Bathymetry and latitude modify lake warming under ice

In late winter, solar radiation is the main driver of water motion in ice-covered lakes. The resulting circulation and mixing determine the spatial distribution of heat within the lake and affect the heat budget of the ice cover. Although under-ice lake warming is often modeled as a one-dimensional (1D) vertical process, lake bathymetry induces a relative excess heating of shallow waters, creating horizontal density gradients. This study shows that the dynamic response to these gradients depends sensitively on lake size and latitude – Earth's rotation – and is controlled by the Rossby number. In the ageostrophic limit, horizontal density gradients drive cross-shore circulation that transports excess heat to the lake interior, accelerating the under-ice warming there. In the geostrophic regime, the circulation of the near- and off-shore waters decouples, and excess heat is retained in the shallows. The flow regime controls the fate of this excess heat and its contribution to water-induced ice melt.

Latitude and bathymetry modify lake warming under ice

In late winter, solar radiation is the main driver of water motion in ice-covered lakes. The resulting circulation and mixing determine the spatial distribution of heat within the lake and affect the heat budget of the ice cover. Although under-ice lake warming is often modeled as a one-dimensional vertical process, lake bathymetry induces a relative excess heating of shallow waters, creating horizontal density gradients. This study shows that the dynamic response to these gradients depends sensitively on lake size and latitude – Earth rotation – and is controlled by the Rossby number. In the ageostrophic limit, horizontal density gradients drive cross-shore circulation that transports excess heat to the lake interior, accelerating the under-ice warming there. In the geostrophic regime, the circulation of the near- and off-shore waters decouple and excess heat is retained in the shallows. The flow regime controls the fate of this excess heat and its contribution to water-induced ice-melt.

Photoelectric heating effects on the evolution of luminous disc galaxies

ABSTRACT Photoelectric heating (PEH) influences the temperature and density of the interstellar medium (ISM), potentially also affecting star formation. PEH is expected to have a stronger effect on massive galaxies, as they host larger dust reservoirs compared to dwarf systems. Accordingly, in this paper, we study PEH effects in Milky Way-like galaxies using a smoothed particle hydrodynamics code, which self-consistently implements the evolution of the gas, dust, and interstellar radiation field. Dust evolution includes dust formation by stars, destruction by SNe, and growth in dense media. We find that PEH suppresses star formation due to the excess heating that reduces the ISM density. This suppression is seen across the entire range of gas fractions, star-formation recipes, dust models, and PEH efficiencies investigated by our code. The suppression ranges from negligible values to approximately a factor of five depending on the specific implementation. Galaxy models having higher gas fractions experience higher star-formation suppression. The adopted dust model also alters the extent of star-formation suppression. Moreover, when PEH is switched on, galaxy models show higher gas outflow rates and have higher loading factors, indicative of enhanced SNe feedback. In gas-rich models (i.e. a gas fraction of 0.5), we also find that PEH suppresses the formation of disc clumps via violent disc instabilities, and thus suppresses bulge formation via clump migration to the central regions.

Divergent consensuses on Arctic amplification influence on mid-latitude severe winter weather

<p>The Arctic has warmed more than twice as fast as the global average since the late 20<sup>th</sup> century, a phenomenon known as Arctic amplification (AA).  Recently, there have been significant advances in understanding the physical contributions to AA and progress has been made in understanding the mechanisms linking AA to mid-latitude weather variability.  Observational studies overwhelmingly support that AA is contributing to winter continental cooling.  While Arctic warming is strongest at the surface, it extends throughout the mid-troposphere. In addition, the sea ice loss and associated warming is not uniform across the Arctic, but rather regionally focused including in the Barents-Kara Seas, a key region for disrupting the polar vortex.  The probability of severe winter weather increases across the Northern Hemisphere continents following polar vortex disruptions.  While some model experiments support the observational evidence, the majority of modeling results show little connection between AA and severe mid-latitude weather. Rather the excess warming generated in the Arctic due to sea ice loss and other mechanisms is not redistributed vertically in model simulations, but rather horizontally suggesting the export of excess heating from the Arctic to lower latitudes.  Divergent conclusions between model and observational studies, and even intra-model studies, continue to obfuscate a clear understanding of how AA is influencing mid-latitude weather.</p>

Safety of Transvaginal Scan Estimated from Ultrasonic Bioeffects

ABSTRACT The embryo and fetus are generally studied using ultrasound imaging in pregnancy; however, ultrasound wave is absorbed by biological tissues to elevate the temperature. The growing embryonic and fetal tissue tends to be damaged by heating; thus, excess heating that damages young sensitive growing tissue should be prevented in ultrasound diagnosis. Hence, the thermal status of diagnostic ultrasound should be known with thermal index (TI), of which the determination and application are discussed in this chapter. Peculiar problem to transvaginal scan and thermal problem in febrile patient are discussed. Additionally, the cavitation, which is related with negative pressure, develops high pressure, high temperature, and free radicals that damage embryonic and fetal tissues. Therefore, the mechanical index (MI) has to be determined, measuring negative pressure of ultrasound. The MI is determined for the safety of diagnostic ultrasound. The ultrasound device output intensity that suppresses fetal amniotic JTC-3 cultured cell growth was determined, where 240 mW/cm2 or less output intensity did not suppress the cell growth, namely, the diagnostic ultrasound has no bioeffect when the output is lower than 240 mW/cm3. The as low as reasonably achievable principle in the Doppler method of 0.1 TI will be discussed. Three experimental reports of hazardous effects of ultrasound are discussed. How to cite this article Maeda K. Safety of Transvaginal Scan Estimated from Ultrasonic Bioeffects. Donald School J Ultrasound Obstet Gynecol 2017;11(1):1-6.

Models for symbiotic stars in the light of the data

Different single and binary models of symbiotic stars are examined. Single star models encounter a number of problems, and binary models are probable. There are however difficulties in the interpretation of radial velocities. Accretion disks play a role in some cases, but winds especially from the cool component must be taken into account in realistic models. There is some evidence of excess heating of the outer layers of the cool component. Outbursts may be related to sudden changes in the characteristics of the cool star wind.