Cold Mass Research Articles

Intensification and shutdown of deep convection in the Labrador Sea were caused by changes in atmospheric and freshwater dynamics

Labrador Sea winter convection forms a cold, fresh and dense water mass, Labrador Sea Water, that sinks to the intermediate and deep layers and spreads across the ocean. Convective mixing undergoes multi-year cycles of intensification (deepening) and relaxation (shoaling), which have been also shown to modulate long-term changes in the atmospheric gas uptake by the sea. Here I analyze Argo float and ship-based observations to document the 2012-2023 convective cycle. I find that the highest winter cooling for the 1994-2023 period was in 2015, while the deepest convection for the 1996-2023 period was in 2018. Convective mixing continued to deepen after 2015 because the 2012-2015 winter mixing events preconditioned the water column to be susceptible to deep convection in three more years. The progressively intensified 2012-2018 winter convections generated the largest and densest class of Labrador Sea Water since 1995. Convection weakened afterwards, rapidly shoaling by 800 m per year in the winters of 2021 and 2023. Distinct processes were responsible for these two convective shutdowns. In 2021, a collapse and an eastward shift of the stratospheric polar vortex, and a weakening and a southwestward shift of the Icelandic Low resulted in extremely low surface cooling and convection depth. In 2023, by contrast, convective shutdown was caused by extensive upper layer freshening originated from extreme Arctic sea-ice melt due to Arctic Amplification of Global Warming.

Meteorological Characteristics of a Continuous Ice-Covered Event on Ultra-High Voltage Transmission Lines in Yunnan Region in 2021

Yunnan plays a pivotal role in transmitting electricity from west to east within China’s Southern Power Grid. During 7–13 January 2021, a large-scale continuous ice-covering event of ultra-high voltage (UHV) transmission lines occurred in the Qujing area of eastern Yunnan Province. Based on ERA5 reanalysis data and meteorological observation data of UHV transmission line icing in China’s Southern Power Grid, the synoptic causes of the icing are comprehensively analyzed from various perspectives, including weather situations, vertical stratification of temperature and humidity, local meteorological elements, and atmospheric circulation indices. The results indicate a strong East Asian trough and a blocking high directing northern airflow southward ahead of the ridge. Cold air enters the Qujing area and combines with warm and moist air from the subtropical high pressure of 50–110° E. As warm and cold air masses form a quasi-stationary front over the northern mountainous area of Qujing due to topographic uplift, the mechanism of “supercooling and warm rain” caused by the “warm–cold” temperature profile structure leads to freezing rain events. Large-scale circulation indices in the Siberian High, East Asian Trough, and 50–110° E Subtropical High regions provided clear precursor signals within 0–2 days before the icing events.

Problem of increased humidity in ice arenas and possible solutions

This paper reviews the problem of high humidity in an ice arena in Sochi and ways of solving it. The authors consider the ventilation system structure and determine the causes of the high humidity—moisture in the water vapor forms and a cold surface of ice cools the surrounding space and objects. The consequences of this air state are fogging over the ice surface, namely, condensate formation, which exacerbates the quality of the ice rink, corrosion of steel and iron structures, and mold attack. In addition, the facility microclimate is uncomfortable for people to stay there. During this study, the authors identified several ways to achieve the necessary indoor air parameters. The first method is sorption dehumidification. This system can function at low temperatures and cope with extreme dampness, but it has significant costs. The second method, which is simpler and more effective, is assimilation. This method is based on the ability of warm air masses to hold a larger amount of water vapor than cold air masses. This method for improving the air parameters is more effective when required to modify an existing ventilation system. In this particular case, in the ice arena in Sochi, assimilation was the most effective method. Air coolers with a drift eliminator were installed in the existing ventilation system. The calculation of the selected heat exchangers was performed using ventilation equipment selection software (VESS).

