Larry J. Paxton

Control of equatorial ionospheric morphology by atmospheric tides

[1] A newly discovered 1000-km scale longitudinal variation in ionospheric densities is an unexpected and heretofore unexplained phenomenon. Here we show that ionospheric densities vary with the strength of nonmigrating, diurnal atmospheric tides that are, in turn, driven mainly by weather in the tropics. A strong connection between tropospheric and ionospheric conditions is unexpected, as these upward propagating tides are damped far below the peak in ionospheric density. The observations can be explained by consideration of the dynamo interaction of the tides with the lower ionosphere (E-layer) in daytime. The influence of persistent tropical rainstorms is therefore an important new consideration for space weather. Citation: Immel, T. J., E. Sagawa, S. L. England, S. B. Henderson, M. E. Hagan, S. B. Mende, H. U. Frey, C. M. Swenson, and L. J. Paxton (2006), Control of equatorial ionospheric morphology by atmospheric tides, Geophys. Res. Lett., 33, L15108, doi:10.1029/2006GL026161. [2] The ionosphere is the region of highest plasma density in Earth’s space environment. It is a dynamic environment supporting a host of plasma instability processes, with important implications for global communications and geo-location applications. Produced by the ionization of the neutral atmosphere by solar x-ray and UV radiation, the uppermost ionospheric layer has the highest plasma density with a peak around 350–400 km altitude and primarily consists of O + ions. This is called the F-layer and it is considered to be a collisionless environment such that the charged particles interact only weakly with the neutral atmosphere, lingering long after sunset. The E-layer is composed of molecular ions and is located between 100–150 km where collisions between ions and neutrals are much more frequent, with the result that the layer recombines and is reduced in density a hundredfold soon after sunset [Rees ,1 989;Heelis, 2004]. The respective altitude regimes of these two layers are commonly called the E- and F-regions. [3] The ionosphere glows as O + ions recombine to an excited state of atomic oxygen (O I) at a rate proportional to

Initial observations with the Global Ultraviolet Imager (GUVI) in the NASA TIMED satellite mission

[1] The Global Ultraviolet Imager (GUVI) instrument carried aboard the NASA TIMED satellite measures the spectral radiance of the Earth’s far ultraviolet airglow in the spectral region from 120 to 180 nm using a cross-track scanning spectrometer design. Continuous operation of the instrument provides images of the Earth’s disk and limb in five selectable spectral bands. Also, spectra at fixed scanning mirror position can be obtained. Initial results demonstrate the quantitative functionality of the instrument for studies of the Earth’s dayglow, aurora, and ionosphere. Moreover, through forward modeling, the abundance of the major constituents of the thermosphere, O, N2, and O2 and thermospheric temperatures can be retrieved from observations of the limb radiance. Variations of the column O/N2 ratio can be deduced from sunlit disk observations. In regions of auroral precipitation not only can the aurora regions be geographically located and the auroral boundaries identified, but also the energy flux Q, the characteristic energy Eo, and a parameter fo that scales the abundance of neutral atomic oxygen can be derived. Radiance due to radiative recombination in the ionospheric F region is evident from both dayside and nightside observations of the Earth’s limb and disk, respectively. Regions of depleted F-region electron density are evident in the tropical Appleton anomaly regions, associated with so-called ionospheric ‘‘bubbles.’’ Access to the GUVI data is provided through the GUVI website www.timed.jhuapl.edu\guvi. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 0355 Atmospheric Composition and Structure: Thermosphere—composition and chemistry; 0358 Atmospheric Composition and Structure: Thermosphere—energy deposition; 2407 Ionosphere: Auroral ionosphere (2704); KEYWORDS: airglow, aurora, ultraviolet, imaging, satellite, atmosphere

Models of Venus neutral upper atmosphere - Structure and composition

Abstract Models of the Venus neutral upper atmosphere, based on both in-situ and remote sensing measurements, are provided for the height interval from 100 to 3,500 km. The general approach in model formulation was to divide the atmosphere into three regions: 100 to 150 km, 150 to 250 km, and 250 to 3,500 km. Boundary conditions at 150 km are consistent with both drag and mass spectrometer measurements. A paramount consideration was to keep the models simple enough to be used conveniently. Available observations are reviewed. Tables are provided for density, temperature, composition (CO 2 , O, CO, He, N, N 2 , and H), derived quantities, and day-to-day variability as a function of solar zenith angle on the day- and nightsides. Estimates are made of other species, including O 2 and D. Other tables provide corrections for solar activity effects on temperature, composition, and density. For the exosphere, information is provided on the vertical distribution of normal thermal components (H, O, C, and He) as well as the hot components (H, N, C, O) on the day- and nightsides.

Effect of atmospheric tides on the morphology of the quiet time, postsunset equatorial ionospheric anomaly

longitudinal wave number four pattern in the magnetic latitude and concentration of the F region peak ion density when measured at a fixed local time. In a new comparison of two data sets with observations made by the OGO 4 satellite, this pattern is seen to be persistent over many days around equinox during magnetically quiet conditions close to solar maximum but can be dominated by other processes such as cross-equator winds during other periods. It is found that the longitudinal variability is created by a processes occurring in the dayside ionosphere. A longitudinal modulation of the dayside equatorial fountainisthemostlikelydrivingmechanism.ThroughcomparisonwithGWSM-02model,it isshownthatthepredictedmodulationofthedaysidethermosphericwindsandtemperaturesat E region altitudes created by non-migrating diurnal tides can explain the modulation in the dayside equatorial fountain. This result highlights the importance of understanding the temporal variability of tropospheric weather systems on our understanding and possible predictability of the development of the F region ionosphere. It may also provide a possible further means of testing our understanding of atmospheric tides on a global scale.

