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Monthly mean temperature deviation from the zonal mean in December near 285 km at UT = 12:00 as a function of latitude and longitude (local time).
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Discovered almost four decades ago, the midnight temperature maximum (MTM) with typical magnitudes of 50-100 K has been regularly observed by satellite and ground-based instruments in the tropical upper thermosphere. Although several mechanisms have been suggested to explain the phenomenon, previous attempts to reproduce it with comprehensive therm...
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Context 1
... a sample horizontal structure see Figure 5), sometimes exhibiting more variability in the time of occurrence and smaller magnitudes. In agreement with the analysis of Herrero and Spencer [1982], at a given height the magni- tude is typically largest in summer (e.g., Figure 1, bottom), and it continues to increase with height in most locations. ...
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... Figure 5 presents a horizontal structure of DT near 285 km in December, which is consistent with the AE-E climatology at solstice conditions [Herrero and Spencer, 1982], including the common observation that in summer the tropical MTM peaks earlier and attains larger mag- nitudes than in winter [e.g., Faivre et al., 2006]. As the V-shape structure depicted in Figure 5 migrates westward, the MTM will appear moving poleward to an observer on the ground [Herrero and Spencer, 1982;Meriwether et al., 2008]. ...
Context 3
... Figure 5 presents a horizontal structure of DT near 285 km in December, which is consistent with the AE-E climatology at solstice conditions [Herrero and Spencer, 1982], including the common observation that in summer the tropical MTM peaks earlier and attains larger mag- nitudes than in winter [e.g., Faivre et al., 2006]. As the V-shape structure depicted in Figure 5 migrates westward, the MTM will appear moving poleward to an observer on the ground [Herrero and Spencer, 1982;Meriwether et al., 2008]. Our simulations also show the MTM extend well into mid-latitudes [cf. ...
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... A bow-wave structure of small-scale waves observed in nighttime thermospheric densities at 400 km, similar to the one seen in Figure 5, has recently prompted Forbes et al. [2008] to suggest that these waves and perhaps the MTM may be at least partially generated in situ by the fast movement of the evening terminator through the thermo- sphere. Our simulations clearly demonstrate (Figure 3) that the MTM originates in the lower thermosphere from sources possibly connected to the middle and lower atmosphere. ...
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Citations
... The influence of semidiurnal and other higher-order tides was seen during MTM (e.g., Mayr et al., 1979;Herrero et al., 1983;Fesen, 1996;Colerico and Mendillo, 2002), which caused an increase in the nightglow emission intensity during midnight and post-midnight hours. A significant magnitude of MTM was seen in simulations by the Whole Atmosphere Model, and lower atmospheric forcing was found to contribute to the MTM (Akmaev et al., 2009;Fang et al., 2016). ...
... We note that in Figure 2k the extent of the MTM in longitude is ∼30° which corresponds to 2 hr. This variability could result from tidal variability because the MTM is related to the superposition of tides (e.g., Akmaev et al., 2009;Fesen, 1996). Additionally, the relationship between the MTM and the neutral winds is dominated by tidal motions of the lower thermosphere. ...
We report results from a self‐consistent global simulation model in which a large‐scale equatorial plasma bubble (EPB) forms during a midnight temperature maximum (MTM). The global model comprises the ionospheric code SAMI3 and the atmosphere/thermosphere code WACCM‐X. We consider solar minimum conditions for the month of August. We show that an EPB forms during an MTM in the Pacific sector and is caused by equatorward neutral wind flows. Although this is consistent with the theoretical result that a meridional neutral wind (V) with a negative gradient (∂V/∂θ < 0) is a destabilizing influence [Huba & Krall, 2013, https://doi.org/10.1002/grl.50292] (where a northward meridional neutral wind V is positive and θ is the latitude and increases in the northward direction), we find that the primary cause of the EPB is the large decrease in the Pedersen conductance caused by the equatorward winds.
... The M-GITM GW model contains analogous features near the dusk terminator as well as near midnight although the locations of these features are different by 1 or 2 hr of local time. The post-midnight feature somewhat resembles the midnight temperature maximum in the Earth's thermosphere (Akmaev et al., 2009) as well as the midnight temperature enhancement at Venus (Brecht et al., 2011). The former is likely a result of wave interactions and propagation from the lower atmosphere while the latter is associated with dynamical heating. ...
