Cold Mass Research Articles

Dynamics of the Polar Front in the southwestern area of Svalbard, Norway

We have investigated the dynamics of the Polar Front (PF) in the southwestern area of Svalbard, where the dynamics are defined by the interaction between the Sørkapp Current (transporting cold and fresh Arctic-type water) and the West Spitsbergen Current (carrying the warmer and more saline Atlantic Water from the Norwegian Sea). Our approach was based on the global circulation model predictions. In accord with the model, the cold and fresher Arctic water masses originated from the eastern side of Svalbard and were flowing along the southern-most point of Svalbard into the southwestern area of Svalbard. This cold and fresher water was spreading and pushing warmer and more saline Atlantic water offshore. The model currents indicated that cold and fresher water masses were mostly transported northward along the south-western coast of Svalbard. In accord with the model and observed density profiles, the PF is a density compensated front with the density gradient mostly in the top 50-75 m. Presence of strong density gradients in the upper 50-75 m of the PF leads to the development of the submesoscale processes as surface frontogenesis and nonlinear Ekman transport. We found strong presence of surface frontogenesis at the PF in the model. The second submesoscale process, the nonlinear Ekman transport, is due to the forcing interaction. During the considered time frame, the winds were blowing mostly from the north-east to south-west across the PF, and therefore, the along-front wind component was very small, resulting in weak non-linear Ekman transport at the PF front.

Investigation of cold tube structure on flow characteristics and energy separation in vortex tube based on numerical and thermodynamic analyses

A combined approach of computational fluid dynamics modelling, experimental validation and thermodynamic analysis is used to investigate the effect of cold end tube geometry (namely, straight tube, divergent tube, convergent tube, and convergent-divergent tube) on flow characteristics and energy separation, which to improve the energy efficiency and sustainability of the vortex tube in industrial applications. The analyses indicate that the highest axial velocity (212 m/s) and swirl velocity (193 m/s) at different axial locations in the cold tube are demonstrated in the divergent and convergent-divergent structures, respectively. The divergent tube shows better energy separation at lower cold mass fraction, while the convergent-divergent tube is dominant at higher cold mass fraction. The highest coefficient of performance is found at μc = 0.6, with maximum cooling and heating energy transfer efficiencies of 0.112 and 0.103, respectively. By innovatively incorporating the work-heat transfer theory into structural investigation of cold tubes, it is found that tangential viscous shear effect is the dominant factor in energy separation process. It is noteworthy that the highest net energy transfer of 973 W is achieved by convergent-divergent tube at a cold mass fraction of 0.7.

The recent increasing frequency of strong cooling event in Southwest China in February

AbstractA strong cooling event refers to a sharp change in the average temperature over a short period. The rapid change of temperature has important effect on human health and is highly concerned recent years. Based on the observed temperature data set from stations in Southwest China (SWC) from 1979 to 2017, this paper analyses the characteristics of the strong cooling event (SCE). The result shows that SCE occurs with the highest frequency during the time from February to May. Among them, the frequency of SCE in February exhibits an abrupt change before and after 2005 with a significant increase. Further study reveals that the change of SCE frequency in February is associated with the large‐scale background circulation patterns. After 2005, there is a cyclonic circulation anomaly in Northeast Asia and an anticyclonic circulation anomaly in the Tibet Plateau (TP). This pattern provides a favourable condition for the southward movement of cold air mass, thereby increasing the frequency of SCE in SWC. Furthermore, it is revealed that there is a strong correlation between the variation of SCE frequency in February and sea surface temperatures (SST) in the Northwest Pacific in January before 2005. The cold SST anomaly could favour the occurrence of extreme TD events in SWC through vertical circulation. After 2005, the correlation between SCE and Northwest Pacific SST is not significant. The sea ice in the northern Barents Sea and Kara Sea becomes the dominant impact factor. The abnormally low sea ice concentration is conducive to strengthen the meridional circulation over East Asia, leading to an increasing frequency of SCE in SWC.

