Neutral Temperature Profiles Research Articles

An Observational Case Study of a Radiation Fog Event

A micrometeorological fog experiment was carried out in Budapest, Hungary during the winter half year of 2020–2021. The field observation involved (i) standard meteorological and radiosonde measurements; (ii) surface radiation balance and energy budget components, and (iii) ceilometer measurements. 23 fog events occurred during the whole campaign. Foggy events were categorized based on two different methods suggested by Tardif and Rasmussen (2007) and Lin et al. (2022). Using the Present Weather Detector and Visibility sensor (PWD12), duration of foggy periods are approximately shorter (~ 9%) compared to ceilometer measurements. The categorization of fog based on two different methods suggests that duration of radiation fogs is lower compared to that of cloud base lowering (CBL) fogs. The results of analysis of observed data about the longest fog event suggest that (i) it was a radiation fog that developed from the surface upwards with condition of a near neutral temperature profile. Near the surface the turbulent kinetic energy and turbulent momentum fluxes remained smaller than 0.4 m2 s–2 and 0.06 kg m–1 s–2, respectively. In the surface layer the vertical profile of the sensible heat flux was near constant (it changes with height ~ 10%), and during the evolution of the fog, its maximum value was smaller than 25 W m–2, (ii) the dissipation of the fog occurred due to increase of turbulence, (iii) longwave energy budget was close to zero during fog, and a significant increase of virtual potential temperature with height was observed before fog onset. The complete dataset gives an opportunity to quantify local effects, such as tracking the effect of strengthening of wind for modification of stability, surface layer profiles and visibility. Fog formation, development and dissipation are quantified based on the micrometeorological observations performed in suburb area of Budapest, providing a processing algorithm for investigating various fog events for synoptic analysis and for optimization of numerical model parameterizations.

What Is the Altitude of Thermal Equilibrium?

AbstractThermal equilibrium in planetary atmospheres occurs at altitudes where the ion, electron, and neutral temperatures are equal. Thermal equilibrium is postulated to occur in the collision‐dominated ionosphere. This postulated altitude is above the lower boundary of all empirical models of planetary ionospheres. Physics‐based model predictions of the altitude cannot be validated due to a lack of adequate simultaneous observations of temperature profiles. This study presents temperature profiles from simultaneous observations on Atmosphere Explorer–C below 140 km and quiet‐time neutral observations from Thermosphere Ionosphere Mesosphere Energy and Dynamics/Global UltraViolet Imager over Millstone Hill. These are compared with profiles from physics‐based models with a discussion of their respective limitations. We conclude that there does not yet exist a quantitative understanding of the ion, electron, and neutral thermalization processes in low‐altitude planetary ionospheres. Progress on this topic requires an adequate database of simultaneous ion, electron, and neutral temperature profiles in the 110–140 km altitude range.

High‐Resolution Optical Observations of Neutral Heating Associated With the Electrodynamics of an Auroral Arc

AbstractWe present results that indicate the existence of two distinct neutral heating processes associated with a discrete auroral arc over Svalbard. Within the order of seconds, the thermospheric temperature profile displays a significant response to the arc on spatial scales smaller than 10 km. It is suggested that both heating signatures are associated with the electrodynamic system responsible for the formation of the arc. Pedersen currents produce a temperature increase of approximately 100 K, observed at altitudes between 80 and 160 kilometres, directly adjacent to the arc structure and on its poleward edge only. In contrast, field‐aligned currents produce a variable temperature increase, of approximately 50 K, which is observed within the arc itself and constrained to a narrow altitude range between 90 and 110 km. By utilizing a range of observations and new analysis methods we are able to measure the atmospheric neutral temperature profile, over auroral altitudes, at unprecedented temporal and spatial scales. The High Throughput Imaging Echelle Spectrograph records high‐resolution emission spectra of the aurora, which are then fitted with synthetic N2 spectra, generated with modeled N2 volume emission rate profiles and a library of trial temperature profiles. The N2 volume emission rate profiles are retrieved from the Southampton ionospheric model using precipitating particle energies and fluxes obtained from Auroral Structure and Kinetics and the EISCAT Svalbard Radar. The application of this technique allows us to produce a time series of neutral temperature profiles and measure the localized heating of the neutral atmosphere resulting from the electrodynamics of the arc.

