On Jan 28, 12:47Â*pm, "Alastair McDonald"
wrote:
"N_Cook" wrote in message

...





Alastair McDonald wrote in message
...
I have just been made aware of this article which seems to suggest
something
I had suspected: that lunar tides are linked with jet streams. The
article
is entitled:

"Equatorial Ionospheric Electrodynamic Perturbations During Southern
Hemisphere Stratospheric Warming Events"

But the abstract says:

"We also compare these data with extensive recent
results that showed the fundamentally important role of lunar semidiurnal
tidal effects on low latitude electrodynamic perturbations during of
arctic
SSW events."

http://onlinelibrary.wiley.com/doi/1...bstract;jsessi...
9A2C47D3C86E8784D17AA97B850BB8.d01t04

If SSWs are caused by waves in jet streams breaking, then there is some
sort
of connection with lunar tides.

Cheers, Alastair.

Why just lunar tides? the solar component of the tides are half as strong
as
lunar ones

Just been alerted to this article, which may answer your question! I am not
claiming to understand this at the moment, but I expect in a few years time
a simple explanation will become available.

Lunar and solar tidal variabilities in mesospheric winds and EEJ strength
over Tirunelveli (8.7°N, 77.8°E) during the 2009 major stratospheric warminghttp://onlinelibrary.wiley.com/doi/10.1029/2012JA018236/abstract;jses...

