National Space Science and Technology Center

The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from ∼8 keV to ∼40 MeV over the full unocculted sky. The onboard trigger threshold is ∼0.7 photons cm −2 s −1 (50–300 keV, 1 s peak). GBM generates onboard triggers for ∼250 GRBs per year.

Tropical montane cloud forests (TMCFs) depend on predictable, frequent, and prolonged immersion in cloud. Clearing upwind lowland forest alters surface energy budgets in ways that influence dry season cloud fields and thus the TMCF environment. Landsat and Geostationary Operational Environmental Satellite imagery show that deforested areas of Costa Rica's Caribbean lowlands remain relatively cloud-free when forested regions have well-developed dry season cumulus cloud fields. Further, regional atmospheric simulations show that cloud base heights are higher over pasture than over tropical forest areas under reasonable dry season conditions. These results suggest that land use in tropical lowlands has serious impacts on ecosystems in adjacent mountains.

We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (∝ t -α with 3 ≲ α 1 ≲ 5), followed by (2) a very shallow decay (0.5 ≲ α 2 ≲ 1.0), and finally (3) a somewhat steeper decay (1 ≲ α 3 ≲ 1.5). These power-law segments are separated by two corresponding break times, t break,1 ≲ 500 s and 10 3 s ≲ t break,2 ≲ 10 4 s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve ( t break,1 ) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (α 2 ) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve ( t break,2 ). This energy injection increases the energy of the afterglow shock by at least a factor of f ≳ 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

Abstract Precipitation is a key source of freshwater; therefore, observing global patterns of precipitation and its intensity is important for science, society, and understanding our planet in a changing climate. In 2014, the National Aeronautics and Space Administration (NASA) and the Japan Aerospace Exploration Agency (JAXA) launched the Global Precipitation Measurement (GPM) Core Observatory (CO) spacecraft. The GPM CO carries the most advanced precipitation sensors currently in space including a dual-frequency precipitation radar provided by JAXA for measuring the three-dimensional structures of precipitation and a well-calibrated, multifrequency passive microwave radiometer that provides wide-swath precipitation data. The GPM CO was designed to measure rain rates from 0.2 to 110.0 mm h−1 and to detect moderate to intense snow events. The GPM CO serves as a reference for unifying the data from a constellation of partner satellites to provide next-generation, merged precipitation estimates globally and with high spatial and temporal resolutions. Through improved measurements of rain and snow, precipitation data from GPM provides new information such as details on precipitation structure and intensity; observations of hurricanes and typhoons as they transition from the tropics to the midlatitudes; data to advance near-real-time hazard assessment for floods, landslides, and droughts; inputs to improve weather and climate models; and insights into agricultural productivity, famine, and public health. Since launch, GPM teams have calibrated satellite instruments, refined precipitation retrieval algorithms, expanded science investigations, and processed and disseminated precipitation data for a range of applications. The current status of GPM, its ongoing science, and its future plans are presented.

Due to the influence of evaporation on land‐surface temperature, thermal remote sensing data provide valuable information regarding the surface moisture status. The Atmosphere‐Land Exchange Inverse (ALEXI) model uses the morning surface temperature rise, as measured from a geostationary satellite platform, to deduce surface energy and water fluxes at 5–10 km resolution over the continental United States. Recent improvements to the ALEXI model are described. Like most thermal remote sensing models, ALEXI is constrained to work under clear‐sky conditions when the surface is visible to the satellite sensor, often leaving large gaps in the model output record. An algorithm for estimating fluxes during cloudy intervals is presented, defining a moisture stress function relating the fraction of potential evapotranspiration obtained from the model on clear days to estimates of the available water fraction in the soil surface layer and root zone. On cloudy days, this stress function is inverted to predict the soil and canopy fluxes. The method is evaluated using flux measurements representative at the watershed scale acquired in central Iowa with a dense flux tower network during the Soil Moisture Experiment of 2002 (SMEX02). The gap‐filling algorithm reproduces observed fluxes with reasonable accuracy, yielding ∼20% errors in ET at the hourly timescale, and 15% errors at daily timesteps. In addition, modeled soil moisture shows reasonable response to major precipitation events. This algorithm is generic enough that it can easily be applied to other thermal energy balance models. With gap‐filling, the ALEXI model can estimate hourly surface fluxes at every grid cell in the U.S. modeling domain in near real‐time. A companion paper presents a climatological evaluation of ALEXI‐derived evapotranspiration and moisture stress fields for the years 2002–2004.