On the relationship between flux transfer events, temperature enhancements, and ion upflow events in the cusp ionosphere

[1] A transit of the dayside aurora across the field-of-view of the EISCAT Svalbard Radar occurred on 20 December 1998. This offered an excellent opportunity to study the spatial structure of the cusp/cleft aurora using meridian scanning photometer and incoherent scatter radar. We were able to identify distinct regions of upflow driven by ion heating (type 1) and upflow driven by electron heating (type 2) around poleward moving auroral forms, a transient auroral feature tied to flux transfer events. A quiet period before the auroral transit allowed us to estimate a neutral temperature profile, which enabled calculation of the ion-neutral relative wind. We found evidence for purely ion heating-driven upflow equatorward of the cusp auroral boundary, and for electron heating-driven upflow near the equatorward auroral boundary. The greatest upflow occurred near the center of the cusp aurora when both ion and electron temperatures were enhanced. The observed upflows were greater than expected from ambipolar diffusion alone, suggesting that ion-neutral frictional heating did contribute to upflow events in most cases. The great variability observed in ion temperature indicates that the ion flow was greatly structured within the aurora. Type 1–2 upflows may be considered as spatial structures of active cusp. Upflows are observed at various times in their evolution, and one upflow event, estimated to be 5–10 minutes old, showed a lifting of the F region of some 100 km, indicating a hybrid of type 1 and type 2.

A revised method to extract thermospheric parameters from incoherent scatter observations

Height distribution of ionospheric plasma parameters in the F2-region is closely related to height distribution of the main thermospheric parameters. Therefore, they can be extracted from ionospheric observations solving an inverse problem of aeronomy. A self-consistent approach to the Ne(h) modeling at the F2-region heights has been applied to solve the problem. Using routine incoherent scatter radar observations (Ne(h), Te(h), Ti(h), Vi(h) profiles) the method yields a self-consistent set of main aeronomic parameters responsible for the F2-region formation. The list of derived parameters includes: neutral temperature profile Tn(h) depending on the exospheric temperature Tex, the temperature at 120 km T120 and the shape-parameter S, which determine the temperature profile, concentration of neutral species [O], [O2], [N2], vertical plasma drift W, which may be converted to the meridional thermospheric wind Vnx, total solar EUV flux and ion composition (O+, O2 +, NO+, N2 +, N+) as a result of Ne(h) fitting. Therefore, the method gives a complete description of the upper atmosphere condition in the vicinity of incoherent scatter facility for the periods of observation. Analysis of all available EISCAT (CP-1, CP-2) observations has shown wide deviations from MSIS-86 model predictions for geomagnetically disturbed conditions while the retrieved parameters are close to the model ones for quiet periods. The approach turns out to be very useful for physical analyses of the F2-layer disturbance mechanisms giving a complete picture of the phenomenon in question. Limitations and problems related to method application are discussed. Under existing conditions when thermospheric observations are not conducted currently the proposed method may be considered a real tool for thermosphere investigation and monitoring at least for the periods of ISR observations.

Physical mechanism of strong negative storm effects in the daytime ionospheric F2 region observed with EISCAT

Abstract. A self-consistent method for daytime F-region modelling was applied to EISCAT observations during two periods comprising the very disturbed days 3 April 1992 and 10 April 1990. The observed strong Ne decrease at F2-layer heights originated from different physical mechanisms in the two cases. The negative F2-layer storm effect with an NmF2 decrease by a factor of 6.4 on 3 April 1992 was produced by enhanced electric fields (E≈85 mV/m) and strong downward plasma drifts, but without any noticeable changes in thermospheric parameters. The increase of the O+ + N2 reaction rate resulted in a strong enrichment of the ionosphere with molecular ions even at F2-layer heights. The enhanced electric field produced a wide mid-latitude daytime trough on 03 April 1992 not usually observed during similar polarization jet events. The other strong negative storm effect on 10 April 1990 with a complete disappearance of the F2-layer maximum at the usual heights was attributed mainly to changes in neutral composition and temperature. A small value for the shape parameter S in the neutral temperature profile and a low neutral temperature at 120 km indicate strong cooling of the lower thermosphere. We propose that this cooling is due to increased nitric oxide concentration usually observed at these heights during geomagnetic storms.Key words. Atmospheric composition and structure · Thermosphere · Ionosphere · Ion chemistry and composition · Atmosphere interactions

Physical mechanism of strong negative storm effects in the daytime ionospheric F2 region observed with EISCAT

<strong class="journal-contentHeaderColor">Abstract.</strong> A self-consistent method for daytime F-region modelling was applied to EISCAT observations during two periods comprising the very disturbed days 3 April 1992 and 10 April 1990. The observed strong N<i>_e</i> decrease at F2-layer heights originated from different physical mechanisms in the two cases. The negative F2-layer storm effect with an <i>N_m</i>F2 decrease by a factor of 6.4 on 3 April 1992 was produced by enhanced electric fields (<strong>E</strong>&#x2248;85 mV/m) and strong downward plasma drifts, but without any noticeable changes in thermospheric parameters. The increase of the O⁺ + N₂ reaction rate resulted in a strong enrichment of the ionosphere with molecular ions even at F2-layer heights. The enhanced electric field produced a wide mid-latitude daytime trough on 03 April 1992 not usually observed during similar polarization jet events. The other strong negative storm effect on 10 April 1990 with a complete disappearance of the F2-layer maximum at the usual heights was attributed mainly to changes in neutral composition and temperature. A small value for the shape parameter <i>S</i> in the neutral temperature profile and a low neutral temperature at 120 km indicate strong cooling of the lower thermosphere. We propose that this cooling is due to increased nitric oxide concentration usually observed at these heights during geomagnetic storms.<br><br><b>Key words.</b> Atmospheric composition and structure · Thermosphere · Ionosphere · Ion chemistry and composition · Atmosphere interactions

