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All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Shallow and Deep Latent Heating Modes Over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

The global hydrological cycle is central to the Earth's climate system, with rainfall and the physics of its formation acting as the key links in the cycle. Two-thirds of global rainfall occurs in the Tropics. Associated with this rainfall is a vast amount of heat, which is known as latent heat. It arises mainly due to the phase change of water vapor condensing into liquid droplets; three-fourths of the total heat energy available to the Earth's atmosphere comes from tropical rainfall. In addition, fresh water provided by tropical rainfall and its variability exerts a large impact upon the structure and motions of the upper ocean layer. Three-dimensional distributions of latent heating estimated from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR)utilizing the Spectral Latent Heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated latent heating averaged over the tropical oceans is estimated as approx.72.6 J/s (approx.2.51 mm/day), and that over tropical land is approx.73.7 J/s (approx.2.55 mm/day), for 30degN-30degS. It is shown that non-drizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems, deep systems and congestus. A rough estimate of shallow mode contribution against the total heating is about 46.7 % for the average tropical oceans, which is substantially larger than 23.7 % over tropical land. While cumulus congestus heating linearly correlates with the SST, deep mode is dynamically bounded by large-scale subsidence. It is notable that substantial amount of rain, as large as 2.38 mm day-1 in average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that even in the region with SST warmer than 28 oC, large-scale subsidence effectively suppresses the deep convection, remaining the heating by congestus clouds. Our results support that the entrainment of mid-to-lower-tropospheric dry air, which accompanies the large-scale subsidence is the major factor suppressing the deep convection. Therefore, representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and resultant large-scale circulation.

Takayabu, Yukari N.↗
NASA NTRS2010

Explosive Volcanic Eruptions from Linear Vents on Earth, Venus and Mars: Comparisons with Circular Vent Eruptions

Conditions required to support buoyant convective plumes are investigated for explosive volcanic eruptions from circular and linear vents on Earth, Venus, and Mars. Vent geometry (linear versus circular) plays a significant role in the ability of an explosive eruption to sustain a buoyant plume. On Earth, linear and circular vent eruptions are both capable of driving buoyant plumes to equivalent maximum rise heights, however, linear vent plumes are more sensitive to vent size. For analogous mass eruption rates, linear vent plumes surpass circular vent plumes in entrainment efficiency approximately when L(sub o) > 3r(sub o) owing to the larger entrainment area relative to the control volume. Relative to circular vents, linear vents on Venus favor column collapse and the formation of pyroclastic flows because the range of conditions required to establish and sustain buoyancy is narrow. When buoyancy can be sustained, however, maximum plume heights exceed those from circular vents. For current atmospheric conditions on Mars, linear vent eruptions are capable of injecting volcanic material slightly higher than analogous circular vent eruptions. However, both geometries are more likely to produce pyroclastic fountains, as opposed to convective plumes, owing to the low density atmosphere. Due to the atmospheric density profile and water content on Earth, explosive eruptions enjoy favorable conditions for producing sustained buoyant columns, while pyroclastic flows would be relatively more prevalent on Venus and Mars. These results have implications for the injection and dispersal of particulates into the planetary atmosphere and the ability to interpret the geologic record of planetary volcanism.

Glaze, Lori S.↗
NASA NTRS2005

Gas-Tolerant Device Senses Electrical Conductivity of Liquid

The figure depicts a device for measuring the electrical conductivity of a flowing liquid. Unlike prior such devices, this one does not trap gas bubbles entrained in the liquid. Usually, the electrical conductivity of a liquid is measured by use of two electrodes immersed in the liquid. A typical prior device based on this concept contains large cavities that can trap gas. Any gas present between or near the electrodes causes a significant offset in the conductivity reading and, if the gas becomes trapped, then the offset persists. Extensive tests on two-phase (liquid/ gas) flow have shown that in the case of liquid flowing along a section of tubing, gas entrained in the liquid is not trapped in the section as long as the inner wall of the section is smooth and continuous, and the section is the narrowest tubing section along the flow path. The design of the device is based on the foregoing observation: The electrodes and the insulators separating the electrodes constitute adjacent parts of the walls of a tube. The bore of the tube is machined to make the wall smooth and to provide a straight flow path from the inlet to the outlet. The diameter of the electrode/insulator tube assembly is less than the diameter of the inlet or outlet tubing. An outer shell contains the electrodes and insulators and constitutes a leak and pressure barrier. Any gas bubble flowing through this device causes only a momentary conductivity offset that is filtered out by software used to process the conductivity readings.

