The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally... more
The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric disturbances (TIDs) radially outbound and inbound along entire Great-Circle loci at primary speeds of ∼300–350 m/s (depending on the propagation direction) and 500–1,000 km horizontal wavelength for front shocks, going around the globe for three times, passing six times over the continental US in 100 h since the eruption. TIDs following the shock fronts developed for ∼8 h with 10–30 min predominant periods in near- and far- fields. TID global propagation is consistent with the effect of Lamb waves which travel at the speed of sound. Although these oscillations are often confined to the troposphere, Lamb wave energy is known to leak into the thermosphere through channels such as atmospheric resonance at acoustic and gravity wave frequencies, carrying substantial wave amplitudes at high altitudes. Prevailing Lamb waves have been reported in the literature as atmospheric responses to the gigantic Krakatoa eruption in 1883 and other geohazards. This study provides substantial first evidence of their long-duration imprints up in the global ionosphere. This study was enabled by ionospheric measurements from 5,000+ world-wide Global Navigation Satellite System (GNSS) ground receivers, demonstrating the broad implication of the ionosphere measurement as a sensitive detector for atmospheric waves and geophysical disturbances.
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<p>During Sudden Stratospheric Warming events, the ionosphere exhibits phase-shifted semi-diurnal perturbations, which are typically attributed to vertical coupling associated with the semi-diurnal lunar tide (M2). Our... more
<p>During Sudden Stratospheric Warming events, the ionosphere exhibits phase-shifted semi-diurnal perturbations, which are typically attributed to vertical coupling associated with the semi-diurnal lunar tide (M2). Our understanding of ionospheric responses to M2 is limited. This study focuses on fundamental vertical coupling processes associated with the latitudinal extent and hemispheric asymmetry of ionospheric M2 signatures, using total electron content data from the eastern Asian and American sectors. Our results illustrate that the asymmetry maximizes at around 15°N and 20°S magnetic latitudes. In the southern hemisphere, the M2-like signatures extend deep into midlatitude and, in the American sector, encounter the Weddell Sea Anomaly. The M2 amplitude is larger in the northern hemisphere and such asymmetry is more distinct in the eastern Asian sector. The hemispheric asymmetry of M2 signatures in the low latitude can be primarily explained by the trans-equatorial wind modulation of the equatorial plasma fountain. Other physical processes could also be relevant, including hemispheric asymmetry of the M2 below the F region, the ambient thermospheric composition and ionospheric plasma distribution, and the geomagnetic field configuration.</p>
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One of the most important requirements for the space weather community is to improve ionospheric predictions for HF radio communications. During geomagnetic storm periods, the ionosphere undergoes dramatic variations including both... more
One of the most important requirements for the space weather community is to improve ionospheric predictions for HF radio communications. During geomagnetic storm periods, the ionosphere undergoes dramatic variations including both increases and decreases of electron density compared with quiet days. A key component of understanding the observed ionospheric variations is to also understand the neutral thermosphere variations. In this
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Travelling ionospheric disturbances (TIDs) represent a key dynamic process of energy transfer in horizontal and vertical directions, and one of the important sources of ionospheric variability. Acoustic gravity waves (AGWs) play a key... more
Travelling ionospheric disturbances (TIDs) represent a key dynamic process of energy transfer in horizontal and vertical directions, and one of the important sources of ionospheric variability. Acoustic gravity waves (AGWs) play a key role in coupling of different atmospheric regions through momentum and energy transfer, and TIDs are thought to be the manifestations of AGWs at ionospheric heights. The incoherent scatter method is well suited for TID studies as it enables TIDs detection in multiple ionospheric parameters (electron density, ion and electron temperatures, plasma velocity), and thus provides critical information needed to examine different hypothesis about association of TIDs with their sources. In 2016, two coordinated measuring campaigns have been held near the vernal equinox and summer solstice using Kharkiv (49.6 N, 36.4 E) and Millstone Hill (42.6 N, 288.5 E) IS radars. The goal of joint observations was to detect TIDs and estimate their characteristics during thes...
