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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Implications of natural sources for the latitudinal gradients of NO/y/ in the unpolluted troposphere

The latitudinal distributions of tropospheric odd nitrogen (NO/y/) due to lightning discharges and stratospheric injection are studied by estimating latitude dependences of the sources and the rainout sink from data obtained in August-September, 1977, and May-June, 1978, during project GAMETAG. A one-dimensional (latitude dependent) model is developed for the annually, zonally, and vertically averaged concentration of trace species, NO(y) being treated as a single species, which decouples the NO(y) calculation from the rest of the model since NO(y) has no chemical sources or sinks in the troposphere. The equation governing the NO(y) distribution is solved using finite differences with 33 uniformly spaced grid points in the micron range of -1 to 1. The distribution due to the stratospheric source has a minimum in the tropics, and there are broad maxima centered in the 25-30 degree region in both hemispheres. The calculated NO(y) due to lightning has a maximum near 15 degrees S, and it decreases to nearly a fourth of the maximum value near the poles. The drop off from the maximum is sharper in the Southern Hemisphere in comparison with the Northern Hemisphere.

Hameed, S.↗
NASA NTRS2015

Lightning Protection and Structural Bonding for the B2 Test Stand

With the privatization of the space industry, NASA has entered a new era. To explore deeper parts of the solar system, NASA is developing a new spacecraft, the Space Launch System (SLS), capable of reaching these destinations, such as an asteroid or Mars. However, the test stand that is capable of testing the stage has been unused for many years. In addition to the updating/repair of the stand, more steel is being added to fully support the SLS. With all these modifications, the lightning protection system must be brought up to code to assure the protection of all personnel and assets. Structural bonding is a part of the lightning protection system. The focus of this project was to assure proper structural bonding. To begin, all relevant technical standards and the construction specifications were reviewed. This included both the specifications for the lightning protection and for general construction. The drawings were reviewed as well. From the drawings, bolted structural joints were reviewed to determine whether bonding was necessary. Several bolted joints were determined to need bonding according to the notes in the drawings. This exceeds the industry standards. The bolted joints are an electrically continuous joint. During tests, the stand experiences heavy vibration that may weaken the continuity of the bolted joint. Therefore, the secondary bonding is implemented to ensure that the structural joint has low resistance. If the structural joint has a high resistance because of corrosion, a potential gradient can occur that can cause a side flash. Damage, injury, or death can occur from a side flash so they are to be prevented. A list of the identified structural joints was compiled and sent to the contractor to be bonded. That covers the scope of this project.

Kinard, Brandon↗
NASA NTRS2016

Scientific and Technical Assistance for the Deployment of a Flexible Airborne Spectrometer System During C-MAPExp and COMEX: COMEX Version - 1.9T

The COMEX (CO2 and MEthane eXperiment) campaign supports the mission definition of CarbonSat and HyspIRI (Hyperspectral Infrared Imager) by providing representative airborne remote sensing data ‐ MAMAP (Methane Airborne MAPper) for CarbonSat; the Airborne Visual InfraRed Imaging Spectrometer (Classic & Next Generation) AVIRIS‐C/AVIRIS‐NG for HyspIRI ‐ as well as ground-based and airborne in‐situ data. The objectives of the COMEX campaign activities are (see Campaign Implementation Plan (RD‐4)): 1. Investigate spatial/spectral resolution trade‐offs for CH4 anomaly detection and flux inversion by comparison of MAMAP‐derived emission estimates with AVIRIS/AVIRIS‐NG derived data. 2. Evaluate sun‐glint observation geometry on CH4 retrievals for marine sources. 3. Characterize the effect of Surface Spectral Reflectance (SSR) heterogeneity on trace gas retrievals of CO2 and CH4 for medium and low‐resolution spectrometry. 4. Identify benefits from joint SWIR/TIR (ShortWave InfraRed/Thermal InfraRed ) data for trace gas detection and retrieval by comparison of MAMAP and AVIRIS/AVIRIS‐NG NIR/SWIR data with MAKO (Aerospace Corp.)TIR data. The ability to derive emission source strength for a range of strong emitting targets by remote sensing will be evaluated from combined AVIRIS‐NG and MAMAP data, adding significant value to the HyspIRI campaign AVIRIS‐NG dataset. The data will be used to quantify anomalies in atmospheric CO2 and CH4 from strong local greenhouse gas sources e.g. localized industrial complexes, landfills, etc. and to derive CO2 and CH4 emissions estimates from atmospheric gradient measurements. The original campaign concept was developed by University of Bremen and BRI. The COMEX campaign is funded bilaterally by NASA and ESA (European Space Agency). Whereas NASA funds the US part of the project via a contract with Dr. Ira Leifer, BRI (Bubbleology Research International), the contribution of MAMAP to the COMEX campaign is funded by ESA within the COMEX‐E project and NASA with respect to a 50 percent contribution to the flight-related costs of flying MAMAP on a US aircraft. The Data Acquisition Report (RD‐9) describes the instrumentation used, the measurements made by the team during the COMEX campaign in May/June 2014 and August/September 2014 in California, and an initial assessment of the data quality.

