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It is well-known that equatorial plasma bubbles (EPBs) are highly correlated to the post-sunset rise of the ionosphere on a climatological basis. However, when proceeding to the daily EPB development, what controls the day-to-day/longitudinal variability of EPBs remains a puzzle. In this study, we investigate the underlying physics responsible for the day-to-day/longitudinal variability of EPBs using the Sami3 is A Model of the Ionosphere (SAMI3) and the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X). Simulation results on October 20, 22, and 24, 2020 were presented. SAMI3/WACCM-X self-consistently generated midnight EPBs on October 20 and 24, displaying irregular and regular spatial distributions, respectively. However, EPBs are absent on October 22. We investigate the role of gravity waves on upwelling growth and EPB development and discuss how gravity waves contribute to the distributions of EPBs. Of particular significance is that we found the westward wind associated with solar terminator waves and gravity waves causes midnight vertical drift enhancement and collisional shear instability, which provides conditions favorable for upwelling growth and EPB development. The converging and diverging winds associated with solar terminator waves and midnight temperature maximum also affect the longitudinal distribution of EPBs. The absence of EPBs on October 22 is related to the weak upward drift induced by weak westward wind associated with solar terminator waves.

The Naval Research Laboratory first-principles ionosphere model SAMI3/ESF is performed to study the interaction between the nighttime medium-scale traveling ionospheric disturbances (MSTIDs) and equatorial plasma bubbles (EPBs). The synthetic dynamo currents are imposed into the potential equation to induce polarization electric fields for generating the MSTIDs. Simulations demonstrate that the MSTIDs can inhibit the upward growth of EPBs; however, MSTIDs alone are insufficient to explain the disappearance of EPBs. We found that the meridional winds likely contribute to the disappearance of MSTIDs by reducing the background electron density and polarization electric fields within the EPBs. Then, the MSTIDs transport plasma to fill the EPB depletions up via E × B drifts. Both MSTIDs and meridional winds are necessary to comprehend the underlying mechanism of EPB disappearance. Additionally, we also found that the zonal and vertical E × B drifts within the MSTIDs affect the morphology of EPBs, leading to a reverse-C shape structure.

Total electron content (TEC) observations can provide insights into electron density variations in the ionosphere. Such variations are associated with many aspects of ionospheric dynamics, including traveling ionospheric disturbances. In the present work we assimilate observations of TEC and horizontal TEC gradients into the SAMI3 (SAMI3 is Another Model of the Ionosphere 3D) ionosphere model. Assimilation into SAMI3 is accomplished using an ensemble Kalman filter implemented within LightDA, an extensible data assimilation library. Our TEC gradient observations are obtained from the Very Large Array Low-band Ionosphere and Transient Experiment (VLITE) and the TEC measurements are derived from GNSS receiver data. VLITE provides high precision and high spatial resolution TEC gradient observations over a small area, while GNSS observations supplement these with global coverage. By leveraging TEC observations in a physics-based model through data assimilation, we aim to improve our understanding of ionospheric processes and develop tools for improved ionospheric forecasting capabilities.

The SAMI3/ESF (Sami3 is also a model of the ionosphere/equatorial spread $F$) code is used to simulate the growth of equatorial plasma bubbles in the presence of a background wind field based on me...

The Naval Research Laboratory first-principles ionosphere model SAMI3/ESF is performed to study the interaction between the nighttime medium-scale traveling ionospheric disturbances (MSTIDs) and equatorial plasma bubbles (EPBs). The synthetic dynamo currents are imposed into the potential equation to induce polarization electric fields for generating the MSTIDs. Simulations demonstrate that the MSTIDs can inhibit the upward growth of EPBs; however, MSTIDs alone are insufficient to explain the disappearance of EPBs. We found that the meridional winds likely contribute to the disappearance of MSTIDs by reducing the background electron density and polarization electric fields within the EPBs. Then, the MSTIDs transport plasma to fill the EPB depletions up via E × B drifts. Both MSTIDs and meridional winds are necessary to comprehend the underlying mechanism of EPB disappearance. We also found that the zonal and vertical E × B drifts within the MSTIDs affect the morphology of EPBs, leading to a reverse-C shape structure.

The Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code is used to examine the physics of metallic layers at altitudes from 80 to 160 km. Re...

On 21 August 2017, a total solar eclipse traversed the continental United States and caused large-scale changes in ionospheric densities. These were detected as changes in medium-and high-frequency radio propagation by the Solar Eclipse QSO Party citizen science experiment organized by the Ham Radio Science Citizen Investigation (hamsci.org). This is the first eclipse-ionospheric study to make use of measurements from a citizen-operated, global-scale HF propagation network and develop tools for comparison to a physics-based model ionosphere. Eclipse effects were observed +/- 0.3 hr on 1.8 MHz, +/- 0.75 hr on 3.5 and 7 MHz, and +/- 1 hr on 14 MHz and are consistent with eclipse-induced ionospheric densities. Observations were simulated using the PHaRLAP raytracing toolkit in conjunction with the eclipsed SAMI3 ionospheric model. Model results suggest 1.8, 3.5, and 7 MHz refracted at h >= 125 km altitude with elevation angles theta >= 22 degrees, while 14 MHz signals refracted at h < 125 km with elevation angles theta < 10 degrees. NSF [AGS-1552188/479505-19C75] NAF acknowledges the support of NSF Grant AGS-1552188/479505-19C75. Kp and DST indices were obtained from the Kyoto WDC. F10.7 data were accessed through the OMNI database at the NASA Space Physics Data Facility. GOES data are provided by NOAA SWPC. RBN data are provided by reversebeacon.net, with thanks to F. Ceglia, P. Smith, and R. Williams. We thank the global amateur radio community and the ARRL for making the SEQP possible. The results published in this paper were obtained using the HF propagation toolbox, PHaRLAP, created by Manuel Cervera, Defence Science and Technology Group, Australia (manuel.cervera@dsto.defence.gov.au). This toolbox is available by request from its author. SAMI3 outputs are available by contacting J. Huba at huba@nrl.navy.mil. We acknowledge the use of the Free Open Source Software projects used in this analysis: Ubuntu Linux, python, matplotlib, NumPy, SciPy, pandas, and others. NAF thanks R. M. Frissell and L. J. Lanzerotti for helpful discussions.

Recent studies suggest that the hydrogen (H) density in the exosphere and geocorona might differ from previously assumed values by factors as large as 2. We use the SAMI3 (Sami3 is Also a Model of the Ionosphere) and Comprehensive Inner Magnetosphere-Ionosphere models to evaluate scenarios where the hydrogen density is reduced or enhanced, by a factor of 2, relative to values given by commonly used empirical models. We show that the rate of plasmasphere refilling following a geomagnetic storm varies nearly linearly with the hydrogen density. We also show that the ring current associated with a geomagnetic storm decays more rapidly when H is increased. With respect to these two space weather effects, increased exosphere hydrogen density is associated with reduced threats to space assets during and following a geomagnetic storm.

The erosion of the plasmasphere during a storm is analyzed using the Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code, coupled to the Rice Convection Model (RCM) of the inner magnetosphere and ring current. We reproduce the commonly-observed post-storm plasmasphere profile, with strong erosion outside of a sharp, post-storm plasmapause and weak erosion inside the plasmapause. We find that inclusion of the ring current E field sharpens the post-storm plasmapause. In the case of a weak storm, erosion inside the post-storm plasmapause might not occur. In all cases, plasma flows are dominated by E × B drifts. For strong storms, we find that erosion, both inside and outside of the post-storm plasmapause, is caused by outward E × B drifts.

We present quantitative predictions of the impact of the upcoming total solar eclipse on the ionosphere and plasmasphere using the Naval Research Laboratory (NRL) model Sami3 is Also a Model of the Ionosphere (SAMI3). The eclipse will occur over the continental United States on 21 August 2017. Our simulation results indicate that in the vicinity of the eclipse (1) the total electron content (TEC) decreases by up to ∼ 5 TEC units (TECU; 1 TECU = ×1016 m−2) which is a ∼ 35% decrease in TEC, (2) the electron density decreases by a factor of ∼ 50% in the F region, (3) the electron temperature decreases by up to ∼800 K in the plasmasphere, and (4) the O+ velocity changes from ∼40 m s−1 upward to ∼20 m s−1 downward in the F region. Interestingly, the continental size modification of the ionospheric conductance modifies the global electric field, which should lead to measurable changes in the TEC in the southern conjugate hemisphere ( ≲1 TECU).

