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NASA NTRS2002

Extreme Lightning Flash Rates as an Early Indicator of Severe Storms

Extreme lightning flash rates are proving to be an early indicator of intensifying storms capable of producing tornadoes, damaging winds and hail. Most of this lightning is in the cloud, where the naked eye can not see it. Recent global observations of thunderstorms from space indicate that giant electrical storms (supercells and convective complexes) with flash rates on the order of 1 flash per second are most common over the land masses of the America sub-tropics and equatorial Congo Basin. Within the United States, the average tornado warning lead time on a national basis is about 11 min. The real-time observation of extreme flash rates and the rapid increase in the in-cloud flash rate, signalling the intensification of the storm updraft, may provide as much as a 50% increase in severe storm warning lead time.

Goodman, Steven J.↗

NASA NTRSDate not supplied

Lightning Flash Behavior and Convective Characteristics in Hurricanes Florence (2018), Dorian (2019), and Laura (2020)

Lightning is a useful tool in forecasting and understanding the behavior of tropical cyclones (TCs). Flash extent density (FED) has been found to be indicative of strength and intensification in TCs, but optical energy is a newer parameter that has not been studied intensively. This presentation analyzes the relationship between convective characteristics, such as updraft speed and updraft size, and Geostationary Lightning Mapper (GLM) optical energy, flash area, and FED in Hurricanes Florence (2018) and Laura (2020). The maximum optical energy values were analyzed for each minute from the innermost 100 kilometers of the eye to determine if there was a relationship between optical energy, flash area, updraft behavior, and intensification. Microwave imagery and tail-doppler radar (TDR) were examined during rapid increases in flash energy to connect updraft size and strength to these spikes. Early results show an increase in size of a moderate updraft occurring just prior to an increase in lightning optical energy and TC intensity, while smaller updrafts coincide with a decrease in intensity or little to no change in intensity. Continuing work aims to investigate the role of moderate updraft size in lightning behavior and TC intensity.

Kiahna Mollette↗

NASA NTRS1980

Radar observations of cleft dynamics

A continuous radar monitoring, during a six hour period which included an onset and recovery of global substorm activity, of an ionospheric density enhancement associated with the cleft is reported. Observations of the cleft showed a rapid equatorward excursion to 70 deg Lambda before occurrence of a major substorm intensification, continued location at low magnetic latitude during substorm expansion, and a poleward retreat to about 73.5 deg Lambda during substorm recovery in response to a northward turning of the IMF. Furthermore, the latitudinal width of the cleft density enhancement varied from less than 1 deg during the presubstorm equatorward motion to about 4 deg after substorm recovery.

Foster, J. C.↗

NASA NTRS1988

Asymptotic modal analysis and statistical energy analysis of an acoustic cavity

A basic asymptotic theory for structural wall/acoustic cavity interaction is presented, and the analysis is illustrated with examples of the acoustic cavity response to a prescribed wall motion. Although, when spatially averaged, the classical modal analysis (CMA) response approaches the asymptotic modal analysis (AMA) response more rapidly as the number of modes increases, it is shown that information about local response intensification is lost in the averaging process. A larger bandwidth at a given center frequency is found to contain more excited modes than a smaller bandwidth; however, the AMA is slightly more accurate in the smaller bandwidth. All AMA asymptotes were shown to be approached from below by a CMA with fixed bandwidth and increasing center frequency.

Kubota, Y.↗

NASA NTRS2006

A Numerical Study of Hurricane Erin (2001): Shear and the Organization of Eyewall Vertical Motion - Part II

A high-resolution numerical simulation of Hurricane Erin (2001) is used to examine the organization of vertical motion in the eyewall and how that organization responds to a large and rapid increase in the environmental vertical wind shear and subsequent decrease in shear. During the early intensification period, prior to the onset of significant shear, the upward motion in the eyewall was concentrated in small-scale convective updrafts that formed in association with regions of concentrated vorticity (herein termed mesovortices) with no preferred formation region in the eyewall. Asymmetric flow within the eye was weak. As the shear increased, an azimuthal wavenumber 1 asymmetry in storm structure developed with updrafts tending to form on the downshear to downshear-left side of the eyewall. Continued intensification of the shear led to increasing wavenumber 1 asymmetry, large vortex tilt, and a change in eyewall structure and vertical motion organization. During this time, the eyewall structure was dominated by a vortex couplet with a cyclonic (anticyclonic) vortex on the downtilt-left (downtilt-right) side of the eyewall and strong asymmetric flow across the eye that led to strong mixing of eyewall vorticity into the eye. Upward motion was concentrated over an azimuthally broader region on the downtilt side of the eyewall, upstream of the cyclonic vortex, where low-level environmental inflow converged with the asymmetric outflow from the eye. As the shear diminished, the vortex tilt and wavenumber 1 asymmetry decreased, while the organization of updrafts trended back toward that seen during the weak shear period.