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ABSTRACT A strong positive storm phase was observed by both the Millstone Hill and Arecibo incoherent scatter radars during a moderate geomagnetic storm on 10 September 2005. The positive storm phase featured an interesting UT–altitude... more
ABSTRACT A strong positive storm phase was observed by both the Millstone Hill and Arecibo incoherent scatter radars during a moderate geomagnetic storm on 10 September 2005. The positive storm phase featured an interesting UT–altitude profile of the F region electron density enhancement that closely resembles the Greek letter L. The radar measurements showed that the uplift of the electron density peak height corresponded to a strong upward ion drift, whereas the subsequent falling of the peak height coincided with a downward ion drift. Using realistic, time-dependent ionospheric convection and auroral precipitation as input, the thermosphere– ionosphere electrodynamics general circulation model (TIEGCM) is able to reproduce the same L-like structure in the electron density profile, along with many large-scale features in electron temperature and vertical ion drift as observed by the radars. Over the 3-day period of 8–10 September, our simulation results show an error of 1%–4% for hmF2, electron, and ion temperatures at both radar locations. The estimated error for NmF2 is about 9% at Millstone Hill and 19% at Arecibo. However, the simulated vertical ion drifts are less accurate, with the normalized root-mean-square errors of 72% at Millstone Hill and 52% at Arecibo, due largely to model’s inability to capture the large temporal fluctuations measured by the radars. However, it reproduces reasonably well the overall large-scale variations during the 3-day period, including the storm-time-enhanced upward ion drift that is responsible for the interesting F region density profile. The model is also able to reproduce the temporal and spatial total electron content variations as shown in the global GPS maps. The comparison with the GUVI O/N2 is less satisfactory, although there is a general agreement in terms of relative O/N2 changes during the storm in the longitudinal sector between 60°W and 80°W where the radars are located. The detailed data–model comparison carried out in this study is helpful not only to validate the model but also to interpret the complex observations. The TIEGCM simulations reveal that it is the enhanced meridional neutral wind, not the penetration electric field, that is the primary cause of the L structure of the F region electron density profile.
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The Ionospheric Data Assimilation Four-Dimensional (IDA4D) technique has been coupled to Sami3 is Another Model of the Ionosphere (SAMI3). In this application, ground- and space-based GPS Total Ele...
We present a new high resolution empirical model for the ionospheric total electron content (TEC). TEC data are obtained from the global navigation satellite system (GNSS) receivers with a 1 x 1 sp...
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This work conducts a statistical study of the subauroral polarization stream (SAPS) feature in the North American sector using Millstone Hill incoherent scatter radar measurements from 1979 to 2019...
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Ground-based spectrometers have been deployed to measure the concentration, velocity, and temperature of ozone in the mesosphere and lower thermosphere (MLT), using low-cost satellite television electronics to observe the 11.072-GHz line... more
Ground-based spectrometers have been deployed to measure the concentration, velocity, and temperature of ozone in the mesosphere and lower thermosphere (MLT), using low-cost satellite television electronics to observe the 11.072-GHz line of ozone. The ozone line was observed at an altitude near 95 km at 38°N, 71°W using three spectrometers located at the Massachusetts Institute of Technology’s Haystack Observatory (Westford, Massachusetts), Chelmsford High School (Chelmsford, Massachusetts), and Union College (Schenectady, New York), each pointed south at 8° elevation. Observations from 2009 through 2014 were used to derive the nightly averaged seasonal variation of the 95-km altitude meridional wind velocity, as well as the seasonally averaged variation of the meridional wind with local solar time. The results indicate a seasonal trend in which the winds at 95 km are directed southward at about 10 m s−1 in the summer of the Northern Hemisphere and northward at about 10 m s−1 in the...
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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... more
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. Peak stratospheric temperature at 90N and 10hPa level was reached
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For several decades, it has been well known that stratospheric sudden warming (SSW) events dramatically disrupt circulation and temperature in the stratosphere and mesosphere. Recent experimental and modeling efforts present strong... more
For several decades, it has been well known that stratospheric sudden warming (SSW) events dramatically disrupt circulation and temperature in the stratosphere and mesosphere. Recent experimental and modeling efforts present strong evidence of major variations at higher altitudes, from the lower thermosphere to the upper thermosphere and ionosphere, and in a wide range of latitudes. This progress was made possible due to the superposition of several factors: a series of strong SSW events in recent winters; prolonged unusually low levels of solar and geomagnetic activity, which allowed unambiguous determination of ionospheric effects related to the low atmosphere drivers; and coordinated efforts by the space physics community to collect and analyze data during these SSW events. We will summarize recent observational and modeling evidence of strong coupling between the stratosphere and ionosphere during SSW events. The primary features of this coupling include the tidal character of ionospheric variations, large magnitudes, and persistence of variations for several days after the peak of stratospheric warming. Both observations and numerical simulations point to the important roles of quasi-stationary planetary waves, which become strong prior to the stratospheric warmings. As these planetary waves propagate upward and equatorward, they interact non-linearly with tidal modes, producing amplification in the amplitudes of migrating and non-migrating tides in the mesosphere-lower thermosphere region. The tidal winds can modulate electric fields through the ionospheric wind dynamo (at ~115 km). At low latitudes, these modulated electric fields map along magnetic field lines to higher altitudes and produce tidal variations in vertical ion drifts, electron density, and equatorial electrojet. Significant uncertainties in our understanding of the manifestation of stratospheric sudden warmings on the middle and upper atmosphere remain, including the relative roles of different types of planetary waves, gravity waves, solar and lunar tides, changes in the background circulation, and solar activity. They present an exciting challenge for the space physics community.