The Resolved Star Formation Law in NGC 7469 from JWST, ALMA, and VLA

We investigate the star formation process within the central 3.3 kpc region of the nearby luminous infrared Seyfert NGC 7469, probing scales ranging from 88 to 330 pc. We combine JWST/MIRI imaging with the F770W filter, with CO(2 – 1) and the underlying 1.3 mm dust continuum data from the Atacama Large Millimeter/submillimeter Array, along with Karl G. Jansky Very Large Array radio continuum observations at 22 GHz. NGC 7469 hosts a starburst ring which dominates the overall star formation activity. We estimate the global star formation rate (SFR) ∼ 11.5 M ⊙ yr−1 from the radio at 22 GHz, and a cold molecular gas mass M(H2) ∼ 6.4 × 109 M ☉ from the CO(2 – 1) emission. We find that the 1.3 mm map shows a morphology remarkably similar to those traced by the 22 GHz and the 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission observed with JWST. The three tracers reproduce the morphology of the starburst ring with good agreement. We further investigate the correlations between the PAHs, the SFR, and the cold molecular gas. We find a stronger correlation of the PAHs with star formation than with CO, with steeper correlations within the starburst ring (n > 2) than in the outer region (n < 1). We derive a correlation between the SFR and the cold molecular gas mass surface densities, the Kennicutt–Schmidt (K-S) star formation law. Comparisons with other galaxy populations, including starburst galaxies and active galactic nuclei, highlighted that NGC 7469 exhibits an intermediate behavior to the K-S relations found for these galaxy populations.

Spring circulation characteristics and formation mechanism in the Beibu Gulf

Spring circulation in the Beibu Gulf remains an underinvestigated research topic. Model results validated by observations reveal that the northern and southern parts of the Beibu Gulf are controlled by an enclosed cyclonic gyre and a cyclonic gyre, respectively, while in the vertical, the circulation at the surface differs from those in the middle and deep layers. Contrary to that of the classical view, the modeled Qiongzhou Strait (QS) current flows eastward during some days in spring. This eastward current has an occurrence proportion of 29.3–55.4%, and its longest duration period is 7~18 d. The average current in the QS in spring is approximately westward except in some typical years. In spring, the northern Beibu Gulf is affected by the cold water mass (CWM), which is depicted by the 12°C and 10°C isolines in strong and weak years, respectively. Sensitivity experiments show that the heat flux is dominant in the northern Beibu Gulf via the effect of the CWM, and the monsoon wind favors the formation of the cyclonic gyre. Conversely, the cyclonic gyre in the southern Beibu Gulf is jointly driven by the monsoon wind and heat flux, with the effect of the monsoon wind being more significant. The current off the northern coast of Vietnam (VNC) can be either northeastward or southwestward in spring in different years. The VNC is mainly controlled by the elevation gradient along the northern coast of Vietnam, and the Coriolis force, horizontal advection, and vertical diffusion also play significant roles. Additionally, the CWM is mainly controlled by the heat flux whereas the monsoon wind plays a secondary role. And the VNC, current in the QS, CWM, and cyclonic gyre jointly affect nutrient distributions in the northern Beibu Gulf.

Computational fluid dynamics of flow boiling and conjugate heat transfer characteristics in a mini/micro-channel printed circuit steam generator

Numerical investigation of printed circuit heat exchanger PCHE was carried out for the water-steam system to optimize the design parameters for the possible use of PCHE as a steam generator in integral nuclear reactors- thus targeting efficient renewable energy by enhancing heat transfer. Heat fluxes, overall heat transfer coefficient (OHTC), and volume fraction of steam in a single channel of PCHE are reported for counter-current flow arrangement. The numerical model consisted of 1mm∗1.5mm single hot and cold channel. The heat transfer parameters were calculated using the Volume of Fluid (VOF) model in ANSYS Fluent with boundary conditions: top/bottom adiabatic; left/right periodic; mass flow inlet and pressure outlet. The effect of cold side degree of inlet subcooled (DISC) – varied from 100 to 0 K with a decrement of 20 K- and mass flux (200 to 500 kg/m2.s on OHTC, vapor fraction, pressure drop, and effectiveness was studied. For the fixed degree of subcooled, the OHTC and pressure drop increase as cold side mass flux increases. Similarly, for the fixed mass flux at varying DISC, the OHTC increases and pressure drop decreases for low mass fluxes up to 200 kg/m2.s because most of the channel remains in the nucleate boiling regime. However, with further increase in mass flux opposite trends in OHTC and pressure drop were observed due to single phased regime. The vapor fraction of steam increases with lower DISC at low mass fluxes and decreases with the increase in mass flux. The effectiveness decreases as the cold side inlet temperature approaches saturation temperature at 3 MPa.

