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Three extreme cold events successively occurred across East Asia and North America in 2020/21 winter. This study investigates the underlying mechanisms for these record-breaking persistent cold events from the isentropic mass circulation (IMC) perspective. Results show that the midlatitude cold surface temperature anomalies always cooccurred with the high-latitude warm anomalies, which was closely related to the strengthening of the low-level equatorward cold air branch of IMC, particularly along the climatological cold air routes over East Asia and North America. Specifically, the two cold surges over East Asia in early winter were results of intensification of cold air transport there, influenced by the Arctic sea ice loss in autumn. The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures (SSTs) explained the concurrent anomalous warmth there. This enhanced a wavenumber-1 pattern and the upward wave propagation, inducing a simultaneous and long-lasting stronger poleward warm air branch (WB) of IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming (SSW) event on January 4. The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch and hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February. Results do not yield a robust direct linkage from La Nina to the SSW, IMC changes, and cold events, though the extratropical warm SSTs have contributions to the February cold surge in North America.

Mid-level stratiform precipitations during the passage of warm fronts were detailedly observed on two occasions (light and moderate rain) by a 355 nm polarization lidar and water vapor Raman lidar, both equipped with waterproof transparent roof windows. The hours-long precipitation streaks shown in the lidar signal (X) and volume depolarization ratio (δv) reveal some ubiquitous features of the microphysical process of precipitating hydrometeors. We find that for the light-rain case precipitation that reaches the surface begins as ice-phase-dominant hydrometeors that fall out of a shallow liquid cloud layer at altitudes above the 0 ∘C isotherm level, and the depolarization ratio magnitude of falling hydrometeors increases from the liquid-water values (δv) to the ice/snow values (δv>0.20) during the first 100–200 m of their descent. Subsequently, the falling hydrometeors yield a dense layer with an ice/snow bright band occurring above and a liquid-water bright band occurring below (separated by a lidar dark band) as a result of crossing the 0 ∘C level. The ice/snow bright band might be a manifestation of local hydrometeor accumulation. Most falling raindrops shrink or vanish in the liquid-water bright band due to evaporation, whereas a few large raindrops fall out of the layer. We also find that a prominent δv peak (0.10–0.40) always occurs at an altitude of approximately 0.6 km when precipitation reaches the surface, reflecting the collision–coalescence growth of falling large raindrops and their subsequent spontaneous breakup. The microphysical process (at ice-bright-band altitudes and below) of moderate rain resembles that of the light-rain case, but more large-sized hydrometeors are involved.

We explore the decoupling physics of a stratocumulus-topped boundary layer (STBL) moving over cooler water, a situation mimicking warm-air advection (WADV). We simulate an initially well-mixed STBL over a doubly periodic domain with the sea surface temperature decreasing linearly over time using the System for Atmospheric Modeling large-eddy model. Due to the surface cooling, the STBL becomes increasingly stably stratified, manifested as a near-surface temperature inversion topped by a well-mixed cloud-containing layer. Unlike the stably stratified STBL in cold-air advection (CADV) that is characterized by cumulus coupling, the stratocumulus deck in the WADV is unambiguously decoupled from the sea surface, manifested as weakly negative buoyancy flux throughout the subcloud layer. Without the influxes of buoyancy from the surface, the convective circulation in the well-mixed cloud-containing layer is driven by cloud-top radiative cooling. In such a regime, the downdrafts propel the circulation, in contrast to that in CADV regime for which the cumulus updrafts play a more determinant role. Such a contrast in convection regime explains the difference in many aspects of the STBLs including the entrainment rate, cloud homogeneity, vertical exchanges of heat and moisture, and lifetime of the stratocumulus deck, with the last being subject to a more thorough investigation in Part II. Finally, we investigate under what conditions a secondary stratus near the surface (or fog) can form in the WADV. We found that weaker subsidence favors the formation of fog whereas a more rapid surface cooling rate does not. Significant Statement The low-lying blanketlike clouds, called stratocumulus (Sc), reflect much incoming sunlight, substantially modulating Earth’s temperature. While much is known about how the Sc evolves when it moves over warmer water, few studies examine the opposite situation of Sc moving over colder water. We used a high-resolution numerical model to simulate such a case. When moving over cold water, the Sc becomes unambiguously decoupled from the water surface, distinctive from its warm counterpart in which the Sc interacts with the water surface via intermittent cauliflower-like clouds called cumulus clouds. Such decoupling influences many aspects of the Sc–sea surface system, which combine to alter the ability of the Sc to reflect sunlight, thereby influencing the climate. This work laid the foundation for future work that quantifies the contribution of such a decoupled Sc regime to Earth’s radiative budget and climate change.

The infiltration of warm and humid air from the outside into a freezer results in frost accumulation around the evaporator in household refrigerators. This can significantly reduce the cooling capacity of refrigerators. In this study, the pressure, temperature, and frost around a proposed drain tube were monitored through in-situ measurements until the first defrost process (about 54 h). The proposed drain tube has 220 times higher hydraulic resistance and shows 55 times lower inflow in computational fluid dynamics (CFD) analysis. Once the door of the freezer compartment is opened and closed, external warm air replaces the cold air in the freezer. Negative pressure is produced by the shrinkage of this external air under low-temperature conditions. The other role of the drain tube is to vent air between the outside and inside of the refrigerator under negative pressure. To release the negative pressure, the proposed drain tube has a movable shutter. In the CFD results, the secondary inlet increases the inflow by 3.2 times compared to the inflow in an I-type tube. To determine the design, the weight and inner diameter of the drain tube were changed. The performance of the proposed tube was validated by the lack of blockage of discharge until the first defrost process. The movable shutter did not allow the negative pressure to exceed -100 Pa by facilitating air venting after opening the door for 10 seconds and then closing it.