Self-consistent modelling of the daytime electron density profile in the ionospheric F region

Abstract. A theoretical self-consistent method for the description of daytime Ne(h) profiles in the ionospheric F region measured by EISCAT is proposed. It is based on the use of a theoretical F-region model and measured electron density, Ne(h), electron, Te(h), and ion temperature, Ti(h), and field-aligned plasma drift Vl(h) profiles. The method describes the observed Ne(h) profile with high accuracy for quiet and disturbed conditions. Two versions of the method are considered: in the first the exospheric temperature Tex is derived from a procedure minimizing [log(Ne(h)obs / Ne(h)cal]2, in the second Tex is deduced from the ion energy conservation in the F region. The method allows us to infer from the incoherent-scatter observations: concentrations of atomic oxygen, [O], molecular oxygen, [O2], molecular nitrogen, [N2] the vertical plasma drift, W, the exospheric temperature. Tex, and the shape parameter S in the neutral temperature profile. The ratio ([O+]/Ne) calculated by the theoretical model is used to correct Te(h), Ti(h) and Ne(h) profiles routinely measured with EISCAT which are known to depend strongly on the actual applied ion-composition model. Such a correction is especially important for geomagnetically disturbed periods when the F region is strongly enriched with molecular ions. We conclude that four of the six thermospheric parameters, namely [O], [N2], W and Tex can be confidently inferred from the EISCAT observations, while the other two derived parameters, [O2] ans S are less reliable. The method can be used for the analysis of long-term (seasonal, solar cycle) as well as for day-to-day variations of the thermospheric parameters and the F-region ion composition using daytime incoherent-scatter observations.

Neutral and ion composition changes in the F region over Millstone Hill during the Equinox Transition Study

We use overhead ionospheric incoherent scatter radar data from Millstone Hill to deduce the stormtime variations of the thermospheric temperature, O and N2 densities, and F1 region ion composition during the Equinox Transition Study of September 17–24, 1984. Using the measured neutral temperature profile and O density at 400 km altitude, we extrapolate to determine O density changes in the lower thermosphere. Using these O densities and the measured electron densities, we deduce the variation of the N2 density. Our initial attempt leads to the deduction of large depletions in both O and N2 in the lower thermosphere. On using the MSIS model neutral temperatures for the extrapolation, however, we compute O depletions having magnitudes more comparable with theoretical predictions and N2 variations consistent with expected thermal expansion effects. We speculate that the radar‐measured neutral temperatures were contaminated by ion‐neutral frictional heating effects during the disturbed periods of the ETS and that this served to invalidate neutral density extrapolations made with these temperatures. Further, we compute the height of 50% O+ ion composition in the F1 region and the height of the peak electron density in the ionosphere, and, upon comparing these, find that the height of the peak on the disturbed days was located in the lower F1 region molecular‐ion layer rather than in the F2 region O+ layer. This occurrence has serious consequences for methods of deducing neutral winds from the height of the F layer, for these methods rely on the peak containing primarily O+ ions.

Properties of industrial dense gas plumes

Hazardous gases and vapors are often discharged into the atmosphere from industrial plants during catastrophic events (e.g. Union Carbide incident in Bhopal, India). In many cases the discharged components are more dense than air and settle to the ground surface downstream from the stack exit. In the present paper, the buoyant plume model of Hoult, Fay and Forney (1969, J. Air Pollut. Control Ass. 19, 585–590.) has been altered to predict the properties of hazardous discharges. In particular, the plume impingement point, radius and concentration are predicted for typical stack exit conditions, wind speeds and temperature profiles. Asymptotic expressions for plume properties at the impingement point are also derived for a constant crosswind and neutral temperature profile. These formulae are shown to be useful for all conditions.

4721582 Toxic gas absorbent and processes for making same

Hazardous gases and vapors are often discharged into the atmosphere from industrial plants during catastrophic events (e.g. Union Carbide incident in Bhopal, India). In many cases the discharged components are more dense than air and settle to the ground surface downstream from the stack exit. In the present paper, the buoyant plume model of Hoult, Fay and Forney (1969, J. Air Pollut. Control Ass. 19, 585–590.) has been altered to predict the properties of hazardous discharges. In particular, the plume impingement point, radius and concentration are predicted for typical stack exit conditions, wind speeds and temperature profiles. Asymptotic expressions for plume properties at the impingement point are also derived for a constant crosswind and neutral temperature profile. These formulae are shown to be useful for all conditions.

