New results on the mid-latitude midnight temperature maximum

Abstract

Abstract. 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. Keywords. Ionosphere (mid-latitude ionosphere)

The Effect of Midnight Temperature Maximum Winds on Post‐Midnight Equatorial Spread F

“…The strong equatorward winds that often precede the MTM can form a converging wind pattern over the latitude range (±30 • ) of these simulations. Note that this is not the same as the MTM-associated local converging wind analyzed by Mesquita et al (2018) using these data. Second, the sudden decrease in zonal winds, which is correlated with the MTM, can also enhance ESF growth (Huba et al, 2009).…”

“…Observations of this MTM wind pattern have been recently obtained over a large region of North America, using the North American Thermosphere Ionosphere Observing Network (NATION; Mesquita et al, 2018). The regional-scale NATION wind dataset shows rapid changes in wind strength and direction.…”

“…Winds were measured using the five Fabry-Perot interferometer (FPI) observatories that make up the NATION instrument (Mesquita et al, 2018). The wind data, some of which is adapted for use in our simulations and displayed in Figure 1, is centered on 38 • N, 85 • W and was measured beginning on 28 December 2013.…”

“…The wind data, some of which is adapted for use in our simulations and displayed in Figure 1, is centered on 38 • N, 85 • W and was measured beginning on 28 December 2013. In Mesquita et al (2018), the authors used an inversion analysis based on the work of Harding et al (2015) to produce the wind field presented in Figure 1. Here, the wind vectors are denoted by 'wind flags' where the symbol is at the base of the the vector (i.e., they are not directional arrowheads).…”

Investigation of Nighttime MSTIDS Observed by Optical Thermosphere Imagers at Low Latitudes: Morphology, Propagation Direction, and Wind Filtering

“…The authors observed that MSTIDs rarely propagate to magnetic latitudes less than 15°, and it occurs during the low solar activity period. Narayanan et al (2014) pointed out two physical explanations for that: first, the increasing intensity due to midnight pressure bulge shift to the poles (further details about midnight pressure bulge can be found in Figueiredo, Buriti, et al, 2017;Mesquita et al, 2018) when MSTIDs occur late at night and second, when MSTIDs propagate before midnight, it encounters the equatorial ionization anomaly that limits its propagation toward the equator. Amorim, and Candido (2008), which presented velocities ranging from 50 to 100 m/s.…”