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An observing system simulation experiment (OSSE) is a modeling experiment used to evaluate the value of a new observing system. when actual observational data are not available. An OSSE system [...]

For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. [...]

Device-level current transients are induced by injecting carriers using two-photon absorption from a subbandgap pulsed laser and recorded using wideband transmission and measurement equipment. These transients exhibit three distinct temporal trends that depend on laser pulse energy as well as the transverse and vertical charge generation location. The nature of the current transient is controlled by both the behavior of the subcollector-substrate junction and isolation biasing. However, substrate potential modulation, due to deformation of the subcollector-substrate depletion region, is the dominant mechanism affecting transient characteristics. Index Terms--Current transient, electrostatic potential modulation, SiGe HBT, two-photon absorption.

The effects of device orientation on heavy ion-induced multiple-bit upset (MBU) in 65 nm SRAMs are examined. The MBU response is shown to depend on the orientation of the device during irradiation. The response depends on the direction of the incident ion to the n- and p-wells of the SRAM. The MBU response is simulated using Monte Carlo methods for a space environment. The probability is calculated for event size. Single-bit upsets in the space environment account for 90% of all events with exponentially decreasing probabilities of larger MBU events. Index Terms--Multiple-bit upset, MBU, MCU, SEU, heavy ion, SRAM, MRED, GEANT4, soft error.

Monte-Carlo radiation transport code is coupled with SPICE circuit level simulation to identify regions of single event upset vulnerability in an SEU hardened flip-flop, as well as predict single event upset cross sections and on-orbit soft error rates under static and dynamic operating conditions. Index Terms--Geant4, MRED, rate prediction, SEU, SPICE.

As integrated circuits become smaller and more complex, it has become increasingly difficult to simulate their responses to radiation. The distance and time scales of relevance extend over orders of magnitude, requiring a multi-scale, hierarchical simulation approach. This paper demonstrates the use of multi-scale simulations to examine two radiation-related problems: enhanced low-dose-rate sensitivity (ELDRS) in bipolar transistors and single-event effects (SEE) in CMOS integrated circuits. Examples are included that demonstrate how information can be passed from simulation tools operating at one level of abstraction to those operating at higher levels, while maintaining accuracy and gaining insight. Index Terms--Integrated circuits, multi-scale simulation, radiation, single-event effects, total ionizing dose.

Microbeam measurements and TCAD simulations are used to examine the effects of ion angle of incidence on the charge collected from events occurring in a Silicon Germanium (SiGe) Heterojunction Bipolar Transistor (HBT). The results identify the geometrically driven charge-collection mechanisms that dominate the low LET broad beam SEU response. The deep trench isolation that surrounds the transistor significantly modulates the charge transport and, therefore, the charge collected by the collector. A new way of estimating critical charge, [Q.sub.crit], for upset in SiGe HBT circuits is proposed based on TCAD simulation results and measured broadbeam data. Index Terms--Deep trench isolation (DTI), HBT, IBICC, silicon germanium (SiGe), single event upset (SEU), TCAD.

Single event latchup (SEL) in a 65 nm CMOS technology is examined with respect to strike angle of incidence and variations in device temperature. A significant difference in device sensitivity is observed with a change in the orientation of grazing angle strikes. The impact of an extremely high aspect ratio sensitive volume on SEL rate is discussed. It is suggested that SEL experiments should be conducted at various lateral orientations when near-grazing beam angles are tested. Index Terms--Radiation effects, single event latchup, 65 nm.

Heavy ion cross section data taken from a hardened-by-design circuit are presented which deviate from the traditional single sensitive volume or classical rectangular parallelepiped model of single event upset. TCAD and SPICE analysis demonstrate a SEU mechanism dominated by multiple node charge collection. Monte Carlo simulation is used to model the response and predict an on-orbit error rate. Index Terms--Geant4, MRED, rate prediction, SEU.

Proton-induced energy deposition in a silicon P-i-N focal plane array is analyzed with Monte Carlo based simulations. These simulations include all physical processes, including events resulting from multiple particles incident on a single pixel, to describe the experimental data accurately. Post-processing of Monte Carlo simulations is done to account for the effects of pile up (multiple hits on a single pixel during one integration time) and non-radiation-induced noise in experiment. The results are compared with experimental data, and demonstrate how direct ionization dominates the cross section, yet fluctuations in dE/dx cause a broad range of energy depositions not addressed by an average LET calculation. An event rate is predicted for a full space proton flux and the dominance of direct ionization is shown and compared to computation using constant LET methods in CREME96. This comparison shows that at lower energies, CREME96 sufficiently predicts the event rate, but at higher energies a high fidelity simulation method is needed to capture the distribution. Index Terms--Energy deposited, event rate, focal plane array, Geant4, Monte Carlo, pile up.

