Post-midnight bubbles and scintillations in the quiet-time June solstice: possible forcing from lower atmosphere
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Post-midnight bubbles and scintillations
in the quiet-time June solstice: possible
forcing from lower atmosphere
E. Yizengaw1, J. Retterer1, E. E. Pacheco1, P. Roddy2, K.
Groves1, R. Caton2, P. Baki3, C. Valladares1, and R. Stoneback4
1Institute
for Scientific Research, Boston College; 2AFRL, Kirtland
AFB, 3Technical University of Kenya, Kenya; 4UTD
Outline Is the post-midnight bubbles, we often observed, a leftover from dusk sector or independently generated? If it is independently generated, then what cause it, especially during magnetically quiet period? Does post-midnight bubbles have longitudinal dependence? If so why?
Dusk sector in-situ bubbles distribution
DMSP Observations:
Gentile et al., 2011
In Africa (Long ~ -20° to 52°)
dusk sector irregularities are
active almost all seasons
during solar max.
C/NOFS Observations
Yizengaw et al.
Dusk sector bubbles/Scintillation
distribution, estimated from the ground
S4 index: 2010
Bubble detection
360 technique from
19 – 24 LT 300
the ground-based
240 observations
180
120
Bubbles from 60
ground-based
GPS TEC S4 index: 2011
360
300
240
180
120
60
S4 index from 360
S4 index: 2012
ground-based 300
240
GPS TEC 180
120
60
Yizengaw et al., AG, 2013
Longitudinal variability of bubbles
Dusk sector (1900 – 2400 LT) Dawn sector (0000 – 0500 LT)
TEC depth
Post-midnight bubbles in detail! It drifts westward with a zonal speed of ~160m/s
Quiet time post-midnight bubbles!
Yizengaw et al., GRL, 2013 How250
about
MHzlong
VHFterm observation?
receiver in Kenya
Means of identifying quiet time post-
midnight bubbles/irregularities
dN = In the root-mean-square value
of the relative density deviation
from the mean density calculated
as an envelop of ambient density,
which is averaged every minute
(∼400 km spatially).
To minimize additional factors
(altitude variation) that cause the
deviation (dN) to vary, we
normalized dN by background
density (No), and obtained dN/No
We then use dN/N as proxy
for bubble occurrence
Quiet time post-midnight bubbles
Occurrence distribution
Quiet time post-midnight Scintillation
All time observations
included
(2010 – 2012)
250 MHz VHF receiver
in Nairobi, Kenya
Only quiet time
observation included
(2010 – 2012)What controls R-T instability growth rate and formation of bubbles?
PBMOD modelling to identify the causes of these
quiet time post-midnight bubbles
It seems the prime cause is
vertical drift?
What cause this strong upward
drift at this local time sector, and
during magnetically quiet times?
6hrs 2hrs
4hrs 1hrs Sporadic E-layer presence! If so
3hs what is the primary mechanism
CF-ALT CF-LAT for the formation of Es layer?
Apx ALT
♣ meteors that can cause
ionization,
♣ polarized electric field
associated with the MSTID, and
♣ Charged dust particles due to
Yizengaw et al., GRL, 2013 strong gusty windsQuiet time post-midnight Bubbles
ITC Zone
region during
summer
ITC Zone
region during
winter
Intertropical Convergence Zone (ITCZ) of the surface
winds can drive dust particle to higher altitude!The effects of winds on RTI growth rate
Recent modeling studies shows that the meridional winds not
only stabilize (reduce the RTI growth rate) but also
destabilize (increase RTI growth rate) the onset of ESF.
Equator ward meridional wind
(wind profile with a negative
gradient as a function of
latitude) decrease conductivity
and destabilize the onset of ESF
by increasing RTI growth rate.
Pole ward meridional wind
(wind profile with a positive
gradient as a function of
latitude) increase conductivity
and stabilize the onset of ESF by
Huba and Krall, GRL, 2013 decreasing RTI growth rateSummary Modeling results show that the postmidnight bubbles are also initiated in the same way that the postsunset bubbles are generated; i.e., due to vertical drifts. The abundant appearance of sporadic E layer in the June solstice could be a source of eastward polarization E-field that leads to the quiet time postmidnight bubbles. The upwelling of dust particles, especially over Sahara desert, and meteors shower could be possible sources of sporadic E Recent modeling studies also show that the F-region meridional winds has significant effect on the onset of bubble generation.
You all are invited for ISEA-14 meeting!
The 14th International Symposium on Equatorial
Aeronomy (ISEA-14) will be held in Africa for the first
time in more than four decades.
October 19-23, 2015
Bahir Dar, Ethiopia (Source of Blue Nile)
Here are the hardworking MSO members
Jonathan Makela, University of Illinois, USA
Jorge L. Chau, IAP, Germany
Philip Erickson, MIT Haystack Observatory, USA
Kazuo Shiokawa, Nagoya University, Japan
Duggirala Pallamraju, Physical Research Laboratory, India
Claudia Stolle, GFZ Potsdam, Germany
Anja Stromme, SRI, USA/Norway
Marco Milla, JRO, Peru
Endawoke Yizengaw, Boston College, USATopics to be discussed at ISEA-14 meeting! Magnetosphere-Ionosphere-Thermosphere coupling impact at low- and mid-latitudes Longitudinal dependence of equatorial electrodynamics and storm-enhanced density Ionospheric irregularities and scintillations New results from recently deployed instrumentation Equatorial aeronomy related to atmosphere-ionosphere coupling Future opportunities using upcoming new mission and planned ground-based instrumentation For more info. http://www.bdu.edu.et/isea14/
If you have a hard time of African Geography!
Thank you!
General Instrumentation in Africa
Six Years ago One Year ago
Thank you!Longitudinal variability of bubbles
Dusk sector (1900 – 2400 LT) Dawn sector (0000 – 0500 LT)
TEC depthLongitudinal variability of bubbles
Bubble detection technique from
the ground-based observations
Dusk sector (1900 – 2400 LT) Dawn sector (0000 – 0500 LT)Pre- and Post-midnight Electric field!
Addis Ababa
Jicamarca
de La Beaujardiere, et al., 2009Is the ionosphere calm during quiet time? (Of course not a few days coincidence)
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