O'Connor, Edward W.↗
NASA NTRS2011

Space Systems - Safety and Compatibility of Materials - Method to Determine the Ignition Susceptibility of Materials or Components to Particle Impact

The scope of this International Technical Specification is to provide a method to determine the ignition susceptibility of materials and components to particle impact. The method can be used to determine the conditions at which ignition and consumption of a specimen material occurs when impacted by single or multiple particles entrained in a flow of gaseous oxygen (GOX). Alternatively, the method can be used to determine if a specific material or component is subject to ignition and sustained combustion in a given flow environment when impacted by single or multiple particles entrained in a flow of GOX.

Hirsch, David B.↗
NASA NTRS2003

Noncircular Cross Sections Could Enhance Mixing in Sprays

A computational study has shown that by injecting drops in jets of gas having square, elliptical, triangular, or other noncircular injection cross sections, it should be possible to increase (relative to comparable situations having circular cross section) the entrainment and dispersion of liquid drops. This finding has practical significance for a variety of applications in which it is desirable to increase dispersion of drops. For example, in chemical-process sprays, increased dispersion leads to increases in chemical- reaction rates; in diesel engines, increasing the dispersion of drops of sprayed fuel reduces the production of soot; and in household and paint sprays, increasing the dispersion of drops makes it possible to cover larger surfaces. It has been known for some years that single-phase fluid jets that enter flow fields through noncircular inlets entrain more fluid than do comparable jets entering through circular inlets. The computational study reported here was directed in part toward determining whether and how this superior mixing characteristic of noncircular single phase jets translates to a similar benefit in cases of two-phase jets (that is, sprays). The study involved direct numerical simulations of single- and two-phase free jets with circular, elliptical, rectangular, square, and triangular inlet cross sections. The two-phase jets consisted of gas laden with liquid drops randomly injected at the inlets. To address the more interesting case of evaporating drops, the carrier gas in the jets was specified to be initially unvitiated by the vapor of the liquid chemical species and the initial temperature of the drops was chosen to be smaller than that of the gas. The mathematical model used in the study was constructed from the conservation equations for the two-phase flow and included complete couplings of mass, momentum, and energy based on thermodynamically self-consistent specification of the enthalpy, internal energy, and latent heat of vaporization of the vapor.

Bellan, Josette↗
NASA NTRS2012

Numerical Simulation of Noise from Supersonic Jets Passing Through a Rigid Duct

The generation, propagation and radiation of sound from a perfectly expanded Mach 2.5 cold supersonic jet flowing through an enclosed rigid-walled duct with an upstream J-deflector have been numerically simulated with the aid of OVERFLOW Navier-Stokes CFD code. A one-equation turbulence model is considered. While the near-field sound sources are computed by the CFD code, the far-field sound is evaluated by Kirchhoff surface integral formulation. Predictions of the farfield directivity of the OASPL (Overall Sound Pressure Level) agree satisfactorily with the experimental data previously reported by the author. Calculations also suggest that there is significant entrainment of air into the duct, with the mass flow rate of entrained air being about three times the jet exit mass flow rate.

Kandula, Max↗
NASA NTRS2014

Sensitivity of Tropical Cyclones to Parameterized Convection in the NASA GEOS5 Model

The sensitivity of tropical cyclones (TCs) to changes in parameterized convection is investigated to improve the simulation of TCs in the North Atlantic. Specifically, the impact of reducing the influence of the Relaxed Arakawa-Schubert (RAS) scheme-based parameterized convection is explored using the Goddard Earth Observing System version5 (GEOS5) model at 0.25 horizontal resolution. The years 2005 and 2006 characterized by very active and inactive hurricane seasons, respectively, are selected for simulation. A reduction in parameterized deep convection results in an increase in TC activity (e.g., TC number and longer life cycle) to more realistic levels compared to the baseline control configuration. The vertical and horizontal structure of the strongest simulated hurricane shows the maximum lower-level (850-950hPa) wind speed greater than 60 ms and the minimum sea level pressure reaching 940mb, corresponding to a category 4 hurricane - a category never achieved by the control configuration. The radius of the maximum wind of 50km, the location of the warm core exceeding 10 C, and the horizontal compactness of the hurricane center are all quite realistic without any negatively affecting the atmospheric mean state. This study reveals that an increase in the threshold of minimum entrainment suppresses parameterized deep convection by entraining more dry air into the typical plume. This leads to cooling and drying at the mid- to upper-troposphere, along with the positive latent heat flux and moistening in the lower-troposphere. The resulting increase in conditional instability provides an environment that is more conducive to TC vortex development and upward moisture flux convergence by dynamically resolved moist convection, thereby increasing TC activity.