Dynamical heating and cooling are prominent features of planetary atmospheres resulting in thermospheric structures on Venus, Earth and Mars. The purpose of this study is to determine the location and amplitude of localized heating regions in the Martian thermosphere, confirm that they occur in regions of wind convergence and compare the observed dynamical heating with that predicted by a global thermospheric model. This investigation uses several years of data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission including observations made by the Neutral Gas and Ion Mass Spectrometer (NGIMS) as well as the Extreme Ultraviolet Monitor (EUVM). Specifically, the analysis focuses on several years of horizontal wind, temperature, and composition data. EUVM measurements provide a solar forcing context for the neutral thermosphere data sets and aid in the statistical analysis. Statistical results are compared with two versions of the Mars Global Ionosphere Thermosphere (M‐GITM) global circulation model: one that includes gravity wave parametrization and a version without gravity wave effects. Data analysis indicates that heating features exist around 2–3 and 17–18 local solar time. These locations coincide with regions of converging winds and are in better agreement with M‐GITM when a gravity wave parametrization is included in the model. An oscillation in the observed wind field also results in convergence and a density enhancement near 15 local time. While a similar oscillation is reproduced by the model, the amplitude is much lower than observed and may be a result of modeled zonal winds that are too low.
... The MTM is an increase in temperature that occurs near local midnight. Modeling work suggests that the MTM should extend from low-latitudes into midlatitudes (Akmaev et al., 2009) and recent observations have supported this prediction (Hickey et al., 2014). The MTM has been observed in both the northern and southern hemispheres, away from the magnetic equator, as a rapidly moving airglow enhancement associated with and following an increase in the thermosphere temperature (e.g., M. J. Colerico et al., 2006;Herrero & Spencer, 1982;Hickey et al., 2018;Spencer et al., 1979). ...
... This understanding of the MTM temperature and pressure bulge was supported by earlier radar studies by Behnke and Harper (1973) and Harper (1973), who demonstrated that a reversal of the meridional component of the thermospheric winds from equatorward to poleward forced the ionosphere downward, causing the brightness of the brightness wave (Friedman & Herrero, 1982). Recent modeling efforts have shown the importance of the semidiurnal, terdiurnal, and high order wave modes in the production of the MTM (Akmaev et al., 2009;Fesen, 1996). The MTM and its characteristic wind patterns (equatorward before the bulge passes; poleward after the bulge passes) tend to appear earlier near the equator and later at higher latitudes (Akmaev et al., 2009;Hickey et al., 2014). ...
... Recent modeling efforts have shown the importance of the semidiurnal, terdiurnal, and high order wave modes in the production of the MTM (Akmaev et al., 2009;Fesen, 1996). The MTM and its characteristic wind patterns (equatorward before the bulge passes; poleward after the bulge passes) tend to appear earlier near the equator and later at higher latitudes (Akmaev et al., 2009;Hickey et al., 2014). ...
The SAMI3/equatorial spread F (Sami3 is also a model of the ionosphere/ESF) code is used to simulate the growth of equatorial plasma bubbles in the presence of a background wind field based on measured winds. The measured winds exhibit the well‐known “midnight temperature maximum” (MTM) pattern, in which an equatorward wind occurs simultaneously with a cessation in the zonal wind. The MTM is often preceded by strong equatorward winds (about 100 m/s). The circumstance where the MTM winds are symmetric across the equator is considered; here the meridional wind component in the southern hemisphere is the reverse of the northern meridional wind. The timing of the wind pattern relative to the imposition of a seed for the ESF instability is explored. We find that the simultaneous occurrence of a seed wave and a strong converging meridional wind pattern can produce post‐midnight ESF. We further find that the seed wave and the sudden cessation of the zonal winds can also produce post‐midnight ESF. The Magnetic mEridional NeuTrAl Thermospheric code verifies the occurrence of converging meridional wind patterns such as those simulated here, based on ionosonde data. Results suggest that regional‐scale wind measurements would aid in the prediction signal‐disrupting ionospheric bubbles.