The paper examines the influence of the main mode of interannual variability of the North Atlantic climate system—the North Atlantic Oscillation (NAO)—on the hydrophysical and hydrometeorological characteristics of the Nordic seas. A new scheme of the ocean–atmosphere interaction in the Atlantic sector of the Arctic Basin is proposed. In the positive NAO phase, the amount of Atlantic water inflow through the Faroe–Shetland Channel into the Norwegian Sea decreases, as well as the specific heat transfer to the atmosphere. Cyclonic activity becomes more active over the marginal seas of the Eurasian shelf in winter in the positive NAO phase. Cyclone trajectories are displaced to the north, which contributes to advection of warm air to the water area of the Nordic seas, and in the Barents Sea region, the frequency of southerly winds increases. The water temperature in the Nordcape Current in this period rises, and the ice extent of the Barents Sea decreases. The processes in the ocean–atmosphere–ice system in the Western Arctic in the negative NAO phase occur in the opposite direction. These conclusions were obtained for a time interval characterized by negative values of the Atlantic Multidecadal Oscillation (AMO index). During the positive phase of the AMO, which began to prevail in the 2000s, the processes in the ocean–atmosphere–ice system of the Barents Sea apparently occurred mainly under the influence of advection of Atlantic water with elevated temperatures.

High-resolution modeling is implemented to investigate an evolution of two quasi-tropical cyclones (QTC) over the Black Sea: in September of 2005 and 2018. For comparison, the quasi-tropical hurricane Zorba, that developed over the Mediterranean Sea at the end of September 2018, is considered. An assessment of factors leading to the origination and intensification of QTCs is carried out, and the predictability of the phenomenon is studied. The authors tried to reduce the analysis to the parameters obtained directly as a result of mesoscale nonhydrostatic modeling. In all the considered cases, the period of active development of cyclones was preceded by the formation of a core of warm air above the sea surface; the moisture inflow from the lateral boundaries was more important in the moisture balance. It is found that coarser spatial resolution predictions are more successful for large QTCs.

As a result of climate warming, glacial meltwater discharge has been increasing in Greenland. During the summers of 2015 and 2016, there were rapid increases in discharge from Qaanaaq Glacier in northwestern Greenland. These discharges resulted in floods that destroyed the road linking the settlement of Qaanaaq to Qaanaaq Airport. Field measurements were performed and a numerical model of glacier runoff was developed to quantify these discharges. The high discharge associated with the 2015 flood, estimated at 9.1 m3 s−1 (hourly mean), resulted from intensive glacier melting due to warm air temperature and strong winds, while the high discharge associated with the 2016 flood resulted from heavy rainfall (90 mm d−1) that led to a peak discharge estimated at 19.9 m3 s−1. The developed model, when used to investigate future glacier runoff under warming conditions, revealed a nonlinear increase in glacial melt with increasing temperature. Additionally, the model forecasted a threefold increase in total summer discharge, owing to a 4 °C rise in temperature. Thus, this study quantified the impact of a changing climate on glacier runoff, which gives insight into future risks of flood hazards along the coast of Greenland.

An explosive cyclone that took place over the Northwestern Pacific from 12 UTC 18 to 18 UTC 21 November 2007 was investigated. The synoptic situations and structure of this cyclone were documented by using the 1°×1° final analysis data of the National Center for Environmental Prediction. This cyclone developed explosively around 18 UTC 19 and reached its maximum deepening rate (MDR, 1.3 Bergeron) around 06 UTC 20 November 2007. At its MDR moment, the surface cyclone center was located in the downstream of the upper-level trough and northern entrance zone of the upper-level jet. The diagnosis using Zwack-Okossi equation suggested that cyclonic-vorticity advection and warm air advection acted to deepen this cyclone, while adiabatic cooling suppressed its development. In an investigation of this cyclone development, numerical sensitivity results obtained by using the Weather and Research Forecasting model showed that the latent heat release in the lower level had less contribution, whereas the surface sensible and latent fluxes played important roles. With a warmer ocean surface, the cyclone tended to intensify. Two topography tests were designed to examine the mountain influences on the development of this cyclone: removing a mountain and doubling the height of a mountain. Results show that the Changbai Mountains suppressed the development of the cyclone by preventing the southern moisture air from invading the inland. Without the moisture air, no latent heat release occurs when this cyclone passes over the Changbai Mountains.

This paper brings out the interconnection of flash rate density (FRD) with convection and stability parameters over Andhra Pradesh (AP), India. The convection parameters include rainfall, relative humidity, specific humidity, surface air temperature (SAT) and air temperature (at 850 mb). The stability parameters include convective available potential energy (CAPE), lifted index, K-index, total totals index (TTI), humidity index and total precipitable water. Both convective and stability parameters indicate good correlation with lightning activity. SAT and AT 850 mb have shown good correlations with lightning, which is a clear indication of interaction between warm air and dry air. CAPE and TTI have shown strong positive correlation with lightning activity. The correlation coefficient between FRD and CAPE is 0.81. We have also studied the influence of convective and stability parameters during lightning and no lightning activity. Later, we also attempted the estimation of lightning activity by using artificial neural network model. By using convection and stability parameters, six learning algorithms were used for training the artificial neural network. Scaled conjugate gradient backpropagation training algorithm has given the better estimation, whereas resilient backpropagation training algorithm has shown the poor estimation of FRD.

The current study investigated the triggering mechanism of a record-breaking heavy rain process in the area near the Tianshan Mountains in Xinjiang, an arid region in China, from July 31 to August 1, 2016, based on the simulation using the Weather Research and Forecasting (WRF) model. The results illustrated that the rainstorm system was generated in the middle atmosphere of the western Aksu region near the Tianshan Mountains and gradually evolved into a multicell linear echo during system evolution. The cold air transported from the Tianshan Mountains partly reached the low altitudes during the downhill process, and the warm southwest air from Aksu was lifted, forming oblique updraft airflow. The other part of the cold air converged with the southeastern warm air in the middle atmosphere, and the transportation and convergence of the water vapor related to the southwestern, southeastern, and oblique updraft airflows provided good water vapor conditions for the storm system. Meanwhile, the inclined upward air transported cloud water and ice-phase particles to high altitudes, mixing the two and generating a large amount of supercooled cloud water, which was very beneficial for the development and maintenance of the storm system. These conditions were favorable for power, heat, water vapor, and water condensate particles, which enabled the development and maintenance of the rainstorm system on the convergence line, thus triggering this rare rainstorm process during the movement to the northeast.

