Large Temperature Perturbations Research Articles

Thermal effects of nonlinear acoustic-gravity waves propagating at thermospheric temperatures matching high and low solar activity

Numerical high-resolution modeling of nonlinear acoustic-gravity waves (AGWs) generated at the Earth's surface and propagating to the thermosphere shows that wave characteristics are depending on modifications in the mean density, temperature, molecular dissipation and composition due to variations of solar activity (SA). Amplitudes of temperature wave perturbations are generally larger at high SA at altitudes above 150 km, due to larger mean temperature and smaller molecular heat conductivity. Increasing kinematic coefficients of molecular heat conduction and viscosity result in stronger decreasing AGW amplitudes at altitudes larger 150 km at low SA. Dissipating AGWs generally produce heating at altitudes below 120 km. At larger heights, AGWs generally heat the thermosphere at low SA and cool it at high SA. Wave enthalpy fluxes are mainly upwards below 120 km altitude and downwards above 150 km at high SA, where they may have directions opposite to the upward wave energy fluxes. Downward wave enthalpy fluxes correspond to AGW cooling the upper atmosphere at high SA. Nonlinear dissipating AGWs may produce upward and downward transport of atmospheric mass. These mass flows may produce adiabatic heat influxes in the upper atmosphere. Mainly positive residual wave-induced mass flows at altitudes higher 150 km may contribute to the wave cooling of the upper atmosphere. Wave breaking and interactions between waves and the mean flow in the nonlinear model are stronger at higher amplitudes of AGW excitation at the ground, which lead to bigger energy losses for larger-amplitude waves. At high SA, resulting effects in the thermosphere depend on the balance between, on one hand, increases in wave amplitudes, caused by weaker molecular dissipation and smaller transfer of the wave energy to the wave-induced jet flows, and, on the other hand, decreases in the amplitudes due to higher density and larger AGW reflection. The thermal effects of waves in the upper atmosphere may depend on competitions between heating due to dissipation of the upward wave energy flux and cooling due to divergence of the downward wave entropy (or potential enthalpy) flux. At high SA, larger mean temperatures and larger temperature perturbations might increase magnitudes of downward wave entropy fluxes, which may result in more frequent downward wave enthalpy fluxes and wave cooling of the upper atmosphere.

THERMAL ANOMALIES PRIOR TO THE 2015 GORKHA (NEPAL) EARTHQUAKE FROM MODIS LAND SURFACE TEMPERATURE AND OUTGOING LONGWAVE RADIATIONS

Earthquakes can generate thermal anomalies in the atmosphere at low altitudes. Pending well-focused detailed studies, such phenomenon may be referred to as a precursor for earthquake prediction. However, today the pre-earthquake thermal anomalies are not clear enough. In this paper, the thermal anomalies prior to the April 25, 2015 Mw 7.8 Gorkha (Nepal) earthquake are investigated from the Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST), air temperature and Outgoing Longwave Radiations (OLR) data. The 2D and 3D wavelet transformation techniques are used to interpret the real time enhancement of the daily MODIS and OLR data before the impending earthquake. Using the wavelet density spectrum, pre-earthquake anomalies in MODIS and OLR are found in connection to the impending earthquake. The spatial images of MODIS and OLR show the evolutionary pattern of the emanation of ions from the epicenter and the surrounding area. The most important feature revealed by the spatial analysis is the eastward migration of temperature clouds due to a strong electric field. The satellite based LST data showed deviation, which crosses the upper bound by 5 °C. All the observations in our case study strongly support the notion of pre-earthquake thermal anomalies. Based on the analysis of the results, it can be concluded that the overabundance of ions from the seismogenic zone is responsible for prompting large temperature perturbations in atmospheric layers.