The effect of 11th rib excision on perioperative outcomes in patients undergoing partial nephrectomy for upper pole renal tumors

IntroductionWe aimed to evaluate the effect of eleven11th rib resection.on the perioperative period TRIFECTA criteria in patients who underwent retroperitoneal partial nephrectomy (PN) with the diagnosis of upper pole kidney tumors.Materials and methodsWe conducted a retrospective analysis of the data of the patients who underwent Open PN for upper pole renal masses between 2018 and 2023. The patients were divided into two groups: PN with rib resection and PN without rib resection. The demographic characteristics, tumor sizes, PADUA scores, warm–cold renal ischemia times, mass excision and tumor bed suturing times, histopathological tumor type and surgical margin positivity of the patients were examined. Both groups were evaluated comparatively based on this data.ResultsThe renal nephrometry scores of the two groups were similar. The total renal ischemia time was significantly shorter in the patients who underwent a rib resection than in those who did not (p < 0.001). Both the tumor excision and tumor bed suturing times were significantly shorter in the group that underwent a rib resection than in the group that did not (p < 0.001). The Clavien–Dindo complication grades were statistically similar between the two groups.ConclusionComplex in nature and high–risk renal masses located in the upper pole of the kidney, partial nephrectomy performed with an 11th rib resection can be considered a reliable surgical option with a shorter ischemia time, supporting the preservation of long-term renal function.

Valuable Content Marketing: Strategies for B2B Success

Conventional promoting strategies, known for their interruptive nature, are losing adequacy in the present computerized scene. Organizations are battling to catch B2B client consideration with meddling techniques like cold pitches and mass publicizing. This examination investigates a strong new methodology: Marketing digital content to businesses. B2B Content Advertising: A Solution to Traditional Marketing Problems B2B digital content marketing is positioned in this study as an inbound marketing strategy. Dissimilar to nosy strategies, inbound showcasing draws in clients by furnishing them with significant and applicable substance. This substance, circulated decisively through website pages, online entertainment, and different channels, encourages trust and lays out the brand as a dependable wellspring of data. Here are a few key focal points: Esteem Added Quality written substance makes all the difference: Making great substance that tends to the particular necessities and difficulties looked by B2B crowds is vital. This content ought to be seen as enlightening, important, drawing in, and convenient. From Offering to Making a difference: A shift in mindset: B2B content promoting requires a huge social shift inside showcasing groups. It requires progressing from a "offering" mindset to a "making a difference" one. This requires an adjustment of promoting goals, strategies, measurements, and ranges of abilities. The Distributer Outlook: Fruitful B2B content promoting requests a "distributing" approach. Brands should foster a profound comprehension of their interest group's data needs and purchasing venture.

An experimental investigation on the effects of the vortex tube material, swirl generator material and the tube length to diameter ratio on vortex tube performance

The current research investigates the effects of the swirl generator material, the tube length to diameter (L/D) ratio, and the vortex tube housing material on its performance. Two vortex tube were designed and constructed using either stainless or brass. In addition to testing different materials for the housing, 5 different materials were examined as potential options for the swirl generator, including stainless steel, brass, polyamide, acrylic and wood. All were having nozzle number of 6. The study encompassed three main areas: examining the impact of various L/D ratios on an entirely stainless vortex tube (ESVT) and an entirely brass vortex tube (EBVT), exploring various swirl generator materials at an optimal L/D ratio for the stainless vortex tube and the brass vortex tube, and investigating the influence of an optimal swirl generator material with varying L/D ratios for the stainless and brass vortex tubes. Operating conditions were controlled for all tests, the natural refrigerant, compressed air was used, the inlet pressure was set to 3.0 bar and the cold mass fraction was varied from 0.40 to 0.90. The results revealed that the performance of the ESVT was greater than the EBVT. The best combination was the polyamide swirl generator and brass vortex tube with an L/D ratio of 19.0. This resulted in the maximum isentropic efficiency of 0.27 at a cold mass fraction of about 0.47.

