Characteristics of nighttime E-region over Arecibo: Dependence on solar flux and geomagnetic variations

Electron concentration (Ne) inferred from Incoherent Scatter Radar (ISR) measurements has been used to determine the influence of solar flux and geomagnetic activity in the ionospheric E-region over Arecibo Observatory (AO). The approach is based on the determination of column integrated Ne, referred to as E-region total electron content (ErTEC) between 80 and 150 km altitude regions. The results discussed in this work are for the AO nighttime period. The study reveals higher ErTEC values during the low solar flux periods for all the seasons except for summer period. It is found that the E-region column abundance is higher in equinox periods than in the winter for low solar activity conditions. The column integrated Ne during the post-sunset/pre-sunrise periods always exceeds the midnight minima, independent of season or solar activity. This behavior has been attributed to the variations in the coupling processes from the F-region. The response of ErTEC to the geomagnetic variability is also examined for different solar flux conditions and seasons. During high solar flux periods, changes in Kp cause an ErTEC increase in summer and equinox, while producing a negative storm-like effect during the winter. Variations in ErTEC due to geomagnetic activity during low solar flux periods produce maximum variability in the E-region during equinox periods, while resulting in an increase/decrease in ErTEC before local midnight during the winter/summer periods, respectively.     

Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Monolithic Interferometer Design and Test

The design and laboratory tests of the interferometers for the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument which measures thermospheric wind and temperature for the NASA-sponsored Ionospheric Connection (ICON) Explorer mission are described. The monolithic interferometers use the Doppler Asymmetric Spatial Heterodyne (DASH) Spectroscopy technique for wind measurements and a multi-element photometer approach to measure thermospheric temperatures. The DASH technique and overall optical design of the MIGHTI instrument are described in an overview followed by details on the design, element fabrication, assembly, laboratory tests and thermal control of the interferometers that are the heart of MIGHTI.     

Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Instrument Design and Calibration

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument was built for launch and operation on the NASA Ionospheric Connection Explorer (ICON) mission. The instrument was designed to measure thermospheric horizontal wind velocity profiles and thermospheric temperature in altitude regions between 90 km and 300 km, during day and night. For the wind measurements it uses two perpendicular fields of view pointed at the Earth’s limb, observing the Doppler shift of the atomic oxygen red and green lines at 630.0 nm and 557.7 nm wavelength. The wavelength shift is measured using field-widened, temperature compensated Doppler Asymmetric Spatial Heterodyne (DASH) spectrometers, employing low order échelle gratings operating at two different orders for the different atmospheric lines. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere. The MIGHTI requirements, the resulting instrument design and the calibration are described.     

Spatio-temporal dynamics in the phenology of croplands across the Indo-Gangetic Plains

Spatio-temporal dynamics in land surface phenology parameters observed over croplands can inform on crop-climate interactions and, elucidate local to regional scale vulnerabilities either due to climate change or prevailing sub-optimal agricultural practices. Here, we observe spatio-temporal trends in land surface phenology parameters (cropping intensity, length of growing season and productivity) for kharif and rabi cropping seasons from satellite data across the Indo-Gangetic Plains from 1982 to 2006. The productivity of the Indo-Gangetic Plains croplands is of regional importance and is a vital component of Indian national food security efforts. Aside from local and intra-state heterogeneity in observed trends there was a clear west-to-east gradient in cropping intensity. Key observed trends include increasing cropping intensity in the eastern IGP, increasing number of growing days per year in Bihar, Uttar Pradesh and Haryana and increasing productivity in both cropping seasons across the IGP. This information is a crucial input to integrated assessments of the croplands to ensure management of the agricultural system shifts towards a trajectory of climate-resilience and environmental sustainability.     

Comparison of the transport codes HZETRN,HETC and FLUKA for galactic cosmic rays

The HZETRN deterministic radiation code is one of several tools developed to analyze the effects of harmful galactic cosmic rays (GCR) and solar particle events on mission planning and shielding for astronauts and instrumentation. This paper is a comparison study involving the two Monte Carlo transport codes, HETC–HEDS and FLUKA and the deterministic transport code, HZETRN. Each code is used to transport an ion from the 1977 solar minimum GCR spectrum impinging upon a 20 g/cm² aluminum slab followed by a 30 g/cm² water slab. This research is part of a systematic effort of verification and validation to quantify the accuracy of HZETRN and determine areas where it can be improved. Comparisons of dose and dose equivalent values at various depths in the water slab are presented in this report. This is followed by a comparison of the proton and forward, backward and total neutron flux at various depths in the water slab. Comparisons of the secondary light ion ²H, ³H, ³He and ⁴He fluxes are also examined.     