A Theory for the Balance between Warm Rain and Ice Crystal Processes of Precipitation in Mixed-Phase Clouds

Abstract Mixed-phase clouds contain both supercooled cloud liquid and ice crystals. In principle, precipitation may be initiated either by the liquid phase or by the ice phase. Ice crystals may grow by vapor diffusion to become snow (“ice crystal process”), forming “cold” precipitation. Equally, cloud droplets, when large enough, coalesce to form “warm” precipitation by the “warm rain process.” Warm rain could be supercooled and freeze as “warm” graupel. In the present paper, a new simplified theoretical analysis is provided to examine the microphysical system consisting of three species of hydrometeor, namely, cloud liquid, “cold ice” (crystals, snow), and “warm rain” (frozen or supercooled). This is obtained by nondimensionalizing and simplifying the evolution equations for the mass of each species. Analytical formulas are given for equilibria. Feedback analysis shows that the sign of the feedback is linked to the abundance of precipitation, with a neutral surface in the 3D phase space. The system’s precipitation amount explodes while in the initial unstable regime, crossing the neutral surface and approaching the equilibrium point that is a stable attractor. Positive and negative feedbacks are elucidated. In a standard case, the cold ice mass is about 1000 times larger than the warm rain mass. To illustrate the physical behavior of the theory, sensitivity tests are performed with respect to environmental conditions (e.g., aerosol, updraft speed) and microphysical parameters (e.g., riming and sedimentation rates for cold ice). Cold ice prevails, especially in fast ascent, due to its low bulk density, favoring slow sedimentation and a wide cross-sectional area for riming. Significance Statement The theory elucidates how the ice phase can prevail in the precipitation from any mixed-phase clouds with supercooled cloud liquid and crystals. The ice phase radically suppresses cloud liquid by riming when active and “wins” the competition against coalescence. This prevalence of ice is shown to arise from the low bulk density of snow. The cloud is viewed as a system of negative and positive feedbacks that prevail in realms of stability and instability in a 3D phase space.

Mapping a Lower Limit on the Mass Fraction of the Cold Neutral Medium Using Fourier-transformed H i 21 cm Emission Line Spectra: Application to the DRAO Deep Field from DHIGLS and the HI4PI Survey

We develop a new method for spatially mapping a lower limit on the mass fraction of the cold neutral medium by analyzing the amplitude structure of Tˆb(kv) , the Fourier transform of T b (v), the spectrum of the brightness temperature of the H i 21 cm line emission with respect to the radial velocity v. This advances a broader effort exploiting 21 cm emission line data alone (without absorption line data, τ) to extract integrated properties of the multiphase structure of the H i gas and to map each phase separately. Using toy models, we illustrate the origin of interference patterns seen in Tˆb(kv) . Building on this, a lower limit on the cold gas mass fraction is obtained from the amplitude of Tˆb at high k v . Tested on a numerical simulation of thermally bi-stable turbulence, the lower limit from this method has a strong linear correlation with the “true” cold gas mass fraction from the simulation for a relatively low cold gas mass fraction. At a higher mass fraction, our lower limit is lower than the “true” value, because of a combination of interference and opacity effects. Comparison with absorption surveys shows a similar behavior, with a departure from linear correlation at N H I ≳ 3–5 × 1020 cm−2. Application to the DRAO Deep Field from DHIGLS reveals a complex network of cold filaments in the Spider, an important structural property of the thermal condensation of the H i gas. Application to the HI4PI survey in the velocity range −90 < v < 90 km s−1 produces a full sky map of a lower limit on the mass fraction of the cold neutral medium at 16.′2 resolution. Our new method has the ability to extract a lower limit on the cold gas mass fraction for massive amounts of emission line data alone with low computing time and memory, pointing the way to new approaches suitable for the new generation of radio interferometers.

Thermodynamic and Dynamic Components of Winter Temperature Changes in Western Canada, 1950–2020