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ABSTRACT Daytime neutral winds in the lower thermosphere between 90 and 130 km from Incoherent Scatter Radars at Millstone Hill Observatory (42N, 288E) and Arecibo Observatory (18N, 293E) in March 1991, and from WINDII on UARS in... more
ABSTRACT Daytime neutral winds in the lower thermosphere between 90 and 130 km from Incoherent Scatter Radars at Millstone Hill Observatory (42N, 288E) and Arecibo Observatory (18N, 293E) in March 1991, and from WINDII on UARS in March/April 1993 have similar wind structures in the local time domain. Both ground-based and space-based measurements show strong diurnal tides below 110 km and semi-diurnal tides above 110 km at 18N, and strong semi-diurnal tides at 42N. The results are also in good agreement with recent simulations from TIME-GCM. There are some discrepancies between ISR and WINDII measurements regarding the tidal amplitude and phase, partially, due to the different observation periods of the available data.
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ABSTRACT We present experimental evidence of a link between the lower atmosphere and mid-latitude thermosphere and ionosphere using observations of neutral winds and ion temperatures by Millstone Hill ISR (42.6N, 288.5E) during... more
ABSTRACT We present experimental evidence of a link between the lower atmosphere and mid-latitude thermosphere and ionosphere using observations of neutral winds and ion temperatures by Millstone Hill ISR (42.6N, 288.5E) during stratospheric warming of January 2008. Temperature data reveal alternating regions of cooling in the large altitude range (150-300 km above ground) and warming in a narrow altitude band (120- 140 km above ground). Both warming and cooling variations reach 70-80K (11-16% of the background temperature) and are pronounced mostly in the morning and afternoon hours. The temporal and altitudinal variation in the temperature anomaly suggests it might be related to semidiurnal modulation, and the amplitude of semidiurnal tide in wind data is increased around the time of maximum in stratospheric warming. We rule out seasonal trend, solar flux and geomagnetic activity as significant causes of such variation and suggest that it is associated with stratospheric warming. Alternating areas of warm and cold vertical zones in the atmosphere are a well established phenomena, with mesospheric cooling accompanying stratospheric warming. Our observations show for the first time that areas of warming and cooling extend to altitudes of upper thermosphere (up to 300 km) and suggest that processes responsible for generation of sudden stratospheric warmings may also impact the lower and upper thermosphere and ionosphere.
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ABSTRACT Magnetospheric electric fields driven by the solar wind and interplanetary magnetic field can directly penetrate from high latitudes to lower latitudes. In addition, penetration electric fields exhibit distinctive... more
ABSTRACT Magnetospheric electric fields driven by the solar wind and interplanetary magnetic field can directly penetrate from high latitudes to lower latitudes. In addition, penetration electric fields exhibit distinctive longitudinal/local time variations, with a strongly eastward penetration electric field on the dayside, which is the main cause of positive ionospheric storms, and a westward electric field on the nightside, which may lead to negative storms. Furthermore, enhanced Joule heating dissipation in the high-latitude polar region produces large pressure gradients that drive neutral winds equatorward toward mid and low latitudes, even into the opposite hemisphere. These neutral winds surges also have a strong longitudinal dependence, and thus produce longitudinal structures in the mid- and low-latitude ionosphere. This paper presents a combined observational and modeling study of the latitudinal and longitudinal variations during two events of penetration electric fields on 9 November 2004 and 17 April 2002, respectively. The NCAR Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIEGCM) will be used to illustrate some of the salient features in the ionosphere, including vertical ion drift, electron density, and global TEC. An emphasis is placed on the inter-comparison of the simulation results with radar and satellite data in order to unveil the physical processes responsible for the observed latitudinal and longitudinal variations in the mid- and low-latitude regions.
