles, boats, trucks, and any equipment that and with acceptable accuracy. Unfortunately, the sun is not
moves and needs precision location measurements. always “normal”. Solar events have a significant impact on our
There are several ways in which space weather impacts ionosphere that can and do put it outside the normal parameters
GPS function. GPS radio signals travel from the satellite to the _ that in many cases cannot be corrected for. Most of these abnor-
receiver on the ground, passing through the Earth’s ionosphere. mal events are not effectively communicated to the user commu-
The charged plasma of the ionosphere bends the path of the GPS _ nities. If you put blind faith in what your GPS or GPS integrated
radio signal similar to the way a lens bends the path of light. In _ chart plotter is telling you, you need to reassess your navigation
the absence of space weather, GPS systems compensate for the _ practices, or at least increase your insurance coverage!