Cheers, Alastair.- Hide quoted text -

- Show quoted text -

Lunar�dependent equatorial ionospheric electrodynamic effects
during sudden stratospheric warmings
B. G. Fejer,1 M. E. Olson,1 J. L. Chau,2 C. Stolle,3 H. Lühr,3 L. P.
Goncharenko,4
K. Yumoto,5 and T. Nagatsuma6
Received 13 January 2010; revised 4 March 2010; accepted 12 March
2010; published 28 August 2010.
[1] We have used plasma drift and magnetic field measurements during
the 2001–2009
December solstices to study, for the first time, the longitudinal
dependence of equatorial
ionospheric electrodynamic perturbations during sudden stratospheric
warmings.
Jicamarca radar measurements during these events show large dayside
downward drift
(westward electric field) perturbations followed by large morning
upward and afternoon
downward drifts that systematically shift to later local times. Ground�
based magnetometer
measurements in the American, Indian, and Pacific equatorial regions
show strongly
enhanced electrojet currents in the morning sector and large reversed
currents (i.e.,
counterelectrojets) in the afternoon sector with onsets near new and
full moons during
northern winter warming periods. CHAMP satellite and ground�based
magnetic field
observations indicate that the onset of these equatorial afternoon
counterelectrojets is
longitude dependent. Our results indicate that these large
electrodynamic perturbations
during stratospheric warming periods are due to strongly enhanced
semidiurnal lunar wave
effects. The results of our study can be used for forecasting the
occurrence and evolution
of these electrodynamic perturbations during arctic winter warmings.
Citation: Fejer, B. G., M. E. Olson, J. L. Chau, C. Stolle, H. Lühr,
L. P. Goncharenko, K. Yumoto, and T. Nagatsuma (2010),
Lunar�dependent equatorial ionospheric electrodynamic effects during
sudden stratospheric warmings, J. Geophys. Res., 115,
A00G03, doi:10.1029/2010JA015273.
1. Introduction
[2] The quiet time low�latitude ionospheric electric fields
are generated by dynamo action of thermospheric neutral
winds [e.g., Richmond, 1995a; Heelis, 2004]. In the equatorial
region the zonal electric fields drive strong daytime
lower E region eastward currents, called equatorial electrojets,
in narrow latitudinal bands centered at the dip equator
[e.g., Richmond, 1995b]. The zonal electric fields also drive
equatorial E and F region vertical plasma drifts which have
been studied extensively using radar and satellite measurements
[e.g., Fejer, 1997].
[3] The initial geomagnetic field measurements near the
magnetic equator have already indicated the large variability
of the equatorial electrojet intensity. Bartels and Johnston
[1940] reported the occasional occurrence of afternoon
depressions in the electrojet horizontal magnetic field component
(DH) below their nighttime values during geomagnetic
quiet days. They suggested that the largest variations, on
so�called “big L days,� were due to the superposition of
highly magnified lunar tides on the normal quiet time variation.
Morning and afternoon quiet time anomalous equatorial
electrojet current reversals, called counterelectrojets, have
been extensively studied since the nineteen sixties [e.g., Gouin,
1962; Gouin and Mayaud, 1967; Hutton and Oyinloye, 1970;
Rastogi, 1973]. Comprehensive reviews of these studies were
by published by Mayaud [1977] and Marriott et al. [1979].
The quiet time current reversals are confined to the equatorial
electrojet region and are most common during low solar
activity years [Rastogi, 1974b]. They can occur for a week or
so, but not necessarily on the same days, at longitudes separated
by more than a few hours. Afternoon counterelectrojets
occur mainly near new and full moons (lunar ages 0000 and
1200); morning counterelectrojets are most common after the
lower and upper transits (lunar ages 9 and 21) [Onwumechilli
and Akasofu, 1972; Hutton and Oyinloye, 1970; Rastogi,
1974a, 1975].
[4] In the Indian sector, counterelectrojets are most frequent
in the afternoon hours of the June solstices; in the American
sector, counterelectrojets are most common in the morning
hours of December solstices [Patil et al., 1990]. However,
as pointed out by Mayaud [1977], it is remarkable that all
published examples of magnetically quiet time very large
1Center for Atmospheric and Space Sciences, Utah State University,
Logan, Utah, USA.
2Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Lima,
Peru.
3Helmholtz Centre Potsdam,GeoForschungsZentrum, Potsdam,Germany.
4Haystack Observatory,Massachusetts Institute of Technology, Westford,
Massachusetts, USA.
5Space Environment Research Center, Kyushu University, Fukuoka,
Japan.
6Applied Electromagnetic Research Center, National Institute of
Information and Communications Technology, Tokyo, Japan.
Copyright 2010 by the American Geophysical Union.
0148�0227/10/2010JA015273
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, A00G03, doi:
10.1029/2010JA015273, 2010
A00G03 1 of 9
counterelectrojet events are from the December solstice.
Several studies suggested that these events result from the
superposition of the lunar semidiurnal wave over the solar
daily wave, but they also noted that highly enhanced lunar
tides would be required to explain the occasionally observed
very large semidiurnal current perturbations since lunar tides
can normally account only for much smaller variations.
Bhargava and Sastri [1977] derived a semidiurnal magnetic
field component with a maximum around 1000 LT and a