Abstract Most of the globe has experienced significant warming trends that have been attributed to anthropogenic climate change. However, these rates of warming are also influenced by short-term climate fluctuations driven by atmospheric circulation dynamics, resulting in inconsistent trend magnitudes in both time and space. This research evaluated winter (December–February) temperature trends over 1950–2020 at 91 climate stations across British Columbia (BC), Alberta (AB), and Saskatchewan (SK), Canada, and determined the components attributed to thermodynamic and dynamic (atmospheric circulation) factors. A synoptic climatological approach was used to classify atmospheric circulation patterns in the midtroposphere, relate those patterns to surface temperature, and evaluate changes in frequency. Moderate to high temperature increases over 71 years were found for most of the region, averaging 3.1°C in southern SK to 4.1°C in central-northern AB, and a maximum of 5.8°C in northern BC. Low to moderate increases were found for southern BC, averaging 1.2°C. Changes in atmospheric circulation accounted for 29% and 31% of observed temperature changes in central-northern BC and AB, respectively. Dynamic factors were a moderate driver in southern AB (18%) and central-northern SK (13%), and low in southern SK (5%). Negative dynamic contributions in southern BC (−6%), suggest that atmospheric circulation changes counteracted thermodynamically driven temperature changes. Results were consistent with trend analyses, indicating this method is well suited for trend detection and identification of thermodynamic and dynamic drivers. Results of this research improve our understanding of the magnitude of winter temperature changes critical for informing adaptation and climate-related policy decisions. Significance Statement Winter temperatures are strongly influenced by atmospheric circulation patterns, which move warm or cold air masses over large distances. We wanted to understand how changes in atmospheric circulation affect observed changes in winter temperatures in three provinces in western Canada. This also helps us to understand how much temperature change is due to anthropogenic (e.g., caused by greenhouse gases and land cover changes) and naturally occurring changes to Earth’s energy balance. Our results highlight the importance of understanding variability when selecting a time series for trend analyses or climate baselines for modeling studies. This study also helps to inform climate-related policies, decision-making, and adaptation strategies.

Spatial and temporal distribution of chlorophyll a concentration in the Sunda Shelf

The Sunda Shelf, characterized as an oligotrophic region, exhibits relatively low chlorophyll concentrations, with interannual variations primarily driven by winter chlorophyll levels exceeding 0.2 mg m−3. Utilizing multisensor satellite data spanning from 1999 to 2019, we harnessed the Data Interpolating Empirical Orthogonal Functions (DINEOF) method to perform a comprehensive reconstruction of chlorophyll a concentration in the southern South China Sea (SSCS). The findings reveal pronounced seasonal and interannual variations in chlorophyll levels, characterized by a peak in January and a subsequent decline until April. Additionally, under the prevailing southwest monsoon, a secondary chlorophyll peak was observed in August, followed by a slight decrease until October. Wind speed (WS) and sea surface temperature (SST) emerged as significant influencing factors at the seasonal scale, displaying notable correlations with spatial and temporal changes in chlorophyll concentrations. Importantly, the monsoon’s role outweighs that of SST in regulating seasonal chlorophyll dynamics on the Sunda Shelf within the SSCS. The study highlights a strong negative correlation between chlorophyll and SST, indicating that nutrient inputs from winter upwelling stimulate phytoplankton growth. The strength of the Sunda Shelf upwelling is influenced by cyclonic circulation in the South China Sea, while El Niño–Southern Oscillation events modulate monsoon intensity, impacting cold water masses and cyclonic circulation strength. These findings contribute to a better understanding of seasonal and interannual chlorophyll dynamics in the SSCS, particularly on the Sunda Shelf, and their ecological implications.

Resilience of reefal foraminifera to anthropogenic influences from reef areas (Pirangi, Maracajaú, and Açu) in Rio Grande do Norte (RN, Brazil)

We have studied seven symbiont-bearing foraminiferal species to evaluate the condition of sedimentary reef areas (Pirangi, Maracajaú, and Açu) in Rio Grande do Norte (RN, Brazil). The species are: Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Borelis schlumbergeri, Heterostegina antillarum, Peneroplis carinatus, and Laevipeneroplis proteus. This paper focuses on the quantitative distributions of the first two species in Maracajaú and Pirangi, considering micro-habitat variation, shelf zonation, and anthropogenic disturbances. Amphistegina gibbosa, which is more abundant than A. hemprichii, is prevalent in coral or coral-rubble substrates, whereas Amphisorus hemprichii is better represented in seagrass habitats. Our dataset from Pirangi and Maracajaú is based on 123 samples collected over three years through diver collection, grab samples, and underwater videographic surveys. Compared to other Brazilian reefs, species diversity at Pirangi is low, and the community is impoverished near tourism sites. These areas, especially Pirangi, may also be affected by pollution from domestic sewage and industrial waste. In Maracajaú, the community appears healthier, except in sites heavily impacted by tourism. Data from 84 foraminiferal samples from Açu show well-preserved symbiont-bearing foraminifera (SBF), indicating good water quality, with microhabitat variations likely due to natural factors. A quantitative examination of the foraminiferal species revealed the presence of a Caribbean-type reef community, including Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Heterostegina antillarum, Homotrema rubra, Peneroplis carinatus, and Laevipeneroplis proteus. Additionally, among 65 species, living Buccella peruviana were found with a very restricted distribution in organic-rich sediments associated with upwelling wind events, highlighting areas of cold water upwelling on the outer shelf. The spatial distribution of this species indicates that cold waters are bringing nutrients through tidal currents perpendicular to the shelf edge, likely using canyons and valleys to transport nutrients and cold water masses into the partially filled incised valley of the ancient Açu River. Changes in diversity appear to be primarily induced by anthropogenic influences on the inner shelf rather than the outer shelf.