The SMART (Space Measurement of A Rocket-released Turbulence) experiment will demonstrate the production of electromagnetic waves in the space environment via a cascade of plasma physics processes. A sounding rocket will release heavy atoms into the upper ionosphere at high speed (∼10 km/s) across the magnetic field. These atoms photoionize and the magnetic field traps them, leading to a ring distribution in velocity space. An ion ring distribution is unstable to electrostatic lower hybrid waves with perpendicular wavelengths much shorter than the electron skin depth. Nonlinear induced scattering of lower hybrid waves produces electromagnetic magnetosonic and whistler waves with wavelengths large compared to the skin depth. Due to their large group velocities, these electromagnetic waves rapidly escape the experimental (or source) region and propagate into the radiation belts where the amplitude is expected to be similar to large lightning generated whistlers. In this talk, we will describe these plasma processes, the experimental design of SMART, the theoretical and computational work underway to quantitatively predict the results of the experiment, and the ways in which these processes are expected to play important roles in the near-Earth space environment.

Measurements show that plasmasphere refilling rates decrease with increasing solar activity, while paradoxically, the vertical integration of the plasmasphere electron density (pTEC) increases with increasing solar activity. Using the Naval Research Laboratory SAMI2 (Sami2 is Another Model of the Ionosphere) and SAMI3 (Sami3 is Also a Model of the Ionosphere) codes, we simulate plasmasphere refilling following a model storm, reproducing this observed phenomenon. In doing so, we find that the refilling rate and resulting pTEC values are sensitive to the oxygen profile in the thermosphere and exosphere: the supply of H+ in the topside ionosphere is limited by the local O+ density, through H+O+→H++O charge exchange. At solar minimum, the O+ supply simply increases with the O density in the exosphere. At solar maximum, we find that O-O+ collisions limit the O+ density in the topside ionosphere such that it decreases with increasing O density. The paradox occurs because the pTEC metric gives electrons in the topside ionosphere more weight than electrons in the plasmasphere.

The NRL ionosphere/plasmasphere model SAMI3 has been modified to support the NASA ICON mission. Specifically, SAMI3_ICON has been modified to import the thermospheric composition, temperature, and winds from TIEGCM-ICON and the high-latitude potential from AMIE data. The codes will be run on a daily basis during the ICON mission to provide ionosphere and thermosphere properties to the science community. SAMI3_ICON will provide ionospheric and plasmaspheric parameters such as the electron and ion densities, temperatures, and velocities, as well as the total electron content (TEC), peak ionospheric electron density (NmF2) and height of the $F$ layer at NmF2 (hmF2).

Some wave-like features in the longitudinal distribution of equatorial plasma bubbles understood in association with diurnal eastward propagating zonal wave number 3 nonmigrating tide (DE3) in the dayside. However, whether or not the wave features are the daytime DE3 signature has not yet been rigorously investigated. This study investigates (1) the existence of the DE3 signature in the longitudinal distribution of bubbles by analyzing the first Republic of China (ROCSAT-1) satellite data acquired in 2000–2002 and (2) the role of daytime DE3 in the creation of bubbles by examining the linear growth rate of the generalized Rayleigh-Taylor (R-T) instability. The linear growth rate is derived from the “Sami2 is Another Model of the Ionosphere” model simulation results. In the longitudinal distribution of bubbles derived from ROCSAT-1 observations, the wave number 4 component, the representative characteristic of DE3, is a weak feature. In addition, the amplitude and phase of the wave number 4 component do not show a consistent behavior in comparison with those of DE3. Our numerical calculation results show that the linear growth rate of the R-T instability is not sensitive to the variation of the daytime vertical plasma drift. These results indicate that the DE3 signature in the occurrence rate of bubbles is not obvious and the effect of daytime DE3 on the creation of bubbles is negligible.