High-accuracy experimental study of performance characteristics of optimised Ranque-Hilsch vortex tube

In this paper we present high-accuracy experimental measurements of the performance characteristics of an optimised Ranque-Hilsch vortex tube of cylindrical counter-flow design. Although this is a relatively mature research area, the published high-accuracy experimental data with quantified measurement uncertainty is very limited. The purpose is to provide a reference data-set for CFD method validation and calibration. The vortex tube design is a performance-optimum based on existing literature. We characterize the temperature separation, energy separation, efficiency, and coefficients of performance for three inlet pressures (3.0 bar, 5.0 bar and 7.0 bar) and for atmospheric back pressure. Performance characteristics are presented as a function of cold gas mass fraction. The lowest non-dimensional cold-exit temperature (normalised by inlet temperature) was 0.87, the highest coefficient of performance (decrease in enthalpy flux of the cold stream normalized by work needed to compress air to the inlet pressure) was 0.137, and the highest isentropic efficiency (ratio of the actual energy lost by cold stream to energy that would have been lost in an isentropic expansion of the entire inlet stream from the inlet pressure to the cold-exit pressure) was 0.16.

A Retrospective on how Cryostats have changed with Cryostat Use and the Cooling Methods used to keep Superconducting Magnets Cold

Prior to the invention of the vacuum flask by James Dewar in 1895, cryogenic temperatures below 100 K could not be sustained very long. The Development of the modern cryostat was an extension of the basic Dewar vacuum flask. The design of the cryostat, its insulation, and the cold mass support system is a function of the cryostat’s intended use. The type of refrigeration available also influenced the development insulation systems, support systems, transfer lines and electrical leads that are part of the cryostat. In recent years the availability and the cost of helium has been a significant factor in cryostat design and the methods used to cool and cool-down cryostats. This paper explores the historical development of today’s cryostats and how that can be tied to the source of cryogenic cooling. This paper is focused on earth bound cryostats. Some of the same principles can be applied cryostats used in space.

Design, configuration, and thermal optimization of advanced cryostats

To address new challenges in the design of current and future advanced cryostats, guidelines can be developed by leveraging successful technical experience with existing cryostat assemblies. A brief review of eleven representative advanced cryostat designs is presented, based on six typical cooling methods, including cryogen baths, dry cryostats, mixed-cooling method, continuous cryogen flow, dilution refrigeration, and demagnetization. Also provided are engineering figures, tables-plots, and equations that can be used to design, configure, and optimize the thermal performance of cryostats. The following technical data are introduced: optimal Carnot power versus temperature for various two heat intercept stations in cryostat support, ten representative performances of different MLI blankets at various (Th-Tc), and a graphical summary of the ‘MLI patch-cover-crack’ experiments, among others. The cold mass thermally isolated in cryostats could be a quantum apparatus, test specimen, instruments in-space, or superconducting (SC) devices. The cryostat must provide all functional interfaces for obtaining the required data. The design methodologies for crucial components of a cryostat are discussed in-depth, including: 1) creating a lightweight support structure and placing thermal anchors in optimal locations, 2) designing MLI systems with cost-effective thermal shields, and 3) constructing sophisticated structures to accommodate heavy RF couplers or current leads.

Weld Qualification of the Cold Mass of the Superconducting Quadrupoles Magnets (MQXF) for the HL-LHC Project

Weld Qualification of the Cold Mass of the Superconducting Quadrupoles Magnets (MQXF) for the HL-LHC Project

Cryogenic aspects of a 20 MW class low-temperature superconducting generator for the renewables industry