Point Sources↗
NASA NTRS2017

Cryogenic Refractive Index of Heraeus Homosil Glass

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.34-3.16 microns and temperature range of 120-335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASAs Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a field-widened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitivity performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dn/dT) and dispersion relation (dn/d(lamda)) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in literature.

cryogenic↗
NASA NTRS2017

Cryogenic Refractive Index of Heraeus Homosil Glass

This paper reports measurements of the refractive index of Homosil (Heraeus) over the wavelength range of 0.343.16 m and temperature range of 120335 K. These measurements were performed by using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the NASAs Goddard Space Flight Center. These measurements were in support of an integrated Structural-Thermal-Optical-Performance (STOP) model that was developed for a field-widened Michelson interferometer that is being built and tested for the High Spectral Resolution Lidar (HSRL) project at the NASA Langley Research Center (LaRC). The cryogenic refractive index measurements were required in order to account for the highly sensitivity performance of the HSRL instrument to changes in refractive index with temperature, temperature gradients, thermal expansion, and deformation due to mounting stresses. A dense coverage of the absolute refractive index over the aforementioned wavelength and temperature ranges was used to determine the thermo-optic coefficient (dndT) and dispersion relation (dnd) as a function of wavelength and temperature. Our measurements of Homosil will be compared with measurements of other glasses from the fused silica family studied in CHARMS as well as measurements reported elsewhere in literature.

Homosil↗
NASA NTRSDate not supplied

The Response of the Quasi-Biennial Oscillation to Increased CO and its Modulation by Composition Feedbacks

The Quasi-Biennial Oscillation (QBO) impacts the large-scale circulation by altering lower stratospheric meridional temperature gradients which alter the propagation of upward propagating planetary waves. Proposed teleconnections of the QBO include impacts on the stratospheric polar vortices, extratropical surface winter climate, and the Madden-Julian Oscillation. However, long-term projections of the QBO remain highly uncertain. While recent multi-model investigations (Richter et al. 2019, Butchart et al. 2020) show that the amplitude of the QBO weakens robustly among models, changes in QBO period and stability remain highly uncertain. Here we examine the QBO response to increased greenhouse gases using the NASA Goddard Institute for Space Studies Middle Atmosphere Model E2.2 (Rind et al., 2020; Orbe et al. 2020). Compared to lower vertical resolution versions of ModelE, E2.2 also has a higher model top (0.002 hPa) and employs additional interactive non-orographic gravity wave drag sources from convection and shear, which produce a sufficiently realistic QBO, thus rendering it suitable for use in climate change studies. Overall, we find that both the QBO period and amplitude decrease in response to increased CO , the former related to increased lower stratospheric momentum fluxes (associated with convection) and the latter associated partly with a stronger residual mean circulation. Experiments integrated using fully interactive chemistry also reveal that ozone feedbacks significantly impact the magnitude of the QBO amplitude response. Finally, integrations using fixed (pre-industrial) sea surface temperatures (SST) show that the QBO amplitude responds differently to rapid adjustments versus SST feedbacks, as compared to the QBO period.

Quasi-Biennial Oscillation↗
NASA NTRS1994

The gradient of meteorological and chemical variables across the tropopause

The downward transport of air through the tropopause can bring substantial amounts of ozone and reactive nitrogen into the upper troposphere. In this cold region of the atmosphere, O3 is particularly effective as a greenhouse gas. As part of the North Dakota Thunderstorm Project in June 1989, the NCAR Sabreliner made five flights through the tropopause. We measured ozone, nitric oxide (NO), total reactive nitrogen (NO(y)), carbon monoxide (CO), and water vapor (H2)), and took grab samples for hydrocarbon (HC) analysis. Hydrocarbons, CO, and H2O, species with sources primarily at the earth's surface, showed a strong concentration decrease with increasing altitude, while O3 and NO(y), species with a source in the stratosphere, showed a strong concentration increase with increasing altitude. Stratospheric concentrations of NO(x), NO(y), and H2O were all high relative to winter observations made during NASA's AASE. We suggest that midlatitude thunderstorms may inject wet, NO-rich air into the lower stratosphere. Calculation based on measured ratios of NO(x) and NO(y) to O3 yield a total flux of reactive nitrogen from the Northern Hemisphere stratosphere into the troposphere of 1 to 2 Tg(N) yr(exp -1) with about 8 percent in the form of NO(x). This value is higher than reported estimates of total stratospheric nitrogen fixation.