To address challenges of assessing space weather modeling capabilities, the CommunityCoordinated Modeling Center is leading a newly establishedInternational Forum for Space WeatherModeling Capabilities Assessment. This paper presents preliminary results of validation of modeled foF2 (F2 layer critical frequency) and TEC (total electron content) during the first selected 2013 March storm event (17 March 2013). In this study, we used eight ionospheric models ranging from empirical to physics-based, coupled ionosphere-thermosphere and data assimilation models. The quantities we considered are TEC and foF2 changes and percentage changes compared to quiet time background, and the maximum and minimum percentage changes. In addition, we considered normalized percentage changes of TEC. We compared the modeled quantities with ground-based observations of vertical Global Navigation SatelliteSystem TEC (provided by Massachusetts Institute of Technology Haystack Observatory) and foF2 data (provided by Global Ionospheric Radio Observatory) at the 12 locations selected in middle latitudes of the American and European-African longitude sectors. To quantitatively evaluate the models’ performance, we calculated skill scores including correlation coefficient, root-mean square error (RMSE), ratio of the modeled to observed maximum percentage changes (yield), and timing error. Our study indicates that average RMSEs of foF2range from about 1 MHz to 1.5 MHz. The average RMSEs of TEC are between ~5 and ~10 TECU (1 TEC Unit= 1016el/m2). dfoF2[%] RMSEs are between 15% and 25%, which is smaller than RMSE of dTEC[%] ranging from30% to 60%. The performance of the models varies with the location and metrics considered.

In this study, we use the three-dimensional, physics-based numerical model, SAMI3 (Sami3 is Another Model of the Ionosphere), to self-consistently generate nighttime, electrified, medium-scale traveling ionospheric disturbances (MSTIDs) at midlatitudes. These are the first numerical simulations to use the fundamental, physics-based equations in a full flux tube model for the self-consistent generation of MSTIDs. We show that a random perturbation results in the development of modes consistent with the Perkins instability and that the growth rate of a specified k perturbation agrees well with linear theory. We also present synthetic observations of MSTIDs: total electron content, integrated 630.0 nm airglow emission, E × B drift, and electron density. The modeling results show the signature of the instability in the geomagnetic conjugate hemisphere, which has been previously observed experimentally. The qualitative descriptions of the E × B drift and electron density profiles of the MSTIDs provided by SAMI3 are found to be consistent with experimental studies of MSTIDs found in the literature.

[1] For the first time, equatorial plasma depletions (EPDs) have been imaged in the longitude-altitude plane using radiotomography. High-resolution (~10 km) reconstructions of electron density were derived from total electron content (TEC) measurements provided by a receiver array in Peru. TEC data were obtained from VHF/UHF signals transmitted by the Coherent Electromagnetic Radio Tomography (CERTO) beacon on the C/NOFS satellite. EPDs generated premidnight were observed near dawn. On one night, the bubble densities were highly reduced, 100–1000 km wide, and embedded within a layerlike ionosphere. Three nights later, the EPDs exhibited similar features but were embedded in a locally uplifted ionosphere. The C/NOFS in situ instruments detected a dawn depletion where the reconstruction showed lifted EPDs, implying that the postmidnight electric fields raised sections of ionosphere to altitudes where embedded/reactivated fossil EPDs were detected as dawn depletions. Satellites flying under domelike distortions of the ionosphere may observe these distortions as broad plasma decreases (BPDs).

[1] The impact of meridional winds on the onset and evolution of equatorial spread F (ESF) is studied using the NRL ionosphere model SAMI3/ESF. The prevailing belief is that meridional winds have a stabilizing effect on the onset of ESF. In this letter, it is shown that this is not necessarily the case and that meridional winds can be destabilizing. We find that a wind profile with a positive gradient as a function of latitude (∂V m ∕ ∂θ ≥ 0) is a stabilizing influence on the generalized Rayleigh-Taylor instability; a wind profile with a negative gradient (∂V m ∕ ∂θ

International audience; Ionospheric irregularities associated with horizontal magnetic fields below 200 km altitude are observed at Mars. Plasma density modulations of up to 200% are observed during such events and appear correlated with fluctuations in the magnetic field. The observed fluctuations are likely Doppler shifted and represent spatial structures at length scales of 15-20 km or less. Conditions in the Martian ionosphere below 200 km are synonymous with the terrestrial E region, where ionospheric irregularities have been extensively studied. Interestingly, the irregularities at Mars appear to be electromagnetic in nature, in contrast to the electrostatic nature of irregularities at Earth. It is currently unclear what the primary drivers of these irregularities at Mars are, and further study is needed to explain these important phenomenon within the Martian ionosphere.

