John M. Holt

Midlatitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966 to 1987

Ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar (ISR) observations at a lower midlatitude site, Shigaraki, in East Asia [Otsuka et al., 1998] and Millstone Hill, a typical subauroral midlatitude site in North America [Zhang and Holt, 2004]. The French Saint Santin ISR, with a geographic latitude slightly higher but an apex latitude 14° lower than Millstone, collected bistatic and quadristatic measurements for over two solar cycles beginning in September 1965. A database of these data, containing observations between 1966 and 1987, has been used in this study in order to establish the midlatitude ionospheric climatology, in particular that of the upper atmosphere thermal status, as well as empirical models for space weather applications. This paper presents, in comparison with the Millstone Hill results, variations of ion and electron temperatures (Ti and Te) with solar activity, season, time of the day, and altitude. The F2 region Te at St. Santin is found to be lower than at Millstone between March and July, when the St. Santin electron density Ne is relatively higher. The midday Te below 300 km increases with F10.7, as at Millstone Hill. Above 300 km it tends to decrease with F10.7 at St. Santin, while it increases in summer at Millstone Hill. Ti between 250 and 350 km peaks midway between spring and summer. We have also created St. Santin ionospheric models for Ne, Te, and Ti using a bin-fit technique similar to that used for the Millstone Hill models. Comparisons with corresponding IRI predications indicate good agreement in Ti at high solar activity, and above the F2 peak, Te from the IRI tends to be higher than both the St. Santin and Millstone Hill models.

Ionospheric local model and climatology from long-term databases of multiple incoherent scatter radars

Empirical ionospheric local models have been developed from long-term data sets of seven incoherent scatter radars spanning invariant latitudes from 25 to 75 in American, European and Asian longitudes at Svalbard, Tromso, Sondrestrom, Millstone Hill, St. Santin, Arecibo and Shigaraki. These models, as important complements to global models, represent electron density, ion and electron temperatures, and ion drifts in the E and F regions, giving a comprehensive quantitative description of ionospheric properties. A case study of annual ionospheric variations in electron density and ion temperature is presented based on some of these models. Clear latitudinal, longitudinal, and altitude dependency of annual and semiannual components are found.

A statistical study of ionospheric profile parameters derived from Millstone Hill incoherent scatter radar measurements

Diurnal, seasonal, and solar activity variations of the bottomside electron density profile parameters B0 and B1, representing the F2 layer thickness and shape, are studied using a large incoherent scatter radar dataset for Millstone Hill covering the period 1976 - 2002. These results are compared with the latest IRI model. Our statistical study is characterized by morning and afternoon falls in the diurnal variation of B0 for seasons other than summer and a similar to 15% change in B1 over a solar cycle, features not fully well represented by the standard IRI model. The standard IRI B1, however, is very close to observations in terms of the diurnal variation.

Thermospheric poleward wind surge at midlatitudes during great storm intervals

United States. National Aeronautics and Space Administration (Living with a Star NNX15AB83G)

Solar EUV flux, exospheric temperature and thermospheric wind inferred from incoherent scatter measurements of the electron density profile at Millstone Hill and Shigaraki

[1] We explore a method for inferring solar EUV flux, atmospheric composition and wind using ionospheric electron density Ne profile measurements. Incoherent scatter radar data from Millstone Hill and Shigaraki measured on October 5, 1989 are assimilated into a theoretical model whose driving forces, solar EUV flux, exosphere temperature Tex, and meridional wind, are adjustable. Adjustments are made to give best match between the model Ne profile and the data. The derived Tex values, found to be low near noon at Millstone and high in the afternoon at Shigaraki, are essentially those required to give the [O]/[N-2] ratio necessary to fit the data. Our inferred EUV fluxes for the two sites are similar. Our technique of using profile data may resolve the ambiguity in deriving EUV and [O]/[N-2] from electron-density measurements.

Ionospheric ion temperature climate and upper atmospheric long-term cooling†

It is now recognized that Earths upper atmosphere is experiencing a long-term cooling over the past several solar cycles. The potential impact of the cooling on societal activities is significant, but a fundamental scientific question exists regarding the drivers of the cooling. New observations and analyses provide crucial advances in our knowledge of these important processes. We investigate ionospheric ion temperature climatology and long-term trends using up-to-date large and consistent ground based datasets as measured by multiple incoherent scatter radars (ISRs). The very comprehensive view provided by these unique observations of the upper atmospheric thermal status allows us to address drivers of strong cooling previously observed by ISRs. We use observations from two high latitude sites at Sondrestrom (Invariant latitude 73.2°N) from 1990-2015, and Chatanika/Poker Flat (Invariant latitude 65.9°N) over the span of 1976-2015 (with a gap from 1983-2006). Results are compared to conditions at the mid-latitude Millstone Hill site (Invariant latitude 52.8°N) from 1968-2015. The aggregate radar observations have very comparable and consistent altitude dependence of long-term trends. In particular, the lower F region (< 275 km) exhibits dayside cooling trends that are significantly higher (-3 to -1K/year at 250 km) than anticipated from model predictions given the anthropogenic increase of greenhouse gases. Above 275 km, cooling trends continue to increase in magnitude but values are strongly dependent on magnetic latitude, suggesting the presence of significant downward influences from non-neutral atmospheric processes.