Incoherent scatter radars provide high quality physical measurements of the ionosphere which are useful for a wide variety of investigations Recently an emphasis has been placed on long duration observational runs which last on the order... more
Incoherent scatter radars provide high quality physical measurements of the ionosphere which are useful for a wide variety of investigations Recently an emphasis has been placed on long duration observational runs which last on the order of one month In October 2002 EISCAT Svalbard and Millstone Hill Radars conducted first ever long duration experiments for over 30 consective days Zhang
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To address challenges of assessment of modeling capabilities, the CCMC (Community Coordinated Modeling Center) initiated a series of community-wide model validation projects, such as the GEM, CEDAR and GEM-CEDAR Modeling Challenges. The... more
To address challenges of assessment of modeling capabilities, the CCMC (Community Coordinated Modeling Center) initiated a series of community-wide model validation projects, such as the GEM, CEDAR and GEM-CEDAR Modeling Challenges. The CEDAR ETI (Electrodynamics Thermosphere Ionosphere) Challenge focused on the ability of ionosphere-thermosphere (IT) models to reproduce basic IT system parameters, such as electron and neutral densities, NmF2, hmF2, and TEC. Model-data time series comparisons were performed for a set of selected events with different levels of geomagnetic activity (quiet, moderate, storms). The follow-on CEDAR-GEM Challenge aims to quantify geomagnetic storm impacts on the IT system. On-going studies include quantifying the storm energy input, such as increase in auroral precipitation and Joule heating, and quantifying the storm-time variations of neutral density and TEC. The community-wide model validation activities involve international collaborations (e.g., between the CCMC and UK Met Office) to enhance the studies. In this paper, we focus on results of validation of IT models for reproducing storm impacts on TEC. In order to quantify storm impacts on TEC, we considered several parameters: TEC changes compared to quiet time (the day before storm), TEC difference between 24-hour intervals, and maximum increase/decrease during the storm. We investigated the spatial and temporal variations of the parameters during storm events (e.g., 2006 AGU storm) using ground-based GPS TEC measurements in several longitude sectors where data coverage is relatively better. The latitudinal variations were also studied. We obtained modeled TEC from various IT models. The parameters from the models were compared with each other and with the observed values. We quantified performance of the models in reproducing the TEC variations during the storm using skill scores. Model output and observational data used for the challenge will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) as a resource for the space science communities to use.
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SUMMARY Space weather is a fairly new field in science today and has very interesting effects on the humans and technology in general. Geomagnetic storms are a part of space weather and the solar-terrestrial connection. These storms... more
SUMMARY Space weather is a fairly new field in science today and has very interesting effects on the humans and technology in general. Geomagnetic storms are a part of space weather and the solar-terrestrial connection. These storms greatly affect the earth's ...
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ABSTRACT Presented here are several cases of midnight temperature maximum (MTM) observations using the Millstone Hill Incoherent Scatter Radar (ISR) and Arecibo ISR. The MTM, a temperature enhancement in the upper atmosphere (at ~300 km... more
ABSTRACT Presented here are several cases of midnight temperature maximum (MTM) observations using the Millstone Hill Incoherent Scatter Radar (ISR) and Arecibo ISR. The MTM, a temperature enhancement in the upper atmosphere (at ~300 km altitude), is a poorly understood phenomenon as observations are sparse. An upward propagating terdiurnal tide and coupling between atmospheric regions may play a large part in the generation of the MTM, yet this phenomenon and its implications are not fully understood. Two nights (6 March 1989 and 12 July 1988) show clear cases of the MTM occurring between 30-34°N with amplitudes of ~100 K and at ~18°N with amplitudes of ~40 K. The MTMs occurred later at the higher latitude. Experiments in 2013 also show a clear MTM at 34° and 36° N from 250-350 km altitude. The ionospheric measurements presented here demonstrate a new application of a well-established technique to study atmospheric parameters and allow us to study the latitudinal extent of the MTM. The results provide evidence of the phenomenon occurring at latitudes and altitudes not previously sampled by radar techniques, showing that the MTM is not just an equatorial process, but one that can easily reach mid-latitudes. Simultaneous measurements with a Fabry-Perot Interferometer allow us to compare the neutral temperatures with the ion temperature. Overall, these are key observations that point to large scale effects that can help constrain model outputs at different heights and latitudes.