[1] The study of the plasmasphere is extremely important to understanding space weather phenomena; for example, it plays a critical role in the regulation of radiation belt dynamics. In this paper, the first 3D simulation of the plasmasphere based on the first-principles physics model SAMI3 is presented. We include the co-rotation potential, the neutral wind dynamo potential, and a time-dependent Volland-Stern-Maynard-Chen potential to model the response of the convection potential to an idealized magnetic storm. We find that prior to the storm the plasmasphere is largely toroidal and symmetric in magnetic local time with He+/H+ ~ 5–10%. After the storm, the plasmasphere substantially contracts because plasma is convected away from the outer plasmasphere by the enhanced convection velocity. Moreover, a plume-like structure forms in the mid-afternoon sector because of the modified convection pattern associated with the storm. Additionally good agreement is found between the simulation results and data for the L-shell dependence of the equatorial electron density as well as the electron density along the field line at a given L-shell under quiet geomagnetic conditions.

Recent advances in space-based heliospheric observations, laboratory experimentation, and plasma simulation codes are creating an exciting new cross-disciplinary opportunity for understanding fast energy release and transport mechanisms in heliophysics and laboratory plasma dynamics, which had not been previously accessible. This article provides an overview of some new observational, experimental, and computational assets, and discusses current and near-term activities towards exploitation of synergies involving those assets. This overview does not claim to be comprehensive, but instead covers mainly activities closely associated with the authors’ interests and reearch. Heliospheric observations reviewed include the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) on the National Aeronautics and Space Administration (NASA) Solar Terrestrial Relations Observatory (STEREO) mission, the first instrument to provide remote sensing imagery observations with spatial continuity extending from the Sun to the Earth, and the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Japanese Hinode spacecraft that is measuring spectroscopically physical parameters of the solar atmosphere towards obtaining plasma temperatures, densities, and mass motions. The Solar Dynamics Observatory (SDO) and the upcoming Solar Orbiter with the Heliospheric Imager (SoloHI) on-board will also be discussed. Laboratory plasma experiments surveyed include the line-tied magnetic reconnection experiments at University of Wisconsin (relevant to coronal heating magnetic flux tube observations and simulations), and a dynamo facility under construction there; the Space Plasma Simulation Chamber at the Naval Research Laboratory that currently produces plasmas scalable to ionospheric and magnetospheric conditions and in the future also will be suited to study the physics of the solar corona; the Versatile Toroidal Facility at the Massachusetts Institute of Technology that provides direct experimental observation of reconnection dynamics; and the Swarthmore Spheromak Experiment, which provides well-diagnosed data on three-dimensional (3D) null-point magnetic reconnection that is also applicable to solar active regions embedded in pre-existing coronal fields. New computer capabilities highlighted include: HYPERION, a fully compressible 3D magnetohydrodynamics (MHD) code with radiation transport and thermal conduction; ORBIT-RF, a 4D Monte-Carlo code for the study of wave interactions with fast ions embedded in background MHD plasmas; the 3D implicit multi-fluid MHD spectral element code, HiFi; and, the 3D Hall MHD code VooDoo. Research synergies for these new tools are primarily in the areas of magnetic reconnection, plasma charged particle acceleration, plasma wave propagation and turbulence in a diverging magnetic field, plasma atomic processes, and magnetic dynamo behavior., United States. Office of Naval Research, Naval Research Laboratory (U.S.)