GEOS5↗
NASA NTRS2016

On the Importance of High Frequency Gravity Waves for Ice Nucleation in the Tropical Tropopause Layer

Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.

simulation↗
NASA NTRS2016

Formation of Oxides in the Interior of Friction Stir Welds

In friction stir welding (FSWing) the actual solid state joining takes place between the faying surfaces which form the weld seam. Thus the seam trace is often investigated for clues when the strength of the weld is reduced. Aluminum and its alloys are known to form a native, protective oxide on the surface. If these native surface oxides are not sufficiently broken up during the FSW process, they are reported to remain in the FSW interior and weaken the bond strength. This type of weld defect has been referred to as a lazy "S", lazy "Z", joint line defect, kissing bond, or residual oxide defect. Usually these defects are mitigated by modification of the process parameters, such as increased tool rotation rate, which causes a finer breakup of the native oxide particles. This study proposes that there may be an alternative mechanism for formation of oxides found within the weld nugget. As the oxidation rate increases at elevated temperatures above 400ºC, it may be possible for enhanced oxidation to occur on the interior surfaces during the FSW process from entrained air entering the seam gap. Normally, FSWs of aluminum alloys are made without a purge gas and it is unknown how process parameters and initial fit up could affect a potential air path into the interior during the processing. In addition, variations in FSW parameters, such as the tool rotation, are known to have a strong influence on the FSW temperature which may affect the oxidation rate if internal surfaces are exposed to entrained air. A series of FSWs were made in 3 different thickness panels of AA2219 (0.95, 1.27 and 1.56 cm) at 2 different weld pitches. As the thickness of the panels increased, there was an increased tendency for a gap to form in advance of the weld tool. If sufficient air is able to enter the workpiece gap prior to consolidation, the weld temperature can increase the oxidation rate on the interior surfaces. These oxidation rates would also be accelerated in areas of localized liquation. Metallographs from the weld panels showed indications of liquation at the grain boundaries. In FSWs of thicker panels, these regions of liquation were found to be heavily oxidized. The quality of the FSWs was evaluated from tensile testing at room temperature. As the panel thickness increased, a slight decrease in tensile strength was observed which was attributed to the presence of oxides. No oxide formation was observed in the thinner workpieces, although there were indications of localized liquation at the grain boundaries. Results from this study will assist in a better understand of the mechanisms of oxide formation in FSW interiors and provide methodology for minimizing their occurrence.

Schneider, Judy↗
NASA NTRS2016

Documentation of the Recirculation in a Closed-Chamber Rotor Hover Test

A rotor hover test was performed inside the JPL 25-foot-diameter Space Simulator. The 40-inch-diameter rotor was tested at two locations in the chamber-on the chamber centerline and 2m off-axis. The rotor was tested in both upright and inverted configurations for 500 < RPM < 2000. Fluorescent tufts were used to identify regions of recirculation. Velocities on the entrainment side of the rotor were measured. Tabulated values for the mean entrainment velocity components and the corresponding root mean square velocity fluctuations are provided. Unsteady velocity measurements provide a description of the turbulence ingested into the rotor plane and quantify the unsteady velocity field that the Mars Scout Helicopter can expect to encounter during free flight inside the Space Simulator.

Rotor Hover Test↗
NASA NTRS2017

Pluto: Fluidized Transport of Tholins by Heating of the Subsurface

New Horizons images of Pluto show evidence of the transport of the colored non-ice component across the surface, with substantial accumulations in some areas of low elevation. The non-ice component is presumed to be tholin produced in the atmosphere as a precipitating aerosol, in the surface ices by photolysis or radiolysis, or both. We model the surface layer of N2 ice with varying amounts of incorporated tholin particles to explore the heating within the ice that occurs by the solid-state greenhouse effect. We find that in plausible models of the contaminated N2 surface ice the triple point temperature (63.15K) is reached at a depth of approximately less than 1m. At that depth the confining pressure of the ice column is much less than the triple point pressure (12.52 kPa), so N2 should convert to the gas phase, exerting pressure on the overburden. When the gas pressure exceeds the strength of the confining ice, a breakout on the surface will occur, fluidizing fragments of ice and its contaminants that are then free to flow downhill, rafted on entrained gas, similar in some ways to the pyroclastic volcanic phenomenon known as nuée ardente. The digital elevation map of Pluto made from stereo images shows some surface regions that may have been stripped of the N2 layer, exposing H2O ice (presumed to be bedrock) below, with a corresponding accumulation of dark material that was that was the previously entrained particulate tholin. Accumulations of tholin are found associated with some of the fossae, and some cover preexisting topography to depths of up to a few hundred meters.

