mtm observations using three incoherent scatter...
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MTM Observations Using Three Incoherent Scatter Radars
Abstract We compare incoherent scatter radar (ISR) observations of the midnight temperature maximum (MTM) collected at three sites: the Jicamarca Radio Observatory, Peru (-11.95°, 283.13°), the Millstone Hill Observatory, USA (42.62°, 288.51°), and the Arecibo Observatory, Puerto
Rico (18.35°, 293.25°). The MTM is a local maximum in the neutral temperature around midnight. Variations in the nighttime plasma temperatures Te and Ti, determined by ISR techniques, should reflect variations in the neutral temperature Tn. We characterize the MTM in terms of
amplitude, time of occurrence and width. We present data on the seasonal dependence of the amplitude and time of occurrence of the MTM along with an analysis of the altitude dependence. These three sites allow us to exam the latitudinal extent of the MTM. Data from Millstone
Hill are obtained using south pointing low elevation scans. This provides us with data between 30° and 34° N. We have observed the MTM at multiple altitudes, between 250 and 400 km at all three sites. Nights with simultaneous observations of the MTM using the Arecibo ISR and
the Millstone Hill ISR are analyzed. Preliminary results indicate that the MTM occurs later at Millstone Hill and earlier at Jicamarca. It also appears that the amplitude is greater at higher latitudes.
Introduction The midnight temperature maximum (MTM) is a local maximum in the neutral
temperature around midnight. It is thought to be caused by the combination of in-situ
thermal excitation, ion-neutral momentum coupling and lower atmosphere tidal waves
penetrating into the thermosphere. The absence of any plasma production by absorption of
EUV radiation during the night allows the electron and ion temperatures to relax to the
neutral temperature in the thermosphere. Thus variations in the nighttime plasma
temperatures Te and Ti, determined by ISR techniques, should reflect variations in the
neutral temperature Tn. The MTM has been studied using incoherent scatter radar (ISR)
since this technique was developed. Figure 1(a) shows a statistical study of the MTM at
Jicamarca from Bamgboye and McClure (B&M) (1982) showing that the MTM occurs
earlier in local summer and later during local winter. Figure 1(b) shows an MTM at
Arecibo in 1971 reported by Harper (1973) who only analyzed five nights.
Fig 2 (a) An example of the fitting procedure on data from Arecibo at 293 km on the night of 16
Nov 1990 from Martinis et al. (2013). The purple line shows where we define the time of
occurrence. The amplitude is the difference between the green line and the blue line at the time of
occurrence. (b) Ion and electron temperatures during the nighttime period. Ion temperatures are in
black and electron temperatures are in red.
For this study we are comparing MTM data taken
from three different sites: the Jicamarca Radio
Observatory, Peru, the Millstone Hill Observatory,
USA , and the Arecibo Observatory, Puerto Rico.
Jicamarca and Arecibo are at similar geographic
latitudes in opposite hemispheres but are at different
This Work
Fig 5 Seasonal behavior of the local time of occurrence of the MTM at 300 km (a) and 330 km (b).
The asterisks are the mean for the given month. Bars represent 1 sigma variability.
The Jicamarca Radio Observatory allows us to study the MTM in the southern
hemisphere and very close to the magnetic equator. Figure 6(a) shows an MTM at
Jicamarca on 11 March 2011 at 24 LT.
Fig 6 (a) Ti and (b) Ne versus time and altitude at Jicamarca on the night of 11 Mar 2011.
In Figure 6 we see that in addition to the temperature enhancement there is also an
enhancement in electron density that is correlated with the temperature increase. We
developed a technique to easily extract one altitude from these color plots and fit the data
with the technique employed to analyze Arecibo data (Fig 7(a)).
Fig 7 (a) An analysis of ion temperature at Jicamarca at 300 km on 11 Mar 2011. (b) Another
example of an MTM on 6 Oct 2010 at 300 km
We present a statistical study similar
to the one done at Arecibo. Ti data
before 1996 were not available,
including the 1960s data used in the
B&M study. Results for 250 km and
300 km are shown in Fig 8. There is
not enough data to make any
conclusions about seasonal variation
but we can note that the trend is not
consistent with the seasonal
variation from B&M (Figure 1(a)).
Fig 8 Seasonal behavior of the local time of occurrence of the MTM at 250 km (a) and 300 km (b) at
Jicamarca. The asterisks are the mean of the data for the given month. Bars represent 1 sigma
variability
The Millstone Hill Observatory has a steerable ISR that
gives us the ability to look at ionospheric parameters at
multiple altitudes and multiple latitudes on a given night
(Fig 9).We have been able to observe several instances
of the MTM using the Millstone Hill (MH) ISR when it
was collecting data from ~30° N. Two nights with an
MTM detected using the MH ISR in its low elevation
scans are shown in Figures 10(a) and 11(a). Data from
the Arecibo ISR were also available for these nights and
are shown in Figures 10(b) and 11(b).
Summary
Fig 11 Observations of an MTM on 6 Mar 1989 using (a) the Millstone Hill ISR at 32° N (a) and (b)
the Arecibo ISR. The MTM is visible at multiple altitudes from both sites.