Extraordinarily frequent and long-lasting snowstorms affected China in January 2008, causing extensive social and economic damages. The potential predictability of such extreme events on the sub-seasonal timescale has been evaluated using results from the hindcast experiments by the Beijing Climate Center Climate System Model. The spatial distribution of precipitation during the period can be successfully reproduced with a 10–15 days leadtime, although the intensity is weaker than observations. The model’s success lies in the timely prediction of large-scale atmospheric circulation anomalies, such as the atmospheric blocking over the mid-high latitudes and the southwesterly flow associated with the Bay of Bengal trough in the low latitudes, but the predicted cold air is too strong while the warm air too weak, leading to an underestimation of precipitation along the main rainbelt. Meanwhile, the capture of those circulation anomalies in the initial states and their persistence in subsequent model predictions has played a key role in the predictability of such an extreme event. Detailed analysis has shown that sea surface temperature and low-frequency signals, such as the Arctic Oscillation and the Madden–Julian Oscillation, may also be important during the process.

Summary Data from MERIS onboard Envisat and MODIS onboard Terra and Aqua for 15–16 May 2010 were used to study powerful imprints of atmospheric gravity waves (AGWs) on the western part the Black Sea surface. Two cold fronts crossed the sea following the warm front and caused the AGWs which modulated the sea surface. Imprints of AGWs appeared as stripes of alternating brightness, they had crest length more than a hundred kilometers and wavelength of units of kilometers. Wave amplitude of AGWs imprints, evaluated by a 90%-depth of light penetration into the sea at 490 nm z90, the value inverse to the diffuse attenuation coefficient Kd_490, was units of decimeterxs. MODIS 250-m data of remote sensing reflectance, wind components and atmospheric pressure near the sea surface were obtained by processing the top of atmosphere data with the SeaDAS software package. Negative correlations of fluctuations of z90 with fluctuations of wind stress and atmospheric pressure were found on the transects of more than ten kilometers. The impact of wind stress on the origination of AGW imprints was found to be determinant, while the impact of atmospheric pressure was not more than units of percent.

Warm-sector rainfall (WSR) occurs, by definition, in a warm-air region that is isolated from any forcing related to synoptic frontal boundaries at the surface. This study explores the use of an object-oriented technique to objectively and automatically identify various WSR events over North China from June to September in 2012–17. A total of 768 substantive events are identified over the 6 years. They have a mean maximum rainfall accumulation of 35 mm h−1. Most such events occur over the plains, with two-frequency maxima: one to the south of the Yanshan Mountain Ranges, and the other near the junction of Henan, Shandong, and Jiangsu provinces. WSR-related rainstorms can form in all warm-season months but are most commonly observed between mid-July and mid-August (40% of all events occurred then). Geographically, the region at greatest risk moves gradually northward from mid-June to mid-August, consistent with the progression of the East Asian summer monsoon. There are two diurnal peaks in WSR activity, one from late afternoon to early evening and the other from late evening to early morning. Three classes of upper-level synoptic pattern seem to be conducive to WSR: (i) a “Mongolia front pattern,” (ii) a “northern China front pattern,” and (iii) a “southern front pattern.” All of these patterns are accompanied by warm and moist southwesterly flow at low levels. Prior to WSR events, there is usually an upper-level trough. According to other studies, such a feature is not usually seen for WSR events in South China.

A systematic analysis of the main weather types influencing southern Australian rainfall is presented for the period 1979–2015. This incorporates two multi-method datasets of cold fronts and low pressure systems, which indicate the more robust fronts and lows as distinguished from the weaker and less impactful events that are often indicated only by a single method. The front and low pressure system datasets are then combined with a dataset of environmental conditions associated with thunderstorms, as well as datasets of warm fronts and high pressure systems. The results demonstrate that these weather types collectively account for about 86% of days and more than 98% of rainfall in Australia south of 25° S. We also show how the key rain-bearing weather systems vary throughout the year and for different regions, with the co-occurrence of simultaneous lows, fronts and thunderstorm conditions particularly important during the spring and summer months in southeast Australia.

In the warm summer of 2017, a landslide failed from the south-east side of the Col des Clochettes on the top of the underlying Trajo Glacier. The study area is at an elevation of about 3500 m a.s.l. in the Gran Paradiso Massif and can be hardly reached by walking from Cogne (Aosta Valley, NW Italy). Studies conducted by field surveys, photogrammetry (structure from motion) and satellite images analysis, integrated with the evaluation of data from meteorological stations have been used to reconstruct the phenomenon and infer its causes. The site is very complex to be studied especially due to logistic problems, therefore, measurements and observations that are common practice in other landslides are very difficult to apply here. So, many of the results achieved are not adequately supported by field studies. Anyway, the following factors could have affected the stability of the slope: i) the tectonic structure of the area, which is reflected on the morphology and on the geomechanics characteristics of the rock masses; ii) the meteorological conditions during 3 months before the main failure, resulting in an extremely high temperature compared to historical data. Moreover, the analysis of multitemporal satellite images allowed to recognize that it was not a single landslide but that the phenomenon is articulated over time in at least five failures in about 2 months. Moreover, several predisposing factors may have been playing an important role in causing the instability: the degradation of permafrost (probably affecting rock mass due to the circulation of warm air and water in the discontinuity systems), the alternance of the freeze-thaw cycles and the availability of a considerable amount of water from rainfalls and nival fusion infiltrating deeply in the rock mass. More common causes such as rains and earthquakes have been excluded.