Braun, Scott A.↗

NASA NTRS1999

Microchemical and Thermal Systems for In-Situ Resource Utilization

Process Intensification and Process Miniaturization can simultaneously be achieved through the application of microfabricated chemical process systems, based on the rapid heat and mass transport in engineered microchannels. Researchers at NASA's Johnson Space Center (JSC) and the Department of Energy's Pacific Northwest National Laboratory (PNNL) are collaboratively developing micro thermal and chemical systems for NASA's Mission to Mars program. Preliminary results show that many standard chemical process components (e.g., heat exchangers, chemical reactors and chemical separations units) can be reduced in hardware volume without a corresponding reduction in chemical production rates. Low pressure drops and improved thermal integration are also accomplished when appropriate scaling rules are applied and when individual microchemical components are packaged together into integral systems.

Wegeng, Robert S.↗

NASA NTRS1999

Microchemical and Thermal Systems for In-Situ Resource Utilization

Wegeng, Robert S.↗

NASA NTRS2000

Micro Thermal and Chemical Systems for In Situ Resource Utilization on Mars

Robotic sample return missions and postulated human missions to Mars can be greatly aided through the development and utilization of compact chemical processing systems that process atmospheric gases and other indigenous resources to produce hydrocarbon propellants/fuels, oxygen, and other needed chemicals. When used to reduce earth launch mass, substantial cost savings can result. Process Intensification and Process Miniaturization can simultaneously be achieved through the application of microfabricated chemical process systems, based on the rapid heat and mass transport in engineered microchannels. Researchers at NASA's Johnson Space Center (JSC) and the Department of Energy's Pacific Northwest National Laboratory (PNNL) are collaboratively developing micro thermal and chemical systems for NASA's Mission to Mars program. Preliminary results show that many standard chemical process components (e.g., heat exchangers, chemical reactors and chemical separations units) can be reduced in hardware volume without a corresponding reduction in chemical production rates. Low pressure drops are also achievable when appropriate scaling rules are applied. This paper will discuss current progress in the development of engineered microchemical systems for space and terrestrial applications, including fabrication methods, expected operating characteristics, and specific experimental results.

Wegeng, Robert S.↗

NASA NTRS1986

Latent heat and cyclone activity in the South Pacific, 10-18 January 1979

This paper examines the heat budget of the tropical South Pacific for the period of January 10-18, 1979 and compares precipitation estimates obtained from the budget equation with those derived from GOES-IR satellite imagery, using data that were part of the total FGGE package. In addition, the relationship between latent heat release and the baroclinic energy conversion is examined for the life cycles of two cyclones which propagated along the South Pacific Convection Zone in that period. It is shown that latent heat plays an important role in the baroclinic energy conversion between potential and kinetic energy through diabatically-induced vertical circulations. For a cyclone where latent heat stays at a high level both spacially and with regard to intensity, there appears to be ample fuel for its intensification. On the other hand, for a filling cyclone, the latent heat impact decreased and the baroclinic conversion fell off rapidly, due to the lack of both potential energy generation and diabatically-induced thermally-direct circulations.

Miller, B. L.↗

NASA NTRS1989

Substorms, plasmoids, flux robes, and magnetotail flux loss on March 25, 1983 - CDAW-8

During a 9-hour period following a storm-sudden commencement, six spacecraft near geosynchronous orbit, one over the pole, and three in the mgnetotail, monitored a complex sequence of magnetospheric variations. Magnetic field compressions associated with the sudden commencement were seen first by the near-earth spacecraft and subsequently by the three down-tail spacecraft with increasing time delays that were consistent with the tailward movement of an interplanetary-shock-associated pressure enhancement. Ground magnetograms and synchronous orbit data are used to identify 7 substorm intensifications during this geomagnetically active period. Six of these intensifications are clearly associated with tail lobe field decreases about 18 R sub E behind the earth. Four of these intensifications are followed by both Bz field increases in the tail lobes at about 18 and about 30 R sub E and by the subsequent observation of rapidly flowing plasma sheet plasma at ISEE 3 about 110 R sub E down the tail. During two substorms where DE 1 was optically observing the auroral oval, the area of the polar cap was observed to decrease as the tail lobe field decreased at 18 R sub E. All these observations are consistent with the substorm associated release of a plasmoid at a neutral line near 20 R sub E.