ABSTRACT Land cover changes ( LCCs ) play an important role in the climate system. Research over recent decades highlights the impacts of these changes on atmospheric temperature, humidity, cloud cover, circulation, and precipitation. These impacts range from the local‐ and regional‐scale to sub‐continental and global‐scale. It has been found that the impacts of regional‐scale LCC in one area may also be manifested in other parts of the world as a climatic teleconnection. In light of these findings, this article provides an overview and synthesis of some of the most notable types of LCC and their impacts on climate. These LCC types include agriculture, deforestation and afforestation, desertification, and urbanization. In addition, this article provides a discussion on challenges to, and future research directions in, assessing the climatic impacts of LCC .

The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was developed and provided to the National Aeronautics and Space Administration's EOS Aqua satellite by the National Space Development Agency of Japan, as one of the indispensable instruments for Aqua's mission. AMSR-E is a modified version of AMSR that was launched December 2002 aboard the Advanced Earth Observing Satellite-II (ADEOS-II). It is a six-frequency dual-polarized total-power passive microwave radiometer that observes water-related geophysical parameters supporting global change science and monitoring efforts. The hardware improvements over existing spaceborne microwave radiometers for Earth imaging include the largest main reflector of its kind and addition of 6.925-GHz channels. These improvements provide finer spatial resolution and the capability to retrieve sea surface temperature and soil moisture information on a global basis. This paper provides an overview of the instrument characteristics, mission objectives, and data products.

Gas accretion onto some massive black holes (MBHs) at the centers of galaxies actively powers luminous emission, but most MBHs are considered dormant. Occasionally, a star passing too near an MBH is torn apart by gravitational forces, leading to a bright tidal disruption flare (TDF). Although the high-energy transient Sw 1644+57 initially displayed none of the theoretically anticipated (nor previously observed) TDF characteristics, we show that observations suggest a sudden accretion event onto a central MBH of mass about 10(6) to 10(7) solar masses. There is evidence for a mildly relativistic outflow, jet collimation, and a spectrum characterized by synchrotron and inverse Compton processes; this leads to a natural analogy of Sw 1644+57 to a temporary smaller-scale blazar.

We demonstrate that a cancellation of absorption occurs on resonance for two (or any even number of) coupled optical resonators, due to mode splitting and classical destructive interference, particularly when the resonator finesse is large and the loss in the resonator farthest from the excitation waveguide is small. The linewidth and group velocity of a collection of such coupled-resonator structures may be decreased by using larger resonators of equal size, by using larger resonators of unequal size where the optical path length of the larger resonator is an integer multiple of that of the smaller one, or by using a larger number of resonators per structure. We explore the analogy between these effects and electromagnetically-induced transparency in an atomic system.

Prokaryotic extremophiles were the first representatives of life on Earth and they are responsible for the genesis of geological structures during the evolution and creation of all currently known ecosystems. Flexibility of the genome probably allowed life to adapt to a wide spectrum of extreme environments. As a result, modern prokaryotic diversity formed in a framework of physico-chemical factors, and it is composed of: thermophilic, psychrophilic, acidophilic, alkaliphilic, halophilic, barophilic, and radioresistant species. This artificial systematics cannot reflect the multiple actions of different environmental factors since one organism could unite characteristics of several extreme-groups. In this review we show the current status of studies in all fields of extremophiles and summarize the limits of life for different species of microbial extremophiles. We also discuss the finding of extremophiles from unusual places such as soils, and briefly review recent studies of microfossils in meteorites in the context of the significance of microbial extremophiles to Astrobiology.

