Altitude Profiles Research Articles

Comparative study of the possible lower ionospheric anomalies in very low frequency (VLF) signal during Honshu, 2011 and Nepal, 2015 earthquakes

We present perturbations in very low frequency (VLF) signals received at Ionospheric & Earthquake Research Centre (IERC) (Lat. 22.50N, Long. 87.48E) during and prior to two earthquakes, one on 11 March 2011 at 11:16:24 LT (M = 9) in Honshu, Japan and another on 12 May 2015 at 12:35:19 LT (M = 7.3) in Kodari, Nepal. The VLF signal transmitted from JJI (22.2 kHz) in Japan (Lat. 32.05N, Long. 131.51E) showed strong shift in VLF-sunrise terminator times towards night-time few days prior to both the earthquakes. These two earthquakes took place near the transmitter JJI and receiver IERC respectively. We simulated the VLF sunrise terminator time shifts using the long wavelength propagation capability (LWPC) code. To effectively represent the D-region ionospheric variabilities, we assumed a mean dynamic perturbation over the path and presented them with a set of effective Wait’s parameters (βeff, ). We have successfully reproduced the temporal trend of the normalized VLF signal amplitude at VLF sunrise terminators for a few days around both the earthquakes. We used Wait’s exponential model for estimating the altitude profile of D-region electron density () at VLF sunrise terminator times around both the earthquakes and quantified the changes of those profiles.

Enhancing the ISIS‐I Topside Digital Ionogram Database

AbstractSelected original analog telemetry tapes from three of the topside‐sounder satellites of the International Satellites for Ionospheric Studies (ISIS) program, namely Alouette 2, ISIS I, and ISIS II, were used in an earlier project to produce more than ½ million digital topside ionograms; the resulting digital topside ionograms from ISIS II were used to produce more than 86,000 globally distributed vertical topside ionospheric electron density profiles Ne(h) that cover a time span of more than a solar cycle. These Ne(h) were produced using the Topside Ionogram Scaler with True height algorithm auto‐scaling software. Before attempting to automatically process Alouette‐2 or ISIS‐I ionograms, a data‐enhancement project was initiated so as to increase the number of ionograms suitable for manual scaling and to increase the auto‐processing success rate. These enhancements were mainly to correct problems that often occurred during the analog‐to‐digital conversion of the original telemetry tapes. Here we illustrate the improvements made to the ISIS‐I digital topside ionograms and compare Ne values at the satellite altitude and Ne(h) profiles, based on the manual scaling of selected ionograms, to both the auto‐scaled values and the predictions of the International Reference Ionosphere 2016 model. The results indicate the need to improve the available auto‐processing software for the new ISIS‐I digital ionograms and that International Reference Ionosphere 2016 predicts midlatitude winter topside Ne values that are too high in the late morning and at noon but too low in the early morning.

Hardware-software system for monitoring of atmospheric water vapor structure in the city of Kazan

Methodology and software to reconstruct the spatial-temporal structure of water vapor in the troposphere by GNSS signals measured by ground-based receivers is developed. In this paper, measurements of a satellite navigation system receiver network located near the city of Kazan are used. It is shown that using a tomographic approach it is possible to reconstruct the altitude profile of the refractive index in the lower atmosphere and its space-time variations. The tomography method gives less smoothed results than Tikhonov’s method.

On Long‐Term SABER CO2 Trends and Effects Due to Nonuniform Space and Time Sampling

AbstractThe Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the TIMED satellite has been continuously operating for more than 16 years, since 2002, monitoring the CO2 concentration on nearly a global scale in the middle and upper atmosphere (from 65 km up to 110 km). A recent reanalysis (Qian et al., 2017, https://doi.org/10.1002/2016JA023825) concluded that different deseasonalizing methodologies may have a strong impact on long‐term trend analysis, ultimately yielding different altitude profiles of the global mean CO2 trend. In this work, we aim to understand how the nonuniform spatial and temporal sampling inherent in the SABER CO2 data set affects the determination of the long‐term trends. In addition, our goal is to disentangle reported differences in SABER CO2 trends due to different time averaging windows and methodologies used for trend estimation. The Whole Atmosphere Community Climate Model is used for synthetic studies of the time series. We demonstrate that, due to the time varying data gaps and nonuniform sampling of local times, different time binning of the SABER CO2 data may indeed bias the long‐term trend estimation. We show and discuss how the 60‐day averaging reduces the bias in relative trends. We also conclude that different deseasonalizing methodologies (averaged over the same temporal bins) yield negligible differences on the trend determination. Taking this into account the global mean CO2 relative trend does not deviate statistically from the tropospheric value below 1 × 10−3 mb (90 km). Above about 90 km, there is a positive slope in the global CO2 trend profile, but with substantially reduced magnitude for 60‐day binned data.