This work draws on experimental and simulation results to derive a generalized SEU response model for bulk SiGe HBTs. The model was validated using published heavy ion and new proton data gathered from high-speed HBT digital logic integrated circuits fabricated in the IBM 5AM SiGe BiCMOS process. Calibrating to heavy ion data was sufficient to reproduce the proton data without further adjustment. The validated model is used to calculate upset event rates for low-earth and geosynchronous orbits under typical conditions. Index Terms--Deep trench isolation, Geant4, geosynchronous orbit, low-earth orbit, rate prediction, silicon-germanium HBT, single-event upset.

The RADSAFE simulation framework is described and applied to model SEU in a 0.25 [micro]m CMOS 4 Mbit SRAM. For this circuit, the RADSAFE approach produces trends similar to those expected from classical rectangular parallelepiped models, but more closely represents the physical mechanisms responsible for SEU in the SRAM circuit. Index Terms--GEANT4, heavy-ion, RADSAFE, SEU, TCAD.

A 25-yr (1981-2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air--Sea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset. The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W [m.sup.-2] between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing. (Page 527)

The Office of Naval Research's Coupled Boundary Layers and Air-Sea Transfer (CBLAST) program is being conducted to investigate the processes that couple the marine boundary layers and govern the exchange of heat, mass, and momentum across the air-sea interface. CBLAST-LOW was designed to investigate these processes at the low-wind extreme where the processes are often driven or strongly modulated by buoyant forcing. The focus was on conditions ranging from negligible wind stress, where buoyant forcing dominates, up to wind speeds where wave breaking and Langmuir circulations play a significant role in the exchange processes. The field program provided observations from a suite of platforms deployed in the coastal ocean south of Martha's Vineyard. Highlights from the measurement campaigns include direct measurement of the momentum and heat fluxes on both sides of the air-sea interface using a specially constructed Air-Sea Interaction Tower (ASIT), and quantification of regional oceanic variability over scales of O(1-104 mm) using a mesoscale mooring array, aircraft-borne remote sensors, drifters, and ship surveys. To our knowledge, the former represents the first successful attempt to directly and simultaneously measure the heat and momentum exchange on both sides of the air-sea interface. The latter provided a 3D picture of the oceanic boundary layer during the month-long main experiment. These observations have been combined with numerical models and direct numerical and large-eddy simulations to investigate the processes that couple the atmosphere and ocean under these conditions. For example, the oceanic measurements have been used in the Regional Ocean Modeling System (ROMS) to investigate the 3D evolution of regional ocean thermal stratification. The ultimate goal of these investigations is to incorporate improved parameterizations of these processes in coupled models such as the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) to improve marine forecasts of wind, waves, and currents.

Simulation results for the full galactic cosmic ray environment demonstrate that current accelerator-based test methods using linear energy transfer as the engineering metric to characterize single event effects are not sufficient to capture the nuclear reaction portion of the response. Nuclear reactions contribute significantly to on-orbit single-event rates as compared to those from direct ionization induced by the primary ions. Based on these results, the applicability of current single-event test methods to predicting on-orbit event rates is examined and improved procedures are identified. For devices with critical charge values that are in the range where nuclear reactions may play a role in determining the event rate, ground-based tests should include irradiation with several types of ions of different energies to identify the contribution of these reactions to the measured SEE cross section. Index Terms--Nuclear reactions, single event effect rate, single event effects.

Delayed charge collection from ionizing events outside the deep trench can increase the SEU cross section in deep trench isolation technologies. Microbeam test data and device simulations demonstrate how this adverse effect can be mitigated through substrate engineering techniques. The addition of a heavily doped p-type charge-blocking buried layer in the substrate can reduce the delayed charge collection from events that occur outside the deep trench isolation by almost an order of magnitude, implying an approximately comparable reduction in the SEU cross section. Index Terms--Deep trench isolation, Ion Beam Induced Charge Collection (IBICC), silicon germanium, Single Event Upset (SEU), substrate engineering.

The probability of proton-induced multiple-bit upset (MBU) has increased in highly-scaled technologies because device dimensions are small relative to particle event track size. Both proton-induced single event upset (SEU) and MBU responses have been shown to vary with angle and energy for certain technologies. This work analyzes SEU and MBU in a 130 nm CMOS SRAM in which the single-event response shows a strong dependence on the angle of proton incidence. Current proton testing methods do not account for device orientation relative to the proton beam and, subsequently, error rate prediction assumes no angular dependencies. Proton-induced MBU is expected to increase as integrated circuits continue to scale into the deep sub-micron regime. Consequently, the application of current testing methods will lead to an incorrect prediction of error rates. Index Terms--Energy deposition cross section, multiple-bit upset (MBU), MRED, single event upset (SEU), SRAM, proton effects.