Surface soil moisture content is highly variable in both space and time. While remote sensing provides an effective methodology for mapping surface moisture content over large areas, it averages within‐pixel variability thereby masking the underlying heterogeneity observed at the land surface. This variability must be better understood in order to rigorously evaluate sensor performance and to enhance the utility of the larger‐scale remotely sensed averages by quantifying the underlying variability that remote sensing cannot record explicitly. In support of the Southern Great Plains 1997 (SGP97) Hydrology Experiment (a surface soil moisture mapping mission conducted between June 18 and July 17, 1997, in central Oklahoma) an investigation was conducted to characterize soil moisture variability within remote sensing footprints (approximately 0.64 km 2 ) with more certainty than would be afforded with conventional gravimetric moisture content sampling. Nearly every day during the experiment period, portable impedance probes were used to intensively monitor volumetric moisture content in the 0‐ to 6‐cm surface soil layer at six footprint‐sized fields scattered over the SGP97 study area. A minimum of 49 daily moisture content measurements were made on most fields. Higher‐resolution grid and transect data were also collected periodically. In total, more than 11,000 impedance probe measurements of volumetric moisture content were made at the six sites by over 35 SGP97 participants. The wide spatial distribution of the sites, combined with the intensive, near‐daily monitoring, provided a unique opportunity (relative to previous smaller‐scale and shorter‐duration soil moisture studies) to characterize variations in surface moisture content over a range of wetness conditions. In this paper the range and temporal dynamics of the variability in moisture content within each of the six fields are described, as are general relationships between the variability and footprint‐mean moisture content. Results indicate that distinct differences in mean moisture content between the six sites are consistent with variations in soil type, vegetation cover, and rainfall gradients. Within fields the standard deviation, coefficient of variation, skewness, and kurtosis increased with decreasing moisture content; the distribution of surface moisture content evolved from negatively skewed/nonnormal under very wet conditions, to normal in the midrange of mean moisture content, to positively skewed/nonnormal under dry conditions; and agricultural practices of row tilling and terracing were shown to exert a major control on observed moisture content variations. Results presented here can be utilized to better evaluate sensor performance, to extrapolate estimates of subgrid‐scale variations in moisture content across the entire SGP97 region, and in the parameterization of soil moisture dynamics in hydrological and land surface models.

Robust satellite‐derived moisture stress indices will be beneficial to operational drought monitoring, both in the United States and globally. Using thermal infrared imagery from the Geostationary Operational Environmental Satellites (GOES) and vegetation information from the Moderate Resolution Imaging Spectrometer (MODIS), a fully automated inverse model of Atmosphere‐Land Exchange (ALEXI) has been used to model daily evapotranspiration and surface moisture stress over a 10‐km resolution grid covering the continental United States. Examining monthly clear‐sky composites for April–October 2002–2004, the ALEXI evaporative stress index (ESI) shows good spatial and temporal correlation with the Palmer drought index but at considerably higher spatial resolution. The ESI also compares well to anomalies in monthly precipitation fields, demonstrating that surface moisture has an identifiable thermal signature that can be detected from space, even under dense vegetation cover. Simple empirical thermal drought indices like the vegetation health index do not account for important forcings on surface temperature, such as available energy and atmospheric conditions, and can therefore generate spurious drought detections under certain circumstances. Surface energy balance inherently incorporates these forcings, constraining ESI response in both energy‐ and water‐limited situations. The surface flux modeling techniques described here have demonstrated skill in identifying areas subject to soil moisture stress on the basis of the thermal land surface signature, without requiring information regarding antecedent rainfall. ALEXI therefore may have potential for operational drought monitoring in countries lacking well‐established precipitation measurement networks.

This study investigates the relationship of total lightning activity and updraft characteristics, such as updraft volume and maximum updraft speed, for a number of storms of different types occurring in the High Plains and in Northern Alabama. Ground‐based Doppler and dual polarimetric radar observations were used to compute updraft characteristics. Also, ground‐based total lightning data were available at both locations. Results show that time series of updraft volume in the charging zone (at temperatures colder than −5°C) with vertical velocities greater than either 5 or 10 m s −1 have clear relationships with total lightning activity ( r = 0.93). Furthermore, these relationships between updraft volume and lightning activity for the storm types of the two climate regimes tend to converge when considering only the subfreezing layers of the clouds. Neither the maximum nor the mean updraft speed correlate as well with total lightning activity ( r = <0.8) as updraft volume. Through expanded study designed to explore further regime variability (or lack thereof) of updraft volume‐lightning flash rate relationships, better or refined parameterizations for the numerical forecasting of lightning and/or detection and prediction of storm intensity could be realized.