New Horizons↗
NASA NTRS2014

Seasonal Evolution of Saturn's Polar Temperatures and Composition

The seasonal evolution of Saturn's polar atmospheric temperatures and hydrocarbon composition is derived from a decade of Cassini Composite Infrared Spectrometer (CIRS) 7-16 micrometers thermal infrared spectroscopy. We construct a near-continuous record of atmospheric variability poleward of 60 deg from northern winter/southern summer (2004, Ls = 293 deg) through the equinox (2009, Ls= 0 deg) to northern spring/southern autumn (2014, Ls = 56 deg). The hot tropospheric polar cyclones that are entrained by pro-grade jets within 2-3 deg of each pole, and the hexagonal shape of the north polar belt, are both persistent features throughout the decade of observations. The hexagon vertices rotated westward by approx. equal to 30 deg longitude between March 2007 and April 2013, confirming that they are not stationary in the Voyager-defined System III longitude system as previously thought. Tropospheric temperature contrasts between the cool polar zones (near 80-85 deg) and warm polar belts (near 75-80 deg) have varied in both hemispheres, resulting in changes to the vertical wind shear on the zonal jets in the upper troposphere and lower stratosphere. The extended region of south polar stratospheric emission has cooled dramatically poleward of the sharp temperature gradient near 75 deg S (by approximately -5 K/yr), coinciding with a depletion in the abundances of acetylene (0030 +/- 0.005 ppm/yr) and ethane (0.35 +/- 0.1 ppm/yr), and suggestive of stratospheric upwelling with vertical wind speeds of w approx. equal to +0.1 mm/s. The upwelling appears most intense within 5 deg latitude of the south pole. This is mirrored by a general warming of the northern polar stratosphere (+5 K/yr) and an enhancement in acetylene (0.030 +/- 0.003 ppm/yr) and ethane (0.45 +/- 0.1 ppm/yr) abundances that appears to be most intense poleward of 75 deg N, suggesting subsidence at w approx. equal to -0.15 mm/ s. However, the sharp gradient in stratospheric emission expected to form near 75 deg N by northern summer solstice (2017, Ls = 90 deg) has not yet been observed, so we continue to await the development of a northern summer stratospheric vortex. The peak stratospheric warming in the north occurs at lower pressure levels (p less than 1 mbar) than the peak stratospheric cooling in the south (p greater than 1 mbar). Vertical motions are derived from both the temperature field (using the measured rates of temperature change and the deviations from the expectations of radiative equilibrium models) and hydrocarbon distributions (solving the continuity equation). Vertical velocities tend towards zero in the upper troposphere where seasonal temperature contrasts are smaller, except within the tropospheric polar cyclones where w approx. equal to +0.02 mm/s. North polar minima in tropospheric and stratospheric temperatures were detected in 2008-2010 (lagging one season, or 6-8 years, behind winter solstice); south polar maxima appear to have occurred before the start of the Cassini observations (1-2 years after summer solstice), consistent with the expectations of radiative climate models. The influence of dynamics implies that the coldest winter temperatures occur in the 75-80 deg region in the stratosphere, and in the cool polar zones in the troposphere, rather than at the poles themselves. In addition to vertical motions, we propose that the UV-absorbent polar stratospheric aerosols entrained within Saturn's vortices contribute significantly to the radiative budget at the poles, adding to the localized enhancement in the south polar cooling and north polar warming poleward of +/-75 deg.

polar temperatures↗
NASA NTRS2019

The Interaction Between Boundary Layer and Convection Schemes in a WRF Simulation of Post‐Cold‐Frontal Clouds over the ARM East North Atlantic Site

