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NASA NTRS1992

X-ray observations of sunspot penumbral structure

High-resolution coronal observations with the Normal Incidence X-ray Telescope (NIXT) reveal previously unobserved structure in the magnetic fields above a sunspot. The X-ray images are precisely aligned with a continuum photospheric image taken at the same time. The X-ray brightness traces magnetic field lines and shows: (1) that none of the bright loops originate in the spot umbra and (2) that some field lines emerging from the inner penumbra connect to regions far away from the spot. Such large-scale structures must remain distinct from the shallowly inclined fields in the outer penumbra. In particular, they cannot be involved in any interchange between the bright and dark filaments. This imposes constraints on models of penumbral convection.

Sams, B. J., III↗

NASA NTRS1994

Features of steady magnetospheric convection

The large-scale patterns of ionospheric convection and particle precipitation are described during two intervals of steady magnetospheric convection (SMC) on November 24, 1981. The unique data set used in the analysis includes recordings from the worldwide network of magnetometers and all-sky cameras, global auroral images from the Dynamics Explorer (DE) 1 spacecraft, and particle precipitation data from low-altitude National Oceanic and Atmospheric Administration (NOAA) 6 and NOAA 7 spacecraft. The data show that intense magnetospheric convection continued during more than 10 hours under the steady southward interplanetary magnetic field without any distinct substorm signatures. All data sets available confirmed the stable character of the large-scale magnetospheric configuration during this period. In particular, the magnetic flux threading the polar cap was stable (within 10%) during 3.5 hours of continued DE 1 observations. The dayside cusp was located at an unusually low latitude (70 deg CGL). The nightside auroral pattern consisted of two distinct regions. The diffuse aurora in the equatorward half of the expanded (10 deg wide) auroral oval was well-separated from the bright, active auroral forms found in the vicinity of the poleward boundary of the oval. The twin-vortex convection pattern had no signature of the Harang discontinuity; its nightside 'convection throat' was spatially coincident with the poleward active auroras. This region of the auroral oval was identified as the primary site of the short-lived transient activations during the SMC intervals. The energetic particle observations show that the auroral precipitation up to its high-latitude limit is on closed field lines and that particle acceleration up to greater than 30-keV energy starts close to this limit. The isotropic boundaries of the greater than 30-keV protons and electrons were found close to each other, separating regions of discrete and diffuse precipitation. This suggests that these precipitation types originate on the very taillike and very dipolelike field lines, respectively.

Yahnin, A.↗

NASA NTRS2001

Modeling of Convective-Stratiform Precipitation Processes: Sensitivity to Partitioning Methods

Six different convective-stratiform separation techniques, including a new technique that utilizes the ratio of vertical and terminal velocities, are compared and evaluated using two-dimensional numerical simulations of a tropical [Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE)] and midlatitude continental [Preliminary Regional Experiment for STORM-Central (PRESTORM)] squall line. Comparisons are made in terms of rainfall, cloud coverage, mass fluxes, apparent heating and moistening, mean hydrometeor profiles, CFADs (Contoured Frequency with Altitude Diagrams), microphysics, and latent heating retrieval. Overall, it was found that the different separation techniques produced results that qualitatively agreed. However, the quantitative differences were significant. Observational comparisons were unable to conclusively evaluate the performance of the techniques. Latent heating retrieval was shown to be sensitive to the use of separation technique mainly due to the stratiform region for methods that found very little stratiform rain.

Lang, S. E.↗

NASA NTRS2002

The Most Extreme Thunderstorms on Earth

This study presents a comprehensive examination of the spectrum of storm types and their attributes worldwide (between 35N and 35S latitude), and as a function of season, location, and convective regime using the observed lightning, microwave scattering, and reflectivity signatures from NASA's Tropical Rainfall Measuring Mission (TRMM) low-Earth orbiting observatory. A global, multi-year data set (1998-2000) indicates that the deepest thunderstorms (having reflectivity in excess of 50 dBZ at 9 km altitude) occur in all the sub-tropical continents and occasionally over the open ocean, but are most common over the Americas. The most intense storms have the greatest lightning rates, lowest brightness temperatures and greatest depth of reflectivity- all indicative of strong updrafts and a well-developed volume of precipitation-sized ice particles. Mesoscale convective systems occurring within or in association with forcing from the sub-tropical continents are the most prolific lightning producers. The greatest flash rate to date of 993 flashes per minute was observed by NASA's Lightning Imaging Sensor on May 6, 1999 during an overpass of a pre-frontal squall line extending from Tennessee to Louisiana. The global distribution and frequency of thunderstorms, and the most recent summary of the extreme storms observed from space, in particular, will be discussed in greater detail.