... The MTM is an increase in temperature that occurs near local midnight. Modeling work suggests that the MTM should extend from low-latitudes into midlatitudes (Akmaev et al., 2009) and recent observations have supported this prediction (Hickey et al., 2014). The MTM has been observed in both the northern and southern hemispheres, away from the magnetic equator, as a rapidly moving airglow enhancement associated with and following an increase in the thermosphere temperature (e.g., M. J. Colerico et al., 2006;Herrero & Spencer, 1982;Hickey et al., 2018;Spencer et al., 1979). ...
... This understanding of the MTM temperature and pressure bulge was supported by earlier radar studies by Behnke and Harper (1973) and Harper (1973), who demonstrated that a reversal of the meridional component of the thermospheric winds from equatorward to poleward forced the ionosphere downward, causing the brightness of the brightness wave (Friedman & Herrero, 1982). Recent modeling efforts have shown the importance of the semidiurnal, terdiurnal, and high order wave modes in the production of the MTM (Akmaev et al., 2009;Fesen, 1996). The MTM and its characteristic wind patterns (equatorward before the bulge passes; poleward after the bulge passes) tend to appear earlier near the equator and later at higher latitudes (Akmaev et al., 2009;Hickey et al., 2014). ...
... Recent modeling efforts have shown the importance of the semidiurnal, terdiurnal, and high order wave modes in the production of the MTM (Akmaev et al., 2009;Fesen, 1996). The MTM and its characteristic wind patterns (equatorward before the bulge passes; poleward after the bulge passes) tend to appear earlier near the equator and later at higher latitudes (Akmaev et al., 2009;Hickey et al., 2014). ...
... The MTM is an increase of about 50 to 200 K in neutral temperature in the upper atmosphere that creates a local maximum in the temperature near local midnight. The formation mechanism for the MTM is not fully understood but results from the Whole Atmosphere Model (WAM) indicate that the generation of the MTM may be largely due to effects from an upward propagating terdiurnal tidal wave in addition to other, smaller, nonlinear interaction effects (Akmaev et al., 2009). Recent observations of the MTM and its effects support this explanation (e.g., Hickey et al., 2014Hickey et al., , 2018. ...
The midnight temperature maximum (MTM) and equatorial spread F (ESF) are common processes in the low‐latitude ionosphere and thermosphere. This work shows the first interaction between the brightness wave (BW), associated with the MTM, and plasma depletions, associated with ESF. Observations from the El Leoncito all‐sky imager (ASI) (31.8°S, 69.3°W, 19.7°S magnetic latitude) show concurrent observations of a plasma depletion and a BW. As the BW passes through the depletion, the depletion is modified and becomes an enhancement. Concurrent measurements at the conjugate location show an airglow depletion, indicating that the enhancement is an evolution of the depletion and not a separate feature and that it only occurs in one hemisphere. Previous model results were able to recreate the evolution of an airglow depletion into an enhancement when there is a poleward wind combined with converging zonal winds. We discuss how these wind conditions are often associated with the MTM/BW and can explain this observed enhancement.
... The combination of temperature and density, which has been shown to cause non-monotonic results in this study, may very well be an im- portant factor in the study of MTM. Thus, if one wants to fully reproduce the observation results, we suggest other ex- tra factors associated with temperature variations should also be considered, such as different tidal modes from the lower atmosphere ( Akmaev et al., 2009). Our findings of the turn- ing temperature tendencies can help as a guide for choos- ing the background temperature in future modeling attempts to obtain intensities of nightglow brightness comparable to those observed from ground or from space. ...
The ISUAL payload onboard the FORMOSAT-2 satellite has often observed airglow
bright spots around midnight at equatorial latitudes. Such features had been
suggested as the signature of the thermospheric midnight temperature maximum
(MTM) effect, which was associated with temperature and meridional neutral
winds. This study investigates the influence of neutral temperature and
meridional neutral wind on the volume emission rates of the 630.0 nm
nightglow. We utilize the SAMI2 model to simulate the charged and neutral
species at the 630.0 nm nightglow emission layer under different
temperatures with and without the effect of neutral wind. The results show
that the neutral wind is more efficient than temperature variation in
affecting the nightglow emission rates. For example, based on our estimation,
it would require a temperature change of 145 K to produce a change in the
integrated emission rate by 9.8 km-photons cm−3 s−1, while it only
needs the neutral wind velocity to change by 1.85 m−1 s−1 to
cause the same change in the integrated emission rate. However, the emission
rate features a local maximum in its variation with the temperature. Two
kinds of tendencies can be seen regarding the temperature that corresponds to
the turning point, which is named the turning temperature (Tt) in
this study: firstly, Tt decreases with the emission rate for the
same altitude; secondly, for approximately the same emission rate,
Tt increases with the altitude.