Downward Mediterranean Cloudiness Beyond Little Ice Age Background Variability

Cloudiness–sea interaction substantially influences Earth’s climate by shaping precipitation patterns and radiative budgets. However, our understanding of long-term variations in land-based cloud cover, spanning over decades, centuries, and more, remains limited. This study presents the most extensive reconstruction to date of the annual total cloud cover fraction across the Mediterranean, spanning 1500–2022 CE. A notable shift occurred after 1818, marked by a surge in multidecadal variability and a sustained decline in cloud cover. This change has been attributed to several factors, including the eruption of Mount Tambora in Indonesia in 1815, intensified solar forcing, and a positive phase of the Atlantic Multidecadal Oscillation. These factors collectively reshaped cloudiness beyond typical background variability. By shedding light on the complex interactions with the climate system, our findings suggest that temperature changes may drive increased cloudiness in the Mediterranean when influenced by cold air masses through advection. This emphasizes the need for a deeper exploration of the impact of clouds on regional atmospheric circulation and climate changes. Ultimately, our enhanced understanding of the relationship between cloudiness and climate change provides valuable insights for climate models. While these models consistently project a decrease in cloudiness over the Mediterranean, our findings can also be helpful in understanding cloud variability in other parts of the globe.

Identification of cross-equatorial northerly surge (CENS) relationship to very heavy rain events in Jakarta

CENS is a meteorological phenomenon in the form of surface wind flow originating from the South China Sea (SCS), very strongly across the equator. CENS is closely related to the increase in average rainfall in parts of Indonesia. There has been very heavy rainfall on January 18, 2022 in the Jakarta area which resulted in flooding. Therefore, this study focuses on seeing if there is a CENS relationship that is factor in increasing rainfall in the Jakarta area on January 18, 2022. The results showed that the NCS began to form on January 16-17, 2022 with a Siberian High of 1040.6 hPa and the propagation of cold air masses from Asia to the south which was an indicator of CENS. The next day, the CENS phenomenon began to occur, characterized by meridional wind speeds in the 105˚- 115˚BT region of less than -5 m/s. This phenomenon triggers the strengthening of the northeast Asian monsoon flow so that the area south of the equator, including Jakarta, gets a large moisture transport from the SCS. This causes the potential for the formation of high convective clouds to trigger very heavy rain and cause flooding in the Jakarta area on January 18, 2022.

Egg parasitoids of Thaumetopoea pityocampa in the region of Gyumyurdzhinski Snezhnik in Eastern Rhodopes, Bulgaria

The region of Gyumyurdzhinski Snezhnik in the Eastern Rhodopes is the closest in Bulgaria to the Aegean Sea. However, the climate is characterized by specific parameters that are determined by its relief. It is poorly protected from the invasion of cold air masses from the north. From the south, the Gyumyurdzhinski Snezhnik hill restrains the Mediterranean influence. The orography of the area favors the retention of cold air masses and a further drop in temperatures. The experimental material for the study includes 5 generations of Thaumetopoea pityocampa (2016, 2017, 2018, 2019, and 2022), collected in 31 locations of four State Forestry Enterprises: Kirkovo, Ardino, Momchilgrad, and Zlatograd. The sample for analysis included 693 egg batches with 148420 eggs in them. Seven primary egg parasitoids were established in this region: Ooencyrtus pityocampae, Baryscapus servadeii, Pediobius bruchicida, Anastatus bifasciatus, Eupelmus vesicularis, E. vladimiri, Trichogramma sp. and one hyperparasitoid (B. transversalis). Dominant parasitoids were B. servadeii and O. pityocampae, and E. vladimiri and P. bruchicida &amp;ndash; occasional parasitoids. The hyperparasitoid B. transversalis participated in the complex with a relatively low share. The survival of the egg parasitoids in the laboratory conditions, in which the samples were kept, was low. The total mortality of the parasitoids in larval and adult stages was 47.8%. After collecting the samples, in laboratory conditions, a total of 442 individuals of the hyperparasitoid B. transversalis emerged, of which 56.3% were females and 43.7% were males. The average number of pine processionary&amp;nbsp;moth eggs in a batch was 214.2. 70.8% of all the eggs in the samples hatched successfully. The egg parasitoids are a very serious natural factor, regulating the density of the pine processionary moth, but their impact varied from 2.1% to 30.3%. The natural characteristics of the area, the air temperature during the stages of eggs and young larvae, are favorable for the development of the pine processionary moth. Unhatched larvae without the influence of entomophages were 7.2%.

