Space Weather

Space weather refers to the "weather" in space.  These short term variations of the near-Earth environment are due to changes in solar activity on all time scales from the 11-year solar cycle (more like space climate),  to individaul storms, solar flares, coronal mass ejections (CMEs), geomagnetic storms, etc. that can occur on time scales of minutes to days.  When the sun is active, the Earth can experience increases in both electromagnetic radiation from the sun, as well as increases in particles (electrons, protons) arriving at the Earth.  This increase in radiation can impact the Earth's magnetosphere, ionosphere and atmosphere, and the entire near-Earth environment.

These solar storms and space weather can have major implications on our everyday lives.  Below we can see some of the areas impacted by space weather, from satellites and GPS navigation systems, to power outages, pipeline corrosion, and communication blackouts.  With the increased number of space technologies used today in our lives (from cell phones, GPS, TV, internet, etc.) space storms can result in tremendous damage in a very short time.  If we are aware of these storms ahead of time (similar to regular weather on Earth) we could better prepare and take precautions before it is too late.  Hence, a new field is developing to try and better understand and predict these solar storms, and their impacts on the Earth's systems.



One of the major impacts of solar variability is on the Earth's ionosphere and magnetosphere.  On the ground we can study these interactions and changes using our sensors in the ULF, ELF and VLF frequncy range.  Below we can see two examples of space weather interactions with the Earth, detected with our ULF sensors in Israel.  The first (left) is related to the changes in solar radiation impacting the ionosphere during day and night.  The left image shows the long term ULF amplitude measurments (0.01Hz) in Israel (y-axis) that show the "terminator effect" at sunrise and less at sunset (x-axis is time of day).  The Kp index of geomagnetic activity is also shown in red.  Note that due to the changing length of the day during the year, we can a wavy pattern in the ULF data around sunrise and sunset.  The black curved line shows the time of sunrise and sunset above our station throughout the year.  Another interesting phenomenon is what we know as the Ionospheric Alfven Resonances (IAR) that can be seen as diagonal lines between 0.5-4 Hz during nighttime only, in the right hand plot below.  These resonant lines represent the "wiggling" of the magnetic field lines that enter the Earth at our latitude.  The sources of these wiggling field lines is still uncertain.  However, the frequency of these resonance lines increases during the nighttime hours, and they can tell us about the properties of the ionosphere and magnetosphere from the ground.




In the VLF range we can also study the lower ionosphere by tracking the background levels of atmospheric noise in this frequency band, primarily from lightning.  These radio waves are reflected off the lower ionosphere, and therefore any changes in the lower ionosphere due to solar storms or solar activity will be detected in our ground-based observations of VLF radiation here in Israel.  One interesting recent finding was that the solar rotation rate of 27 days can be nicely detected in our VLF measurements in Israel.  The sun rotates once every 27  Earth days, and since the sun's surface is not uniform, there are small variations in the amount of energy leaving the sun from different regions, arriving at the Earth with a periodicity of 27 days.  These small changes impact the ionosphere, which impacts the propagation of VLF waves within the Earth-ionosphere waveguide.  Below we can see the variations in our VLF measurements (representing the background noise from lightning), and various solar indices that often show the 27-day variability of the sun.  Note that this was close to the recent deep solar minimum, and therefore not all indices show clearly the 27-day changes.  However, when all indices agree and are in phase, there is a clear anti-correlation with the VLF noise measurements.  Furthermore, when often the solar indices show no 27-day signal, the VLF data still show clearly the solar variability at 27-days, implying that monitoring VLF measurements continuously may supply more reliable information on the solar rotation, than the solar indices themselves!  The physical meaning of this anti-correlation is that the 27-day solar rotation modulates the height of the lower ionosphere (D-region) and the reflection height moves up and down every 27 days.  As the reflection height moves down into the denser atmosphere, more VLF waves from lightning are absorbed, and as the reflection height rises, less absorption occurs.  In this way we receive at our station less or more background radiation from distance storms.  Our calcualtions show that the modulation is of the order of 4-5 km in height of the reflection layer in the D-region of the ionopshere.



References:

    Rycroft, M.J., S. Israelsson and C. Price, 2000: The global atmospheric electric circuit, solar activity and climate change, J. Atmos. Solar-Terr. Phys., 62, 1563-1576.
    Price, C., and V. Mushtak, 2002:  The impact of the August 27, 1998, gamma ray burst on the Schumann resonances, J. Atmos. Solar-Terr. Phys., Vol. 63 (10), 1043-1047.
    Menikov, A., C. Price, G. Satori and M. Fullekrug, 2004: Influence of the Solar Terrminator Passages on Schumann Resonance Parameters, Journal of Atmospheric and Solar-Terrestrial Physics, 66, 1187-1194.
    Pechony, O., and C. Price, 2004, Schumann resonance propagation parameters calculated with a Partially-Uniform Knee Model on Earth, Venus, Mars and Titan, Radio Science, 39, RS5007, doi:10.1029/2004RS003056.
    Zomer, A., C. Price, L. Alperovich, M. Finkelstein and M. Merzer, 2008:  ULF amplitude observations at the dawn/dusk terminators, J. Atmos. Elect., 28(1), 2-29.
    Reuveni, Y., and C. Price, 2009:  A new approach for monitoring the 27-day solar rotation using VLF radio noise on the Earth's surface, J. Geophys. Res. - Space Phys., 114, A10306, doi:10.1029/2009JA014364.
    Reuveni, Y., C. Price, E. Greenberg and A. Shuval, 2010:  Atmospheric noise statistics from VLF measurements in the eastern Mediterranean, Radio Science, 45, RS5015, doi:10.1029/2009RS004336.


Related websites:

<>Space Weather
Space Weather Today
Space Weather Center