Late Quaternary TEX86 paleotemperatures from the world’s largest desert lake, Lake Turkana, Kenya

Wetter climatic conditions prevailed across northern and Equatorial Africa during the terminal Pleistocene until the middle Holocene, a climate event known as the “African Humid Period” (AHP). Although hydrologic changes during this period are well-known, very few records of temperature are available for evaluating the mechanisms and dynamics of climate change during the AHP across tropical Africa. To quantify changes in temperature during the onset and termination of the AHP, the TEX86 temperature proxy was used to generate a 14,000 year record of the surface temperature of Lake Turkana. This biomarker and related measures have been used to reconstruct regional and high-latitude paleotemperatures from the oceans and other continental systems, including other large African lakes. Although Lake Turkana’s climate and hydrology are very different from other large African lakes, our reconstruction exhibits a temperature history that shares a number of climatic trends with previous reconstructions. The TEX86 temperatures from Lake Turkana from 14 to 0.4 ka range from 24.3 to 28.6 °C, with a gradual decrease in temperature from early to late Holocene. This cooling roughly follows northern hemisphere summer insolation, similar to the trend observed in Lake Victoria and other regional records. However, the record from Turkana contains many abrupt temperature shifts not seen in other large lakes in the region. Multi-century-scale fluctuations persist through most of the record, and can be attributed to periods of lake mixing. Larger temperature perturbations are likely associated with changes in evaporation and cloud cover.

Dynamics of 3D isolated thermal filaments

Simulations have been carried out to establish how electron thermal physics, introduced in the form of a dynamic electron temperature, affects isolated filament motion and dynamics in 3D. It is found that thermal effects impact filament motion in two major ways when the pressure perturbation within the filament is supported primarily through a temperature increase as opposed to density: they lead to a strong increase in filament propagation in the bi-normal direction and a significant decrease in net radial propagation. Both effects arise from the temperature dependence of the sheath current which leads to a non-uniform floating potential, with the latter effect supplemented by faster pressure loss. The reduction in radial velocity can only occur when the filament cross-section loses angular symmetry. The behaviour is observed across different filament sizes and suggests that filaments with much larger temperature perturbations than density perturbations are more strongly confined to the near SOL region.

Eastward propagating planetary waves with periods of 1–5 days in the winter Antarctic stratosphere as revealed by MERRA and lidar

AbstractThis study presents the first report of planetary wave (PW) influences on significant temperature perturbations (10–20 K) within a course of one day detected by an Fe lidar from 35 to 51 km in the austral winter of 2011 at McMurdo (77.8°S, 166.7°E), Antarctica. Such large temperature perturbations are captured in the Modern Era Retrospective‐Analysis for Research and Applications (MERRA) data and correspond to various phases of eastward propagating PWs with periods of 1–5 days as revealed in MERRA. The strongest PW dominating the temperature perturbations has a period of 4–5 days with wavenumber −1. A 2−day wave with wavenumber −2 and a 1.25−day wave with wavenumber −3 also have significant influences. We find that these eastward propagating PWs are highly confined to winter high latitudes, likely because negative refractive indices equatorward of ~45°S result in evanescent wave characteristics and prevent the PWs from propagating to lower latitudes. The Eliassen‐Palm flux divergence and instability analyses suggest that barotropic/baroclinic instability at 50°S–60°S induced by the stratospheric polar night jet and/or the “double‐jet” structure is the most likely wave source. Such instability in the region poleward of 70°S is a complementary source for the 4−day wave, where we find that the heat flux of the 4−day wave is large and transported from ~70°S toward the pole above 40 km. This transport direction is likely linked to the meridional gradient of background temperature. The migrating diurnal tide near 78°S in the upper stratosphere is discernable, but significantly smaller than that of the dominant 4−day wave.

Analysis of a magnetorheological damper incorporating temperature dependence

Aside from external environmental heating, a magnetorheological (MR) damper may internally self-heat due to both resistive heating by the electromagnetic coil and to a greater extent, by dissipating mechanical energy into thermal energy. Temperature can significantly alter damper behaviour, as the fluid viscosity and accumulator gas pressure are highly dependent on temperature. Therefore, to improve the understanding of the behaviour of a linear stroke MR damper, a damper designed for a ground vehicle seat suspension, its performance is characterised over temperatures ranging from 0 to 100°C. A hydro-mechanical analysis is used to represent MR damper behaviour when it is subjected to large temperature perturbations and captures contributions from fluid viscosity, fluid inertia and pneumatic compressibility. The effect of damper self-heating on the identified model parameters is presented and the connection of these parameters to physical properties is also discussed.

