3.2 Microburst/precipitation observations
Microbursts are observed on both FIREBIRD CubeSats (FU3 and FU4) and on
AC6-A. Both missions provide good radial coverage of the microburst
region but have limited MLT coverage. Therefore, as described above, we
supplement these observations with POES/MetOp electron precipitation
(BLC fluxes between 84.7 keV - 320.8 keV).
For the first 9-hour period (Figure 1a), FU3, FU4, and AC6-A made
measurements between ~8 to 11 MLT and
~20 to 23 MLT and POES/MetOp pass through most MLTs
(with limited coverage between 10 and 15 MLT, see Figure S1). We observe
a strong electron precipitation region beginning around 4 MLT, extending
from approximately 4 to 5 L. This region continues until about 8 MLT,
with additional microburst observations from FIREBIRD and AC6-A between\(\sim\)9 to 10 MLT from 5 to 8 L. There are no microburst observations
past this MLT due to observational limits (i.e. there are two additional
AC6-A passes through 11 MLT, but no FIREBIRD and limited POES/MetOp
passes), but there is strong electron precipitation observed just past
12 MLT. It should be noted that POES/MetOp does observe electron
precipitation in the 10 to 12 MLT region (see Figure S3), but these
observations do not exceed our threshold profile and are therefore not
counted as strong electron precipitation. The observations in these
regions are also very limited (see Figure S1).
For the second 9-hour period (Figure 1b), FU3, FU4, and AC6-A made
measurements between ~6 to 14 MLT and
~16 - 24 MLT and POES/MetOp sampled many MLT regions
(again, with limited coverage between 10 and 15 MLT). A large (4 - 7 L)
precipitation region (observed by POES/MetOp) initiates around 6 MLT
that continues until 12 MLT (note that a smaller region also occurs from
2 - 6 MLT). There are microburst observations extending from 7 to 14
MLT, extending from 4.5 - 8 L. Another region of precipitation is
observed between 14 to 22 MLT around 3 to 6 L, but no chorus is observed
even though Arase took observations throughout this region. Therefore,
it is likely that this dusk precipitation region is caused by other
waves such as EMIC waves [e.g. Capannolo et al. , 2021]. It
should be noted that Arase observed He+-band EMIC waves from
~15:30 to 15:45 UT. During this time no chorus waves
were detected. Unfortunately, we cannot determine if precipitation bands
caused by EMIC waves were observed rather than microbursts [Blum
et al. , 2016] due to the limitations of POES/MetOp as mentioned
above.
For the third 9-hour period (Figure 1c), FU3, FU4, and Ac6-A made
measurement between ~6 to 14 MLT and ~16
- 24 MLT and POES/MetOp observed at most MLTs. Precipitation on
POES/MetOp is observed within most MLT regions, and microbursts are
observed from ~5 – 8 L between 7 and 10 MLT.