minimum near 1500 LT superposed on the electrojet horizontal
field during afternoon counterelectrojet events, and
Alex et al. [1986] suggested that these perturbations were due
to lunar�solar tidal waves. Lunar controlled counterelectrojets
persist for several days, exhibit a systematic change in the
diurnal pattern, and tend to occur over longer longitudinal
ranges [Rangarajan and Rastogi, 1993].
[5] Numerous studies examined the effects of lower atmospheric
processes on equatorial electric fields and currents.
Stening [1977] suggested an association of equatorial
counterelectrojets
and stratospheric warmings. Chen [1992] showed
2 day oscillations in the intensity of the equatorial ionization
anomaly, which is driven by the vertical plasma drift (zonal
electric field). Forbes and Leveroni [1992] identified a quasi
16 day oscillation on the electrojet DH intensity during a
large northern winter stratospheric disturbance possibly due
to the upward penetration of a free Rossby mode excited in the
winter stratosphere. Somayajulu et al. [1993] reported westward
meteor zonal winds in the altitude region of 90–105 km
at Trivandrum (8.5°N, 77°E) during five afternoon counterelectrojet
days in January 1987, and eastward winds during
normal electrojet days. Stening et al. [1996] pointed out that
this and other counterelectrojet events during northern winter
were accompanied by eastward�to�westward upper atmosphere
wind reversals at a height of 99 km at Saskatoon,
Canada (35°S, 107°W), and that they generally occurred
during sudden stratospheric warming (SSW) periods. On the
other hand, northern summer counterelectrojet events at
Trivandrum, sometimes persisting for several days, were not
associated with changes in the Saskatoon winds. Stening
[1989] and Gurubaran [2002] pointed out that equatorial
counterelectrojet events could result from the dynamo effects
of global wind changes. Stening et al. [1997] used numerical
simulations to show that lunar tidal amplitudes and phases
undergo large changes during stratospheric warmings. Rastogi
[1999] suggested that quiet time counterelectrojet events
during low solar activity northern winter months result from
changes in the ionospheric wind system associated with
stratospheric warmings.
[6] Sudden stratospheric warming (SSW) is a large�scale
meteorological process in the winter polar region caused by
the rapid growth of quasi�stationary planetary waves and their
interaction with the stratospheric mean circulation [Matsuno,
1971]. These events strongly affect the background wind,
temperature, chemistry and wave activity of the middle
atmosphere, as well as the vertical thermodynamic coupling
in a large range of altitudes and latitudes [e.g., Labitzke, 1981;
Andrews et al., 1987; Liu and Roble, 2002; Hoffmann et al.,
2002; Shepherd et al., 2007; Pancheva et al., 2008].
[7] Low�latitude mesospheric and lower thermospheric
effects associated with polar stratospheric warmings have
been the subject of intense recent scientific interest [e.g.,
Vineeth et al., 2007; Sridharan and Sathishkumar, 2008].
Recently, Chau et al. [2009] reported a unique semidiurnal
signature lasting for several days on equatorial F region vertical
plasma drifts measured at the Jicamarca Radio Observatory
(11.9°S, 76.8°W; dip latitude 1°N) during a minor
SSW event in January 2008. Vineeth et al. [2009] suggested
that SSWs lead to higher occurrence of quasi 16 day periodicity
of equatorial counterelectrojets and that stronger
counterelectrojets are associated with more intense warmings.
Sridharan et al. [2009] used magnetic field and mesospheric
wind measurements in the Indian region to show that major
arctic SSW events affect the day�to�day variability of equatorial
counterelectrojets through the enhancement of semidiurnal
tides.
[8] In this study, we use Jicamarca radar measurements and
global satellite and ground�based magnetic field observations
during 2001–2009 northern winters to study, for the first time,
the longitude�dependent equatorial electrodynamic perturbations
during SSW events. Our results suggest that these
large electrodynamic perturbations most likely result from
strong sudden enhancements of longitude�dependent lunar
tidal wave effects during stratospheric warmings.
2. Data
[9] We have used vertical plasma drifts obtained from
Doppler radar measurements of 150 km echoes by the
Jicamarca Unattended Long�term Ionosphere and Atmosphere
(JULIA) radar system at the Jicamarca Radio Observatory
(11.9°S, 76.8°W; 0.8°N magnetic), near Lima, Peru. These
measurements are generally made between about 0900 and
1600 LT with a time resolution of 5 min and also provide
accurate estimates of the F region vertical plasma drifts and
ionospheric zonal electric fields [e.g., Kudeki and Fawcett,
1993; Chau and Woodman, 2004]. However, they were only
made during a relatively small number of days during our
2001–2009 northern winter periods of interest.
[10] We have determined the strength of the equatorial
electrojets in the American, Indian, and Japanese sectors from
the difference of the horizontal magnetic fields measured at
pairs of stations, one close to the geomagnetic equator and
another a few degrees off. These stations are Jicamarca and
Piura (5.2°S, 80.6°W; 6.8° magnetic) in the American sector,
Tirunelveli (8.7°N, 77.8°E; 0.5°S magnetic) and Alibag
(18.6°N, 72.9°E; 10°N magnetic) in the Indian region, and
Yap (9.3°N, 138.5°E; 0.5°N magnetic) and Biak (1.1°S,
136.0°E; 9.7°S) in the Pacific sector. We have also used the