Re-entry trajectory optimization using pigeon inspired optimization based control profiles

In this paper, the entry trajectory optimization problem of lifting type re-entry vehicle with path constraints is solved using Pigeon Inspired Optimization (PIO). Entry trajectory optimization problem involves finding the control profiles, bank angle, and angle of attack to guide the vehicle safely to the destination. The proposed approach parametrizes the bank angle to be a linear function of energy while the angle of attack is considered to be a monotonic function of Mach number. Thus, the problem of finding control profiles is transformed into three parameter search problem. The PIO algorithm is used to find the values of these parameters that minimizes the objective function. The terminal heading angle offset is minimized using traditional bank reversal logic. A new approach is proposed in which the bank angle is modulated to eliminate the oscillations observed in the altitude profile of an entry vehicle with a high lift to drag ratio (L/D). A methodology to satisfy the given load factor constraint is also proposed, as an alternative to traditional penalty factor approach used for incorporating path constraints in PIO algorithm. The proposed approach is further validated by considering sub-cases with different load factor limits and bank angle as the only control variable. The angle of attack profile obtained from the previous case is considered as the nominal profile. The proposed trajectory optimization strategy using PIO algorithm is simulated for Common Aero Vehicle with high L/D ratio (CAV-H) with different load factor constraint limits. The results show that the obtained angle of attack profile minimizes the peak heat rate experienced by the vehicle and bank angle modulation eliminates the oscillations in the altitude profile as well as makes the entry trajectory satisfy the load factor constraint.

NO<sub>2</sub> and HCHO measurements in Korea from 2012 to 2016 from Pandora spectrometer instruments compared with OMI retrievals and with aircraft measurements during the KORUS-AQ campaign

Abstract. Nine Pandora spectrometer instruments (PSI) were installed at eight sites in South Korea as part of the KORUS-AQ (Korea U.S.-Air Quality) field study integrating information from ground, aircraft, and satellite measurements for validation of remote sensing air-quality studies. The PSI made direct-sun measurements of total vertical column NO2, C(NO2), with high precision (0.05 DU, where 1 DU =2.69×1016 molecules cm−2) and accuracy (0.1 DU) that were retrieved using spectral fitting techniques. Retrieval of formaldehyde C(HCHO) total column amounts were also obtained at five sites using the recently improved PSI optics. The C(HCHO) retrievals have high precision, but possibly lower accuracy than for NO2 because of uncertainty about the optimum spectral window for all ground-based and satellite instruments. PSI direct-sun retrieved values for C(NO2) and C(HCHO) are always significantly larger than OMI (AURA satellite Ozone Monitoring Instrument) retrieved C(NO2) and C(HCHO) for the OMI overpass local times (KST=13.5±0.5 h). In urban areas, PSI C(NO2) 30-day running averages are at least a factor of two larger than OMI averages. Similar differences are seen for C(HCHO) in Seoul and nearby surrounding areas. Late afternoon values of C(HCHO) measured by PSI are even larger, implying that OMI early afternoon measurements underestimate the effect of poor air quality on human health. The primary cause of OMI underestimates is the large OMI field of view (FOV) that includes regions containing low values of pollutants. In relatively clean areas, PSI and OMI are more closely in agreement. C(HCHO) amounts were obtained for five sites, Yonsei University in Seoul, Olympic Park, Taehwa Mountain, Amnyeondo, and Yeoju. Of these, the largest amounts of C(HCHO) were observed at Olympic Park and Taehwa Mountain, surrounded by significant amounts of vegetation. Comparisons of PSI C(HCHO) results were made with the Compact Atmospheric Multispecies Spectrometer CAMS during overflights on the DC-8 aircraft for Taehwa Mountain and Olympic Park. In all cases, PSI measured substantially more C(HCHO) than obtained from integrating the CAMS altitude profiles. PSI C(HCHO) at Yonsei University in Seoul frequently reached 0.6 DU and occasionally exceeded 1.5 DU. The semi-rural site, Taehwa Mountain, frequently reached 0.9 DU and occasionally exceeded 1.5 DU. Even at the cleanest site, Amnyeondo, C(HCHO) occasionally exceeded 1 DU.