Goodman, Steven J.↗

DOE OSTI2022

Microphysical Piggybacking in the Weather Research and Forecasting Model

Abstract This paper presents incorporation of the microphysical piggybacking into the Weather Research and Forecasting (WRF) model. Microphysical piggybacking is to run a single simulation applying two microphysical schemes, the first scheme driving the simulation and the second piggybacking this simulated flow. “Driving the simulation” means that the simulated microphysical processes, affect the cloud buoyancy and thus force the simulated flow. In contrast, the piggybacking variables are advected by the simulated flow and undergo microphysical transformation, but they do not affect the simulated flow (like in prescribed flow—kinematic—simulations). The two sets of variables (driver and piggybacker) include temperature, water vapor mixing ratio, and all microphysical variables. We provide details of implementing piggybacking into the WRF model, illustrate its applications, and demonstrate the benefits of this methodology in two idealized three‐dimensional cases: (a) a squall line case applying two microphysics schemes, the Thompson bulk microphysics scheme and the University of Pécs/NCAR bin (UPNB) scheme. The piggybacking simulations revealed that the microphysics‐dynamics interaction plays a more important role than the pure microphysical size sorting effect in the transition zone formation. (b) A case of daytime shallow‐to‐deep convective development over land. This case uses the UPNB scheme and contrasts convection developing in environments with either pristine or polluted cloud condensation nuclei (CCN). The piggybacking results indicated that the increase of cloud cover and decrease of supersaturation are mainly associated with the microphysical effect of increasing CCN while the change of precipitation on the ground is also influenced by microphysics‐dynamics interactions.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2025

Identifying synoptic controls on boundary layer thermodynamic and cloud properties in a regional forecast model

Although most of our understanding of boundary layer cloudiness is based on idealized, subtropical, barotropic marine environments, boundary layer clouds exist across a range of conditions. In this study, we use the Naval Research Laboratory's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) and an automated cold-front-relative analysis framework to explore the boundary layer structure associated with low clouds across a transect through the cold front of a midlatitude synoptic cyclone. The model credibly captures boundary layer structure in line with conceptual models of midlatitude cyclones and ground-based observations at Graciosa Island in the Azores. The warm sector is conditionally unstable, with clouds that are too shallow and with too little liquid water, compared to cloud property retrievals from satellite and surface-based instruments. The cold-frontal region exhibits convection associated with weak stability and ascent. Northwest of the cold front, the boundary layer is well mixed, deeper, and capped by a strong inversion maintained by large-scale subsidence. Simulated clouds in frontal and post-frontal regions are mostly too thick, with too much liquid water and too little cloud base drizzle. The post-frontal clouds are associated with grid-scale updrafts, which appear to be the model's attempt to represent mesoscale organization of cellular convection typically observed in the cold sector of midlatitude cyclones. The deep, well-mixed post-frontal boundary layers and cloudiness are maintained by strong surface fluxes, as in cold air outbreaks. Our analysis framework serves as a unique approach to model verification, and our results offer insights into differences in boundary layer cloud behavior between subtropical and synoptic cold-sector regimes.

Eissner, Jordan M. [Univ. of Kansas, Lawrence, KS ↗

NASA NTRS1973

Heating of foods in space-vehicle environments

In extended space missions, foods will be heated to enhance the psychological as well as the physiological well-being of the crew. In the low-gravity space environment natural convection is essentially absent so that the heat transfer within the food is by conduction alone. To prevent boiling in reduced pressure environments the maximum temperature of the heating system is severely limited. The Skylab food-heating system utilizes a tray with receptables for the food containers. The walls of the receptacles are lined with thermally controlled, electrical-resistance, blanket-type heating elements. A finite difference model is employed to perform parametric studies on the food-heating system. The effects on heating time of the (1) thermophysical properties of the food, (2) heater power level, (3) initial food temperatures, (4) container geometry, and (5) heater control temperature are presented graphically. The optimal heater power level and container geometry are determined.

Bannerot, R. B.↗

NASA NTRS1991

Effects of radiation and turbulence on the diabatic heating and water budget of the stratiform region of a tropical cloud cluster

A twi-dimensional kinematic model has been used to diagnose the thermodynamic, water vapor, and hydrometeor fields of the stratiform clouds associated with a mesoscale tropical cloud cluster. The model incorporates ice- and water-cloud microphysics, visible and infrared radiation, and convective adjustment. It is intended to determine the relative contributions of radiation, mycrophysics, and turbulence to diabatic heating, and the effects that radiation has on the water budget of the cluster in the absence of dynamical interactions. The model has been initialized with thermodynamic fields and wind velocities diagnosed from a GATE tropical squall line. It is found that radiation does not directly affect the water budget of the stratiform region, and any radiative effect on hydrometeors must involve interaction with dynamics.