magnetic field measurements in the Peruvian region to estimate
ionospheric vertical plasma drifts (zonal electric fields)
using the methodology developed by Anderson et al. [2002].
These derived drifts are generally in good agreement with the
vertical drifts measured by the Jicamarca radar, except
between dawn and about 1000 LT, when they often underestimate
the measured upward drifts.
[11] The polar�orbiting Challenging Minisatellite Payload
(CHAMP) satellite has been making high�quality magnetic
field (accuracy of about 0.1 nT)measurements since July 2000.
The satellite has an orbital period of 93 min and advances
about 23° westward from orbit to orbit. Equatorial electrojet
current distributions are determined from CHAMP measurements
by first removing magnetic field contributions from
other sources, and then using a very general current model
which makes the results independent of the satellite altitude
A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03
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and ambient field geometry [e.g., Lühr et al., 2004; Manoj
et al., 2006]. In this study, we present CHAMP equatorial
magnetic field measurements in the afternoon sector from
late December 2002 through January 2003.
3. Results
3.1. Electrodynamic Effects During December 2002
and January 2003
[12] Figure 1 shows the development of the December
2002 to January 2003 minor stratospheric warming events.
The top plots present the zonal mean temperatures at 10 hPa
(about 32 km) at 90°N, the mean zonal winds averaged over
60°N, and the corresponding 30 year mean temperatures and
zonal winds obtained from the National Center for Environmental
Prediction (NCEP). The bottom plots give the daily
solar decimetric flux and the 3 h Kp indices.
[13] Figure 1 indicates that the December 2002 highlatitude
stratospheric temperatures and zonal winds were
mostly above and below their 30 year mean values,
respectively. The temperature started to increase rapidly on
28 December, reached its maximum on 31 December, and
then slowly decreased until about 12 January; the second
and third warmings started on 14 and 24 January and
reached peak values on 16 and 26 January. During the first
two warmings, the longitudinal averaged eastward winds
decreased by about 10 and 30 m/s below their average values,
respectively.
[14] Figure 2 shows the daytime vertical plasma drifts
obtained from Doppler measurements of 150 km echoes
over Jicamarca during the first 2002–2003 warming and the
corresponding quiet time averages. Figure 2 shows large
downward drift (westward electric field) perturbations during
30 December to 1 January, which is indicative of an abnormally
large reduction in the ionospheric daytime eastward
electric fields. This was followed by a very large and sudden
increase in the morning upward drifts on 2 January. The
resulting very large semidiurnal drift perturbations (upward in
the morning and downward in the afternoon) shifted gradually
to later local times from 2 January through 6 January.
Incoherent scatter radar measurements during the stronger
January 2008 SSW event presented by Chau et al. [2009]
show basically an identical perturbation drift pattern after
about 0900 LT, and even larger upward drift enhancements
in the early morning period.
[15] The vertical drifts derived from Jicamarca and Piura
magnetic field measurements during December 2002 to
January 2003 are presented in Figure 3. The slant line indicates
the local times of the equatorial crossings of the CHAMP
satellite. The December data show large drift day�to�day
variability. Figure 3 also shows small upward morning and
large downward afternoon drifts during 29–31 December,
large sudden increase in the upward morning and downward
afternoon drifts on 2 January, and the gradual shift of the
semidiurnal�like perturbation drift pattern to later local times
Figure 1. Stratospheric polar zonally averaged temperature,
zonal wind (positive eastward), from the National Center for
Environmental Prediction, and decimetric solar flux and Kp
indices for December 2002 to January 2003. The median
values are shown as black circles.
Figure 2. Vertical plasma drift velocities of 150 km radar
echoes measured with the Jicamarca Unattended Long�term
Ionosphere and Atmosphere system. The smooth curve
denotes the mean drifts.
A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03
3 of 9
over a period of a few days leading to increased upward drifts
in the afternoon and decreased or reversed drifts in the
morning. A smaller but weaker perturbation drift pattern also
occurred during 19–25 January after an interval of much
smaller daytime drifts on 15–18 January. Figure 3 also show
relatively large 2 day modulations on the vertical drifts.
[16] Figure 4 shows the daytime DH, which reflects the
intensity of the equatorial electrojet, in the Peruvian, Indian,
and Pacific sectors between 1 December 2002 and 29 January
2003. In this period, new moons occurred on 4 December
and 2 January, and full moons occurred on 19 December and
18 January. The December data illustrate the typical day�today
variability of the daytime electrojet currents with the
absence of correlated large temporal perturbation drift patterns
in these longitudinal sectors. After the late December
warming onset, the electrojet intensities first weakened for
about 2 days and then, around new moon, suddenly developed
very similar multiday perturbation patterns with largely
enhanced morning eastward and afternoon westward currents