A distributed multi-heat source phased control method was designed with the aim of reducing the heating energy consumption of electric vehicles. The method uses multiple-heat sources, namely battery cooling waste heat, motor cooling waste heat and heat pump air conditioning, to heat vehicles in stages. To design this method, the heat generated by an electric vehicle heating system was first numerically analysed. The distribution regions of various heat sources were then optimised and the functional relationships between the heat produced by multiple heat sources were established. The law of temperature distribution in different regions of automobiles was explored for heat produced by multiple heat sources. The method can synthesise the temperature difference outside of the car, the heat release sequence of the heating components and the comfort requirements of passengers. It can also reasonably select the working mode of warm air. A low-temperature test of warm air conditioning was carried out to compare the difference between this method and the conventional heating method of new energy vehicles. The system saved 60% energy while running at an ambient temperature of −22 °C for 2 h. No power battery energy was needed at −5 °C, verifying the superiority of the proposed method.

Since the early twentieth century, observations have shown that the ocean surface has warmed almost globally, but the rate of sea surface temperature (SST) rise in the Kuroshio region (KR) has been twice that of the global-mean. This study focuses on the mechanisms driving long-term changes in SST in the KR during the period 1951–2010 using observations, reanalysis data, and 10-member ensembles of historical simulations based on a global climate model (GCM) called MIROC 5.2. The observational data indicates that SST in the KR slightly decreased until around 1980, but rapidly increased afterwards. The MIROC5.2 historical experiment reproduced the observed multidecadal changes in the KR SST, and a signal-to-noise analysis showed that one third to half of the changes were attributable to a forced component, represented by the ensemble mean. Comparison of historical runs with another ensemble in which sulfate aerosols were fixed at preindustrial levels, highlighted that multidecadal SST changes in the KR were primarily driven by sulfate aerosols, contributing to the warming for 1981–2010 as much as greenhouse gases. Analyses of the MIROC5.2 ensemble mean revealed that the key factor for enhanced warming after the 1980s in the KR was a high-pressure trend over the North Pacific. This is because it advects warm air to the northwestern Pacific in the lower troposphere and causes a northward shift in the Kuroshio current. The presence of this mechanism was supported by a significant correlation between SST trends in the KR and high-pressure trends over the North Pacific based on historical simulations from 27 GCMs, and a large ensemble of historical simulations using MIROC6. These results demonstrate the importance of an externally forced atmospheric circulation response over the North Pacific as it relates to enhanced ocean surface warming in the KR.

The frost-free refrigerator typically uses a bottom-placed calrod heater to remove frost on evaporator surface. However, the mismatch between full coverage of frost and bottom-up heat transfer extends defrost duration, and warm air intrusion into freezing cabinets (FCs) during defrosting leads to increased FC-temperature rise and overall energy consumption. Therefore, comprehensive measures were applied in this article to enhance defrost performance of the frost-free refrigerator. A special fan cover was adopted which opened during cooling cycles to supply cold air into cabinets normally, but closed during defrosting to block warm air intrusion passage. Moreover, an extra heater (60 W) was inserted in the middle height of the evaporator besides the original bottom one (180 W) to form better frost-heat match. Results show the fan cover and dual heaters altogether reduced defrost duration by 4.5 min and FC-temperature rise by 2.7 °C. Lower FC-temperature after defrost further declined energy consumption for the subsequent recovery cycle, which compensated for its increase for the defrost cycle and dominated the 1.2% reduction in overall energy consumption of the refrigerator. Both measures proved effective in enhancing defrost performance. However, the middle heater may affect cooling cycle performance of the refrigerator, necessitating further investigation.

—Electric heating of hives can be employed to help bee colonies survive cold snaps and minimize honey consumption by bee clusters. However, since our understanding of behavioral patterns of winter bee clusters is limited, this sometimes leads to the death of a colony or induces elevated honey consumption. In this work, the physical processes within the hive environment were modeled using Comsol software version 5.3. The simulation was carried out for a fixed outdoor temperature with variable heater power, as well as for a fixed heater power and variable ambient temperature. Analysis of thermograms indicated that with an operating heating device, the warmest zone shifted to the lower part of the winter cluster, which is biologically plausible. It was also shown that the use of the heaters increased the volume of warm air within a hive, providing the bees with a better opportunity to access new food reserves, which is especially important in the spring. The simulation demonstrated that in a heated hive energy output by the bees at low temperatures decreased from 3600 to 1900 W/m3, that is, by nearly two times. This decrease in the energy output is certain to diminish honey consumption. Simulation was also employed to optimize the power input to the heaters using the criteria of minimum temperature fluctuations within the hive and prevention of heater surface overheating.

The data of atmospheric reanalysis NCEP/NCAR over 1948–2017 (R-1) and NCEP/DOE over 1979–2017 (R-2) have been used to show that variations of the Caspian Sea level are closely correlated with the long-term variations in the field of surface wind in the sea region caused by the transformation of atmospheric circulation over Eurasia. Winds of the eastern and northern rhumbs have been shown to play the main role in variations of evaporation over the Caspian Sea. In the periods of level drop in the Caspian Sea (1948–1976 and 1996–2017), eastern winds dominate, bringing dry and warm air from Central Asia and thus contributing to an increase in water evaporation from the Caspian Sea. In the periods of level rise in the Caspian Sea (1977–1995), northern winds dominate, which cause a decrease in the rate of evaporation. Calculations of evaporation over the Caspian Sea water area using reanalysis data R-1 and R-2 fully confirm these conclusions. A close correlation has been shown to exist between evaporation and the level of the Caspian Sea. The coefficients of correlation between the nonstandardized increments of evaporation and level in the Caspian Sea are –0.86 and –0.75 by R-1 and R-2, respectively. Moreover, the contribution of evaporation to the current drop in the Caspian Sea level by data of improved reanalysis R-2 is greater than that by R-1, because the inflow of air masses from the nearby dry region of the Central Asia according to R-2 has been greater in the recent decade.