Dickerson, Russell R.↗
NASA NTRS1995

Synoptic maps of solar wind parameters from in situ spacecraft observations

Solar wind observations from the Interplanetary Monitoring Platform-8 (IMP-8) and Pioneer Venus Orbiter (PVO) spacecraft from 1982 until 1988 are combined to construct synoptic maps of solar wind parameters near 1 AU. Each map consists of 6 months of hourly averaged solar wind data, binned by heliographic latitude and Carrington longitude and projected back to the Sun. These maps show the structure and time evolution of solar wind streams near 1 AU in the heliographic latitudes of +/- 7.25 deg and provide and explicit picture of several phenomena, such as gradients, changes in the inclination of the heliospheric current sheet, and the relative positions of various structures in the inner heliosphere, that is difficult to obtain from single-spacecraft observations. The stream structure varied significantly during the last solar cycle. Between 1982 and early 1985, solar wind parameters did not depend strongly on heliographic latitude. During the last solar minimum, the solar wind developed significant latitudinal structure, and high-speed streams were excluded from the vicinity of the solar equator. The interplanetary magnetic field was strongly correlated with the coronal field, and the current sheet tended to coincide with the coronal neutral line. The solar wind speed showed the expected correlations with temperature, interplanetary magnetic field, and distance from the current sheet. The solar wind speed was anticorrelated with density, but the regions of highest density occurred east of the heliospheric current sheet and the regions of lowest solar wind speed. This is consistent with compression at the leading edge of high-speed streams.

Gazis, P. R.↗
NASA NTRSDate not supplied

Analysis and Optimization of Baseline Single Aisle Aircraft for Future Electrified Powertrain Flight Demonstrator Comparisons

The purpose of this study is to provide baseline single-aisle vehicles for future comparisons NASA’s Electrified Powertrain Flight Demonstrator (EPFD) turbofan powered Vision Systems. Both a large single-aisle (≈150 passenger) and a small single-aisle (≈100 passenger) vehicle will be analyzed using NASA’s General Aviation Synthesis Program and a modernized Python-based version of this program that enables efficient gradient-based optimization of both the airframe and propulsion that currently is being referred to as GASPy. A technology build-up will be conducted to bring the current State-of-the-art vehicles to a projected 2035 technology level by incorporating estimations for improvements in aerodynamics, structures, and propulsions. These vehicles can be used in NASA’s future EPFD project as baselines to measure the benefits of future hybrid and fully electric aircraft against. The advanced, large single-aisle will then be used to demonstrate the benefits of a coupled engine-airframe optimization for fuel burn reduction.

Carl J Recine↗
NASA NTRS1988

First Viking results - Magnetic field measurements

The magnetic field experiment on the Swedish Viking satellite consists of a triaxial fluxgate magnetometer system with the sensors mounted on a 2-m boom. Transverse magnetic field perturbations are readily observed which identify the large-scale auroral and cusp-region Birkeland current (BC) systems. A sharp gradient was observed in the dayside region near apogee and 08:40 MLT during a pass on March 25, 1986 which has been interpreted as an earthward-flowing BC of 8 micro-A/sq m. When projected to ionospheric altitudes it is estimated that the current density is 200 micro-A/sq m.