The correct representation of lowlevel midlatitude clouds found in the wake of cold fronts strongly relies on the representation of planetary boundary layer (PBL) and convection processes, which are typically parameterized separately in numerical models. Using the Weather Research and Forecasting Model (WRF), this study investigates how distinct pairs of PBL and convection parameterization schemes represent cloud fraction in the postcoldfrontal region. The simulations focus on the region of the DOEARM Eastern North Atlantic observation site in the Azores Islands in the wake of a cold front that passed on December 25, 2015. Different PBL and convection schemes are combined to create 12 distinct configurations. The main differences between the selected physical parameterizations are the strength of vertical mixing and the entrainment. The simulations produce a wide range of cloud fractions, where some configurations significantly underestimate while others clearly overestimate satellite and surfacebased estimates of cloud fraction. A skill score is used to quantitatively assess the performance of each configuration with respect to groundbased radar data. The key processes that are found to significantly impact the cloud fraction distribution are the strength of the PBL decoupling, the vertical wind shear, entrainment and detrainment rates in shallow convection and the occurrence of drizzle. This indicates that to successfully simulate postcoldfrontal clouds, modeled physics must balance strong internal vertical mixing and weak exchange with the free troposphere. For this case study, cloud fraction was more sensitive to the choice of convection scheme than PBL scheme.

moist convection interaction between parameterizat↗
NASA NTRS2019

Experimental Investigation of a One-Sided Ejector Nozzle

A fundamental exploratory experiment is conducted assessing the performance of a one-sided ejector with the eventual goal of noise reduction for jet engines. The hardware is comprised of an 8:1 rectangular nozzle together with an ejector box whose lower surface is flush with the lower lip of the nozzle. Secondary flow is allowed through a gap between the upper lip of the nozzle and a flap that constitutes the upper surface of the ejector. Wall static pressures and Pitot probe surveys are conducted to evaluate the performance of the ejector with variation of geometric parameters. It is found that addition of vortex generating tabs at the upper lip of the nozzle significantly increases secondary flow entrainment. The entrainment is further enhanced by a divergence of the ejector up-per surface. Limited noise measurements are done. The baseline ejector (without tabs) often encounters flow resonance with accompanying tones. The tabs have the additional benefit of eliminating those tones in all cases. However, for the tabbed case, addition of the ejector produces insignificant further noise reduction. This is due to the fact that the flow remains unmixed on the lower half of the ejector. The focus of ongoing and future efforts is to achieve sufficient mixing of the flow so that the exhaust velocities are uniformly low, while keeping the ejector hardware short and light-weight.

Zaman, K. B. M. Q.↗
NASA NTRS2019

Experimental Investigation of a One-Sided Ejector Nozzle

A fundamental exploratory experiment is conducted assessing the performance of a one-sided ejector with the eventual goal of noise reduction for jet engines. The hardware is comprised of an 8:1 rectangular nozzle together with an ejector box whose lower surface is flush with the lower lip of the nozzle. Secondary flow is allowed through a gap between the upper lip of the nozzle and a flap that constitutes the upper surface of the ejector. Wall static pressures and Pitot probe surveys are conducted to evaluate the performance of the ejector with variation of geometric parameters. It is found that addition of vortex generating tabs at the upper lip of the nozzle significantly increases secondary flow entrainment. The entrainment is further enhanced by a divergence of the ejector upper surface. Limited noise measurements are done. The baseline ejector (without tabs) often encounters flow resonance with accompanying tones. The tabs have the additional benefit of eliminating those tones in all cases. However, for the tabbed case, addition of the ejector produces insignificant further noise reduction. This is due to the fact that the flow remains unmixed on the lower half of the ejector. The focus of ongoing and future efforts is to achieve sufficient mixing of the flow so that the exhaust velocities are uniformly low, while keeping the ejector hardware short and lightweight.

Ejectors↗
NASA NTRS2019

The Role of Oceanic Processes in the Initiation of Boreal Winter Intraseasonal Oscillations over the Indian Ocean

Observational analyses and a hierarchy of ocean general circulation model (OGCM) experiments were performed to understand the influence of oceanic processes on the warm sea surface temperature anomalies (SSTAs) prior to the convection initiation of boreal winter intraseasonal oscillations (ISOs), including the Madden-Julian Oscillation (MJO), in the equatorial Indian Ocean. We found 39 strong ISOs that passed over the Indian Ocean Warm Pool region during the November-April season of the 2001-2012 period. 17/39 ISO events initiated in the Seychelles-Chagos Thermocline Ridge (SCTR) before propagating eastward; the remaining events initiated in the southern Arabian Sea (6) or Warm Pool (16) regions. The SCTR event set was notable in that it contained more global-scale MJOs (71-76%), as defined by the RMM and OMI indices, than the WP events (25-44%). Additionally, ~24% (44%) of the SCTR (Warm Pool) events were preceded by strong oceanic process-induced SSTAs of similar magnitude to those of shortwave radiative and turbulent heat fluxes. The Arabian Sea events, however, were not associated with statistically significant SSTA signals prior to convection. Based on a mixed layer heat budget analysis, entrainment and upwelling reduction were the dominant oceanic processes contributing to the warming, in contrast with boreal summer, when horizontal advection dominated. We examined several case studies, including primary MJO events, where oceanic Rossby waves were associated with the entrainment and upwelling reduction. Two simple atmospheric boundary layer convergence models revealed that the SSTAs contributed at least half of the total convergence and suggested that the ocean dynamical effect was responsible for the majority of SSTA-forced convergence for those case studies. These results underscore the need for climate prediction models to accurately represent the ocean structure and processes to include the effects of oceanic predictors.