The ISR ionospheric model
(ISRIM), a semi-empirical
model developed at MIT
Haystack, is used to reproduce
the MTM from 6 March 1989.
The model outputs what is
expected for a given day of the
year but has no yearly
dependence. The model shows
the MTM at 32° N at ~2 LT
(Fig 12(a)) and Arecibo ~1 LT
Fig 10 Observations of an MTM on 12 Jul 1988 using the (a) Millstone Hill ISR at 34° N
and (b) the Arecibo ISR.
Two important characteristics of the MTM are amplitude of the enhancement and time of
occurrence, both determined here by a function that takes into account diurnal,
semidiurnal and terdiurnal components. The resulting curve is shown in Fig 2(a). In order
to obtain reliable data, nighttime ion and electron temperatures must be equal. Figure 2(b)
shows that ion and electron temperatures are equal during the time the MTM is observed.
.
Fig 1 (a) A statistical study of the time of occurrence of the MTM at Jicamarca using data from 1967 to
1969 (B&M, 1982). (b) An MTM at Arecibo on 26 March, 1971 at 345 km (Harper 1973).
(a) (b)
(b)
Fig 9. Diagram of the Millstone Hill elevation scan process (Oliver, 1984)
Fig 12 Model outputs from the ISR ionospheric model , a semi-
empirical model developed at MIT Haystack, for 6 March at 300
km. (a) At 32° N the MTM is clearly visible. (b) At Arecibo the
MTM is not as prominent but is still visible.
Only recently has the MTM been reproduced successfully in modeling, Key to this success
was the inclusion of varying lower atmosphere sources. We compare data from Arecibo to
outputs from the Whole Atmosphere Model (WAM) (Akmaev et al., 2009). Figure 13(a)
shows all the usable data from March at 300 km at Arecibo. We compare this with the
WAM output in Figure 13(b). The average amplitude at Arecibo (~45 K) agrees with the
model and the overall shape of the average Ti from 18 LT to 6 LT is the same, including
the MTM. The effect of solar activity can be seen in the wide range of Ti, although MTM
amplitudes do not vary much.
Fig 13 (a) All the usable March data from Arecibo. The red line represents the average of the data and
clearly shows an MTM with an amplitude of 45 K. (b) The WAM output at 20 ° N showing the MTM
for March. (c) Seasonal variation of the MTM at Arecibo from the WAM model.
(a) (b)
Dustin Hickey1, C. Martinis1, A. Wright1, W. Oliver1, P. Erickson2, L. Goncharenko2, L. Condori3, N. Aponte4, C.Brum4 1Center for Space Physics, Boston University, 2MIT Haystack Observatory , 3Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, 4Atmospheric Group, Arecibo Observatory, Arecibo, Puerto Rico
Site Observed Latitude
Jicamarca -11.95°
Arecibo 18.35°
Millstone Hill 25°-35°
We looked at the seasonal variation of the MTM at
three different altitudes: 300 km, 330 km, and 367 km.
We started at 300 km (Fig 2) but there was not enough
reliable data to produce statistically significant results.
Fig 3 (a) An apparent MTM in Ti for the 5 Oct 1983 at 308 km. (b) Te is plotted as well (red)
showing how Te and Ti are inconsistent. (c) Ne profiles for Figure 2 (blue) at 2359 LT and Figure
3(a) (black) at 0138 LT
Fig 4 MTM amplitude as a function of
F10.7 for 300 km (red) and 367
(black). The larger points are binned
data with error bars
Figure 3(a) shows an apparent MTM at 0130 LT. The Te vs. Ti test shown in Fig 3(b)
indicates that they are very different at 300 km at Arecibo. This implies that the technique
employed to derive the ionospheric parameters is not providing a correct result. Around
75% of all the cases analyzed at Arecibo at 300 km showed this problem. Low electron
density and large height gradients can affect the way parameters are determined. Fig 3(c)
shows density profiles for these two nights at Arecibo. The 5 October 1983 data (black
curve) shows relatively small electron density (Ne), with no significant height gradient,
while the 16 Nov 1990 data has large Ne with a large height gradient. When studying the
Jicamarca data, the nighttime Te and Ti are forced to be equal.
WAM outputs can be used to investigate seasonal variability. Figure 13(c) shows the
seasonal variability of time of occurrence of the MTM at 300 km. It has a similar trend as
the results in Fig 5 and has similar scattering in the data. This reflects the significant day-
to-day variability existing in the upper atmosphere when coupling from the lower
atmosphere plays an important role.
• The MTM results indicate large day-to-day variability in the upper atmosphere. Data were
fitted using a function including different tidal modes. Proper determination of Ti values
depends on the ionospheric conditions. At Arecibo at night, a ratio Te/Ti different than one
implies bad data, at Jicamarca the ratio is set to one, and at MH the ratio can be different
than one, and data can still be used.
• The MTM occurs earlier in local summer at Arecibo, consistent with the B&M study at
Jicamarca. Conversely, recent results from Jicamarca indicate a later occurrence time when
compared with the B&M study.