The role of Boundary Layer Height (BLH) variations on pollution dispersion over a coastal station in the Southwest Peninsular India

We report the variability of Boundary Layer Height (BLH) and Ventilation Coefficient (VC) over a coastal station in southwest Peninsular India from vertical soundings. Altitude profile of Virtual Potential Temperature (θv) (derived from balloon-borne GPS radiosonde observations) was used to study the seasonal changes of BLH over Thumba (8.5°N, 77°E), a coastal station in southwest Peninsular India. Variability in the BLH is maximum during the pre-monsoon season and minimum during the winter, whereas the VC was found to be highest in the summer and lowest during winter. It is revealing the excellent efficiency in the dispersion of pollutants during the summer monsoon season. Conversely, low VC during winter and post-monsoon seasons showed great potential for pollution at this site. Role of VC on the dispersion of pollution was also examined using surface mass concentration of Black and Organic Carbon (BC and OC), sulphate and columnar Aerosol Optical Depth (AOD). High value of VC lowers the surface mass concentrations of BC, OC and sulphate during winter and maximises during summer monsoon and decreases the pollution potential.

Tristatic observation of polar mesosphere winter echoes with the EISCAT VHF radar on 8 January 2014: a case study

Polar mesosphere winter echoes (PMWE) were observed at 70 km over Tromsø, Norway, on 8 January 2014 using the tristatic configuration of the European incoherent scatter VHF radar. For the interval 11:00–13:00 UT where the strongest patch of PMWE of about 6-min duration was detected, the spectra of the received signal were analysed for the Tromsø site and altitude profiles of spectral parameters were derived. For the remote sites Kiruna and Sodankylä, the Doppler velocities and their vertical shear were determined by using the measured autocorrelation functions. Ducted gravity waves with periods of 5–10 min were found in the vertical wind velocity between 66 and 81 km altitudes. The duct might be formed around 70 and 77 km altitude where horizontal wind maxima were observed with the Kiruna receiver. However, we did not find any close relation between wind shear at 70 km altitude and PMWE at the same height: the wind shear was present for 2 h, but PMWE for only 6 min. Enhanced spectral width in the vertical Tromsø beam was observed for the PMWE patch. We discussed these experimental findings in relation to the winter echo generation mechanism. Our conclusion is that the presence of patchy negatively charged small-sized dust might explain the observations although a gravity wave breaking mechanism cannot be completely rejected.

Martian Electron Temperatures in the Subsolar Region: MAVEN Observations Compared to a One‐Dimensional Model

AbstractPrior to the Mars Atmospheric Volatile EvolutioN (MAVEN) mission, altitude profiles of the electron temperature in the Martian thermosphere were measured only twice. Because the rates of several geophysically important processes depend strongly on the electron temperature, models of the Martian thermosphere and atmospheric escape rates have not been well constrained. In this paper, we use densities and temperatures measured by MAVEN instruments and the one‐dimensional model of Matta et al. (2014, https://doi.org/10.1016/j.icarus.2013.09.006) to test our understanding of the processes that determine the electron temperature. Our analysis is limited to inbound orbits where the magnetic field is within 30° of horizontal and the satellite is within 30° of the subsolar point at altitudes from 120 to 250 km. We introduce empirically adjusted electron temperatures below 180 km, where the MAVEN electron temperature measurements are known to be biased high. We introduce the concept of a local electron heating efficiency, which we define at a given altitude as the ratio of electron heating from photoionization to the total extreme ultraviolet energy deposited. Our analysis shows that MAVEN observations are consistent with the one‐dimensional model below ~210 km if the electron heating efficiency varies with altitude, and the electron temperature is within the empirical bounds below 180 km we introduced. It indicates that above ~210 km electron heat conduction dominates extreme ultraviolet heating in determining electron temperature. Our analysis also suggests that in the subsolar region electrons and neutrals are in thermal equilibrium below 120 km.

An Innovative Diagnostic Film for Structural Health Monitoring of Metallic and Composite Structures.