Churchill, Dean D.↗

NASA NTRS2006

Improving Lightning NO(x) Parameterizations for Global Chemical Transport Models

Parameterization of lightning NO(x) in global chemical transport models requires a method to specify the temporal and geographic distribution of flash rates, an estimate of NO production per flash, and a method to specify the effective vertical distribution of NO production. Flash rate parameterizations using the upward convective cloud mass flux have been developed and tested for several GCM and assimilated meteorological data sets. This parameterization and others involving the cloud-top height and convective precipitation provide a generally acceptable climatological distribution of flashes after normalization with satellite data. However, considerable improvement in terms of geographic and temporal variability may be achieved in the future using cloud microphysics data available from next-generation GCMs. Cloud-resolving case-study simulations of convective transport and lightning NO production have yielded results which are directly applicable to the NO production per flash and the vertical NO distribution portions of the global model lightning parameterizations. In this work we have used cloud-resolving models (the Goddard Cumulus Ensemble Model (GCE) and MM5) to drive an off-line cloud-scale chemical transport model (CSCTM). The CSCTM, in conjunction with aircraft measurements of NO(x) in thunderstorms and ground-based lightning observations, has been used to constrain the amount of NO produced per flash. Observed lightning flash rates have been incorporated into the CSCTM, and several scenarios of NO production per intracloud (IC) and per cloud-to-ground (CG) flash have been tested in each of several case study storms. The resulting NO(x) mixing ratios are compared with aircraft measurements taken within the storm (typically the anvil region) to determine the most likely NO production scenario. The range of values of NO production per flash (or per meter of lightning channel length) that have been deduced from the model will be shown and compared with values of production in the literature that have been deduced from observed NO spikes and from anvil flux calculations. Results show that on a per flash basis, IC flashes are nearly as productive of NO as CG flashes. Estimates of mean NO production per flash vary by a factor of three from one simulated storm to another. Vertical profiles of lightning NOx mass at the end of the 3-D storm simulations have been summarized to yield suggested profiles for use in global models. These profiles show a larger percentage of the total lightning NO(x) mass in the free troposphere than those suggested by Pickering et al. (1998).

Pickering, Kenneth E.↗

NASA NTRS2015

Early Development of the First Earth Venture Mission: How CYGNSS Is Using Engineering Models to Validate the Design

In response to the recommendations made in the National Research Council' s Ear th Science and Applications 2007 Decadal Sur vey, NASA has initiated the Ear th Venture line of mission oppor tunities. The fir st orbital mission chosen for this competitively selected, cost and schedule constrained, Pr incipal Investigator -led oppor tunity is the CYclone Global Navigation Satellite System (CYGNSS). The goal of CYGNSS is to understand the coupling between ocean sur face proper ties, moist atmospher ic thermodynamics, radiation, and convective dynamics in the inner core of a tropical cyclone. The CYGNSS mission is compr ised of eight Low Ear th Obser ving (LEO) micr osatellites that use GPS bi-static scatterometry to measure ocean sur face winds.

Wells, James↗

NASA NTRS1975

Magnetic fields and dense chromospheres in dMe stars

The hypothesis is investigated that dense chromospheres of dMe stars are heated by dissipation of hydromagnetic waves which may be generated in active regions where the nonspot magnetic field strength can be as large as 5 to 10 kG. It is proposed that dMe stars are a set of magnetic stars on the lower main sequence which have strong fields generated by dynamo action in deep convective envelopes, while dM stars are nonmagnetic or weakly magnetic stars having no starspots on their surfaces. The combination of magnetic fields and dense chromospheres in dMe stars is shown to provide consistent evidence for several conclusions, including: (1) the dMe stars which are most likely to be flare stars are those with hydrogen emission lines and (2) propagation of flare-initiated coronal waves can trigger sympathetic stellar flares. It is suggested that grain formation occurs in starspots of dMe stars and that such grains in a circumstellar shell are responsible for the systematic IR excesses of dMe stars relative to dM stars.

Mullan, D. J.↗

NASA NTRS1986

Convective heat transfer from circular cylinders located within perforated cylindrical shrouds

The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied. The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective heat transfer to bare cylinders up to 50%. The maximum enhancement occurred for a radius ratio of 1.4 and ventilation factors between 0.2 and 0.3. It was found that shroud orientation influenced the heat transfer, with maximum heat transfer generally occurring when the shroud's holes were centered on either side of the stagnation line. However, the hole orientation effect is of second order compared to the influence of ventilation factor and radius ratio.

Daryabeigi, K.↗

NASA NTRS1989

Observed structural variability of deep moist convection within a mesoscale convective system

Some radar observations of the convective cloud structure within and around a developing mesoscale convective system (MCS), which attained an eventual horizontal dimension of approximately 100 by 200 km, are reported. Similarities in cloud structure within and outside the MCS include a downshear tilt of the cloud precipitation core and generation of new cells toward the direction of cloud motion and parallel to the major axis of the cloud line. The systematic difference in the longevity and intensity of the clouds is examined.