• A statistical analysis of the MTM amplitude shows a slightly earlier and greater amplitude
MTM at Jicamarca when compared to Arecibo. Results from MH show the MTM
occurring later and with greater amplitude when compared to Arecibo.
• Model results from WAM and the ISRIM are consistent with the radar observations of the
MTM. They also show similar large variability. Imaging observations show MTM effects
occurring at higher latitudes in the southern hemisphere.
References
Akmaev R. A., et al., Tidal variability in the lower thermosphere: Comparison of Whole Atmosphere Model (WAM) simulations with observations from TIMED, Geophys. Res. Lett., 35, 2008
Bamgboye, D.K, and McClure, J.P. , Seasonal Variation in the Occurrence of the Equatorial Midnight Temperature Bulge, Geophysical Research Letters 9 4 (1982), pp. 457–460
Faivre, M., J. W. Meriwether, C. G. Fesen, and M. A. Biondi (2006), Climatology of the midnight temperature maximum phenomenon at Arequipa, Peru, J. Geophys. Res., 111, A06302
Harper R.M., Nighttime meridional neutral winds near 350 km at low to mid-latitudes, Journal of Atmospheric and Terrestrial Physics, 1978, Vol 35, pp. 2023-2034
Martinis, C., et al., The midnight temperature maximum from Arecibo incoherent scatter radar ion temperature measurements. Journal of Atmospheric and Solar-Terrestrial Physics (2013)
Oliver, W. L., Millstone Hill incoherent scatter observations of exospheric temperature over 25 to 60 degrees north latitude, Geophysical Research Letter, vol. 11, Sept. 1984, p. 915-91
Data were taken during a period of 44 years under very
different solar activity conditions. Figure 4 shows how
MTM amplitude and F10.7 index compare at 300 km
(red) and 367 km (black). There is little correlation,
consistent with previous Fabry Perot Interferometer
results (Faivre et al, 2006). This is an important result
when trying to explain the mechanisms responsible for
MTM generation.
Model Comparisons
Millstone Hill and Arecibo
Optical Comparisons
(a) (b)
Jicamarca and Arecibo
20 21 22 23 24 1 2 3 4 5
240
260
280
300
320
340
360
380
400
11-12 March 2011
Local Time
Alt
itu
de
(km
)
600
700
800
900
1000
1100Ti (K)
20 21 22 23 24 1 2 3 4 5
240
260
280
300
320
340
360
380
400
Local Time
11-12 March 2011
Alt
itu
de
(km
)
0
5
10
15
x 1011
Ne (m
-3)
Arecibo
geomagnetic latitudes. We use data from the Millstone Hill Observatory during low
elevation scans to analyze ionospheric parameters closer to Arecibo.
(c)
(a)
The technique provides more reliable data at heights above 300 km, so we looked at ~330
km and ~367 km (height resolution is ~37 km). For comparison we present data from 300
km and 330 km in Fig 5. Significant scatter is observed at both heights but an overall
trend shows earlier occurrence time during local summer. More data is available at 330
km and also has significant scatter. The monthly means show that MTM occurs earlier in
the local summer, consistent with Figure 1(a).
(a) (b)
(b) (a)
(a) (b)
Fig 14 (a) A BW on 12 Mar 2011 from El Leoncito ASI.
(b) Another case observed on 6 Oct 2010 at the same site.
Average MTM Characteristics at Arecibo
300 km (52 cases) 330 km (229 cases)
Amplitude Time Amplitude Time
61 K 0033 LT 51 K 0011 LT
Average MTM Characteristics at Jicamarca
250 km (39 cases) 300 km (50 cases)
Amplitude Time Amplitude Time
93 K 0038 LT 86 K 0010 LT
(b)
Arecibo
(b)
Millstone Hill
(a)
Our results show that the MTM occurs significantly later in September and October
compared with the B&M study. As with Arecibo there is significant scatter but we can
note that, on average, the MTM appears earlier at Jicamarca than it does at Arecibo..
(a)
The midnight collapse that is
sometimes associated with the
MTM can create an optical
signature known as a brightness
wave (BW), an increase in
brightness that propagates
polewards. We have 4 nights
where we observed an MTM at
Jicamarca and an all-sky imager
at El Leoncito, Argentina (~30° S)
Millstone Hill
(a)
Arecibo
(b)
detected a BW. Figure 14 shows brightness zenith averages from the same nights as
Figure 7. The BW occurs ~ 2-3 hours later than the MTM observed at Jicamarca in both
cases. Out of the 44 ISR dates with Ti data since 2006, the ASI detected 23 BWs,
13 nights with no BWs, and 8 nights with clouds or no data.
(c)
(Fig 12(b)). The amplitudes are smaller than the observations.
(a) (b)
(a) (b)
Millstone Hill Arecibo
Amplitude Time Amplitude Time
12 Jul 1988 ~100 K ~3 LT ~60 K ~1 LT
6 Mar 1989 ~100 K ~3 LT ~30 K ~2 LT