... These wind dynamics are critical for specific modeling studies such as the h m F 2 midnight collapse phenomena (Behnke & Harper, 1973;Crary & Forbes, 1986;Dandenault & Richards, 2015;Harper, 1979;Macpherson et al., 1998;Nelson & Cogger, 1971;Seker et al., 2009;Vlasov et al., 2005) and the local variations in thermospheric temperature and density near midnight (Akmaev et al., 2009(Akmaev et al., , 2010Ruan et al., 2014). In the equilibrium case with the ionosphere sunlit, the O + production rate rapidly exceeds the loss rate with increasing altitude in the F 2 region. ...
A global database of ionosonde hmF2 observations was used to develop a global database of equivalent neutral winds, which was then used to develop a new empirical horizontal neutral wind model called the Magnetic mEridional NeuTrAl Thermospheric model. In this paper, we (1) developed and optimized a technique for deriving magnetic meridional thermospheric neutral winds using the altitude of the peak ionosphere (hmF2) observations from bottomside ionospheric sounders, (2) validated these neutral winds with observations from Fabry-Pérot interferometers (FPIs), (3) developed a new model of horizontal, magnetic meridional, equivalent neutral winds in the midlatitude regions from a global database of ionosonde observations spanning the years 1961 to 1990. Our new method for generating the winds compares well with FPI wind observations and illuminates nonphysical behavior in the horizontal thermospheric neutral wind model. Magnetic mEridional NeuTrAl Thermospheric neutral winds compare well with FPI wind observations over both short- and long-time periods, and the model produces winds as a function of the year, day of year, universal time, solar flux, geographic latitude, and geographic longitude. Two major findings are (1) a distinct solar cycle wind variation that was not captured in other empirical models using other data sets and (2) global measurements of ionospheric hmF2, which provide constraints on the global wind field that is particularly valuable considering the persistent lack of space-based F region winds and the inability of FPIs to operate during the day, when cloudy, or under moon-up conditions. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.
... The MTM latitudinal structure was recently modeled by Akmaev et al. (2009) to be a wake-wave shaped disturbance in temperature with a phase lag relative to the latitude; i.e., the timing of the MTM peak occurs later in the evening at higher latitudes. Their study confirms the MTM as be- ing a result of the thermal part of the constructive interfer- ence between the upward propagating and in situ diurnal, semi-diurnal, and other higher-order migrating tidal modes ( Akmaev et al., 2009;Akmaev, 2011). ...
... The MTM latitudinal structure was recently modeled by Akmaev et al. (2009) to be a wake-wave shaped disturbance in temperature with a phase lag relative to the latitude; i.e., the timing of the MTM peak occurs later in the evening at higher latitudes. Their study confirms the MTM as be- ing a result of the thermal part of the constructive interfer- ence between the upward propagating and in situ diurnal, semi-diurnal, and other higher-order migrating tidal modes ( Akmaev et al., 2009;Akmaev, 2011). Among these im- portant findings, Akmaev et al. (2009) found evidence for a weak secondary maximum in their Whole Atmosphere Model (WAM) occurring earlier in the evening. ...
... Their study confirms the MTM as be- ing a result of the thermal part of the constructive interfer- ence between the upward propagating and in situ diurnal, semi-diurnal, and other higher-order migrating tidal modes ( Akmaev et al., 2009;Akmaev, 2011). Among these im- portant findings, Akmaev et al. (2009) found evidence for a weak secondary maximum in their Whole Atmosphere Model (WAM) occurring earlier in the evening. This result agrees with the detection of a secondary MTM peak that was reported by Faivre et al. (2006) from observations in the Pe- ruvian sector. ...