Long-pulse topside radar data acquired at Jicamarca and processed using full-profile analysis are compared to data processed using more conventional, range-gated approaches and with analytic and computational models. The salient features of the topside observations include a dramatic increase in the Te/Ti temperature ratio above the F peak at dawn and a local minimum in the topside plasma temperature in the afternoon. The hydrogen ion fraction was found to exhibit hyperbolic tangent-shaped profiles that become shallow (gradually changing) above the O+-H+ transition height during the day. The profile shapes are generally consistent with diffusive equilibrium, although shallowing to the point of changes in inflection can only be accounted for by taking the effects of E×B drifts and meridional winds into account. The SAMI2 model demonstrates this as well as the substantial effect that drifts and winds can have on topside temperatures. Significant quiet-time variability in the topside composition and temperatures may be due to variability in the mechanical forcing. Correlations between topside measurements and magnetometer data at Jicamarca support this hypothesis.

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts., Comment: 71 pages, 35 figures

A shock precursor in a thin thermal layer above a 3000 K hot surface is measured in a small-scale laboratory experiment. Precursor and thermal layer characteristics are diagnosed using spectroscopy, interferometry, and dark-field shadowgraphy. The experiment is successfully simulated with a code previously validated using large-scale high-explosive tests, thereby demonstrating its applicability to events that differ in energy by 12 orders of magnitude. The simulation shows that a small-scale laboratory experiment can be a good surrogate for infrequent, expensive, and hard to diagnose large-scale tests.

For the first time, post-midnight Equatorial Plasma Depletions (EPDs) have been imaged in the longitude-altitude plane using radio-beacon tomography. High-resolution (∼10 km × 10 km) electron-density reconstructions were created in the area between approximately −90° and −55° longitude near the geomagnetic equator. The reconstructions were created using Total Electron Content (TEC) measurements from an NRL receiver array sited in Peru and the MART inversion algorithm. TEC was derived from the 150 and 400 MHz signals transmitted by the CERTO beacon on the C/NOFS satellite. The MART algorithm requires an “initial guess” ionosphere, which was generated by using in-situ electron density data from the C/NOFS CINDI instrument and electron density profiles from an ionosonde operated by the University of Massachusetts at Lowell (UML). Each initial guess ionosphere was approximated below the F-peak by replicating an ionosonde profile over all longitudes within the imaging region; above the F-peak a Chapman function was fitted to the ionosonde F-peak density and the corresponding CINDI in-situ measurement at each longitude. In this study, EPDs spawned pre-midnight were imaged near dawn. Observed EPDs had widths of 100–1000 km, spacings of 300–900 km, and often appeared “pinched off” at the bottom. Well-developed EPDs appeared on an evening with a very small (4 m/s) Pre-Reversal-Enhancement (PRE), suggesting that postmidnight enhancements of the vertical plasma drift and/or seeding-induced uplifts (e.g. gravity waves) were responsible for driving the Rayleigh-Taylor Instability into the nonlinear regime on this night. On another night the Jicamarca incoherent scatter radar recorded postmidnight (∼0230 LT) Eastward electric fields nearly twice as strong as the PRE fields seven hours earlier. These electric fields lifted the whole ionosphere, including embedded EPDs, over a longitude range ∼14° wide. CINDI detected a dawn depletion in exactly the area where the reconstruction showed an uplifted EPD. Strong Equatorial Spread-F observed by the UML ionosonde during receiver observation times confirmed the presence of ionospheric irregularities.

We review physical processes of ionized plasma and neutral gas coupling in the weakly ionized, stratified, electromagnetically-permeated regions of the Sun’s chromosphere and Earth’s ionosphere/thermosphere. Using representative models for each environment we derive fundamental descriptions of the coupling of the constituent parts to each other and to the electric and magnetic fields, and we examine the variation in magnetization of the components. Using these descriptions we compare related phenomena in the two environments, and discuss electric currents, energy transfer and dissipation. We present examples of physical processes that occur in both atmospheres, the descriptions of which have previously been conducted in contrasting paradigms, that serve as examples of how the chromospheric and ionospheric communities can further collaborate. We also suggest future collaborative studies that will help improve our understanding of these two different atmospheres, which while sharing many similarities, also exhibit large disparities in key quantities.