Nighttime 4-peak Longitudinal Structure of Ionospheric
Plasma Density at Mid-Low latitudes During High and
Extreme Low Solar Activity Years
C., Xiong (1,2), S.Y., Ma (1), H., Lühr (2)
(1). Department of Space Physics, College of Electronic Information, Wuhan
University, Wuhan 430079, China
(2). Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences,
Telegrafenberg, 14473, Potsdam, Germany
(xiongchao@whu.edu.cn syma@whu.edu.cn)
Outline
1. CHAMP and GRACE Ne observation during 23/24 solar
cycle.
2. Nighttime 4-peak Longitudinal Structure of Ionospheric
Plasma Density.
3. Summary.
1. CHAMP and GRACE Ne observation during
23/24 solar cycle.
Electron density in the Earth’s ionosphere, which affects
satellite navigation and communications, is highly variable.
Solar activity, which increases and decreases over an
approximately 11-year cycle, is a key driver of this ionospheric
variability. The most recent solar minimum was unusually
prolonged, leading to unusual changes in the ionosphere.
Data and Measurements
The Planar Langmuir Probe (PLP) on board CHAMP satellite takes in-situ
measurements of the electron density every 15 s. The Ne readings of the PLP have
been verified by comparison against digisonde measurements at Jicamarca. For the
GRACE observation, we make use of the K-band ranging (KBR) system, which
measures the dual one-way range change between the two satellites. The total electron
content (TEC) between the spacecraft can be deduced from the KBR data. When
dividing the horizontal TEC by the distance between the spacecraft we get the average
electron density. A more detailed description of the electron density retrieval is given
in section 3 of Xiong et al.,[2010].
CHAMP and GRACE Ne observation from 2000 to
2010, orbital averages are averaged over 31 days.
CHAMP orbits decay gradually from 450 km to 330 km over the years, while
GRACE stays at about 480 km. We can also see the decline of F10.7, which
reaches the minimum in 2009.
2. Nighttime 4-peak Longitudinal Structure of Ionospheric
Plasma Density.
Recently, growing evidence is provided on longitudinal modulation of ionospheric
quantities by tidal effects originating from the tropical troposphere. Such as For
example, the four-peaked longitudinal structure in ionospheric UV emission, equatorial
electrojet (EEJ) intensity, the total electron content (TEC), the vertical plasma drift and
the equatorial ionization anomaly (EIA). All these studies provide a phenomenological
relation of the wave-number 4 (WN4) structure to the tide mode component of DE3
(diurnal eastward wave number 3).
Longitudinal dependence of the
diurnal variation of the EEJ peak
current density at March
equinox for solar flux, F10.7 = 150.
[Luehr, et al., 2008]
Different from the previous studies, which discuss the wave-4 structure of the
ionosphere quantities and their compiling with DE3 or other tides component, here, we
mainly focus on the nighttime 4-peak longitudinal structure of ionospheric plasma
density at mid-low latitudes during high and extreme low solar activity years. As DE3
maximized around August, we have choos the months around August (from 10, June to
20, Oct.) in high (2002, average F10.7=173 sfu) and low (2008, average F10.7=67 sfu)
solar activity year .
CHAMP 2002
st
sp
CHAMP 2008
st
GRACE 2002
st
sp
sp
GRACE 2008
st
sp
Depletion
North
ward
East
Ward
North
ward
Eastward
EPB occurrence rate and the peak-4 of Ne
EPB occurrence rate versus season/longitude (left) and local time (right) based on
CHAMP PLP observation for the two solar flux activity levels.
EPB around -120°E~-30°E “eat” the Ne and cause Ne depletion.
3. Summary
(1). In 2002, the equatorial ionization anomaly (EIA) and
peak-4 structure of plasma density can be seen around midnight
until 0400LT in the morning. While in 2008, EIA and the peak-4
structure of plasma density only last until 22LT.
(2). The peak at -90°E deeply decreases around 19LT in
2002 and around 20LT in 2008. One possible reason for the peak
decrease at -90°E may be the equatorial plasma bubble (EPB),
which cause the electron density depletion.
(3). The northward movement of the peak in 2002 may be
attributed to the northward neutral wind before midnight around 90°E, which needs further study by the wind model and
observations.
Reference:
1. Lühr, H., Rother, M., Häusler, K., Alken, P., and Maus, S.: The influence of
non-migrating tides on the longitudinal variation of the equatorial electrojet, J.
Geophys. Res., 113, A08313, doi:10.1029/2008JA013064, 2008.
2. Lühr, H., and C. Xiong (2010), IRI‐2007 model overestimates electron density
during the 23/24 solar minimum, Geophys. Res. Lett., 37, L23101,
doi:10.1029/2010GL045430.
3. Wan, W., L. Liu, X. Pi, M.-L. Zhang, B. Ning, J. Xiong, and F. Ding (2008),
Wavenumber-4 patterns of the total electron content over the low latitude
ionosphere, Geophys. Res. Lett., 35, L12104, doi:10.1029/2008GL033755.
4. Xiong, C., J. Park, H. L•uhr, C. Stolle, and S.Y. Ma (2010), Comparing plasma
bubble-occurrence rates at CHAMP and GRACE altitudes during high and low
solar activity,Ann. Geophys., 28, 1647-1658.
Thank you all