The impact of gas accretion and AGN feedback on the scatter of the mass–metallicity relation

ABSTRACT The gas-phase metallicity of galaxies encodes important information about galaxy evolution processes, in particular star formation, feedback, outflows, and gas accretion, the relative importance of which can be extracted from systematic trends in the scatter of the mass–metallicity relation (MZR). Here, we use a sample of low-redshift (0.02 &amp;lt; z &amp;lt; 0.055) galaxies from SDSS to investigate the nature of the scatter around the MZR, the observables and physical processes causing it, and its dependence on galaxy mass. We use cold gas masses inferred from optical emission lines using the technique of Scholte &amp; Saintonge (2023) to confirm that at fixed stellar mass, metallicity and gas mass are anticorrelated, but only for galaxies up to M* = 1010.5 M⊙. In that mass regime, we find a link between the offset of a galaxy from the MZR and halo mass, using the amplitude of the two-point correlation function as a proxy for halo mass; at fixed stellar mass, the most gas-poor galaxies reside in the most massive haloes. This observation is consistent with changes in gas accretion rates onto galaxies as a function of halo mass, with environmental effects acting on satellite galaxies also contributing. At higher stellar masses, the scatter of the MZR does no longer correlate with gas or halo mass. Instead, there is some indication of a link with AGN activity, as expected from models and simulations that metallicity is set by the interplay between gas in- and outflows, star formation, and AGN feedback, shaping the MZR and its scatter.

Evolution of Different Types of Eddies Originating from Different Baroclinic Instability Types

This paper investigates the evolution of global eddies and various types of eddies originating from baroclinic instability (BCI) by utilizing satellite altimetry, Argo profiles, and climatology datasets. The structure of global eddies with regard to potential temperature anomalies experiences downward propagation and spreading from the periods of eddy growth to stabilization. However, from the eddy’s stabilization to the decay period, the process of spreading primarily occurs horizontally, and this process is usually accompanied by weakening. By comparing the evolution of eddies in three typical regions dominated by distinct types of BCI, we found that the basic properties of eddies related to different BCI types evolve similarly; however, there are notable differences in their vertical structures and evolution. Eddies associated with Phillips + Charney_s-type, Charney_s-type, and Eady-type BCIs exhibit dual-core, single-core, and dual-core structures, respectively. In particular, the intrusion of the Okhotsk cold water mass into the Northwest Pacific region forms cold-core anticyclonic eddies, resulting in AEs that are significantly distinct from the rest of the ocean. The evolution of surface-layer cores closely resembles that of the global eddies, while the decay of subsurface and bottom-layer cores is comparably sluggish. Additionally, we examine the impact of local oceanic stratification conditions on eddy decay and determine that stronger vertical gradients result in more vigorous eddy decay, accounting for the concentration of eddies at depths where vertical gradients are weaker during their evolution.

Numerical analysis of a novel coaxial annular tube convective heat switch

Heat switches are commonly used in cryogenic instruments to provide thermal contact or isolation between the hot and cold masses over a temperature range from millikelvin to room temperature. This study presents a new type of convective thermal switch that implements an annular tube design replacing the twin-tube structure. To study the effects of geometry and operating parameters on thermal performance, a computational fluid dynamics (CFD) model is developed. The results show that the designed heat switch provides a thermal conductance of 33.79 mW/K when the end temperatures are 4.2 K and 40 K. In addition, it can automatically change to thermal isolation mode with a residual thermal conductance of 0.19 mW/K. The thermal conductance is increased from 33.79 mW/K to 38.90 mW/K by extending the length of the inner tube. This novel heat switch holds promise for precooling the modern cryogen-free dilution refrigerator (DR) and adiabatic demagnetization refrigerator (ADR).

