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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Emergent Ferroelectric Switching Behavior from Polar Vortex Lattice

We report topologically protected polar textures have provided a rich playground for the exploration of novel, emergent phenomena. Recent discoveries indicate that ferroelectric vortices and skyrmions not only host properties markedly different from traditional ferroelectrics, but also that these properties can be harnessed for unique memory devices. Using a combination of capacitor-based capacitance measurements and computational models, it is demonstrated that polar vortices in dielectric–ferroelectric–dielectric trilayers exhibit classical ferroelectric bi-stability together with the existence of low-field metastable polarization states. This behavior is directly tied to the in-plane vortex ordering, and it is shown that it can be used as a new method of non-destructive readout-out of the poled state.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Interlayer Coupling Controlled Ordering and Phases in Polar Vortex Superlattices

The recent discovery of polar topological structures has opened the door for exciting physics and emergent properties. There is, however, little methodology to engineer stability and ordering in these systems, properties of interest for engineering emergent functionalities. Notably, when the surface area is extended to arbitrary thicknesses, the topological polar texture becomes unstable. Here we show that this instability of the phase is due to electrical coupling between successive layers. We demonstrate that this electrical coupling is indicative of an effective screening length in the dielectric, similar to the conductor–ferroelectric interface. Controlling the electrostatics of the superlattice interfaces, the system can be tuned between a pure topological vortex state and a mixed classical-topological phase. This coupling also enables engineering coherency among the vortices, not only tuning the bulk phase diagram but also enabling the emergence of a 3D lattice of polar textures.

3D ordering↗
NASA NTRS1994

Evolution of MLS Ozone and the Polar Vortex During Winter

The evolution of polar ozone observed by the Upper Atmosphere Research Satellite Microwave Limb Sounder is described for the northern hemisphere (NH) winters of 1991/1992, 1992/1993, and 1993/1994, and the southern hemisphere (SH) winters of 1992 and 1993. Ozone in the mid-stratospheric vortex increases over the winter, with largest increases associated with stratospheric warmings, and a much larger increase in the NH than in the SH.

ozone↗
DOE OSTI2022

Towards computational polar-topotronics: Multiscale neural-network quantum molecular dynamics simulations of polar vortex states in SrTiO3/PbTiO3 nanowires

Recent discoveries of polar topological structures ( e.g ., skyrmions and merons) in ferroelectric/paraelectric heterostructures have opened a new field of polar topotronics. However, how complex interplay of photoexcitation, electric field and mechanical strain controls these topological structures remains elusive. To address this challenge, we have developed a computational approach at the nexus of machine learning and first-principles simulations. Our multiscale neural-network quantum molecular dynamics molecular mechanics approach achieves orders-of-magnitude faster computation, while maintaining quantum-mechanical accuracy for atoms within the region of interest. This approach has enabled us to investigate the dynamics of vortex states formed in PbTiO 3 nanowires embedded in SrTiO 3 . We find topological switching of these vortex states to topologically trivial, uniformly polarized states using electric field and trivial domain-wall states using shear strain. These results, along with our earlier results on optical control of polar topology, suggest an exciting new avenue toward opto-electro-mechanical control of ultrafast, ultralow-power polar topotronic devices.

Linker, Thomas↗
NASA NTRS1993

MLS CLO observations and arctic polar vortex temperatures

Analysis of Upper Altmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) observations in early January 1992 shows a clear relationship between predicted polar stratospheric cloud formation along the back trajectory and elevated ClO amounts. These findings are in good agreement with aircraft observations. The MLS observed variation of ClO amounts within the vortex also fits the pattern of ClO change as a result of air parcel solar exposure and nitric acid photolysis. Outside the polar vortex, the occasional highly elevated ClO appear statistically consistent with MLS measurement noise.