A novel lightweight diagnostic film with sensors/actuators and a multiple-path wiring option using inkjet printing was developed. The diagnostic film allows for systematic, accurate, and repeatable sensor placement. Furthermore, the film is highly flexible and adaptable for placement on complex configurations. The film can be attached to the surface of the structure through a uniform secondary boundary procedure or embedded within the composite layup during curing. The surface-mounted film can simply be peeled off for repair or replacement without scratching or damaging the part. The film offers significant weight reduction compared to other available technologies. A set of extreme temperature, altitude, and vibration environment test profiles were carried out following the Radio Technical Commission for Aeronautics (RTCA) DO-160 document to assess the durability and performance of the diagnostic film for onboard application. The diagnostic film was shown to be durable and reliable in withstanding the variable operational and harsh environmental conditions of tests representing the conditions of regional aircraft.

Possibility of simultaneous [O3] and [CO2] altitude distribution retrievals from the daytime emissions of electronically-vibrationally excited molecular oxygen in the mesosphere

In this study we have formulated the multi-channel method for retrieval of the O(3P), O3 and CO2 volume mixing ratios, Cv,O(3P),Cv,O3 and Cv,CO2, altitude profiles in the daytime mesosphere and lower thermosphere from the simultaneous measurements of intensities of three emissions formed by transitions from three electronically-vibrationally excited states, O2(b1Σg+, v = 2), O2(b1Σg+, v = 1) and O2(b1Σg+, v = 0). Only using the YM2011 model of kinetics of O3 and O2 photolysis (Yankovsky et al., 2016. J. Molec. Spectr., 327, 209–232) allowed us to consider in detail the complex groups of the processes of excitation and quenching of the states O2(b1Σg+, v = 0, 1, 2), the transitions from which form the system of the O2 Atmospheric bands observed in the dayglow of the Earth. For the altitude range 50–85 km we developed in details the two-channel method of simultaneously retrieval of the volume mixing ratios of O3 and CO2. For this method, we succeeded in obtaining formulas that can be used for remote sensing of the Earth atmosphere from satellites.

Vertical diffusion transport of atomic oxygen in the mesopause region consistent with chemical losses and continuity: Global mean and inter-annual variability

This study describes the vertical diffusion velocity and eddy transport coefficient means derived from the climatological measurements of mesospheric [O] by SABER. Fifty years ago, Colegrove et al. (1967) described a process to transition between the two regions of the atmosphere using transport and continuity equations along with a 1-D composition profile. The two parts of this study are calculations of the downward O diffusion velocities and eddy diffusion coefficients using O densities derived from SABER for: 1) the global mean (±55°) and 2) the inter-annual variation of global and equatorial annual mean O densities. The derived transport diffusion velocities range from ∼1 to 4 cm s−1 at 95-83 km, and kzz varies between ∼9.0–5.0 × 105 cm2 s−1 over the same altitude range. The values of kzz derived here in the 80–100 km region are larger at 98 km than those calculated by Salinas et al. (2016) using SABER CO2 measurements and ∼0.5 times less than Qian et al. (2009, 2013 and TIEGCM model) which were derived from studies of thermospheric O/N2 measurements. Consideration of the kzz altitude profiles in the mesosphere, the mean values for both Salinas et al. (2016) and this study is ∼7. E+05 cm2s-1. The standard deviation of the inter-annual variability in kzz (and downward transport velocities) from globally averaged O profiles is <5%. The deviation is slightly larger (7.4%) at the equator, where a QBO trend is noted at 88 km, although not sufficiently large to be detected in the time history of the mesospheric O column density. The global average column density of O in the mesosphere (80–100 km) had a 0.30% change per sunspot. We suggest that model studies may need to consider higher turbulence (and kzz) in the 100–110 km region in order to satisfy both mesospheric and thermospheric composition.