The magnetized and thermally unstable tails of jellyfish galaxies

ABSTRACT Jellyfish galaxies are promising laboratories for studying radiative cooling and magnetic fields in multiphase gas flows. Their long, dense tails are observed to be magnetized, and they extend up to 100 kpc into the intracluster medium (ICM), suggesting that their gas is thermally unstable so that the cold gas mass grows with time rather than being fully dissolved in the hot wind as a result of hydrodynamical interface instabilities. In this paper, we use the arepo code to perform magnetohydrodynamical windtunnel simulations of a jellyfish galaxy experiencing ram-pressure stripping by interacting with an ICM wind. The ICM density, temperature and velocity that the galaxy encounters are time-dependent and comparable to what a real jellyfish galaxy experiences while orbiting the ICM. In simulations with a turbulent magnetized wind, we reproduce observations, which show that the magnetic field is aligned with the jellyfish tails. During the galaxy infall into the cluster with a near edge-on geometry, the gas flow in the tail is fountain-like, implying preferential stripping of gas where the rotational velocity vectors add up with the ram pressure while fall-back occurs in the opposite case. Hence, the tail velocity shows a memory of the rotation pattern of the disc. At the time of the nearest cluster passage, ram-pressure stripping is so strong that the fountain flow is destroyed and instead the tail is dominated by the removal of gas. We show that gas in the tail is very fragmentative, which is a prediction of shattering due to radiative cooling.

Analysis of an Arctic cold air outbreak during autumn and related air mass transformations forced by surface changes and advection in higher altitudes

During marine cold air outbreaks (MCAOs), cold and dry Arctic air masses are transported from the central Arctic southward across the closed sea ice and much warmer open oceans. They experience significant transformations including a rapid heating and moistening, often leading to cloud formation. While intense wintertime MCAOs have been analyzed widely, the air mass transformations during other seasons have been studied sparsely. We address this gap by investigating an MCAO case observed in September 2020. To study the transformation processes, we combine the fifth generation of atmospheric reanalyses of the global climate (ERA5), trajectory calculations, as well as shipborne and airborne measurements. In the central Arctic, observations acquired from aboard the research vessel (RV) Polarstern during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition characterized the initial state of the air mass over closed sea ice. Trajectories indicated the pathway the air mass took from RV Polarstern southward to the Fram Strait. For the first 24 h of the southbound drift, the air masses remained quasi-stationary. Then, still 15 h ahead of the marginal sea ice zone, differential advection across the boundary layer flow introduced humidity and clouds at higher altitudes between 1.5 and 2.5 km. ERA5-derived temperature and humidity tendencies indicated complex vertical interactions. Radiative cloud-top cooling, entrainment, and turbulence were significantly reduced in the lower and enhanced in the upper advected cloud layer. Eventually, the lower cloud deck dissipated. After this confluence of 2 different air masses, observations gathered by Polar 5 in Fram Strait as part of the MOSAiC Airborne observations in the Central Arctic campaign revealed cloudy, moist layers throughout the lowest 3.5 km and an increasing boundary layer height. Comparing the initial with the final state 48 h later, the largest net heating of +8 K was found close to the surface, yet the largest net moistening of +2.5 g kg−1 at an altitude of 1 km, as the initial profile was exceptionally dry here. We conclude that the observed air mass transformations were driven by the surface changes from sea ice to open ocean but additionally strongly impacted by the differential advection of clouds and moisture across the near-surface MCAO flow.

Arctic Warming Triggers Abrupt Ecosystem Shift in North America’s Deepest Lake

Great Slave Lake’s huge cold water mass shielded it from impacts of the rapidly warming climate—until now.

Impact of the water structure in Peter the Great Bay (Japan Sea) on seasonal migrations of sandfish &lt;i&gt;Arctoscopus japonicus&lt;/i&gt;