Survival of Deinococcus radiodurans against laboratory-simulated solar wind charged particles

In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate the charged particles found in the solar wind. Naked cells or cells mixed with dust grains (basalt or sandstone) differing in elemental composition were exposed to electrons, protons, and ions to determine the probability of cell survival after irradiation. Doses necessary to reduce the viability of cell population to 10% (LD(10)) were determined under different experimental conditions. The results of this study indicate that low-energy particle radiation (2-4?keV), typically present in the slow component of the solar wind, had no effect on dehydrated cells, even if exposed at fluences only reached in more than 1000 years at Sun-Earth distance (1 AU). Higher-energy ions (200?keV) found in solar flares would inactivate 90% of exposed cells after several events in less than 1 year at 1 AU. When mixed with dust grains, LD(10) increases about 10-fold. These results show that, compared to the highly deleterious effects of UV radiation, solar wind charged particles are relatively benign, and organisms protected under grains from UV radiation would also be protected from the charged particles considered in this study.     

Interplanetary Lyman α Observations: Intensities from Voyagers and Line Profiles from HST/STIS

We present an analysis of Voyager UVS data obtained between 1993 and mid-2007. These data are used to study the interplanetary background and the hydrogen number density in the outer heliosphere. Two types of observations are studied, first the heliospheric scans performed until 2003 and then the fixed line of sight observations, close to the upwind direction, which are still performed at the end of 2007. We make comparisons with models including multiple scattering and hydrogen distributions derived from self-consistent modeling of the interface region. It is found that there is a remaining discrepancy between models and data. The origin of this difference is unknown but it may be linked to a possible tilting of the heliospheric interface due to the presence of an interstellar magnetic field. We should also estimate alternate sources of emission which are not backscattering of solar photons like collisional excitation of hydrogen in the heliosheath and emission after charge transfer or recombination of proton and electron in HII regions. Line profiles from HST/STIS are also presented.     

Towards Synthesis of Solar Wind and Geomagnetic Scaling Exponents: A Fractional Lévy Motion Model

Mandelbrot introduced the concept of fractals to describe the non-Euclidean shape of many aspects of the natural world. In the time series context, he proposed the use of fractional Brownian motion (fBm) to model non-negligible temporal persistence, the ‘Joseph Effect’; and Lévy flights to quantify large discontinuities, the ‘Noah Effect’. In space physics, both effects are manifested in the intermittency and long-range correlation which are by now well-established features of geomagnetic indices and their solar wind drivers. In order to capture and quantify the Noah and Joseph effects in one compact model, we propose the application of the ‘bridging’ fractional Lévy motion (fLm) to space physics. We perform an initial evaluation of some previous scaling results in this paradigm, and show how fLm can model the previously observed exponents. We suggest some new directions for the future.     

The socioeconomic benefits of Earth science and applications research: reducing the risks and costs of natural disasters in the USA

A wealth of satellite data has provided information on weather and climate phenomena for the past 40 years. Within this period, however, the heavy human and economic costs of natural disasters have increased considerably. Using hurricanes, droughts, floods and earthquakes which occurred in the USA as examples, this article describes how Earth science can be applied to such situations to predict or mitigate their effects. The economic value of providing such information is discussed, as are the issues that can affect how successful its provision will be.     

On Truncation Error Bounds for Sampling Representations of Band-Limited Signals

All sampling representations of band-limited signals involve infinite sums. The truncation error associated with a given representation is defined as the difference between the signal and an approximating sum utilizing a finite number of terms. In this paper truncation error is expressed as a contour integral for Lagrange interpolation, general Hermite interpolation, the Shannon series (cardinal series), the Fogel derivative series, and multidimensional sampling expansions. Truncation error bounds are obtained under various constraints on the signal magnitude, spectral smoothness, and energy content.