MAVEN/IUVS Stellar Occultation Measurements of Mars Atmospheric Structure and Composition

AbstractThe Imaging UltraViolet Spectrograph (IUVS) instrument of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has acquired data on Mars for more than one Martian year. During this time, beginning with March 2015, hundreds of stellar occultations have been observed, in 12 dedicated occultation campaigns, executed on average every 2 to 3 months. The occultations cover the latitudes from 80°S to 75°N and the full range longitude and local times with relatively sparse sampling. From these measurements we retrieve CO2, O2, and O3 number densities as well as temperature profiles in the altitude range from 20 to 160 km, covering 8 orders of magnitude in pressure from ∼2 × 101 to ∼4 × 10−7 Pa. These data constrain the composition and thermal structure of the atmosphere. The O2 mixing ratios retrieved during this study show a high variability from 1.5 × 10−3 to 6 × 10−3; however, the mean value seems to be constant with solar longitude. We detect ozone between 20 and 60 km. In many profiles there is a well‐defined peak between 30 and 40 km with a maximum density of 1–2 ×109 cm−3. Examination of the vertical temperature profiles reveals substantial disagreement with models, with observed temperatures both warmer and colder than predicted. Examination of the altitude profiles of density perturbations and their variation with longitude shows structured atmospheric perturbations at altitudes above 100 km that are likely nonmigrating tides. These perturbations are dominated by zonal wave numbers 2 and 3 with amplitudes greater than 45%.

Trends in stratospheric HCl from the ACE satellite mission

The Montreal Protocol has banned the production of long-lived chlorine-containing gases such as chlorofluorocarbons (CFCs) that deplete stratospheric ozone. These halogenated compounds ultimately form HCl in the upper atmosphere; the effectiveness of the Montreal Protocol can therefore be monitored by measuring stratospheric HCl. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measures infrared solar occultation spectra of the Earth's atmosphere from which altitude profiles of HCl volume mixing ratios (VMRs) are determined. The upper stratospheric HCl VMR time series has a linear trend of −4.8 ± 0.2%/decade for 2004–2017, highlighting the continuing success of the Montreal Protocol.

Impact assessment of pollutants from waste-related operations as a feature of holistic logistic tool

Waste management has still been a developing and progressing field, which demands continual improvements in waste transportation as well as proper selection of locations and technical operation of new treatment facilities. Most of research papers on waste management planning have been dealing with optimisation of network flows, thus minimising the cost and improving economic criteria. The shortest paths to treatment facilities are considered together with detailed analysis of their operation including heat and electricity demands in their vicinity. The tasks sometimes include social and global environmental criterions, however, the direct local consequences also play an important role and should be examined. A decision-making strategy in waste management updated with the local emission impact on the population is proposed in this paper. The paper focuses on the first move in analysing the production, dispersion, and impact of pollutants, originating in transport, with regards to the population living close to routes. The calculation of emission produced during the transport of waste takes into consideration the altitude profiles of routes, container loads, and specific types of vehicles. The consecutive estimated impact on the population reckons with the distances between routes and municipalities as well as their sizes in terms of the numbers of inhabitants, where the transportation routes are divided into smaller segments and dispersion is limited with threshold value. The proposed approach describing the emission effect has been tested using real-life operating data corresponding to the specific, 81 km long route along which approximately 25 t of waste is transported 800 times a year. The impact of pollutants on the population was evaluated and discussed. Results of the analysis were quantified for this route to create an edge characterisation needed for further calculations. This approach applied to the whole network then yields input data needed for future research of novel strategies in facility location problems. Other possible extensions of the presented approach include more accurate dispersion function or detailed calculation of the impact of pollutants with respect to specific locations of residential houses.

Áreas potenciales para el cultivo de girasol en condiciones de temporal en Guanajuato, México

In Mexico, in the last five years, there was a 189.50 to 13 219.84 hectares increase in sunflower crop surface under rainfed conditions. Particularly, in 2016, in the state of Guanajuato, approximately 450 hectares were planted. Cultivation under rainfed conditions requires planning including bioclimatic variables to reach the optimal crop yield and development. This work aims to identify bioclimatic potential areas for sunflower cultivation under rainfed conditions in Guanajuato. In autumn-winter 2016, 45 sunflower fields (distributed in eleven towns) were monitored and stratified. Crop yield associated with maximum and minimum temperature, relative humidity, solar radiation, precipitation, and evapotranspiration were recorded. The data from fields with a higher yield than 1.89 t/ha were used to generate polygons with a saturation of 56 abundance points, to calculate the potential distribution using the Maxent software, with 23 bioclimatic variables as predictors. The variables with the highest contribution percentage to the potential distribution were: average temperature of the driest quarter, altitude, moisture regime, and edaphic profile. The potential areas for sunflower cultivation had a surface of 317 028 hectares where the predominant climate is sub-humid warm, the annual mean temperature is 20 °C, the annual mean rainfall is 600 to 800 mm, and the altitude ranges from 500 to 1500 masl.