Snow cover ablation in the Great Lakes basin is a common and hydrologically important process during the cold season, contributing to a majority of the basin's runoff, and less frequent, extreme ablation events are highly impactful due to an increased flooding risk and warrant specific investigation. A brief climatology of extreme ablation events is presented, where extreme is considered within the top 5% of the distribution. Using synoptic classification techniques, individual weather patterns associated with extreme snow ablation in the Great Lakes basin are isolated. A single pattern deemed the most influential in generating extreme ablation events, southerly flow‐1, is examined in detail, and three case studies are presented to determine the meteorological conditions and surface energy fluxes responsible for ablation. Over 75% of extreme events are associated with southerly flow patterns that predominantly ablate snow with sensible heat fluxes, while rain‐on‐snow patterns induce the remaining extreme events from 1980–2009. Type southerly flow‐1 is responsible for 45% of the extreme events and is characterized by strong southerly advection of warm air into the basin, where sensible heat fluxes of 45–125 Wm⁻² are responsible for the majority of energy transfer into the snowpack. When compared with an average ablation event, an extreme ablation event for southerly flow‐1 exhibits air temperatures, dew point temperatures, and wind speeds that are 3.8°C, 3.0°C, and 1.2 ms⁻¹ warmer and faster than an average event, indicating a greater potential for larger ablation.

The application of air source heat pumps is mainly restricted by the outdoor ambient temperature, which causes poor application effects in the severe cold region of China. This paper proposes an innovative hybrid energy system of “solar air collector + air source heat pump + energy storage” that is utilized to save energy for ultra-low energy building in severe cold region. The feasibility and performance of this hybrid energy system is studied in Hailar which is located in severe cold region of China. The hybrid energy system is introduced and the dynamic characteristics of the key components of the system are analyzed in combination with the local meteorological conditions. The results indicate that, in Hailar, where the outdoor heating calculation temperature is lower than −30 °C and solar energy resources are not particularly abundant, the peak inlet air temperature of the air source heat pump increases by no less than 10 °C and the coefficient of performance of the system is expected to be higher than 3.0 under extremely low temperature conditions. Warm air from solar air collector can be supplied for heating without ASHP operation if its temperature is higher than 25 °C. These results provide some references for the application of the hybrid energy system in the severe cold region of China.

This study investigates the atmospheric mechanisms triggering flash-flood event in Thrace Basin of Turkey on November 27, 2018. Underestimation of this extreme precipitation amounts by NWP global and regional models (i.e. ECMWF, ALARO, WRF) and other meteorological difficulties (i.e. complex topography, land-sea interactions) in weather forecasting disabled disaster risk reduction before the event occurred. Detailed synoptic, thermodynamic, in-situ, and remote sensing analyzing results showed that significant amount of moisture during the afternoon times of the day was transferred to the atmosphere (from ground to 300-hPa) as a consequence of the excessive heating of sea surface temperatures (SSTs) of the Aegean Sea (16.5 °C in Ayvacik-Gulpinar place, 0.9 °C above its long-term normals). Strong southwesterly wind speeds associated with slow meridional movement of mid-latitude cyclone from its origin to the Eastern Mediterranean (EM) enabled transferring of relatively warm moist air to the land areas of Thrace Region (> 300 km fetch distance). Strong updraft and instability conditions under developed a supercell resulted with lightning (totally 63 cloud-to-ground and 59 intra cloud) and heavy rainfall especially Suloglu, Kofcaz, and Edirne settlements with the 12-hour total amounts 160.0, 123.0, and 97.4 mm (rainfall return period ~ 100 years), respectively. Flash-flood event caused numerous injuries and the death of a person and damaged, automobiles, houses, crops, and infrastructure of the Edirne and its neighboring settlements. From Showalter, K, Total of Totals, SWEAT, and CAPE instability indices; SWEAT is most appropriate to represent high possibility of occurrence of severe thunderstorms over the Edirne province owing to low-level moisture, warm air advection and low and mid-level wind speed terms in its equation.

This article reviews synoptic extratropical cyclone research starting from the skilfully constructed conceptual diagrams of the Bergen school in the 1920s. Careful analysis of multiple surface observations allowed Norwegian scientists to deduce the existence of cold and warm fronts and to characterise a complete cyclone lifecycle. Since then, new observing systems and advances in computational capabilities have enabled scientific research which has greatly expanded and enriched our knowledge of extratropical cyclone structure and evolution.

High-resolution numerical simulation results of a squall line initiated along a convergence zone in northeast China on 26 June 2014 were presented in this study. The simulation was performed by a convection-permitting model with coarse and fine grids of 4 and 1.33 km, respectively, and the simulation results were validated against the observation. Results showed that the simulation adequately reproduced the life cycle of the squall line, which allowed detailed investigation of the mechanism of convective initiation in this case. The synoptic condition was favorable for convective initiation and the convection was triggered in a convergence zone, where a branch of dry and cold air and a branch of moist and warm air collided. The water vapor flux divergence was inhomogeneous and some cores of water vapor convergence existed in the convergence zone. These cores were the spots where water vapor converged intensely and the air there was forced to rise, creating favorable spots where the convection was initially triggered. A series of quasi-equally spaced vortices near the surface, which themselves were the result of horizontal shear instability, were accountable for the inhomogeneity of the surface water vapor flux divergence. These vortices rotated the moist air into their north and dry air into their south, thus creating more favorable spots for convective initiation in their north. After initiation, the updraft turned the horizontal vorticity into vertical vorticity in the mid-level. The vortices near the surface collaborated with the vorticity maxima in the mid-level and enhanced the development of convection by providing water vapor.