II. Combined numerical model of ion and neutral composition above 120 km

A coupled neutral-ionic photochemical model has been used to interpret the ionic composition of the Venusian dayside ionosphere measured by the orbiter retarding potential analyser (ORPA) experiment on board the NASA Pioneer-Venus orbiter spacecraft. The electron and ion temperatures also measured by the ORPA are used for calculating the plasma-diffusion coefficients and scale heights for ions. The neutral temperature profiles and the densities of neutral constituents, particularly CO2 and O, play key roles in the determination of the height profiles of the ionic constituents. All these quantities vary substantially in the Venusian thermosphere near the terminator; the models presented are representatives of the solar zenith angle ∼65°. The predicted O2+ densities below ∼200km agree particularly well with observations by the ORPA, but the model values are significantly less than those measured by the orbiter ion mass spectrometer (OIMS). Models predict much smaller densities than observed values for all molecular ions above ∼200km. The reason for the turn-up trend of the concentration gradient of molecular ions observed at these heights by both ORPA and OIMS is unknown. One of the models can predict O+ ion densities above ∼200km compatible with observations, if an effective vertical escape flux (φ108cm−2sec−1) is assumed at the ionopause. The neutral air density required to explain the observed ion composition is about 1.4 times larger than the values measured by the orbiter neutral mass spectrometer (ONMS).

Incoherent scatter measurements of ion‐neutral collision frequencies and temperatures in the lower thermosphere of the auroral region

Incoherent scatter observations performed in March and November 1978 at Chatanika have been used for studying the lower thermosphere in the auroral region. Neutral temperatures and densities have been found during periods without Joule heating. We present mean profiles of temperatures and collision frequencies (approximately proportional to neutral densities) for each month and profiles obtained during four specific nights. Between 93 km and 110 km the mean profiles of temperature are in good agreement with the Jacchia (1971) model, and the profiles of collision frequency are similar to those deduced from the model. Consistency checks between these collision frequencies and temperatures were performed, as were various simulations of the data. Neutral temperature profiles between 90 km and 140 km on the four specific nights show variations from one night to another that are not correlated to magnetic activity. However, there are systematic variations during each night that we suggest are due to atmospheric tides.

Radiative and collision processes in the ionosphere

An account is given of how understanding of the radiative and collision processes occurring in the ionosphere has grown since the advents of sounding rockets and of satellites. Topics covered include the formation and ion-chemistry of D, E, F and topside and the differences between the electron and ion temperature profiles and the corresponding neutral temperature profile.

Radial neutral gas temperature and density profiles in low-pressure argon discharges

In this paper we describe the direct measurement of the neutral gas density and the determination of the neutral temperature profiles in a low-pressure weakly ionized argon discharge. The measurements were made using a single-wavelength coupled cavity laser interferometer to study the neutral density variations in the afterglow of a crowbarred dc (steady-state) discharge. The temporal and radial variations of the neutral gas density in the afterglow were used to infer the dc steady-state gas density and temperature profiles, assuming an ideal gas. It is shown that the profiles are strongly current and pressure dependent and that the axial depletion of neutrals can be as high as 25–30%. Long neutral relaxation times (2–3 msec) were encountered in order to reach thermal equilibrium in the afterglow for the pressures and currents studied (1–10 Torr, 50–350 mA). Radial profiles of the neutral gas density for a fixed pressure and current are in agreement with the hypothesis that neutral heating is caused primarily by collisions with the electron gas, resulting in a convective flow of the hot neutrals radially outward towards the cooler walls.

Upper atmosphere neutral temperature profiles in the auroral zone 1968–1970

Neutral temperatures have been measured above 120 km altitude from observations of the fluorescent emission of aluminium oxide and barium oxide clouds released from rockets launched at ESRANGE, Kiruna. The temperature observations showed a strong correlation with the C9 daily magnetic character rather than with the 3-hr K ν index, expressed approximately by the following equations at morning twilight for 140 and 165 km altitude (average rocket apogee): T(140) = 420 + 25 × C9 (°K) T(165) = 450 + 50 × C9 (°K) A small diurnal variation appeared from the data, the temperature at 165 km being on average 100°K higher during evening twilight than morning twilight. No clear seasonal or longer term variations were apparent from the data. The results indicate a strong auroral zone enhancement of the heating associated with geomagnetic activity.

Diurnal variation of the neutral temperature profile at Arecibo from incoherent scatter measurements and its relevance to the 1400-hour density maximum

Neutral ionospheric temperature profile diurnal variation at Arecibo from incoherent scatter measurements, considering relevance to 1400 hour density maximum