Potemra, T. A.↗
NASA NTRS2007

A Microfabricated Involute-Foil Regenerator for Stirling Engines

A segmented involute-foil regenerator has been designed, microfabricated and tested in an oscillating-flow rig with excellent results. During the Phase I effort, several approximations of parallel-plate regenerator geometry were chosen as potential candidates for a new microfabrication concept. Potential manufacturers and processes were surveyed. The selected concept consisted of stacked segmented-involute-foil disks (or annular portions of disks), originally to be microfabricated from stainless-steel via the LiGA (lithography, electroplating, and molding) process and EDM (electric discharge machining). During Phase II, re-planning of the effort led to test plans based on nickel disks, microfabricated via the LiGA process, only. A stack of nickel segmented-involute-foil disks was tested in an oscillating-flow test rig. These test results yielded a performance figure of merit (roughly the ratio of heat transfer to pressure drop) of about twice that of the 90% random fiber currently used in small ~ 100 W Stirling space-power convertors in the Reynolds Number range of interest (50-100). A Phase III effort is now underway to fabricate and test a segmented-involute-foil regenerator in a Stirling convertor. Though funding limitations prevent optimization of the Stirling engine geometry for use with this regenerator, the Sage computer code will be used to help evaluate the engine test results. Previous Sage Stirling model projections have indicated that a segmented-involute-foil regenerator is capable of improving the performance of an optimized involute-foil engine by 6-9%; it is also anticipated that such involute-foil geometries will be more reliable and easier to manufacture with tight-tolerance characteristics, than random-fiber or wire-screen regenerators. Beyond the near-term Phase III regenerator fabrication and engine testing, other goals are (1) fabrication from a material suitable for high temperature Stirling operation (up to 850 C for current engines; up to 1200 C for a potential engine-cooler for a Venus mission), and (2) reduction of the cost of the fabrication process to make it more suitable for terrestrial applications of segmented involute foils. Past attempts have been made to use wrapped foils to approximate the large theoretical figures of merit projected for parallel plates. Such metal wrapped foils have never proved very successful, apparently due to the difficulties of fabricating wrapped-foils with uniform gaps and maintaining the gaps under the stress of time-varying temperature gradients during start-up and shut-down, and relatively-steady temperature gradients during normal operation. In contrast, stacks of involute-foil disks, with each disk consisting of multiple involute-foil segments held between concentric circular ribs, have relatively robust structures. The oscillating-flow rig tests of the segmented-involute-foil regenerator have demonstrated a shift in regenerator performance strongly in the direction of the theoretical performance of ideal parallel-plate regenerators.

Tew, Roy↗
NASA NTRS2007

A Microfabricated Involute-Foil Regenerator for Stirling Engines

A segmented involute-foil regenerator has been designed, microfabricated and tested in an oscillating-flow rig with excellent results. During the Phase I effort, several approximations of parallel-plate regenerator geometry were chosen as potential candidates for a new microfabrication concept. Potential manufacturers and processes were surveyed. The selected concept consisted of stacked segmented-involute-foil disks (or annular portions of disks), originally to be microfabricated from stainless-steel via the LiGA (lithography, electroplating, and molding) process and EDM. During Phase II, re-planning of the effort led to test plans based on nickel disks, microfabricated via the LiGA process, only. A stack of nickel segmented-involute-foil disks was tested in an oscillating-flow test rig. These test results yielded a performance figure of merit (roughly the ratio of heat transfer to pressure drop) of about twice that of the 90 percent random fiber currently used in small approx.100 W Stirling space-power convertors-in the Reynolds Number range of interest (50 to 100). A Phase III effort is now underway to fabricate and test a segmented-involute-foil regenerator in a Stirling convertor. Though funding limitations prevent optimization of the Stirling engine geometry for use with this regenerator, the Sage computer code will be used to help evaluate the engine test results. Previous Sage Stirling model projections have indicated that a segmented-involute-foil regenerator is capable of improving the performance of an optimized involute-foil engine by 6 to 9 percent; it is also anticipated that such involute-foil geometries will be more reliable and easier to manufacture with tight-tolerance characteristics, than random-fiber or wire-screen regenerators. Beyond the near-term Phase III regenerator fabrication and engine testing, other goals are (1) fabrication from a material suitable for high temperature Stirling operation (up to 850 C for current engines; up to 1200 C for a potential engine-cooler for a Venus mission), and (2) reduction of the cost of the fabrication process to make it more suitable for terrestrial applications of segmented involute foils. Past attempts have been made to use wrapped foils to approximate the large theoretical figures of merit projected for parallel plates. Such metal wrapped foils have never proved very successful, apparently due to the difficulties of fabricating wrapped-foils with uniform gaps and maintaining the gaps under the stress of time-varying temperature gradients during start-up and shut-down, and relatively-steady temperature gradients during normal operation. In contrast, stacks of involute-foil disks, with each disk consisting of multiple involute-foil segments held between concentric circular ribs, have relatively robust structures. The oscillating-flow rig tests of the segmented-involute-foil regenerator have demonstrated a shift in regenerator performance strongly in the direction of the theoretical performance of ideal parallel-plate regenerators.