Variable x-ray and γ-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique γ-ray-selected transient detected by the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any γ-ray burst, whereas its peak luminosity was ∼100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a rare mechanism involving the massive black hole in the nucleus of that galaxy.

Abstract An impact-type Joss–Waldvogel disdrometer (JWD), a two-dimensional video disdrometer (2DVD), and a laser optical OTT Particle Size and Velocity (PARSIVEL) disdrometer (PD) were used to measure the raindrop size distribution (DSD) over a 6-month period in Huntsville, Alabama. Comparisons indicate event rain totals for all three disdrometers that were in reasonable agreement with a reference rain gauge. In a relative sense, hourly composite DSDs revealed that the JWD was more sensitive to small drops (<1 mm), while the PD appeared to severely underestimate small drops less than 0.76 mm in diameter. The JWD and 2DVD measured comparable number concentrations of midsize drops (1–3 mm) and large drops (3–5 mm), while the PD tended to measure relatively higher drop concentrations at sizes larger than 2.44 mm in diameter. This concentration disparity tended to occur when hourly rain rates and drop counts exceeded 2.5 mm h−1 and 400 min−1, respectively. Based on interactions with the PD manufacturer, the partially inhomogeneous laser beam is considered the cause of the PD drop count overestimation. PD drop fall speeds followed the expected terminal fall speed relationship quite well, while the 2DVD occasionally measured slower drops for diameters larger than 2.4 mm, coinciding with events where wind speeds were greater than 4 m s−1. The underestimation of small drops by the PD had a pronounced effect on the intercept and shape of parameters of gamma-fitted DSDs, while the overestimation of midsize and larger drops resulted in higher mean values for PD integral rain parameters.

Abstract We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi’s Gamma-ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering the 10 year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events, 2356 of which we identified as cosmic GRBs. Additional trigger events were due to solar flare events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to the community on the most important observables of the GBM-detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50–300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10–1000 keV, exploiting the full energy range of GBM’s low-energy detectors. Furthermore, information is given on the settings of the triggering criteria and exceptional operational conditions during years 7 to 10 in the mission. This fourth catalog is an official product of the Fermi-GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

Heavy-ion collisions at the LHC—Last call for predictions, Armesto, N, Borghini, N, Jeon, S, Wiedemann, U A, Abreu, S, Akkelin, S V, Alam, J, Albacete, J L, Andronic, A, Antonov, D, Arleo, F, Armesto, N, Arsene, I C, Barnaföldi, G G, Barrette, J, Bäuchle, B, Becattini, F, Betz, B, Bleicher, M, Bluhm, M, Boer, D, Bopp, F W, Braun-Munzinger, P, Bravina, L, Busza, W, Cacciari, M, Capella, A, Casalderrey-Solana, J, Chatterjee, R, Chen, L-W, Cleymans, J, Cole, B A, Valle, Z Conesa Del, Csernai, L P, Cunqueiro, L, Dainese, A, Deus, J Dias de, Ding, H-T, Djordjevic, M, Drescher, H, Dremin, I M, Dumitru, A, El, A, Engel, R, d'Enterria, D, Eskola, K J, Fai, G, Ferreiro, E G, Fries, R J, Frodermann, E, Fujii, H, Gale, C, Gelis, F, Gonçalves, V P, Greco, V, Greiner, C, Gyulassy, M, Hees, H van, Heinz, U, Honkanen, H, Horowitz, W A, Iancu, E, Ingelman, G, Jalilian-Marian, J, Jeon, S, Kaidalov, A B, Kämpfer, B, Kang, Z-B, Karpenko, Iu A, Kestin, G, Kharzeev, D, Ko, C M, Koch, B, Kopeliovich, B, Kozlov, M, Kraus, I, Kuznetsova, I, Lee, S H, Lednicky, R, Letessier, J, Levin, E, Li, B-A, Lin, Z-W, Liu, H, Liu, W, Loizides, C, Lokhtin, I P, Machado, M V T, Malinina, L V, Managadze, A M, Mangano, M L, Mannarelli, M, Manuel, C, Martínez, G, Milhano, J G, Mócsy, Á, Molnár, D, Nardi, M, Nayak, J K, Niemi, H, Oeschler, H, Ollitrault, J-Y, Paić, G, Pajares, C, Pantuev, V S, Papp, G, Peressounko, D, Petreczky, P, Petrushanko, S V, Piccinini, F, Pierog, T, Pirner, H J, Porteboeuf, S, Potashnikova, I, Qin, G Y, Qiu, J-W, Rafelski, J, Rajagopal, K, Ranft, J, Rapp, R, Räsänen, S S, Rathsman, J, Rau, P, Redlich, K, Renk, T, Rezaeian, A H, Rischke, D, Roesler, S, Ruppert, J, Ruuskanen, P V, Salgado, C A, Sapeta, S, Sarcevic, I, Sarkar, S, Sarycheva, L I, Schmidt, I, Shoshi, A I, Sinha, B, Sinyukov, Yu M, Snigirev, A M, Srivastava, D K, Stachel, J, Stasto, A, Stöcker, H, Teplov, C Yu, Thews, R L, Torrieri, G, Pop, V Topor, Triantafyllopoulos, D N, Tuchin, K L, Turbide, S, Tywoniuk, K, Utermann, A, Venugopalan, R, Vitev, I, Vogt, R, Wang, E, Wang, X N, Werner, K, Wessels, E, Wheaton, S, Wicks, S, Wiedemann, U A, Wolschin, G, Xiao, B-W, Xu, Z, Yasui, S, Zabrodin, E, Zapp, K, Zhang, B, Zhang, B-W, Zhang, H, Zhou, D