Energy transport in the thermosphere during the solar storms of April 2002

The dramatic solar storm events of April 2002 deposited a large amount of energy into the Earths upper atmosphere, substantially altering the thermal structure, the chemical composition, the dynam ...

Atomic oxygen in the Martian thermosphere

Modern models of thermospheric composition and temperature and of excitation and radiative transfer processes are used to simulate the O I 130-nm emission from Mars measured by the Mariner 9 ultraviolet spectrometer. We use the Mars thermospheric general circulation model calculations (MTGCM) of Bougher et al. (1988a) and the Monte Carlo partial frequency redistribution multiple scattering code of Meier and Lee (1982). We find that the decline in atomic oxygen through the daylight hours predicted by the MTGCM cannot be reconciled with the excess afternoon brightness seen in the data. Oxygen concentrations inferred from the data show a positive gradient through the day, in agreement with the original analysis by Strickland et al. (1973), although the absolute amounts are somewhat less because we use a larger photoelectron impact excitation and a somewhat larger solar flux in the 130-nm triplet. In addition, the data suggest that the oxygen abundance increases toward high southerly latitudes, in contrast with the MTGCM prediction of high values in the northern (winter) hemisphere. It appears that solar forcing alone cannot account for the observed characteristics of the Martian thermosphere and that wave and tidal effects may profoundly affect the structure, winds, and composition.

High‐resolution vertical E × B drift model derived from ROCSAT‐1 data

[1] The measurements of vertical ion velocity from the first Republic of China satellite (ROCSAT-1) provide a unique database for the development of an annually and longitudinally high-resolution vertical plasma drift model in the equatorial ionosphere. Currently, the ROCSAT-1-based empirical vertical drift models are available for three seasons: equinox and solstices. However, the vertical drift patterns are not precisely divided by the three seasons. A monthly vertical drift model with high longitudinal resolution is desirable to accurately model the low-latitude ionosphere and to identify the coupling between the ionosphere and atmospheric tide. Here we introduce an empirical vertical drift model derived by using the ROCSAT-1 data in three solar flux conditions (F 10.7 180) under K p < 3 + . The local time, day of the year, and longitude of the model are binned by 15 min, 1 month, and 10°, respectively, under each solar flux condition. Our vertical drift model is validated by comparing the model with the measurements of the vertical drift velocity at the Jicamarca Radio Observatory. The characteristics and variability of the vertical drift are briefly discussed.

Anomalous enhancement of ionospheric electron content in the Asian-Australian region during a geomagnetically quiet day

National Natural Science Foundation of China[40725014]; National Important Basic Research Project[2006CB806306]; Knowledge Innovation Program of the Chinese Academy of Sciences

Validation of remote sensing products produced by the Special Sensor Ultraviolet Scanning Imager (SSUSI): a far UV-imaging spectrograph on DMSP F-16

Operational sensors are designed and intended to reliably produce the measurements needed to develop high-value key environmental parameters. The Special Sensor Ultraviolet Spectrographic Imager (SSUSI) is slated to fly on the next five Defense Meteorological Satellite Program launches (beginning with the launch of F16 in Fall 2001). SSUSI will routinely produce maps of ionospheric and upper atmospheric composition and image the aurora. In this paper we describe these products and our validation plans and the process through which we can assure our sponsors and data products users of the reliability and accuracy of these products.

Nitric oxide abundance in the mesosphere/lower thermosphere region : Roles of solar soft X rays, suprathermal N(4S) atoms, and vertical transport

This paper carefully examines the inability of photochemical models to account for the large nitric oxide densities of ∼108 cm−3 at ∼105 km obtained from IR, UV, and microwave measurements. A detailed and up-to-date photochemical model is constructed that incorporates measured YOHKOH soft X ray fluxes, hot N atom chemistry with an energy dependent thermalization cross section and seven reaction sources, and laboratory-constrained N(2D) yields. The resulting model which has well-constrained chemistry compared to past models fails to generate high enough NO densities in comparison with the most reliable measurements of absolute NO concentrations in the lower thermosphere. The sensitivity of the model results and the known uncertainties in the inputs are used to identify where future efforts should be focused. A deficit remains despite an increase in the vertical mixing rates in the lower thermosphere from the very low Kzz profile used in our calculations and/or an increase in the N(2D) yield from electron impact dissociation of N2 from its nominal value of 0.54 to 0.62. The sensitivity of NO profiles to the nascent energy distributions of the atmospheric sources of suprathermal N atoms is illustrated by including the thermalization of suprathermal N atoms with an updated thermalization cross section. The diurnally averaged NO concentration at 105 km is enhanced by factors of 1.2 and 2.6 when the energy distributions of the N atoms from electron impact dissociation of N2 are chosen with peaks near 0.6 eV or 3–4 eV, but deficits of factors of ∼7 and ∼3, respectively, remain. There is higher sensitivity to vertical transport than to variations of chemistry within known uncertainties.