Fairfield, D. H.↗

NASA NTRS1975

Starting vortex, separation bubbles and stall - A numerical study of laminar unsteady flow around an airfoil

The stalling characteristics of an airfoil in a laminar viscous incompressible fluid are investigated. The governing equations in terms of the vorticity and stream function are solved using an implicit finite-difference scheme and point successive relaxation procedure. The development of the impulsively started flow, the initial generation of circulation, and the behavior of the forces at large times are studied. Following the impulsive start, the lift is at first very large and then it rapidly drops. The subsequent growth of circulation and lift is associated with the starting vortex. After incipient separation, the lift increases owing to enlargement of the separation bubble and intensification of the flow rotation in it. The extension of this bubble beyond the trailing edge causes it to rupture and brings about the stalling characteristics of the airfoil. Subsequently, new bubbles are formed near the upper surface of the airfoil and are swept away. The behavior of the lift acting on the airfoil is explained in terms of the strength and sense of these bubbles.

Mehta, U. B.↗

NASA NTRS1999

Total Lightning Activity Associated with Tornadic Storms

Prior studies have examined the association of lightning activity with the occurrence of severe weather. Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. Most recently, we have identified a rapid change (referred to as a "jump") in total flash rate which precedes the occurrence of severe weather by ten or more minutes. This relationship is associated with updraft intensification. In this paper we examine whether there exist unique characteristics of the total lightning and the lightning jumps associated with tornadoes in Florida, and explain how they might relate to the interaction of mesocyclonic shear, the rear flank downdraft and outflow boundaries that can lead to tornadogenesis. In several cases, evidence for diminishment of midlevel rotation and the descent of angular momentum from aloft is present prior to the appearance of the surface tornado. The relatively long lead time between the lighting jump and the occurrence of the tornado is attributed to the time lag between updraft invigoration and the boundary layer spin up of vorticity.

Goodman, Steven J.↗

NASA NTRS2017

Drivers of Precipitation Change: An Energetic Understanding

The response of the hydrological cycle to climate forcings can be understood within the atmospheric energy budget framework. In this study precipitation and energy budget responses to five forcing agents are analyzed using 10 climate models from the Precipitation Driver Response Model Intercomparison Project (PDRMIP). Precipitation changes are split into a forcing-dependent fast response and a temperature-driven hydrological sensitivity. Globally, when normalized by top-of-atmosphere (TOA) forcing, fast precipitation changes are most sensitive to strongly absorbing drivers (CO2, black carbon). However, over land fast precipitation changes are most sensitive to weakly absorbing drivers (sulfate, solar) and are linked to rapid circulation changes. Despite this, land-mean fast responses to CO2 and black carbon exhibit more intermodel spread. Globally, the hydrological sensitivity is consistent across forcings, mainly associated with increased longwave cooling, which is highly correlated with intermodel spread. The land-mean hydrological sensitivity is weaker, consistent with limited moisture availability. The PDRMIP results are used to construct a simple model for land-mean and sea-mean precipitation change based on sea surface temperature change and TOA forcing. The model matches well with CMIP5 ensemble mean historical and future projections, and is used to understand the contributions of different drivers. During the twentieth century, temperature-driven intensification of land-mean precipitation has been masked by fast precipitation responses to anthropogenic sulfate and volcanic forcing, consistent with the small observed trend. However, as projected sulfate forcing decreases, and warming continues, land-mean precipitation is expected to increase more rapidly, and may become clearly observable by the mid-twenty-first century.

Richardson, T. B.↗

NASA NTRS1992

Observables for anticipating tornadogenesis in mesocyclones

We seek to identify an observable for anticipating tornadogenesis in mesocyclones, because such tornadoes are characterized by particularly long life, long and wide path, and high wind speed. We associate tornadogenesis with the transition from a one-cell vortex to a two-cell vortex. In such a transition, 'insertion' of a virtually nonrotating, slowly recirculating core displaces that high-swirl-speed air which is rapidly ascending along a moist-adiabatic locus of thermodynamic states, to an annulus at small but finite distance from the axis of rotation. Such a transition, on a vastly larger lateral scale, is known to characterize intensification of a tropical storm to a typhoon. We examine analytically a quasisteady axisymmetric model of a four-part vortex structure consisting of a bulk potential vortex, near-ground inflow layer, 'eyewall', and 'eye'. We inquire whether such a four-part intense vortex, formed in convectively unstably stratified air, is self-sustaining. In particular, we inquire whether the vertical profile of the angular momentum at the periphery is a discriminant for identifying self-sustaining vortices.