We present measurements of proton-induced single event transients in ultra-low noise HgCdTe IR detector arrays being developed for space-based astronomy and compare to modeling results. Index Terms--HgCdTe, IR detectors, single event transients, space-based astronomy, transient noise.

Proton irradiation decreases the doping concentration and increases the ideality factor and series resistance, but has very little effect on the Schottky barrier height in n-Gallium nitride Schottky diodes. 1.0-MeV protons cause greater degradation than 1.8-MeV protons because of their higher nonionizing energy loss. The displacement damage recovers during annealing. Comparison between Schottky diodes and high electron-mobility transistors suggests that the degradation in both types of devices is predominantly due to carrier removal and mobility degradation caused by radiation-induced defect centers in the crystal lattice, with interface disorder playing a relatively insignificant part in overall device degradation. Index Terms--Gallium (Ga) alloys, Schottky diodes, proton radiation effects.

Simulations show that neglecting ion-ion interaction processes (both particles having Z > 1) results in an underestimation of the total on-orbit single event upset error rate by more than two orders of magnitude for certain technologies. The inclusion of ion-ion nuclear reactions leads to dramatically different SEU error rates for CMOS devices containing high Z materials compared with direct ionization by the primary ion alone. Device geometry and material composition have a dramatic effect on charge deposition in small sensitive volumes for the spectrum of ion energies found in space, compared with the limited range of energies typical of ground tests. Index Terms--Charge deposition, Geant4, heavy ion, MRED, single-event upset (SEU), SEU error rate.

Heavy ion irradiation was simulated using a Geant4 based Monte-Carlo transport code. Electronic and nuclear physics were used to generate statistical profiles of charge deposition in the sensitive volume of an SEU hardened SRAM. Simulation results show that materials external to the sensitive volume can affect the experimentally measured cross-section curve. Index Terms--Cross section, Geant4, MRED, single event upset.

1.8 MeV proton radiation-induced degradation in high electron mobility transistors with Si-doped [Al.sub.x][Ga.sub.1] - x N and thick GaN cap layers is studied up to a fluence of 1 x [10.sup.15] protons/[cm.sup.2]. The thick GaN cap layer reduces sheet charge modulation induced by the surface states, as it electrostatically separates the active device layers from the surface, thereby enhancing the device performance. The devices exhibit good tolerance up to [10.sup.14] protons/[cm.sup.2], with displacement damage being the primary degradation mechanism. Charged defect centers introduced by proton radiation in the active device layers degrade carrier mobility and sheet carrier density. Proton radiation alters the barrier height at the Schottky gate and increases the resistance of the thin film structure. Index Terms--Gallium alloys, modulation-doped field effect transistors (MODFETs), proton radiation effects.

A new software module adding screened Coulomb scattering to the Monte Carlo radiation simulation code Geant4 has been applied to compute the nonionizing component of energy deposited in semiconductor materials by energetic protons and other forms of radiation. This method makes it possible to create three-dimensional maps of nonionizing energy deposition from all radiation sources in structures with complex compositions and geometries. Essential aspects of previous NIEL computations are confirmed, and issues are addressed both about the generality of NIEL and the ability of beam experiments to simulate the space environment with high fidelity, particularly for light ion irradiation at very high energy. A comparison of the displacement energy deposited by electromagnetic and hadronic interactions of a proton beam with published data on GaAs LED degradation supports the conclusion of previous authors that swift light ions and slower heavy ions produce electrically active defects with differing efficiencies. These results emphasize that, for devices with extremely small dimensions, it is increasingly difficult to predict the response of components in space without the assistance of computational modeling. Index Terms--Computational physics, displacement damage, GaAs, Geant4, Monte Carlo, NIEL, nonionizing energy loss, nuclear stopping.

We present spatial and temporal distributions of energy deposition in silicon obtained from Monte Carlo simulations with Geant4. Detailed simulations are performed for protons and alphas over a wide energy range and include contributions from discrete [delta]-rays and nuclear reactions. The simulation technique we employ produces physically realistic complex track structures for which the plausibility is evaluated by comparison to the linear energy transfer, radial dose, and temporal characteristics described in previous works. The variability of events, including the distribution of energy deposition at varying distances from the ion track is discussed. Finally, we examine the temporal evolution of extreme events to investigate the physicality of the common assumption that energy deposition can be considered instantaneous. Index Terms--Alphas, [delta]-rays, energy deposition, Geant4, ion track, metal oxide semiconductor (MOS), Monte Carlo simulation, protons, radial dose, radiation effects, single-event effects.