Schoeberl, M. R.↗
NASA NTRS1995

Interannual Variability of the North Polar Vortex in the Lower Stratosphere During the UARS Mission

Three of the four northern winters since the launch of the Upper Atmosphere Research Satellite (UARS) had daily NMC minimum temperatures in the lower stratosphere that approached or fell below the lowest values experienced during the previous 13 years. These low temperatures were more conducive to formation of polar stratospheric clouds and thus to associated chlorine activation and associated chemical loss of ozone in the lower stratosphere.

North↗
NASA NTRS2001

Troposphere-Stratosphere Dynamic Coupling Under Strong and Weak Polar Vortex Conditions

The relationship between Northern Hemisphere (NH) tropospheric and stratospheric wave-like anomalies of spherical zonal wave number (ZWN) 1 is studied by applying Canonical Correlation Analysis (CCA). A lag-correlation technique is used with 10-day lowpass filtered daily time series of 50- and 500-hPa geopotential heights. Generally stratospheric circulation is determined by ultralong tropospheric planetary waves. During winter seasons characterized either by any anomalously strong or weak polar winter vortex different propagation characteristics for waves of ZWN 1 are observed. The non-linear perspective of the results have implications for medium range weather forecast and climate sensitivity experiments.

Perlwitz, Judith↗
NASA NTRS1996

Polar Vortex Conditions During The 1995-96 Arctic Winter: MLS ClO and HNO3

Microwave Limb Sounder (MLS) measurements of lower stratospheric ClO and HNO3 during the 1995-96 Arctic winter are presented. The 1995-96 Arctic winter was both colder and more persistently cold than usual, leading to an enhancement in lower stratospheric ClO of greater magnitude, vertical extent, and duration than previously observed in the Arctic. Vortex concentrations of HNO3 in mid-December were large due to diabatic descent. Trajectory calculations indicate that localized severe depletions of gas-phase HNO3 in mid-February and early March did not arise from entrainment of midlatitude air into the vortex and were therefore probably related to polar stratospheric cloud (PSC) formation. A strong correlation between temperature and gas-phase HNO3 was evident, consistent with recurring PSC condensation and evaporation cycles.

Santee, M. L.↗
NASA NTRS1996

Polar Vortex Conditions During the 1995-96 Arctic Winter: MLS CL0 and HNO(sub 3)

Microwave Limb Sounder (MLS) measurements of lower stratospheric CLO and HNO(sub 3) during the 1995-96 Arctic winter are presented. The 1995-96 Arctic winter was both colder and more persistently cold than usual, leading to an enhancement in lower stratospheric CLO of greater magnitude, vertical extent, and duration than has been previously observed in the Arctic. Vortex concentrations of HNO(sub 3) in mid-December were large due to diabetic decent. Trajectory calculations indicate that localized severe depletions of gas-phase HNO(sub 3) in mid-February and early March did not arise from intrainment of midlatitude air into the vortex and were therefore probably related to polar stratospheric cloud (PSC) formation.

Microwave Limb Sounder MLS CLO HNO3↗
DOE OSTI2023

Multiscale electric-field imaging of polarization vortex structures in PbTiO 3 /SrTiO 3 superlattices

In ferroelectric heterostructures, the interaction between intrinsic polarization and the electric field generates a rich set of localized electrical properties. The local electric field is determined by several connected factors, including the charge distribution of individual unit cells, the interfacial electromechanical boundary conditions, and chemical composition of the interfaces. However, especially in ferroelectric perovskites, a complete description of the local electric field across micro-, nano-, and atomic-length scales is missing. Here, by applying four-dimensional scanning transmission electron microscopy (4D STEM) with multiple probe sizes matching the size of structural features, we directly image the electric field of polarization vortices in (PbTiO 3 ) 16 /(SrTiO 3 ) 16 superlattices and reveal different electric field configurations corresponding to the atomic scale electronic ordering and the nanoscale boundary conditions. The separability of two different fields probed by 4D STEM offers the possibility to reveal how each contributes to the electronic properties of the film.