This study addresses the role of the atmospheric moisture budget in determining the onset and development of summer droughts over the North American Great Plains (GP) using two state-of-the-art reanalysis datasets. We identified zonal moisture advection as the main cause of severe tropospheric drying during the extreme droughts in the southern GP in 2011 and northern GP in 2012. For both events, the eastward advection of anomalously dry and warm air in the free troposphere in spring set the stage for summer drought. This led to a sharp drop in relative humidity above the boundary layer, enhancing dry entrainment and suppressing deep convection. Further breakdown of the zonal advection into dynamic (caused by circulation anomalies) and thermodynamic (caused by moisture anomalies) contributions reveals dominance of thermodynamic advection in the tropospheric drying observed during the onset of both 2011 and 2012 droughts. The dependence of thermodynamic advection on the moisture gradient links springtime precipitation in the Rockies and southwestern US, the source region of the anomalous dry advection, to the GP summer precipitation (with correlations > 0.4 using gauge-based data). Identifying this previously overlooked precursor of the GP summer droughts improves our predictive understanding of drought onset mechanisms over the region.

Unique observational features of a convective cluster, occurred on 12-Sept-2015, over the rain shadow region in the leeward side of Western Ghats have been presented in this study. The synoptic environment had preconditioned the formation of a convergence zone over the study area. Moisture transport from the Arabian Sea was responsible for the moistening in the lower layers. Boundary layer convective thermals contributed to middle level moistening and subsequent onset of the cloud cluster was accompanied by a sudden surge of moist and warm air into the middle troposphere, and subsequent lifting of freezing level (FL) and wet bulb temperature zero (WBT0) levels. Sudden changes in the FL and WBT0 levels in association with the gust front prior to the initiation of the cloud system has been documented with high-resolution measurements using microwave radiometer and wind profiler. Thermodynamical parameters from radiometer illustrate the percussive conditions for formation of the cloud system. The cloud cluster had resulted in 25.50 mm rainfall, attributing to ~ 91% of convective rain. Intense fall velocity (10–12 ms−1) was noted up to ~ 7 km during the convective rain and the fall velocity was reduced to ~ 7 ms−1 (below the melting layer) during the stratiform counterpart. The cloud system was forecasted using WRF model (version 3.6.1), which was reproduced reasonably well as in the observations and the model output has been analyzed to understand the morphology of the system. The features such as formation of a cold pool, initiation of convective rainfall from the system were well forecasted by the model. Microphysical characteristics of the cloud cluster have also been examined. Riming was the dominant microphysical process within the convective regime. A major contribution to precipitation was from melting of ice hydrometeors especially graupel and snow was noted. Deep warm layer and associated production of supercooled liquid by the lifting of liquid water above the freezing level in updrafts exceeding 15 ms−1 was important for the production of a mixed-phase cloud system. Vapor deposition and aggregation process was noted in the stratiform/anvil counterpart, which also contained mixed phase hydrometeors, primarily of snow.

Over the tropical oceans, the large-scale, meridional circulation drives the accumulation of moist and warm air, leading to a relatively narrow, convectively active band. Therein, deep moist convection interacts with its heterogeneous environment—the intertropical convergence zone (ITCZ)—and organizes into multiscale structures that strongly impact Earth’s hydrological cycle and radiation budget. Understanding the spatial correlations and interactions among deep convective clouds is important, but challenging. These clouds are investigated in this study with the help of large-domain, storm-resolving simulations over the tropical Atlantic. Based on vertically integrated mass flux fields, deep convective updraft cells are identified with object-based techniques and analyzed with respect to their structural behavior and spatial arrangement. The pair-correlation method, which compares simulated pair numbers as a function of pair distance to an appropriately chosen reference, is applied and extended to allow for spatial statistics in a heterogeneous environment (i.e., the ITCZ). Based on pair-correlation analysis, the average probability is enhanced to find an updraft cell pair within 100 km compared to a random distribution. Additionally, the spatial arrangement of larger or stronger cells deviates more from randomness compared to smaller or weaker cells, which might be related to their stronger dynamical interaction mechanisms. Using simplified equilibrium statistics of interacting cells, several spatial characteristics of the storm-resolving simulations can be reproduced.

The interdecadal variations in extratropical anticyclone activity over East Asia during the winters of 1958–2013 were analysed using an objective identification and tracking algorithm for anticyclones. The influence of the interdecadal variation in anticyclone activity over the Mongolian Plateau on the interdecadal variation in East Asian surface air temperature and its possible mechanism was studied. The results showed that the Mongolian Plateau is the key region of anticyclonic activity in East Asia, and the occurrence frequency of anticyclones presented significantly opposite distribution forms in the higher and lower latitudes. An abrupt change in anticyclone activity over the Mongolian Plateau occurred in the late 1970s. From 1958 to the late 1970s, the main anticyclone activity occurred farther northward, whereas the activity was farther southward from the 1980s to 2013. Further study showed that in the period when the anticyclone occurrence frequency in the higher latitudes north of 50°N was lower (higher), while that in the lower latitudes south of 50°N was higher (lower), the surface air temperature of most parts of East Asia, especially the middle and high latitudes, was abnormally high (low). This was due to the anticyclonic activities, the Siberian high faded in the northwest part and expanded in southeast, while the East Asia trough and Ural Mountain blocking high weakened. This was also manifested as the variation in the geopotential height tendency forcing by transient waves. As the anticyclonic wave-breaking intensifies from western Mongolia to Northeast China, the high-frequency momentum flux over this area was significantly enhanced, strengthening the west wind in the higher latitudes from the north side and weakening the west wind in the middle latitudes from the south side. Under the combined force of the above activity, the southward movement of polar cold air was weakened, and the warm air in the middle and low latitudes was more easily transported to the north, resulting in warmer surface air temperatures over most parts of East Asia.