Overlaying the cool southeast Pacific Ocean is the most persistent subtropical stratocumulus cloud deck in the world. It produces a profound affect on tropical climate by shading the underlying ocean and radiatively cooling and stirring up turbulence in the atmosphere. In October 2001, the East Pacific Investigation of Climate undertook an exploratory cruise from the Galapagos Islands to Chile. The cruise gathered an unprecedented dataset, integrating radiosonde, surface, cloud remote sensing, aerosol, and ocean measurements. Scientific objectives included measuring the vertical structure of the ABL in this region, understanding what physical processes are determining the stratocumulus cloud albedo, and understanding the fluxes of heat and water that couple the atmosphere and ocean in this region. An unexpectedly well-mixed stratocumulus-capped boundary layer as a result of a strong inversion was encountered throughout. A strong diurnal cycle was observed, with thicker clouds and substantial drizzle (mainly evaporating above the sea surface) during the late night and early morning. This was driven in part by local diabatic processes, and was reinforced by a surprisingly pronounced diurnal cycle of vertical motion. The vertical motion appears to be an inertia-gravity wave driven by daytime heating over South America that propagates over 1000 km offshore. Much more nocturnal drizzle and pronounced mesoscale cellularity were observed in 'clean' conditions when cloud droplet concentrations and aerosol concentrations were low. Entrainment of dry, warm air is inferred to be the primary regulator of cloud thickness in this region, but drizzle also appears to have a large indirect impact by inhibiting and changing the spatial organization of turbulence.

We examine the limits of performing single-event simulations using pre-averaged radiation events. Geant4 simulations show the necessity, for future devices, to supplement current methods with ensemble averaging of device-level responses to physically realistic radiation events. Initial Monte Carlo simulations have generated a significant number of extremal events in local energy deposition. These simulations strongly suggest that proton strikes of sufficient energy, even those that initiate purely electronic interactions, can initiate device response capable in principle of producing single event upset or microdose damage in highly scaled devices. Index Terms--Charge collection, extreme value statistics, Geant4, linear energy transfer, Monte Carlo simulation, protons, radiation effects, single-event effects, soft errors.

The degradation of AlGaN/AlN/GaN high electron mobility transistors due to 1.8-MeV proton irradiation was measured at fluences up to 3 x [10.sup.15] [cm.sup.-2]. The devices have much higher mobility than AlGaN/GaN devices, but they possess similarly high radiation tolerance, exhibiting little degradation at fluences up to 1 x [10.sup.14] [cm.sup.-2]. Decreased sheet carrier mobility due to increased carrier scattering and decreased sheet carrier density due to carrier removal are the primary damage mechanisms. The device degradation is observed as a decrease in the maximum transconductance, an increase in the threshold voltage, and a decrease in the drain saturation current. Index Terms--Gallium alloys, MODFETs, proton radiation effects.

The effects of 1.8-MeV and 105-MeV proton irradiation on AlGaAs/GaAs heterojunction bipolar transistors (HBTs) are reported. For 1.8-MeV protons, the degradation of the transistors is caused by an increase in the base current and a large decrease in the collector current. The device degradation is much less after irradiation with 105-MeV protons, because of lower nonionizing energy loss (NIEL) in the sensitive region of the device. There is no improvement in device performance after three months of room temperature annealing. Index Terms--Displacement damage, GaAs, heterojunction bipolar transistors (UBTs), nonionizing energy loss (NIEL), proton radiation effects.

Designs and implementation are proceeding for a Global Ocean Observing System (GOOS) and a Global Climate Observing System (GCOS). The initial design for the ocean component of the GCOS, which is also the climate module of the GOOS, was completed in 1995 by the Ocean Observing System Development Panel (OOSDP). This design for an ocean observing system for climate aims to provide ocean observations leading to gridded products, analyses, forecasts, indexes, assessments, and other items needed to detect, monitor, understand, and predict climate variations and change. A summary of the OOSDP report is presented here, beginning with the rationale for such a system and the series of specific goals and subgoals used to focus the design. The instruments, platforms, transmission systems, or processing required to observe the climate variables or quantifiable aspects of the climate system to meet these subgoals are identified. These observing system elements are divided into three categories: 1) elements of existing operational systems, 2) those that should be added now to complete the initial observing system, or 3) elements perhaps not now readily attainable but that should be added to the system at the earliest feasible time. Future research and development likely needed for further development of the system are also identified in the report. The elements needed for each subgoal are ranked as to feasibility (i.e., routine, systematic, timely, and cost-effective characteristics) versus their impact on attaining the subgoal. Priorities among the various subgoals are presented based on the panel's perception of where the immediate and important issues lie. This then provides the basis for an incremental approach to implementation, leading to a coherent conceptual design.