In this paper we give a progress update on the cryogenic design for cooling a 20 MW class, partially superconducting generator with stationary field coils for offshore wind renewables industry [1-2]. This is a continuation of an earlier program on a 10 MW system dating back ten years. Whereas this new power rating increase leads to a radial diameter expansion of the superconducting field coils from 4 to > 9.5 m, it maintains the axial length. We show the design based on this scaled up with enlarged diameter. The field coil size increase asks for higher cooling power that leads to a bigger cold box size to accommodate the cryocoolers. In the design, as many as 8 cryocoolers can be accessed and serviced from the nacelle that houses the main cryogenic components. A typical thermal load balance sheet with all components is given and compared against the available cryocooler cooling power at different operating conditions. Due to the cryocoolers’ local point of contact cooling within the nacelle, the temperature gradient of the thermal shield that fully encloses the cold mass with its embedded field coils needs to be balanced out to minimize the heat burden on the field coils. This requires additional analytical efforts and implementation of further design features. The extended nacelle houses the cold box with its cryogenic infrastructure. The interface for the envisaged cryogenic pushbutton closed-loop circulating system remains invisible, requires no handling of cryogenic liquids and is hermetically closed. The field coil diameter increase also leads to a greater initial helium gas storage volume. In addition, it requires higher initial room temperature fill pressure within the toroidal helium vapor storage tanks and in cooling tubes connecting to the cryocoolers. The toroidal helium gas tanks are thermally coupled with the thermal shield so that helium convection inside the storage tank can improve heat transfer and reduce the temperature gradient of the thermal shield. Besides those heat transfer challenges, additional mechanical strain within this large structure is exerted on the torque tubes during initial cooldown and when energizing field coils. Some of those design challenges are quite unexpected, leading to novel workarounds in order to maintain the chosen cooling strategy. Finally, we assess those design limitations in view of further cryogenic scalability with emphasis on manufacturability and assembly.

Heat transfer performance study of Cu-ethanol/ethylene glycol/propylene glycol-water nanofluids in a wavy-walled tube heat exchanger

With the rapid consumption of nonrenewable energy sources, improving the heat transfer efficiency of conventional fixed tube plate heat exchangers, optimizing their structure, and finding more efficient coolants have become popular topics. In this paper, the cooling effect of ethanol/ethylene glycol/propylene glycol-water solution with a mass fraction of 50 % in a wavy-walled tube heat exchanger was investigated, while Cu nanoparticles with volume fractions of 1.5 % and 3.0 % were added to the cold working mass to form three different nanofluids. The effects of the three nanofluids at different volume fractions on the heat transfer performance of the wavy-walled tube heat exchanger were analyzed with numerical simulations, while the microscopic mechanism of the enhanced thermal conductivity of the nanofluids was investigated using molecular dynamics simulations. The results showed that the thermal conductivity of the nanofluids was greatly enhanced due to the formation of adsorption layers with different properties on the nanoparticle surfaces, and the Cu–ethylene glycol-water nanofluid showed the largest increase in thermal conductivity among the three nanofluids. It was also found that the shell-side pressure drop, convective heat transfer coefficient, and heat exchange quantity of the nanofluid in the wavy-walled tube heat exchanger significantly increased with an increase of volume fraction. The comprehensive heat transfer performance of the three nanofluids was found to be better compared to the base fluid. Cu-ethanol/EG/PG-water nanofluid with a volume fraction of 3.0 % increased the PEC of the heat exchanger by 10.4 %, 19.8 % and 27.6 %, respectively, at a volume flow rate of 1.53 m3/h. Therefore, the Cu-propylene glycol-water nanofluid had the best comprehensive heat transfer performance. Cu-ethanol-water nanofluid volume fraction of 3.0 % reaches a maximum PEC value of about 3.12 at Qv near about 2.0 m3/h, and Cu-EG-water nanofluid volume fraction of 3.0 % has a peak PEC value of about 4.07 at Qv of near about 2.0 m3/h. Therefore, the Cu-ethanol-water and Cu-ethylene glycol-water nanofluids are the optimal solutions for the combined heat transfer performance within the study.