Internal variability in Arctic regional climate simulations: case study for the SHEBA year

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 27:197-209 (2004) - doi:10.3354/cr027197 Internal variability in Arctic regional climate simulations: case study for the SHEBA year Annette Rinke1,*, Philippe Marbaix2, Klaus Dethloff1 1Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, 14473 Potsdam, Germany2Institut d’Astronomie et de Géophysique G. Lemaître, Université Catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium *Email: arinke@awi-potsdam.de ABSTRACT: The sensitivity of a regional climate model (RCM) to lateral boundary forcing (by different numerical weather prediction analysis products and by various temperature perturbations) and to the initial conditions is evaluated for a pan-Arctic domain. The study focuses on seasonal simulations over the period of the Surface Heat Budget of the Arctic Ocean project from October 1997 to September 1998. Small perturbations in the initial and/or lateral boundary conditions can make the model diverge from driving large-scale fields, and the extent to which this occurs depends on the control of the model by the lateral boundary forcing, not on the origin of the perturbation. The model response to a perturbation does not depend on the type of perturbation, and it is largely independent of the magnitude as well as of the source of the perturbation. Both small and large temperature perturbations have similar consequences for the monthly mean atmospheric patterns and the root mean square difference, but the model response depends on the season. Two regimes in the internal variability were found: (1) large variability in autumn/winter and (2) smaller variability in summer. The pronounced magnitude of internal variability must be taken into account in discussing the significance of climate change and climate sensitivity signals in Arctic RCMs. KEY WORDS: Regional climate modeling · Internal variability · Arctic climate Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 27, No. 3. Online publication date: December 08, 2004 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2004 Inter-Research.

On temperature inversions and the mesospheric surf zone

Mesospheric thermal inversions are investigated in a numerical simulation with the Whole Atmosphere Community Climate Model, an upward extension of the National Center for Atmospheric Research's Community Climate Model. The seasonal character, spatial extent, and magnitude of the inversion layers are realistic during winter. In the model, the occurrence of wintertime inversions is a direct consequence of the rapid decay with height of vertically propagating planetary waves, which induces large temperature perturbations in the upper mesosphere to maintain hydrostatic equilibrium. The magnitude of the inversions is highly correlated with planetary wave amplitude, so that large inversions develop during episodes of planetary wave amplification. Gravity waves do not play a major direct role in the formation of the inversions because the largest thermal tendencies associated with gravity wave breaking occur well above the range of altitudes where inversions are found. However, gravity waves play an essential indirect role because they set up a critical line in the upper mesosphere where Rossby waves break in the mesospheric surf zone.

Thin linear thermometer arrays for use in localized cancer hyperthermia

A thin linear array of silicon diodes has been developed to measure one-dimensional temperature profiles in tissue during treatment of cancer by localized hyperthermia. The array is composed of six discrete diodes on three flexible stainless steel wires, with a maximum cross-sectional dimension of 0.5 mm, so that it can be introduced into a tumor area via a small puncture wound. Temperature data are extracted using an external electronics system under microprocessor control; the present overall accuracy of the system is 0.2°C over the range of 37-45°C. The array has been tested in ultrasound, RF, and microwave heating fields. Computer simulation shows this array to be nonperturbing of the thermal field in tissue, so that it can provide accurate temperature data. Development of a batch-fabricated array of twenty diodes on five leads is under way. A monolithic silicon diode array is shown to produce large temperature perturbations because of its high thermal conductivity, while an alternative technology using silicon micromachining and adaptations of existing techniques for lead fabrication should produce an array of low thermal conductivity which can obtain accurate measurements. The present and future arrays should also be suitable for data collection in many in-vivo situations other than hyperthermia.