Observations of ion-neutral coupling associated with strong electrodynamic disturbances during the 2015 St. Patrick's Day storm

We use incoherent scatter radar observations at Millstone Hill (MHO) and Arecibo (AO) and topside ionosphere in-situ DMSP observations during the great geomagnetic storm on 17-18 March 2015 to conduct a focused study on ion-neutral coupling and storm-time ionosphere and thermosphere dynamics. Some of these observations were made around the time of large ionospheric drifts within a Sub-Auroral Polarization Stream (SAPS). During the storm main phase, we identify multiple disturbance characteristics in the North American late afternoon and dusk sector. (1) Strong sub-auroral westward drifts occurred between 20-24 UT near MHO, accompanied by a storm enhanced density plume passage over MHO in the afternoon with a poleward/upward ion drift. The strongly westward flow reached 2000 m/s speed near the poleward plume edge. (2) Prompt penetration electric field signatures, appearing as poleward/upward ion drifts on the dayside over both MHO and AO, were consistent with DMSP vertical drift data, and contributed to plume development. (3) Meridional wind equatorward surges occurred during daytime hours at MHO, followed by 2-3 hr period oscillations at both MHO and AO. The zonal electric field at AO was strongly correlated with the wind oscillation. (4) Large ion temperature enhancements as well as 50+ m/s upward ion drifts throughout the E and F regions were observed during the SAPS period. These were presumably caused by strong frictional heating due to large plasma drifts. The heating effects appeared to drive significant atmospheric upwelling, and corresponding ion upflow was also observed briefly. This study highlights some of the important effects of fast plasma transport as well as other disturbance dynamics on ion-neutral coupling during a single intensification period within a great geomagnetic storm.

High resolution observations of the lower thermosphere at millstone hill during the September 1987 LTCS campaign

Abstract The Millstone Hill incoherent scatter radar operated during 21–25 September 1987 as part of the Lower Thermosphere Coupling Study (LTCS). During the daytime, local E and F-region correlation functions were obtained using a combination of multipulse and lag profile techniques, while during the night, spectral techniques were employed to probe the local and high-latitude F-region. Emphasis has been placed so far on the analysis of temperatures in the lower thermosphere over Millstone Hill which reveal an increase of about 60°K in the mean daytime temperature on the geomagnetically disturbed day, 25 September, relative to the previous quieter days. This is considered to be due to the transport of Joule heat from higher latitudes. Temperature oscillations of 40°K with a 12-hour period were observed on 23 and 25 September exhibiting downward phase propagation consistent with the characteristics of upward propagating semidiurnal tides from the lower atmosphere. Although large variability is noted from day to day, there is a general consistency with tidal theory predictions for those days when tidal oscillations are apparent.

Detection of artificially created negative ion clouds with incoherent scatter radar

Theoretical incoherent scatter (IS) spectra from collisionless F region plasma are calculated taking into account the effect of negatively charged ions. Such ions can significantly change the composition of the local ionosphere when they are created artificially during active chemical release experiments. If IS radar observations are conducted upon such a modified plasma, the interpretation of the scattered radar signal will be complicated by the negative ions, which are not found in the natural (e.g., O+/e−) ionosphere. Specifically, the presence of heavy negative ions will broaden the IS spectrum, making the shoulder peaks sharper, and creating an additional small central hump. A radar spectral analysis program that assumes only the naturally occurring plasma constituents will erroneously attribute such spectral changes to changes in other plasma parameters, such as the temperature ratio Te/Ti. In order to detect heavy negative ions we fix the temperature structure of the ionosphere to a preevent average measurement and interpret any changes in spectral shape during the experiment as being caused by changes in composition, and not by changes in Te/Ti. The Millstone Hill 440-MHz IS radar was used to observe the spatial and temporal development of heavy negative ion plasma clouds created during four active chemical release experiments: the Ionospheric Modification Study (IMS) in 1983, the Space-Plasma Negative Ion Experiments (SPINEX 1 and 2) in 1984 and 1986 (all SF6 releases), and NICARE 1 in 1989 (CF3Br release). Each experiment led to the creation of a region of heavy, negatively charged ions. Concentrations of 10–40% SF6− (146 amu) are reliably detected in the SPINEX 1, SPINEX 2 and IMS data sets. An average uncertainty of ±10% SF6− is present in all three experiments. Concentrations of 30% Br− (80 amu) are further detected in the NICARE 1 release, with uncertainties of ±4%.

Day-to-day variability and solar preconditioning of thermospheric temperature over Millstone Hill

We use a continuous 30 day incoherent scatter radar experiment at Millstone Hill in October 2002 to examine day-to-day thermospheric variability in exospheric temperature Tex. Solar flux and magnetic activity influences as the main driving factors for day-to-day variability are investigated quantitatively. Solar ultraviolet flux levels are based on the TIMED/SEE space weather product, allowing for analysis of ultraviolet flux-Tex correlation. Tex is most sensitive to solar EUV flux with approximately a 2 day delay at wavelengths of 27–34 nm (including 30.4 nm). In particularly, a 20–60 h time delay occurs in Tex response to EUV flux at 27–34 nm band, with shorter delays in the morning and longer delays in the afternoon and at night. The 1 ∼ 2 day delayed Tex response to solar ultraviolet flux and associated thermospheric solar preconditioning (“memory”) are most significant in the daily mean for the 27–34 nm band, in the diurnal and semidiurnal amplitudes for the soft X-ray flux at 0.1–7 nm, and in the diurnal amplitude for longer wavelengths. An empirical model driven only by EUV flux at 27–34 nm from 2 days in advance reproduces 90% of the observed variability in the Tex daily mean. With a 2 day time delay, solar X-ray flux at 0.1–7 nm is correlated positively with Tex diurnal amplitude and negatively with Tex semidiurnal amplitude. Finally, magnetic activity control, as represented by the Dst index, is weaker during the day and stronger at night and is important for the semidiurnal amplitude but not important for the daily mean.