New radar observations of temporal and spatial dynamics of the midnight temperature maximum at low latitude and midlatitude

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 and 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 to 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 midlatitudes. 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.

An incoherent scatter radar study of the midnight temperature maximum that occurred at Arecibo during a sudden stratospheric warming event in January 2010

“…However, we would like to point out that the large increment of ion temperature, ~310 K on 20 January, is seldom seen at Arecibo. The duration of the MTM is comparable to those observed at Arecibo previously [e.g., Hickey et al , ]. One reason for these rapid enhancements is the presence of strong terdiurnal tide.…”

Simultaneous 6300 Å airglow and radar observations of ionospheric irregularities and dynamics at the geomagnetic equator

“…The local maximum in temperature that is measured by both instruments is the MTM. There is very good agreement between the two measurements meaning that the ion temperature is equal to the neutral temperature, as previously shown by Hickey et al (2014). The magnitude of the ion and neutral temperature increases are between 50 and 100 K. These observations are compared with higher-latitude ASI observations in the next section to constrain the morphology of the MTM.…”

“…Figure 12 shows neutral and ion temperature at an altitude of 250 km on 4 April 2014. Although we only present one altitude from the ISR measurements, the MTM occurs at multiple altitudes (Martinis et al, 2013;Hickey et al, 2014). The temperature increase begins just before 05:00 UT and the peak of the temperature increase is just after 06:00 UT (LT = UT − 5).…”

“…Another equatorial phenomenon we discuss in this paper, the MTM, has been studied directly using a variety of instruments such as satellites, incoherent scatter radars (ISR), and FPIs, (Herrero and Spencer, 1982;Hickey et al, 2014;Meriwether et al, 2008). At Jicamarca, the ISR has been used to study the seasonal dependence of the MTM (Bamgboye and McClure, 1982) and the MTM has been observed with FPIs at locations near the magnetic equator (Meriwether et al, 2008;Fisher et al, 2015).…”

WINDII observations of thermospheric O(1D) nightglow emission rates, temperature, and wind: 1. The northern hemisphere midnight temperature maximum and the wave 4

“…Recently, Hickey et al . [] employing the incoherent scatter radar at Millstone Hill (42.6°N, 288.5°E) reported observations of MTM enhancements in ion temperature of the order of ~100 K at 30°N–34°N.…”