On the background of water structure, general patterns of the sandfish Arctoscopus japonicus distribution in Peter the Great Bay are determined on the data of bottom trawl surveys in spring, summer and fall seasons. When the larval stage is finished, the underyearlings of sandfish appear in the trawl catches since July. Depth of their catches by bottom trawl in July-August is 23–60 m, under the temperature of 8–16 о С. Localization of the catches at the upper benthic front corresponds to their pelagic spreading with concentration on the seasonal thermo-pycnocline, so the belts of high catches by bottom trawl are located along the line of the thermocline contact with the bottom. They convert to bottom dwelling in fall season, being concentrated below the benthic front and shifting deeper gradually with the front. The adults dwell at the bottom, permanently in the subsurface waters. Their feeding starts near the coast in May-June when they aggregate below the upper benthic front, avoiding the remnants of the cold Bottom Shelf water mass. Under thickening of the warm surface layer in July-September, they retreat deeper and spread widely at the shelf bottom within the area occupied by the Subsurface Shelf water. Pre-spawning aggregations of adult sandfish are formed at the shelf edge and upper continental slope in October, whereas the non-spawning fish stay in this month on the shelf together with the underyearlings. The adults migrate to the coastal zone in November for spawning on seaweeds. The southern part of the bay is presumably more favorable for the spawning of sandfish, as the underyearlings are absent in its northern part in summer. The sandfish adults wintering is available outside the bay, so the southward migration is supposed in late autumn and the backward migration in spring.

Experimental investigations on heat transfer enhancement in a double pipe heat exchanger using hybrid nanofluids

Abstract Heat exchanger (HE) is an instrument that facilitates the operation of HE between two fluids that are at various temperatures. Double-pipe HEs are used in many organizations because of their low installation, design, maintenance costs, flexibility, and their suitability for high pressure applications. Heat transfer (HT) augmentation techniques (passive, active or compound techniques) are used in heat exchangers to reduce the HT surface area, to increase HT capacity and to reduce pumping power. Passive augmentation techniques are much cheaper and do not involve any external power input. They aim to improve the effective surface area, the residence time of the HT fluid and its thermal conductivity by the usage of nanofluids. Nanofluids are used for cooling applications in organizations, transportation, nuclear reactors, electrical and electronic devices and for biomedical applications. Hybrid nanofluids have higher thermal conductivity, low PD and frictional losses and pumping power as compared to the mono nanofluids. In this present work, experiments are conducted in a double pipe HE using TiO2, and SiC-water nanofluids by varying the volume concentration and cold fluid mass flow rate ranging from 17.5 to 34.5 lpm by making constant hot fluid mass flow rate. Further, experiments are conducted using TiO2–SiC/water hybrid nanofluids. Influence of nano and hybrid nanofluids on the overall HTC and friction factor are experimentally investigated. From the experiments, TiO2–SiC/water hybrid nanofluid with nanoparticle ratio TiO2:SiC = 1:2 is found to be optimum as the heat transfer enhancement is more with less improvement in friction factor. The overall heat transfer, and friction factor enhancement is 22.92 %, and 11.20 % higher respectively when compared with base fluid for TiO2:SiC = 1:2.

Aeolian activities change and possible mechanisms in central Asia on sub-orbital to decadal timescales

The aeolian activity in central Asia (CA)and its relevant dust emissions significantly influenced the global climate changes and biogeochemical cycles. Fully understanding the formation processes and mechanism of aeolian activity in CA is helpful to elevate our knowledge of global climate change, materials cycles and aeolian disasters monitoring and prevention. However, this issue is still controversial at present. We systematically review and integrate the geological archives and instrumental data to trace the variations of aeolian activity on sub-orbital, centennial, and decadal timescales in CA, and assessed the relationship between aeolian activity changes and climate changes, atmospheric circulation system changes and human activities. The result suggested that on the sub-orbital scale, during the past 8500 years, the low intensity and relatively stable aeolian activity occurred during the early to middle Holocene (8500-4000 Cal. Yr B.P.), followed by a more intensive/frequent and more variable aeolian activity conditions during late Holocene (4000-0 Cal. Yr B.P.). On centennial scale, over the past 1000 years, the more intensive (attenuated)aeolian activity occurred during the Little Ice Age (Medieval Warm Period). On the decadal scale, during the last century, aeolian activity in CA has decreased greatly since the 1960s, accompanied by the increasing of temperature and precipitation. Compared to the changes of climate, atmospheric circulation system and human activities, we proposed that the Siberian High (SH) which related to the temperature variations, rather than the precipitation and human activity, largely controlled aeolian activity in CA on the sub-orbital, centennial, and decadal timescales. Cooling at high latitudes markedly enhances the intensity of the SH, which is displaced southward as a result, causing the incursion of cold air masses from high latitudes which result in more robust wind regimes that provide suitable wind regimes for dust emission the study area.