Inferring Nighttime Ionospheric Parameters With the Far Ultraviolet Imager Onboard the Ionospheric Connection Explorer.

The Ionospheric Connection Explorer (ICON) Far Ultraviolet (FUV) imager, ICON FUV, will measure altitude profiles of OI 135.6 nm emissions to infer nighttime ionospheric parameters. Accurate estimation of the ionospheric state requires the development of a comprehensive radiative transfer model from first principles to quantify the effects of physical processes on the production and transport of the 135.6 nm photons in the ionosphere including the mutual neutralization contribution as well as the effect of resonant scattering by atomic oxygen and pure absorption by oxygen molecules. This forward model is then used in conjunction with a constrained optimization algorithm to invert the anticipated ICON FUV line-of-sight integrated measurements. In this paper, we describe the connection between ICON FUV measurements and the nighttime ionosphere, along with the approach to inverting the measured emission profiles to derive the associated O+ profiles from 150-450 km in the nighttime ionosphere that directly reflect the electron density in the F-region of the ionosphere.

ISR Spectra Simulations With Electron‐Ion Coulomb Collisions

AbstractIncoherent scatter radars (ISR) rely on Thomson scattering of very high frequency or ultrahigh frequency radio waves off electrons in the ionosphere and measure the backscattered power spectra in order to estimate altitude profiles of plasma density, electron temperature, ion temperature, and ion drift speed. These spectra result from the collective behavior of coupled ion and electron dynamics, and, for most cases, existing theories predict these well. However, when the radar points nearly perpendicular to the Earth's magnetic field, the motion of the plasma across the field lines becomes complex and Coulomb collisions between electrons and ions become important in interpreting ISR measurements. This paper presents the first fully kinetic, self‐consistent, particle‐in‐cell simulations of ISR spectra with electron‐ion Coulomb collisions. We implement a grid‐based Coulomb collision algorithm in the Electrostatic Parallel Particle‐in‐Cell simulator and obtain ISR spectra from simulations both with and without collisions. For radar directions greater than 5° away from perpendicular to the magnetic field, both sets of simulations match collisionless ISR theory well. For angles between 3° and 5°, the collisional simulation is well described by a simplified Brownian motion collision process. At angles less than 3° away from perpendicular the Brownian motion model fails, and the collisional simulation qualitatively agrees with previous single particle simulations. For radar directions exactly perpendicular to the magnetic field the simulated collisional spectra match those from the Brownian motion collision theory, in agreement with previous single particle simulations.

The analysis is geometrically stable orbits of spacecraft remote sensing of the Еarth

The article reviewed and analyzed the class of geometrically stable orbits (GUO). The conditions of stability in the model of the geopotential, taking into account the zonal harmonics. The sequence of calculation of the state vector of GUO in the osculating value of the argument of the latitude with the famous Ascoli-royski longitude of the ascending node, inclination and semimajor axis. The simulation is obtained the altitude profiles of SEE regarding the all-earth ellipsoid model of the gravitational field of the Earth given 7 and 32 zonal harmonics.

Investigation of the Electron Density Variation During the 21 August 2017 Solar Eclipse

AbstractThis paper presents a comparison of modeled and measured electron densities for the 21 August 2017 solar eclipse across the USA. The location of the instrument was (43.81°N, 247.32°E) where the maximum obscuration of 99.6% occurred at 17.53 hr UT on 21 August. The solar apparent time was 9.96 hr, and the duration of the eclipse was 2.7 hr. It was found that if it is assumed that there are no chromosphere emissions at totality, ~30% coronal emission remaining at totality gave the best fit to the electron density variation at 150 km. The 30% coronal emission estimate has uncertainties associated with respect to uncertainties in the solar spectrum, the measured electron density, and the amount of chromosphere emissions remaining at totality. The agreement between the modeled and measured electron densities is excellent at 150 km with the assumed 30% coronal emission at totality. At other altitudes, the agreement is very good, but the altitude profile would be improved if the model peak electron density (NmF2) decayed more slowly to better match the data. The minimum NmF2 in the model occurs ~10 min after totality when it decreases to 0.55 from its noneclipse value. The minimum of the NmF2 data occurs between 6 and 10 min after totality but is ~15% larger. The total electron content decreases to 0.65 of its preeclipse value. These relative changes agree well with those predicted by others prior to the eclipse.