that systematically shifted to later local times. Strong
morning counterelectrojets were seen around the first and last
quarters (10 and 25 January). The morning and afternoon
current perturbations occurred first and were strongest in the
American sector and developed last and were weakest (particularly
in the afternoon) in the Pacific sector. Similar, but
weaker, current perturbations developed near full moon after
the second warming, when the high�latitude wind perturbations
were even larger. These perturbation events are about
14 days apart, as expected for the lunar semimonthly tide
[Stening, 1989].
[17] Figure 5 illustrates in more detail the longitudedependent
daytimemagnetic field perturbations during the first
SSW episode. We can see again that the afternoon counterelectrojets
occurred first and were strongest in the American
sector and the shift of the perturbation current pattern to later
local times. In particular, there is a clear increase in the time of
the counterelectrojet minimum as the days progress. Figure 5
also shows the effect of geomagnetic activity on the electrojet
intensity, which was strongest during 3–4 January.
[18] The onset of strong semidiurnal electrojet intensity
perturbations close to new and full moons and the shifts of
the current perturbation patterns to later local times with
lunar age suggest the occurrence of highly enhanced lunar
semidiurnal wave effects over a broad range of longitudes
during these SSW events. The shift of the current perturbation
patterns are consistent with the difference in the lengths
of the solar and lunar days.
[19] Figure 4 also shows the occurrence of strong 2 day
wave perturbations on the strength of the electrojet currents
Figure 3. Vertical plasma drift velocities (positive upward)
over Jicamarca derived from magnetic field observations.
The slant line indicates the local time coverage of the
CHAMP satellite.
Figure 4. Equatorial horizontal magnetic field components
in three longitudinal sectors and high�latitude zonally averaged
stratospheric temperatures and zonal winds during
December 2002 and January 2003. The days of new and full
moons are indicated by open and solid circles, respectively.
A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03
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in our three longitudinal sectors. These perturbations appear
to be strongest during SSW events. Pancheva et al. [2006]
studied in detail the global occurrence of 2 day wave activity
during this period, and Aveiro et al. [2009] reported their signatures
on the equatorial electrojet and E region electric fields
in the Brazilian sector.
[20] The polar�orbiting CHAMP satellite made equatorial
electrojet magnetic field measurements in the afternoon
sector between late December 2002 and mid�February 2003.
These measurements made with an orbital period of 93 min
provided about 18 equatorial daytime crossings. Figure 6
presents the equatorial electrojet current densities in the afternoon
sector between late 27 December 2002 and 30 January
2003. The horizontal lines denote the average longitudes of
the ground stations used in our study. We note that the
CHAMP electrojet current densities, obtained by fitting the
full latitudinal profile of the geomagnetic field data, provide
more accurate estimates of the electrojet intensities than
derived from geomagnetic data from pairs of stations. We
note that the current maxima are about 14 days apart. Figure 6
indicates that following the first warming, afternoon
counterelectrojets
occurred at all longitudes and that their onset times
increased toward the east, which is in good agreement with
our ground�based data. Figure 6 also shows more irregular
occurrence of afternoon counterelectrojets during the second
warming, which could be partly due to the precession of the
satellite to earlier to local times.
3.2. Observations During Other Periods
[21] We have examined the currently available Jicamarca
vertical drifts and magnetic field ground�based measurements
in the Peruvian and Indian equatorial regions during
the other December solstices from 2001 to 2009. In these
periods, there were only very limited radar drift measurements.
Strong stratospheric warmings occurred during 2001–
2002, 2003–2004, 2005–2006, and 2008–2009, with the last
being by far the strongest, and there were occurrences of
minor warmings during the other northern winter periods
except for 2004–2005.
[22] Figure 7 shows the equatorial DH data from the
Peruvian and Indian sectors, and the high�latitude temperatures
and winds at 10 hPa from 10 December 2001 to
23 January 2002. Moderate geomagnetic activity on 16, 21,
24 and 31 December and on 10, 11, and 19 January resulted
in noticeable short�term (less then a few hours)DH electrojet
variability, especially in the Peruvian region. Figure 7 shows
large DH perturbations with strongly enhanced morning
eastward and afternoon westward currents starting near new
moon and about nine days after the warming onset, and the
shift of the perturbation patterns to local times.
[23] Figure 8 shows the DH data from Peru and the
corresponding high�latitude temperatures and zonal winds
during the magnetically quiet period from 20 December 2008
to 28 February 2009. In this period, new moons occurred on
Figure 5. Equatorial horizontal magnetic field components
close to the 2 January new moon period during the first
December 2002 to January SSW event. The smooth curves
denote the quiet time values before the SSW onset.