Knupp, Kevin R.↗

NASA NTRS1987

Ultraviolet and visual spectroscopy of DB white dwarfs

Visual wavelength and ultraviolet spectroscopy and model atmospheres of DB white dwarfs are reported. The results yield no evidence for lines of C or any other element besides H or He in the spectra. Upper limits for carbon are in the range C:He less than 10 to the -5th to the -7th for the ultraviolet data and C:He less than 0.01-0.001 for the visual. The upper limits are consistent with the convective dredging theory for the origin of the atmospheric carbon observed in the cooler DQ members of the helium-rich white dwarf sequence. Additional new DBA stars are reported.

Wegner, G.↗

NASA NTRS1990

Magnetic field configuration of the theta aurora

A magnetic configuration of the open magnetosphere is described which is conducive to the formation of the theta aurora when the IMF has a significant northward component. A magnetic field topology and polar cap configuration, derived from a quantitative model of the open magnetosphere that incorporates Crooker's antiparallel merging hypothesis, are presented. Under this hypothesis, when the IMF has a northward component, the dayside merging line bifurcates, leaving a large fraction of the subsolar magnetopause untouched by the merging process. The polar cap, defined by tracing magnetic field lines that connect from the solar wind to the earth, is similarly bifurcated, leaving a sun-aligned stagnation region that is not magnetically connected to the solar wind and may plausibly be associated with the sun-aligned 'bar' of the theta aurora. The model provides testable predictions with regard to the position of this 'convection gap' in both Northern and Southern Hemispheres as functions of IMF direction.

Toffoletto, F. R.↗

NASA NTRS1992

The Capella subcoronal heating efficiency

Using transition region fluxes and high resolution spectra of the Ly-alpha and Mg II h and k lines observed by the GHRS spectrograph, I determine the total flux radiated from each temperature regime in the Capella upper chromosphere and transition region. This contains essentially the same information as the emission measure distribution, but to better suggest physical interpretations of the heating mechanisms it is expressed instead in terms of the efficiency for extracting convection zone energy flux and depositing it over the temperature ranges considered.

Gayley, Kenneth G.↗

NASA NTRS1996

Galactic cosmic radiation model and its applications

A model for the differential energy spectra of galactic cosmic radiation as a function of solar activity is described. It is based on the standard diffusion-convection theory of solar modulation. Estimates of the modulation potential based on fitting this theory to observed spectral measurements from 1954 to 1989 are correlated to the Climax neutron counting rates and to the sunspot numbers at earlier times taking into account the polarity of the interplanetary magnetic field at the time of observations. These regression lines then provide a method for predicting the modulation at later times. The results of this model are quantitatively compared to a similar Moscow State University (MSU) model. These model cosmic ray spectra are used to predict the linear energy transfer spectra, differential energy spectra of light (charge less than or = 2) ions, and single event upsets rates in memeory devices. These calculations are compared to observations made aboard the Space Shuttle.

Badhwar, G. D.↗

NASA NTRS2002

The Structure of A Pacific Narrow Cold Frontal Rainband

A NOAA P-3 instrumented aircraft observed an intense, fast-moving narrow cold frontal Farmhand as it approached the Pacific Northwest coast on 19 February 2001 during the Pacific Coastal Jets Experiment. Pseudo-dual-Doppler analyses performed on the airborne Doppler radar data while the frontal system was well offshore indicated that a narrow ribbon of very high radar reflectively convective cores characterized the Farmhand at low levels with echo tops to approximately 4-5 km. The NCFR exhibited gaps in its narrow ribbon of high reflectively, probably as a result of hydrodynamic instability all no its advancing cold pool leading edge. In contrast to some earlier studies of cold frontal rainbands, density current theory described well the motion of the overall front. The character of the updraft structure associated with the heavy rainfall at its leading edge varied across the gap region. The vertical shear of the cross-frontal low-level ambient flow exerted a strong influence on the updraft character, consistent with theoretical arguments developed for squall lines describing the balance of vorticity at the leading edge. In short regions south of the gaps the vertical wind shear was strongest with the updrafts and rain shafts more intense, narrower, and more erect or even downshear tilted. North of the gaps the wind shear weakened with less intense Dihedrals which tilted upshear with a broader band of rainfall. Simulations using a nonhydrostatic mesoscale nested grid model are used to investigate the gap regions, particularly the balance of cold pool induced to pre-frontal ambient shears at the leading edge. Observations confirm the model results that the updraft character depends on the balance of vorticity at the leading edge. Downshear-tilted updrafts imply that convection south of the gap regions would weaken with time relative to the frontal segments north of the gaps since inflow air would be affected by passage through the heavy rain region before ascent, suggesting a mechanism for gap filling.

Jorgensen, David P.↗