36 MATERIALS SCIENCE↗
NASA NTRS1979

The Martian polar vortex - Theory of seasonal variation and observations of eolian features

Observations of eolian features in the south polar region of Mars show strikingly axisymmetric patterns. The paper presents an explanation for the patterns in terms of the simplest dynamical model possible. Piraglia's (1975) model is simplified by neglecting compressibility and by assuming a cylindrical rather than spherical geometry, but this model is extended by including the nonlinear transport terms (of order Rossby number) and the seasonal mass transfer terms. The proposed model is therefore focused on determining the surface stress in polar regions rather than the atmospheric structure. The model is described, the parameter values are discussed, and the solutions are compared with observations. It is shown that the model predicts seasonal behavior which can be divided into four periods: formation of the south polar cap, its maximum extent, sublimation, and absence.

French, R. G.↗
NASA NTRS2000

Development of the polar vortex in the 1999-2000 Arctic winter stratosphere

The 1999-2000 Arctic stratospheric vortex was unusually cold, especially in the early winter lower stratosphere, with a larger area near polar stratospheric cloud formation temperatures in Dec and Jan, and much lower temperatures averaged over Nov-Jan, than any previously observed Arctic winter.

Ozone loss meteorology arctic stratospheric↗
NASA NTRS2013

Connections Between the Spring Breakup of the Southern Hemisphere Polar Vortex, Stationary Waves, and Air-sea Roughness

A robust connection between the drag on surface-layer winds and the stratospheric circulation is demonstrated in NASA's Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Specifically, an updated parameterization of roughness at the air-sea interface, in which surface roughness is increased for moderate wind speeds (4ms to 20ms), leads to a decrease in model biases in Southern Hemispheric ozone, polar cap temperature, stationary wave heat flux, and springtime vortex breakup. A dynamical mechanism is proposed whereby increased surface roughness leads to improved stationary waves. Increased surface roughness leads to anomalous eddy momentum flux convergence primarily in the Indian Ocean sector (where eddies are strongest climatologically) in September and October. The localization of the eddy momentum flux convergence anomaly in the Indian Ocean sector leads to a zonally asymmetric reduction in zonal wind and, by geostrophy, to a wavenumber-1 stationary wave pattern. This tropospheric stationary wave pattern leads to enhanced upwards wave activity entering the stratosphere. The net effect is an improved Southern Hemisphere vortex: the vortex breaks up earlier in spring (i.e., the spring late-breakup bias is partially ameliorated) yet is no weaker in mid-winter. More than half of the stratospheric biases appear to be related to the surface wind speed biases. As many other chemistry climate models use a similar scheme for their surface layer momentum exchange and have similar biases in the stratosphere, we expect that results from GEOSCCM may be relevant for other climate models.

air-sea interaction↗
NASA NTRS2000

The Interaction Between Dynamics and Chemistry of Ozone in the Set-Up Phase of the Northern Hemisphere Polar Vortex

Understanding stratospheric ozone loss to the point of accurately predicting ozone in the future requires correctly distinguishing chemical from transport-induced changes in ozone. For example, evaluating the impact of chlorine reduction in controlling stratospheric ozone loss requires estimating the amount of ozone lost in chemical reactions in the polar winter and spring. The Northern Hemisphere winter polar region is a particularly crucial and interesting area because it appears that the Northern vortex may currently be poised near the threshold of extreme ozone destruction such as that which now occurs annually in the Antarctic ozone "hole." In this presentation we explore the interaction of ozone transport and chemistry through the Northern late summer and fall seasons as the vortex circulation becomes established. This phase of the seasonal cycle determines the starting point for heterogeneous processes and chlorine-driven loss that take control in the winter vortex. Using a combination of profile data from POAM, HALOE, and in situ measurements, we show that relatively low ozone at high latitudes in the middle stratosphere is associated with vortex airmasses and that these ozone abundances evolve photochemically from characteristically higher values at the end of the summer. The zonal variance of ozone mixing ratio also increases greatly at this time consistent with increasing wave-driven transport. Comparison with a three-dimensional chemistry-transport model is used to generalize the findings from the limited set of observations and quantify the relative roles of transport and chemistry in determining the ozone mixing ratio distributions.

Kawa, S.R.↗