Tew, Roy↗
NASA NTRS1982

Quantitative determination of zero-gravity effects on electronic materials processing germanium crystal growth with simultaneous interface demarcation experiment MA-060, section 5

The crystal growth and segregation characteristics of a melt in a directional solidification configuration under near zero g conditions were investigated. The germanium (doped with gallium) system was selected because it was extensively studied on Earth and because it lends itself to a very detailed macroscopic and microscopic characterization. An extensive study was performed of the germanium crystals grown during the Apollo-Soyuz Test Project mission. It was found that single crystal growth was achieved and that the interface demarcation functioned successfully. On the basis of the results obtained to date, there is no indication that convection driven by thermal or surface tension gradients was present in the melt. The gallium segregation, in the absence of gravity, was found to be fundamentally different in its initial and its subsequent stages from that of the ground based tests. None of the existing theoretical models for growth and segregation can account for the observed segregation behavior in the absence of gravity.

Gatos, H. C.↗
NASA NTRS1990

Patterns in simulated turbulent channel flow

The surface stress is a key diagnostic in wall bounded turbulent flows. Large fluctuations in the stress are believed to be associated with intermittent 'bursting' events during which a large proportion of the turbulence production takes place. If this is so, then a detailed investigation of the structure of the surface stress and its spatial relationship to events within the flow could have wide application in drag reduction and other aspects of flow control. The initial phase of this project, therefore, concentrated on the surface stress field. The first objective is to carry out a statistical analysis of the instantaneous surface stress in a simulated turbulent channel flow, including comparison with multipoint experimental data from a zero pressure gradient turbulent boundary layer. The second objective is to apply a simple pattern recognition procedure to educe the characteristic spatial structure of various flow diagnostics. The final objective is to extend the pattern recognition analysis to examine the whole three dimensional structure of the flow.

Stretch, D.↗
NASA NTRS1997

Pioneer 10 and 11 Data Analysis

This report finishes the work of NASA Grant NAS2-153, which supported data analysis for the UCSD instruments on Pioneers 10 and 11. The data analyzed under this grant span 22 years of interplanetary measurements in the inner and outer heliosphere. The UCSD instruments made their mark in cosmic ray research based upon their high energy thresholds, directional responses, and reliable data streams. one of their primary scientific objectives concerns the size, configuration, and time behavior of the heliosphere. The size scale is inferred from the radial intensity gradient, which is measured between the two spacecraft and extrapolated to interstellar intensity levels at the cosmic ray modulation boundary. This boundary still eludes us, and its position, motion, and the best method of extrapolation are ongoing problems. Current projections place the boundary beyond 100 AU, which may be beyond the termination shock, and raises the question of possible modulation in the heliosheath. Probably our only hope of seeing this region in the immediate future rides on the possibility that the boundary will move inward. Our instruments have recorded many Forbush, or transient, decreases in the outer heliosphere. These observations led us to a model that attributes many of the decreases to solar wind stream-stream interactions, and relates the cosmic ray variations to the locally observed magnetic field magnitude. As the cosmic ray variations in this model result only from topological changes in the modulation integral, the model is a tool for studying the possibility that the 11 year cosmic ray modulation cycle can be accounted for by a superposition of Forbush decreases. The cosmic ray angular distribution function is measurable, given a good telemetry rate, by the UCSD Cerenkov detector which counts particles of energy greater than 500 MeV/n. We obtained statistically significant samples from 1 to 9 AU, at 13 AU, and at 34 AU. The anisotropy tends to be a few tenths of a per cent at all radial distances. A quasiperiodic variation in the east-west anisotropy with period of about 50 days remains unexplained.

Fillius, Walker↗
NASA NTRS1996

Space research activities during missions of the past

For over 30 yr, men and women have lived for various periods of time in a weightless (or free-fall) environment while orbiting the Earth. During these years, we have learned that humans function quite well for short periods of weightlessness, that is, for up to a little more than a year. Some space flight missions have provided physiologic data, including cardiovascular data, from the spacefarers. In fact, some missions have provided laboratories for systematic study of cardiovascular responses and adaptation to space flight. However, the opportunity to obtain physiologic data from people in space is a rarity. It is important to remember that the population sample sizes are small, other stresses may confound the effects of weightlessness, and in some situations the crewmembers are subjects for several experiments at the same time. Furthermore, comparison of cardiovascular data from space flight to data obtained on the ground is sometimes difficult because the subject's posture on the ground is not always reported; in a gravity environment, posture influences the hydrostatic gradient. This over view describes what we have learned about cardiovascular function during flight and after return to Earth.

