Transcript Effects of January 2010 stratospheric sudden warming in

Effects of January 2010 stratospheric sudden warming in the low-latitude ionosphere
L. Goncharenko, A. Coster, W. Rideout, MIT Haystack Observatory, USA
J. Chau, Jicamarca Radio Observatory, Peru
K. Hocke, University of Bern, Switzerland
C. Valladares, Boston College, USA
Abstract.
Conclusions
The winter of 2009-2010 was marked by a significant stratospheric warming event peaking in the end of January 2010. Although
this warming was not as strong as SSW events of 2008 and 2009, it presents a perfect opportunity to study the coupling between
different atmospheric regions under less extreme circumstances. We use GPS TEC and Jicamarca ISR data to study effects of this
SSW event on low-latitude ionosphere. Our results indicate that disturbances in the upper atmosphere during the SSW event of
2010 are consistent with disturbances reported for other SSW cases. We discuss different properties of the observed phenomena
and demonstrate unique features of this time interval.
1.
We report perturbations in vertical drifts at the magnetic equator and 50-100% variations in GPS TEC in the American sector
during the January 2010 SSW event.
2.
Tidal variation in TEC becomes prominent on January 25-26, 2010, after the peak in stratospheric temperature, and lasts for
several days. The amplitude of variation is smaller than in SSW of 2009, likely due to the weaker SSW event.
3.
We analyze TEC oscillations with periods between 2 and 20 days and report strong 2-day activity subsiding during SSW event.
1. Stratospheric and geomagnetic
conditions
SSW peaks on Jan 22, 2010 at 10
hPa level and 90oN
3. GPS TEC data
Mean TEC
no SSW
15 UT
morning
Mean TEC
no SSW
21 UT
afternoon
Same as
Strong PW1 activity, weak PW2
activity
other SSW events
TEC
SSW
15 UT
Increase in geomagnetic activity
on Feb 1-3 to Kp=3-…4
complicates interpretation
Figure 1. Summary of stratospheric and
geomagnetic conditions. Peak stratospheric
temperature at 90oN and 10hPa level was reached on
22 January, and temperature remained above the longterm mean for over two-week period. Strong abatement
in the zonal mean zonal wind at 60oN was observed
starting around January 10 and continuing well into
March 2010. The stratospheric circulation was
determined mostly by a planetary wave 1.
2. Vertical drift over Jicamarca
Figure 2. Observations
of vertical drift over
Jicamarca (red line) in
comparison with FejerSherliess drift model
(black line)
Generally lower
daytime drift during
first days of SSW
event
New
Increase in the pre-reversal
enhancement during SSW
Same as
other SSW events
Variations on Jan
19-20 likely due to
increase in Kp
Typical quite-time
behavior prior to
SSW
4. Planetary wave-type oscillations in GPS TEC data
Stronger upward vertical drift in
the morning, downward drift in
the afternoon during SSW,
persisting for several days (Jan
31 – Feb 3)
TEC
SSW
21 UT
TEC
suppression
in the
afternoon
TEC increase
in the
morning
TEC change,
%, 15 UT
TEC change,
%, 21 UT
New
Characteristics of the ionospheric oscillations with periods between 2 and
20 days are derived from GPS TEC data at single longitude, 75 oW, range
of geographic latitudes from 40oS to 40oN, and for the two-month period,
January – February, 2010. The GPS TEC data is binned in 1-hour bins
for this analysis. We use finite impulse response filter with Hamming
window and forward/backward running.
Figure 5. Example of temporal variation in the 2-day wave activity at 30oS and 75oW for
January – February 2010. Blue line shows time series of TEC data in 1-hour bins. Black line
presents daily mean TEC (16-day running average) and characterizes seasonal change in TEC.
Red line describes 2-day wave, and the green line shows amplitude series (upper envelope).
Amplitude of the 2-day wave reaches ~2 TECu prior to the SSW event and decreases during
the SSW event. It is not clear if decrease in the 2-day wave amplitude is related to the
stratospheric warming.
Figure 6. Daily mean TEC (16-day running average) from 40oS to 40oN and 75oW for the
January – February, 2010 period. Increase in daily mean TEC after day 40 reflects combined
effects of increased solar flux (see F10.7 index in Figure 1) and seasonal change in TEC.
Decrease in daily mean TEC is observed concurrently with the SSW event at all latitudes.
Analysis of longer time series is planned for the future to examine the effects of varying solar flux
and to determine if the decrease in daily mean TEC is related to the SSW event or to the seasonal
change.
Figure 7. Amplitude of planetary wave-type oscillations in
TEC as function of time and wave period for several
latitudes (27oS, 12oS, 3oN, 18oN – southern and northern crests
of equatorial ionization anomaly, magnetic equator, and latitude
above northern crest). Strongest oscillations are found for the 2day and 5-6 day periods, though 8-10 day and 16-day waves
are also present.
Figure 8. Amplitude of planetary wave-type oscillations in
TEC as function of time and geographic latitude for
selected wave periods (2-day, 5-day, 10-day, 16-day). The
2-day wave activity is dominant and reaches 4 TECu in the
EIA crests. Decrease in the 2-day wave is observed during
the SSW event at different latitudes. Complex patterns are
observed for other wave periods.
Figure 3. Observations of ionospheric behavior during stratospheric warming.
Top panels: Typical distribution of total electron content (TEC) in the western
hemisphere at 15 UT (left) and 21 UT (right). Black line shows magnetic equator.
Middle panels: TEC in the morning sector (15 UT) and afternoon sector (21 UT) on
Jan 31, 2010, during SSW. Increase in TEC is observed in the extended range of
longitudes and latitudes in the morning. In contrast to observations during morning
hours, in the afternoon TEC is decreased.
Bottom panels: TEC change expressed in percents. The observed features are
similar to those reported for SSW events of 2008 and 2009, but smaller in
magnitude.
Figure 4. TEC variations at 75oW in local time
and latitude during the January 2010 SSW
event. Top panel – multi-day mean TEC prior to
SSW, determined from data on January 3-9,
2010. Lower panels – difference in TEC from the
mean state during the SSW. Starting on January
25, semidiurnal signature appears in differential
TEC as increase in TEC in the morning and
decrease in TEC in the afternoon, with
secondary weaker increase at 20-22 LT. The
change in TEC reaches maximum values on
February 2, 2010. Though the geomagnetic
activity increases on February 1-3, essential
features of the TEC variation remain the same.
Same as
other SSW events
SSW signature in TEC data
appears as 12-hour wave, with
increase in TEC at ~8-10 LT,
decrease in TEC at 16-18 LT,
and secondary increase at 2022 LT.
Acknowledgments. Work at the MIT Haystack Observatory has been supported by NSF cooperative agreement with the MIT.