Fabry–Perot interferometer (FPI) measurements of thermospheric temperatures and winds show the detection and successful determination of the latitudinal distribution of the midnight temperature maximum (MTM) in the continental mid-eastern United States. These results were obtained through the operation of the five FPI observatories in the North American Thermosphere Ionosphere Observing Network (NATION) located at the Pisgah Astronomic Research Institute (PAR) (35.2° N, 82.8° W), Virginia Tech (VTI) (37.2° N, 80.4° W), Eastern Kentucky University (EKU) (37.8° N, 84.3° W), Urbana-Champaign (UAO) (40.2° N, 88.2° W), and Ann Arbor (ANN) (42.3° N, 83.8° W). A new approach for analyzing the MTM phenomenon is developed, which features the combination of a method of harmonic thermal background removal followed by a 2-D inversion algorithm to generate sequential 2-D temperature residual maps at 30 min intervals. The simultaneous study of the temperature data from these FPI stations represents a novel analysis of the MTM and its large-scale latitudinal and longitudinal structure. The major finding in examining these maps is the frequent detection of a secondary MTM peak occurring during the early evening hours, nearly 4.5 h prior to the timing of the primary MTM peak that generally appears after midnight. The analysis of these observations shows a strong night-to-night variability for this double-peaked MTM structure. A statistical study of the behavior of the MTM events was carried out to determine the extent of this variability with regard to the seasonal and latitudinal dependence. The results show the presence of the MTM peak(s) in 106 out of the 472 determinable nights (when the MTM presence, or lack thereof, can be determined with certainty in the data set) selected for analysis (22 %) out of the total of 846 nights available. The MTM feature is seen to appear slightly more often during the summer (27 %), followed by fall (22 %), winter (20 %), and spring (18 %). Also seen is a northwestward propagation of the MTM signature with a latitude-dependent amplitude. This behavior suggests either a latitudinal dependence of thermosphere tidal dissipation or a night-to-night variation of the composition of the higher-order tidal modes that contribute to the production of the MTM peak at mid-latitudes. Also presented in this paper is the perturbation on the divergence of the wind fields, which is associated with the passage of each MTM peak analyzed with the 2-D interpolation.
... The MTM is an increase in neutral temperature that occurs in the thermosphere around local midnight (Spencer et al., 1979). Equatorial spread F has significant impacts on space weather such as disrupting navigation and communications signals through scintillation (Kintner et al., 2001) and the temporal and spatial variations of the MTM help to describe the role that lower atmospheric tides have on the upper atmosphere (Akmaev et al., 2009). ...
... We present another explanation for the time delay between the observation of the MTM at Jicamarca and the BW occurrence at El Leoncito, based on global model results of the MTM. Akmaev et al. (2009) used a whole atmosphere model (WAM) to reproduce the MTM that shows an apparent poleward motion due to its morphology. The simulated MTM occurs over a range of latitudes and longitudes such that it makes a sideways "V" shape in longitude-latitude space, consistent with results from Herrero and Spencer (1982). ...
In March 2014 an all-sky imager (ASI) was installed at the Jicamarca Radio
Observatory (11.95° S, 76.87° W; 0.3° S MLAT). We
present results of equatorial spread F (ESF) characteristics observed at
Jicamarca and at low latitudes. Optical 6300 and 7774 Å airglow
observations from the Jicamarca ASI are compared with other collocated
instruments and with ASIs at El Leoncito, Argentina (31.8° S,
69.3° W; 19.8° S MLAT), and Villa de Leyva, Colombia
(5.6° N, 73.52° W; 16.4° N MLAT). We use Jicamarca
radar data, in incoherent and coherent modes, to obtain plasma parameters and
detect echoes from irregularities. We find that ESF depletions tend to appear
in groups with a group-to-group separation around 400–500 km and
within-group separation around 50–100 km. We combine data from the three
ASIs to investigate the conditions at Jicamarca that could lead to the
development of high-altitude, or topside, plumes. We compare zonal winds,
obtained from a Fabry–Pérot interferometer, with plasma drifts inferred
from the zonal motion of plasma depletions. In addition to the ESF studies we
also investigate the midnight temperature maximum and its effects at higher
latitudes, visible as a brightness wave at El Leoncito. The ASI at Jicamarca
along with collocated and low-latitude instruments provide a clear
two-dimensional view of spatial and temporal evolution of ionospheric
phenomena at equatorial and low latitudes that helps to explain the dynamics
and evolution of equatorial ionospheric/thermospheric processes.