In this study, the brain and pulse waves of test subjects were measured when the cabin temperature of a vehicle was changed from an uncomfortable range to a comfortable range. In addition, questionnaires on the thermal comfort level of subjects were distributed and the results were analyzed. In the cooling condition, the stress index and ratio between low frequency and high frequency (LF/HF) did not clearly indicate an uncomfortable condition, except when the cabin and vent exit temperatures were 30 °C and 16.5 °C, respectively. When the air temperature from the vent exit was very low, the thermal sensation temperature of test subjects became lower, which could be inferred from the activation of high β wave owing. The subjects also felt uncomfortable because of increasing visual fatigue, which became evident after long periods of driving. In the heating condition, subjects felt great satisfaction because of the warm air flow from the vent exit during the initial test. After the cabin and vent exit temperatures reached 17.5 °C and 37.5 °C, respectively, the subjects remained in the wakefulness state, while simultaneously feeling bored and uncomfortable because of the long driving time.

The results of astroclimate research at the Kara-Dag radioastronomical station (Crimea) from July 22 to September 21, 2017, are presented. The algorithms for processing the data obtained by the atmospheric profile method are analyzed. The broad bands of the MIAP-2 receivers are shown to lead to a non-cosecant dependence of the antenna temperatures on viewing angle. The absorption calculation from three zenith angles by the least-squares method and a reference region with a brightness temperature close to the air temperature is optimal. The patterns of change in atmospheric transparency parameters and their connection with the climatic peculiarities of the observing site are considered. The existing atmospheric circulation is shown to create favorable conditions for nighttime astronomical observations in the millimeter wavelength range on the territory of the Kara-Dag station. Alternative and cheaper approaches to reducing the influence of atmospheric moisture on the measurements in this range than the existing trends are proposed. The first approach consists in choosing a location in a zone with a suitable wind rose and a relief leading to the replacement of moist warm air by dry cold one, for example, in the zones of such local winds as a bora. The second approach suggests the introduction of atmospheric parameter measurements by radiometric methods and allowance for their influence in a real time scale. Since the results obtained are based on limited statistics, they are preliminary ones and stimulate further systematic measurements at Kara-Dag.

Forest fires are a common and destructive natural disaster in Russia. Weather conditions during active forest fire periods in southern Sakha (Eastern Siberia) at high latitudes (58–65°N, 120–140°E) were evaluated. Periods of high fire activity during 2002 to 2016 were identified using MODIS (moderate resolution imaging spectroradiometer) hotspot data by considering the number of daily hotspots and their continuity. Weather conditions during the top seven periods of high fire activity were analyzed using atmospheric reanalysis data for upper (500 hPa) and lower levels (925 hPa). Our results showed that active fires occurred under varied weather conditions and it was difficult to find common weather patterns at both upper- and lower-levels during the seven most active fire periods. Furthermore, it was apparent that the northward movement of warm air masses (cTe: continental temperate) from lower latitudes (∼40°N) toward southern Sakha tended to exacerbate fires mainly due to strong wind conditions during the seven most active fire periods. In particular, on peak hotspot days, warm air masses from the south existed commonly near southern Sakha. This northward movement of warm air masses can be used to forecast fire and predict future fires in the region.

The Great Plains low-level jet (LLJ) is a contributing factor to the initiation and evolution of nocturnal Mesoscale Convective Systems (MCSs) in the central United States by supplying moisture, warm air advection, and a source of convergence. Thus, the ability of models to correctly depict thermodynamics in the LLJ likely influences how accurately they forecast MCSs. In this study, the Weather Research and Forecasting (WRF) model was used to examine the relationship between spatial displacement errors for initiating simulated MCSs, and errors in forecast thermodynamic variables up to three hours before downstream MCS initiation in 18 cases. Rapid Update Cycle (RUC) analyses in 3 layers below 1500 m above ground level were used to represent observations. Correlations between simulated MCS initiation spatial displacements and errors in the magnitude of forecast thermodynamic variables were examined in regions near and upstream of both observed and simulated MCSs, and were found to vary depending on the synoptic environment. In strongly-forced cases, large negative moisture errors resulted in simulated MCSs initiating further downstream with respect to the low-level flow from those observed. For weakly-forced cases, correlations were weaker, with a tendency for smaller negative moisture errors to be associated with larger displacement errors to the right of the inflow direction for initiating MCSs.

An extreme snowstorm event that occurred over Heilongjiang and Jilin Provinces on 24&ndash, 26 November 2013 was related to a cyclone characterized by a back-bent occluded front structure. This study investigates the structure of the back-bent occluded front and snowfall mechanism using multiple observations and NCEP/NCAR 1&deg, &times, 1&deg, reanalysis data in concert with the HYSPLIT model. The main results show that the extreme event was more synoptically governed by the outbreak of the polar vortex and moisture anomaly of the East Sea. The cyclone occurred just ahead of the 500-hPa merged deep trough, and then developed under the effect of the positive vorticity advection ahead of the 500-hPa trough and intense divergence of the upper-level jet. The south-southwest wind strengthened obviously after the merger of the southern and northern branch troughs, which was the main reason behind the cyclone moving northward. The moisture mainly originated from the Sea of Japan, insofar as that dry and cold air in the lower troposphere over the western mainland moistened obviously as it turned southward and passed over the Bohai Sea and the Sea of Japan, supplying abundant moisture for the snowstorm event. The intensity of moisture transport depended on the location and intensity of the cyclone. When the cyclone developed, the dry air continuously intruded into the cyclone&rsquo, s center, and made a conveyor belt of warm air wrap around it. The dry air gradually changed from descending to ascending motion as it moved ahead of the westerly trough, while the moist air in the northern part of the cyclone moved to the west and south and incorporated into the south of the cyclone center. Warm and moist air was lifted and arrived in the northwestern part of the cyclone after the occluded front&rsquo, s formation. Frontogenesis within the comma head was enhanced evidently owing to the rotation and deformation. The convergence between the southeast and northeast winds resulted in intense frontogenesis, leading to the enhancement of the front-scale ascent. Strong ascent formed in the comma head of the cyclone, which resulted in intense snowfall.