Numerical simulations and local entropy generation in a two-phase transcritical carbon dioxide Ranque-Hilsch vortex tube

The Ranque-Hilsch vortex tube arouses a renewed interest as a robust expansion device able to produce thermal energy separation. However, its two-phase transcritical CO2 operation remains unclear. In this work, 3D computational fluid dynamics simulations are performed using the open-source SU2 solver which key features are the implicit time integration and the real gas density-based formulation. The homogeneous equilibrium two-phase model is coupled with both the k−ω shear stress transport and the standard k−ϵ turbulence closures while a fast tabulated version of the Span and Wagner equation of state enables to compute the CO2 properties. First, the validation is performed on pressure measurements, condensation onset positions and visualizations in a transcritical CO2 nozzle available in the literature. Then, the vortex tube transcritical CO2 temperature, energy and phase separations are thoroughly investigated as well as the integral and local entropy generations due to viscous and heat dissipations. The results reveal that the temperature separation is produced below the inlet temperature at both outlets due to real gas effects. It is also shown that the energy separation is reversed as well as the available vortex tube outlet powers for heating and cooling purposes. Furthermore, higher irreversibility due to fluctuating components is unveiled near the vortex tube sharp angles at high cold mass fraction and high inlet operating pressure. Throughout this analysis, compelling arguments in favor of the friction theory for the energy separation phenomenon are also disclosed. Overall, the present work gives useful operation guidelines and sheds light on the complex phenomena at play in a Ranque-Hilsch vortex tube for transcritical CO2 heat pumps.

Observed Seasonal Evolution of the Antarctic Slope Current System off the Coast of Dronning Maud Land, East Antarctica

AbstractThe access of heat to the Antarctic ice shelf cavities is regulated by the Antarctic Slope Front, separating relatively warm offshore water masses from cold water masses on the continental slope and inside the cavity. Previous observational studies along the East Antarctic continental slope have identified the drivers and variability of the front and the associated current, but a complete description of their seasonal cycle is currently lacking. In this study, we utilize two years (2019–2020) of observations from two oceanographic moorings east of the prime meridian to further detail the slope front and current seasonality. In combination with climatological hydrography and satellite‐derived surface velocity, we identify processes that explain the hydrographic variability observed at the moorings. These processes include (a) an offshore spreading of seasonally formed Antarctic Surface Water, resulting in a lag in salinity and thermocline depth seasonality toward deeper isobaths, and (b) the crucial role of buoyancy fluxes from sea ice melt and formation for the baroclinic seasonal cycle. Finally, data from two sub‐ice‐shelf moorings below Fimbulisen show that flow at the main sill into the cavity seasonally coincides with a weaker slope current in spring/summer. The flow is directed out of the cavity in autumn/winter when the slope current is strongest. The refined description of the variability of the slope current and front contributes to a more complete understanding of processes important for ice‐shelf‐ocean interactions in East Antarctica.

Ionised gas kinematics and dynamical masses of z ≳ 6 galaxies from JADES/NIRSpec high-resolution spectroscopy

We explore the kinematic gas properties of six 5.5 &lt; z &lt; 7.4 galaxies in the JWST Advanced Deep Extragalactic Survey (JADES), using high-resolution JWST/NIRSpec multi-object spectroscopy of the rest-frame optical emission lines [OIII] and Hα. The objects are small and of low stellar mass (∼1 kpc; M* ∼ 107 − 9 M⊙), less massive than any galaxy studied kinematically at z &gt; 1 thus far. The cold gas masses implied by the observed star formation rates are about ten times higher than the stellar masses. We find that their ionised gas is spatially resolved by JWST, with evidence for broadened lines and spatial velocity gradients. Using a simple thin-disc model, we fit these data with a novel forward-modelling software that accounts for the complex geometry, point spread function, and pixellation of the NIRSpec instrument. We find the sample to include both rotation- and dispersion-dominated structures, as we detect velocity gradients of v(re)∼100 − 150 km s−1, and we find velocity dispersions of σ0 ∼ 30 − 70 km s−1 that are comparable to those at cosmic noon. The dynamical masses implied by these models (Mdyn ∼ 109 − 10 M⊙) are higher than the stellar masses by up to a factor 40, and they are higher than the total baryonic mass (gas + stars) by a factor of ∼3. Qualitatively, this result is robust even if the observed velocity gradients reflect ongoing mergers rather than rotating discs. Unless the observed emission line kinematics is dominated by outflows, this implies that the centres of these galaxies are dominated by dark matter or that star formation is three times less efficient, leading to higher inferred gas masses.

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.