NASA Discipline Cardiopulmonary↗
NASA NTRS2011

Tropical and Subtropical Cloud Transitions in Weather and Climate Prediction Models: The GCSS/WGNE Pacific Cross-Section Intercomparison (GPCI)

A model evaluation approach is proposed in which weather and climate prediction models are analyzed along a Pacific Ocean cross section, from the stratocumulus regions off the coast of California, across the shallow convection dominated trade winds, to the deep convection regions of the ITCZ the Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/ WGNE) Pacific Cross-Section Intercomparison (GPCI). The main goal of GPCI is to evaluate and help understand and improve the representation of tropical and subtropical cloud processes in weather and climate prediction models. In this paper, a detailed analysis of cloud regime transitions along the cross section from the subtropics to the tropics for the season June July August of 1998 is presented. This GPCI study confirms many of the typical weather and climate prediction model problems in the representation of clouds: underestimation of clouds in the stratocumulus regime by most models with the corresponding consequences in terms of shortwave radiation biases; overestimation of clouds by the 40-yr ECMWF Re-Analysis (ERA-40) in the deep tropics (in particular) with the corresponding impact in the outgoing longwave radiation; large spread between the different models in terms of cloud cover, liquid water path and shortwave radiation; significant differences between the models in terms of vertical cross sections of cloud properties (in particular), vertical velocity, and relative humidity. An alternative analysis of cloud cover mean statistics is proposed where sharp gradients in cloud cover along the GPCI transect are taken into account. This analysis shows that the negative cloud bias of some models and ERA-40 in the stratocumulus regions [as compared to the first International Satellite Cloud Climatology Project (ISCCP)] is associated not only with lower values of cloud cover in these regimes, but also with a stratocumulus-to-cumulus transition that occurs too early along the trade wind Lagrangian trajectory. Histograms of cloud cover along the cross section differ significantly between models. Some models exhibit a quasi-bimodal structure with cloud cover being either very large (close to 100%) or very small, while other models show a more continuous transition. The ISCCP observations suggest that reality is in-between these two extreme examples. These different patterns reflect the diverse nature of the cloud, boundary layer, and convection parameterizations in the participating weather and climate prediction models.

Teixeira, J.↗
NASA NTRS2022

Constraining Arctic Climate Projections of Wintertime Warming With Surface Turbulent Flux Observations and Representation of Surface-Atmosphere Coupling

The drivers of rapid Arctic climate change—record sea ice loss, warming SSTs, and a lengthening of the sea ice melt season—compel us to understand how this complex system operates and use this knowledge to enhance Arctic predictability. Changing energy flows sparked by sea ice decline, spotlight atmosphere-surface coupling processes as central to Arctic system function and its climate change response. Despite this, the representation of surface turbulent flux parameterizations in models has not kept pace with our understanding. The large uncertainty in Arctic climate change projections, the central role of atmosphere-surface coupling, and the large discrepancy in model representation of surface turbulent fluxes indicates that these processes may serve as useful observational constraints on projected Arctic climate change. This possibility requires an evaluation of surface turbulent fluxes and their sensitivity to controlling factors (surface-air temperature and moisture differences, sea ice, and winds) within contemporary climate models (here Coupled Model Intercomparison Project 6). The influence of individual controlling factors and their interactions is diagnosed using a multi-linear regression approach. This evaluation is done for four sea ice loss regimes, determined from observational sea ice loss trends, to control for the confounding effects of natural variability between models and observations. The comparisons between satellite- and model-derived surface turbulent fluxes illustrate that while models capture the general sensitivity of surface turbulent fluxes to declining sea ice and to surface-air gradients of temperature and moisture, substantial mean state biases exist. Specifically, the central Arctic is too weak of a heat sink to the winter atmosphere compared to observations, with implications to the simulated atmospheric circulation variability and thermodynamic profiles. Models were found to be about 50% more efficient at turning an air-sea temperature gradient anomaly into a sensible heat flux anomaly relative to observations. Further, the influence of sea ice concentration on the sensible heat flux is underestimated in models compared to observations. The opposite is found for the latent heat flux variability in models; where the latent heat flux is too sensitive to a sea ice concentration anomaly. Lastly, the results suggest that present-day trends in sea ice retreat regions may serve as suitable observational constraints of projected Arctic warming.

turbulent fluxes↗