Monthly Mission Highlights

Monthly Mission Highlight

 


January 2018

 

 

1) Van Allen Probes completes third cycle around the Earth

 

Over the past 5 years the apogee (high point) of the Van Allen Probes orbit made 3 full circles around Earth. This provided unprecedented observational coverage of radiation belt activity during more than 90 geomagnetic storms. By revisiting the same spacial location at different levels of geomagnetic activity the Probes enable scientists to build a systematic picture of how radiation belts evolve during storms.

 

 

2) Whistler mode chorus waves cause radiation belt losses

 

Microbursts are highly-structured 1/10 second bursts of energetic electrons into Earth’s atmosphere, where they are absorbed. Microbursts are considered to be a major mechanism for radiation belt electrons to be lost. Chorus waves are produced by plasma in near Earth space. They appear as repeated “chirps” that usually rise in pitch, one after another in a semi-random pattern. According to leading theories, microbursts are caused by whistler chorus waves. Two separate studies recently confirmed this theory using Van Allen Probes spacecraft at high altitude to observe the waves with their electric and magnetic field instruments, and a CubeSat in low Earth orbit to detect microbursts. Cubesats are small satellites about the size of a loaf of bread. Both CubeSats, FIREBIRD II and AC6, saw microbursts similar to the pattern of the chorus waves seen at higher altitude, for two separate events. Establishing this theory is a major step in predicting the coming and going of intense radiation belts.

 

Breneman, A. W., Crew, A., Sample, J., Klumpar, D., Johnson, A., Agapitov, O.,…Kletzing, C. A. (2017). Observations directly linking relativistic electron microbursts to whistler mode chorus: Van Allen Probes and FIREBIRD II. Geophysical Research Letters, 44, 11,265–11,272. https://doi.org/10.1002/2017GL075001

 

Mozer, F. S., Agapitov, O. V., Blake, J. B. & Vasko, I. Y. (2017). Simultaneous Observations Of Lower Band Chorus Emissions At The Equator And Microburst Precipitating Electrons In The Ionosphere. Geophysical Research Letters, 44. https://doi.org/10.1002/2017GL076120

 

 

3) Excess electron energy is converted into high frequency wave energy

 

Chorus waves appear as repeated “chirps”, usually rising in pitch, in space plasmas. The Van Allen Probes electric and magnetic field instruments observed chorus waves in the vicinity of Earth’s radiation belts using a special high resolution mode. They saw a different kind of higher frequency wave called Langmuir waves appear embedded within the chorus “chirps”. Scientists used wave theory and observations of electrons inside the waves to conclude that the chorus waves made electron beams, which then produced the Langmuir waves. This understanding of a basic plasma interaction observed in near Earth space can be applied to plasmas throughout the universe.

 

Li, J., Bortnik, J., An, X., Li, W., Thorne, R. M., Zhou, M., ... Spence, H. E. (2017). Chorus wave modulation of Langmuir waves in the radiation belts. Geophysical Research Letters, 44, 11,713–11,721. https://doi.org/10.1002/2017GL075877

 

 

4) New Comprehensive Model of Proton Inner Radiation Belt

 

The inner radiation belt is made of very energetic protons. They can be difficult to measure because the highest energy protons can produce noise in all energy channels of an instrument. Van Allen’s REPT instrument helps overcome the noise problem with an advanced coincidence logic design. Using a deep understanding of the instrument response and an unprecedented 5 years of quality observations, scientists were able to construct a more accurate model of the energy and location of inner belt protons. Spacecraft operators now have a better tool to understand this hazardous environment. 

 

Selesnick, R. S., Baker, D. N., Kanekal, S. G., Hoxie, V. C., & Li, X. (2018). Modeling the proton radiation belt with Van Allen Probes Relativistic Electron-Proton Telescope data. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1002/2017JA024661

 

 

5) Chorus waves observed to travel along magnetic field lines between the Earth and space intact.

 

In space plasmas chorus waves appear as repeated “chirps”, usually rising in pitch. Chorus elements were observed by a ground-based station in Kannuslehto in Northern Finland using two large 30 foot loop antennas. At nearly the same time they were observed by electric and magnetic wave receivers aboard Van Allen Probe A, which was much higher up near the Earth’s radiation belts. They were identified as belonging to the same traveling waves because they exhibited the same pattern of elements. There was a slight delay of 1.3 seconds indicating the travel time. What surprised observers was that they had travelled down from space following a magnetic field line, and reflected back up to the spacecraft, without loosing their shape. 

 

Demekhov, A. G., Manninen, J., Santolík, O., & Titova, E. E. (2017). Conjugate groundspacecraft observations of VLF chorus elements. Geophysical Research Letters, 44, 11,735—11,744. https://doi.org/10.1002/2017GL076139



Page Last Modified: January 30, 2018