Figure 6. Equatorial electrojet afternoon current density
measurements by the CHAMP satellite and high�latitude
stratospheric parameters between late December 2002 and
January 2003. The horizontal lines denote the longitudes
of our ground�based stations.
A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03
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27 December and 26 January and full moons on 11 January
and 9 February. The high�latitude data indicate the occurrence
of a very strong large SSW event from mid�January
through mid�February. The equatorial data do not show
any unusual DH perturbations prior to the SSW onset.
After the warming, however, there were again very large
decreases in the electrojet morning and afternoon currents
on 23–24 January, followed by large sudden increases in
the morning eastward and afternoon westward currents and a
continuous shift of the current reversals to later local times
after the new moon on 27 January.
[24] Figure 9 shows the DH data from the Peruvian region
during 24–28 January 2009 and the corresponding average
values prior to the SSW event. Figure 9 illustrates in more
detail the very large increase in the intensity of the early
morning electrojet intensities from 26 to 27 January and the
following gradual shift of the current reversal times. Jicamarca
incoherent scatter radar measurements (not shown) indicate
that the F region upward drift velocity at about 0900 LT
increased from about 20 m/s on 25 January to about 50 m/s
on 27 January.
[25] The morphology of Jicamarca vertical plasma drift
during the January 2008 SSW event reported by Chau
et al. [2009] is fully consistent with the results presented
above. In that event full moon occurred on 22 January, the
Jicamarca morning upward plasma drifts strongly increased
on 22–23 January. One day later, the Indian DH data (not
shown) show small increases in intensity of the morning
electrojet and strong afternoon counterelectrojet conditions.
The same sequence of events appears to have occurred
during the strong 2003 and 2004 warming period, although
in this case there were no plasma drift measurements and the
Peruvian magnetometer data are less reliable partly due to
geomagnetic effects. The morphology of equatorial DH perturbations
described above has also been inferred from equatorial
measurements during the 2006–2007 SSW event.
[26] We have seen that during SSW events large semidiurnal
perturbations in equatorial plasma drifts and electrojet
currents are associated with lunar tidal wave effects. It is
important to note, however, that lunar tidal effects frequently
modulate the equatorial electric fields and current as
reported in earlier studies. During northern winter, these
effects are seen more often in the Peruvian than in the
Indian sector, as reported in earlier studies. Figure 10 shows
the equatorial DH data from the Peruvian and Indian sectors
and the high�latitude stratospheric temperatures and winds
during December 2004 and January 2005, a northern winter
period without stratospheric warmings. In this case, the
short�term enhancements in the intensities of the electrojet
currents were associated with increase geomagnetic activity.
Figure 10 shows afternoon counterelectrojets and shifts of
the perturbation patterns occurred around the time of the new
moon period on 9 January, and perhaps also close to the new
Figure 8. Equatorial horizontal magnetic field measurements
in the Peruvian sector and high�latitude stratospheric
parameters during December 2008 and January 2009. The
days of new and full moons are also shown.
Figure 7. Equatorial horizontal magnetic field measurements
in the Indian and Peruvian sectors and high�latitude
stratospheric parameters during December 2001 and January
2003. The days of new and full moons are also shown.
A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03
6 of 9
moon period on 24 January. However, these semidiurnal
current perturbations had only fairly small magnitudes.
4. Discussion
[27] We have shown large temporal electrodynamic perturbations
in the equatorial vertical drifts (zonal electric fields)
and electrojet intensities in three widely spaced longitudinal
sectors during SSWevents from the end of December through
early February. These large semidiurnal like perturbations
were preceded by about two days of largely reduced eastward
electric fields and electrojet intensities. The sudden onset of
the large semidiurnal perturbations occurred during the SSW
events and close to the new and full moons (lunar ages 00 and
12 h) and systematically shifted to later local times with lunar
age. Later, large electric field and electrojet current reversals
in the morning occurred near the first and last quarters (lunar
ages 0600 and 1800 h). In the absence of SSW events, the
electric field and current had much smaller perturbations.
These results indicate the large amplification of lunar tidal
wave effects in the equatorial zonal electric fields and electrojet
intensities during arctic stratospheric warmings.
[28] The large electrojet current perturbations during SSW
events shown above occurred first in the American and last
in the Pacific sector. This is consistent with the longitudinal
dependence of afternoon counterelectrojet onsets inferred
from the 2002–2003 CHAMP data. Magnetometer derived
vertical plasma drifts during the 2002–2003 and 2003–2004
SSW events also indicate the earlier occurrence of large
perturbations in the Peruvian than in the Philippine sector