The African Monsoon Multidisciplinary Analysis (AMMA) is a major international campaign investigating far‐reaching aspects of the African monsoon, climate and the hydrological cycle. A special observing period was established for the dry season (SOP0) with a focus on aerosol and radiation measurements. SOP0 took place during January and February 2006 and involved several ground‐based measurement sites across west Africa. These were augmented by aircraft measurements made by the Facility for Airborne Atmospheric Measurements (FAAM) aircraft during the Dust and Biomass‐burning Experiment (DABEX), measurements from an ultralight aircraft, and dedicated modeling efforts. We provide an overview of these measurement and modeling studies together with an analysis of the meteorological conditions that determined the aerosol transport and link the results together to provide a balanced synthesis. The biomass burning aerosol was significantly more absorbing than that measured in other areas and, unlike industrial areas, the ratio of excess carbon monoxide to organic carbon was invariant, which may be owing to interaction between the organic carbon and mineral dust aerosol. The mineral dust aerosol in situ filter measurements close to Niamey reveals very little absorption, while other measurements and remote sensing inversions suggest significantly more absorption. The influence of both mineral dust and biomass burning aerosol on the radiation budget is significant throughout the period, implying that meteorological models should include their radiative effects for accurate weather forecasts and climate simulations. Generally, the operational meteorological models that simulate the production and transport of mineral dust show skill at lead times of 5 days or more. Climate models that need to accurately simulate the vertical profiles of both anthropogenic and natural aerosols to accurately represent the direct and indirect effects of aerosols appear to do a reasonable job, although the magnitude of the aerosol scattering is strongly dependent upon the emission data set.

It is generally believed that a strong updraft in the mixed‐phase region of thunderstorms is required to produce lightning. This is the region where the noninductive charging process is thought to generate most of the storm electrification. Analytic calculations and model results predict that the total lightning frequency is roughly proportional to the product of the downward mass flux of solid precipitation (graupel) and the upward mass flux of ice crystals. Thus far this flux hypothesis has only been tested in a very limited way. Herein we use dual‐polarimetric and dual‐Doppler radar observations in conjunction with total lightning data collected in Northern Alabama and also Colorado/Kansas during two field campaigns. These data are utilized to investigate total lightning activity as a function of precipitation and nonprecipitation ice masses and estimates of their fluxes for different storm types in different climate regions. A total of 11 storms, including single cell, multicell, and supercell storms, was analyzed in the two climatologically different regions. Time series of both precipitation and nonprecipitation ice mass estimates above the melting level show a good relationship with total lightning activity for the 11 storms analyzed (correlation coefficients exceed 0.9 and 0.8, respectively). Furthermore, the relationships are relatively invariant between the two climate regions. The correlations between total lightning and the associated product of ice mass fluxes are even higher. These observations provide strong support for the flux hypothesis.

Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission component, but also includes a statistically highly significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.