West, B. Jason↗
NASA NTRS2019

Emissions Relationships in Western Forest Fire Plumes: I. Reducing the Effect of Mixing Errors on Emission Factors

Studies of emission factors from biomass burning using aircraft data complement the results of lab studies and extend them to conditions of immense hot conflagrations. We illustrate and discuss emission relationships for 422 individual samples from many forest-fire plumes in the Western US. The samples are from two NASA investigations: ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys). This work provides sample-by-sample enhancement ratios (EnRs) for 23 gases and particulate properties. Many EnRs provide candidates for emission ratios (ERs, corresponding to the EnR at the source) when the origin and degree of transformation is understood and appropriate. From these, emission factors (EFs) can be estimated when the fuel dry mass consumed is known or can be estimated using the carbon mass budget approach. This analysis requires understanding the interplay of mixing of the plume with surrounding air. Some initial examples emphasize that measured C(tot) = CO2 + CO in a fire plume does not necessarily describe the emissions of the total carbon liberated in the flames, C(burn). Rather, it represents C(tot) = C(burn) + C(bkgd), which includes possibly varying background concentrations for entrained air. Consequently, we present a simple theoretical description for plume entrainment for multiple tracers from flame to hundreds of kilometers downwind and illustrate some intrinsic linear behaviors. The analysis suggests a Mixed Effects Regression Emission Technique (MERET), which can eliminate occasional strong biases associated with the commonly used normalized excess mixing ratio (NEMR) method. MERET splits C(tot) to reveal C(burn) by exploiting the fact that C(burn) and all tracers respond linearly to dilution, while each tracer has consistent EnR behavior (slope of tracer concentration with respect to C(burn)). The two effects are separable. Two or three or preferably more emission indicators are required as a minimum; here we used ten. Limited variations in the EnRs for each tracer can be incorporated and the variations and co-variations analyzed. The percentage CO yield (or the modified combustion efficiency) plays some role. Other co-relationships involving nitrogen and organic classes are more prominent; these have strong relationships to the C(burn) to O3 emission relationship. In summary, MERET allows fine spatial resolution (EnRs for individual observations) and comparison of similar plumes distant in time and space. Alkene ratios provide us with an approximate photochemical timescale. This allows discrimination and definition, by fire situation, of ERs, allowing us to estimate emission factors.

Chatfield, Robert B.↗
NASA NTRS2021

Evolution of Tropical Cyclone Properties Across the Development Cycle of the GISS-E3 Global Climate Model

The next-generation global climate model from the NASA Goddard Institute for Space Studies, GISS-E3, contains many improvements to resolution and physics that allow for improved representation of tropical cyclones (TCs) in the model. This study examines the properties of TCs in two different versions of E3 at different points in its development cycle, run for 20 years at 0.5 degree resolution, and compares these TCs with observations, the previous generation GISS model, E2, and other climate models. E3 shares many TC biases common to global climate models, such as having too few tropical cyclones, but is much improved from E2. E3 produces strong enough TCs that observation-based wind speed thresholds can now be used to detect and track them, and some storms now reach hurricane intensity; neither of these was true of E2. Model development between the first and second versions of E3 further increased the number and intensity of TCs and reduced TC count biases globally and in most regions. One-year sensitivity tests to changes in various microphysical and dynamical tuning parameters are also examined. Increasing the entrainment rate for the more strongly-entraining plume in the convection scheme increases the number of TCs (though also affecting other climate variables, and in some cases increasing biases). Variations in divergence damping did not have a strong effect on simulated TC properties, contrary to expectations based on previous studies. Overall, the improvements in E3 make it more credible for studies of TC activity and its relationship to climate.

Tropical Cyclones↗