(D. Anderson, private communication, 2009). On the other
hand, magnetic field measurements during the January 1989
SSW event studied by Rangarajan and Rastogi [1993] suggest
the occurrence of large electrojet current perturbations
earlier in the Indian than in the American sector. This indicates
that detailed additional studied are needed to fully characterize
the longitudinal dependence of SSW associated equatorial
electrodynamic disturbances.
[29] Our data suggest that the electric field and current
perturbations are most pronounced during December, but
there are indications that SSW�enhanced electrodynamic
perturbations also occur during equinoctial periods [e.g.,
Stening et al., 1996]. Figure 5 of Fejer and Scherliess [2001],
for example, shows an unusually large increase in the morning
Figure 9. Horizontal magnetic field measurements in the
Peruvian equatorial region during the very large 2009 SSW
event. The smooth curve denotes the average values before
the SSW onset.
Figure 10. Equatorial horizontal magnetic field measurements
in the Indian and Peruvian sectors and high�latitude
stratospheric parameters during December 2004 and January
2005, which was a period without SSW events. The days of
new and full moons are also shown.
A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03
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and early afternoon F region upward plasma drifts over
Jicamarca from 17 to 18 March 1988. This large quiet time
drift increase also occurred on a new moon during a SSW
event and the enhanced upward drifts lasted for at least three
days (the radar measurements ended on 20 March). In this
case, however, there were only very small decreases in the
afternoon drifts relative to their average values. This suggests
that the equatorial electrodynamic signatures of SSW events
might change with season. We note that over Jicamarca,
afternoon vertical drift reversals and corresponding counterelectrojet
events are less frequent during equinox than during
the December solstice.
[30] Simulation studies using the NCAR TIME�GCM
show that, owing to their nonlinear interaction with quasistationary
planetary waves, both the migrating and nonmigrating
tides have largest changes at low latitudes and in
the ionospheric E region [Liu et al., 2010]. They also indicate
that equatorial plasma drifts and, therefore, equatorial electrojet
intensity changes are longitude� and local�time�dependent
with large upward drift (i.e., eastward electric field) perturbations
near 0500 LT around 70°W, and largest downward
drift perturbations around 70°E at the same local time. Our
observations consistently show larger morning eastward
electric field perturbations in the American than in the Indian
sector in good agreement with these simulations. We note,
however, that the large variability of the electrodynamics of
the low�latitude ionosphere during SSW events often also
involve strong gravity, 2 day and longer period planetary
wave effects [e.g., Sathishkumar and Sridharan, 2009; Abdu
et al., 2006].
[31] The equatorial vertical plasma drifts and electrojet
intensities exhibit sudden distinctive signatures during SSW
events which can also be identified in earlier observations.
This suggests that the study of historic global equatorial
magnetic field measurements, which now go back over a
century, could provide additional information on the equatorial
electrodynamic effects of SSWs over several decades.
We note that the meteorological analysis of arctic winter
SSW data extends back only to 1978–1979 and that the historical
stratospheric temperature data presented by Manney
et al. [2005] extends to 1958–1959. The use of global equatorial
magnetic field measurements to infer the occurrence
of SSW events during other seasons and earlier periods will
be a subject of a future study.
5. Summary
[32] We have studied Jicamarca vertical plasma drift and
global equatorial magnetic field measurements during 2001–
2009 arctic SSW events. Our observations show that this
strong high�latitude meteorological process gives rise to large
global equatorial electrodynamic perturbations lasting for
several days. These equatorial perturbations are longitude
dependent and have distinctive magnetic field signatures
which have been reported for several decades. Our results
indicate that lunar semidiurnal tidal wave effects highly
enhanced during SSW events are the most likely source of
these unusual electrodynamic perturbations.
[33] Acknowledgments. We thank A. Bhattacharyya and the Indian
Institute of Geomagnetism for the Tirunelveli and Alibag data. We
thank
NICT for the Yap data and the Solar Terrestrial Environmental
Laboratory,
Nagoya University, for managing the database of the 210 MM magnetic
observations. We also thank D. Siskind and S. Larson for useful
discussions.
The work at Utah State University was supported by the Aeronomy
Program, Division of Atmospheric Sciences, through grant ATM�0534038
and by the NASA Living With a Star (LWS) Program through grant
NNX06AC44G. The Jicamarca Radio Observatory is a facility of the
Instituto
Geofisico del Peru, Ministry of Education, and is operated with
support
from the NSF cooperative agreement ATM�0432565 through Cornell
University.
[34] Robert Lysak thanks Robert Stening and another reviewer for their
assistance in evaluating this paper.
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http://www.haystack.mit.edu/ssw/wp-c..._Fejer_SSW.pdf

That's the way to do it!
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