The paper presents the findings of an in situ research into velocities of air flow initiated by piston effect at the terminal station Garin-Mikhailovsky’s Square of the Novosibirsk Metro. The researchers calculate actual volume of the cold outdoor air inlet to the station and find the relationship between the air flow velocities and train speeds. It is shown that at the outdoor air temperature below −10 °C, the operating warm air curtains fail to ensure heating of the inlet cold outdoor air up to the rated temperature. Based on the full-scale experiment results, the network mathematical model of air flows is refined so that to take into account piston effect in a terminal subway station. The data of the computational exercises on the adjusted mathematical model of air distribution are provided, and the dependences of air volumes in the station entrance halls on the train speed in the Sibirskaya station–Garin-Mikhailovsky’s Square station tunnel are plotted. The most efficient method to reduce the cold outdoor air inlet at the station is to change speeds of the incoming and outgoing trains. In the recommended scenario, trains arrive at a speed of 60 km/h and depart at a speed of 30 km/h. In this case, the average velocity of the inlet cold outdoor air flow in the station entrance hall is decreased 2 times as compared with the air volume in the current speed mode of the subway trains. Furthermore, the power of the operating warm air curtains becomes sufficient to maintain the rated air temperature in the station entrance halls given the outdoor air temperature is −27 °C and above.

Many large confined spaces in tropical countries employ a combination of natural ventilation and mechanical fans for space cooling purposes. However, due to low wind velocity and an inability of mechanical fans to remove warm air, this cooling method is not capable of providing a satisfactory thermal comfort to the occupants. This study aims to find out a simple strategy for improving the thermal comfort inside a mosque building in Malaysia. Field measurements were first carried out to acquire the airflow velocity, air temperature, relative humidity and mean radiant temperature inside the mosque, for a duration of one-year. These data were then used to calculate two thermal comfort indices namely predicted mean vote (PMV) and predicted the percentage of dissatisfied (PPD). A computational fluid dynamic (CFD) method was employed to predict airflow and temperature distributions and to examine the effects of installing exhaust fans on the thermal comfort condition inside the mosque. Parametric flow analyses were conducted to find out the arrangement of the exhaust fans that would produce highest improvement in the PMV and PPD thermal comfort indices. It was found that, under the present ventilation condition, both PMV and PPD values at the selected locations inside the mosque exceed the respective upper limits as recommended in the ASHRAE Standard-55, indicating that the thermal comfort inside the mosque is extremely hot. Results of parametric flow analyses show that installing ten exhaust fans with a 1-m diameter at the south-side wall, at the height of 6 m from the floor, has a potential of reducing the PMV index by 75–95% and the PPD index by 87–91%. This translates into a vast improvement in the thermal comfort inside the mosque building. Keywords: Large confined space, CFD flow simulation, Thermal comfort, Predicted Mean Vote (PMV), Predicted Percentage of Dissatisfied (PPD), Exhaust fan

We revisit the various stratosphere–troposphere coupling relation from the perspective of the meridional mass circulation. We constructed 10-hPa northern annular mode (NAM) phase composites to show the typical spatiotemporal evolution of circulation anomalies during the NAM’s life cycle. Our results indicate that there is large case-to-case difference in the temporal evolution and vertical profile of polar temperature anomalies during NAM events, which shows no strong dependence on the intensity and duration of NAM events, but agrees well with the variations of the three branches of mass circulation at 60°N: the stratospheric poleward warm air branch (ST), the poleward warm air branch in the upper troposphere (WB), and the equatorward cold air branch in the lower troposphere (CB). Such correspondence is due to the dynamic heating and cooling anomalies associated with the redistribution of air masses by the anomalous meridional mass circulation in different isentropic layers. The various relationship among the three mass circulation branches is attributed to anomalous wave activities. The amplitude and westward tilt of waves are always stronger (weaker) throughout the stratosphere before (after) the peak time of negative NAM events, leading to a stronger (weaker) ST before (after) the peak time. Variations in WB and CB are mostly dependent on wave variabilities in the mid- to lower troposphere, leading to variations in the timing of in- or out-of-phase coupling of the ST with the WB and CB, and thus various thermostructure during NAM events. At a later stage of the negative NAM events when the polar temperature becomes colder and the polar jet recovers, the weakened baroclinic instability in the lower stratosphere provides favorable conditions for the strengthening of the WB and CB if wave activities strengthen in the troposphere during that period.

Using interior air layers in building envelopes has become popular in modern building design and construction. With the help of solar radiation, the air natural convection in these air layers provide multiple benefits to the building envelopes. The flow and heat transfer process of the solar driven natural convection in the air channels can greatly influence the performance of these envelopes. This study numerically investigates the flow and heat transfer process in the vertical air channels of double-skin solar facades, and evaluates the influence factors of the temperature and velocity fields, in order to determine the optimal channel thickness. The results show that the flow transition, velocity promotion and temperature increase mainly occur in the near-wall regions. For vertical channels with the height of 2-4m, the thickness of 0.1-0.8m and the input heat flux of 100-400W/m2, the flow rate varies between 0.042 kg/s and 0.255kg/s, and the range of the temperature rise is 0.66-14.70℃. Increases in the channel height and the input heat flux may result in a straight increase in the flowrate and the temperature, while the influence of the channel thickness on the flow rate and the temperature rise is limited. For air channels intending to improve ventilation capacity, the channel thickness should not be bigger than 0.6m; while for channels with the purpose of supplying warm air, the thickness should be less than 0.2m.

Atmospheric fronts include cold fronts, warm fronts, and stationary fronts, and they can be idealized as boundaries between two air masses with different temperatures and other properties. Simple e...