Carrier, G.↗

NASA NTRS2011

A Latent Heat Retrieval and its Effects on the Intensity and Structure Change of Hurricane Guillermo (1997). Part I: The Algorithm and Observations.

The release of latent heat in clouds is an essential part of the formation and I intensification o~hurricanes. The community knows very little about the intensity and structure of latent heating due largely to inadequate observations. In this paper, a new method for retrieving the latent heating field in hurricanes from airborne Dopple~ radar is presented and fields from rapidly intensifying Hurricane Guillermo (1997) are shown.

Guimond, Stephen R.↗

NASA NTRS1994

Physical processes affecting availability of dissolved silicate for diatom production in the Arabian Sea

A passive tracer to represent dissolved silicate concentrations, with biologically realistic uptake kinetics, is successfully incorporated into a three-dimensional, eddy-resolving, ocean circulation model of the Indian Ocean. Hypotheses are tested to evaluate physical processes which potentially affect the availability of silicate for diatom production in the Arabian Sea. An alternative mechanism is offered to the idea that open ocean upwelling is primarily responsible for the high, vertical nutrient flux and consequent large-scale phytoplankton bloom in the northwestern Arabian Sea during the southwest monsoon. Model results show that dissolved silicate in surface waters available for uptake by diatoms is primarily influenced by the intensity of nearshore upwelling from soutwest monsoonal wind forcing and by the offshore advective transport of surface waters. The upwelling, which in the model occurs within 200 +/- 50 km of the coast, appears to be a result of a combination of coastal upwelling, Elkman pumping, and divergence of the coastal flow as it turns offshore. Localized intensifications of silicate concentrations appear to be hydrodynamically driven and geographically correlated to coastal topographic features. The absence of diatoms in sediments of the eastern Arabian Basin is consistent with modeled distributional patterns of dissolved silicate resulting from limited westward advection of upwelled coastal waters from the western continental margin of India and rapid uptake of available silicate by diatoms. Concentrations of modeled silicate become sufficiently low to become unavailable for diatom production in the eastern Arabian Sea, a region between 61 deg E and 70 deg E at 8 deg N on the south, with the east and west boundaries converging on the north at approximately 67 deg E, 20 deg N.

Young, David K.↗

NASA NTRS2009

Life of a Six-Hour Hurricane

Hurricane Claudette developed from a weak vortex in 6 h as deep convection shifted from downshear into the vortex center, despite ambient vertical wind shear exceeding 10 m/s. Six hours later it weakened to a tropical storm, and 12 h after the hurricane stage a circulation center could not be found at 850 hPa by aircraft reconnaissance. At hurricane strength the vortex contained classic structure seen in intensifying hurricanes, with the exception of 7-12 C dewpoint depressions in the lower troposphere upshear of the center. These extended from the 100-km radius to immediately adjacent to the eyewall, where equivalent potential temperature gradients reached 6 K/km. The dry air was not present prior to intensification, suggesting that it was associated with vertical shear-induced subsidence upshear of the developing storm. It is argued that weakening of the vortex was driven by cooling associated with the mixing of dry air into the core, and subsequent evaporation and cold downdrafts. Evidence suggests that this mixing might have been enhanced by eyewall instabilities after the period of rapid deepening. The existence of a fragile, small, but genuinely hurricane-strength vortex at the surface for 6 h presents difficult problems for forecasters. Such a "temporary hurricane" in strongly sheared flow might require a different warning protocol than longer-lasting hurricane vortices in weaker shear.

Shelton, Kay L.↗

NASA NTRS1983

Monitoring tropical-cyclone intensity using environmental wind fields derived from short-interval satellite images

The feasibility of predicting changes in tropical storm intensity based on satellite observations of the dynamical relationships between the large-scale upper and lower tropospheric circulations surrounding the cyclone and the characteristics of the storm's inner core is studied. Rapid-scan visible images from the SMS-1 and GOES-1 satellites were used to examine the local change in relative angular momentum (RAM), the lower and upper tropospheric environmental areal mean relative vorticity and transverse circulation on three consecutive days for tropical storms Caroline (August, 1975), Anita (August and September, 1977) and Ella (September, 1978). The three case studies suggest that storm intensification may be predicted from the storm's local change of net RAM, with this quantity best correlated with storm intensification after a time lag of 6 hours. Intensification is also found to be related to the environmental lower and upper tropospheric areal-mean relative vorticity, and to the upper tropospheric environmental circulation, which acts either to hinder or to enhance the storm's anticyclonic outflow channels.

Rodgers, E.↗