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To improve the initial condition (“analysis”) for numerical weather prediction, we attempt to assimilate observations from the Advanced Microwave Sounding Unit-A (AMSU-A) on board the low-earth-orbiting satellites. The data assimilation system, used in this study, consists of the Data Assimilation Research Testbed (DART) and the Community Earth System Model as the global forecast model. Based on the ensemble Kalman filter scheme, DART supports the radiative transfer model that is used to simulate the satellite radiances from the model state. To make the AMSU-A data available to be assimilated in DART, preprocessing modules are developed, which consist of quality control and bias correction processes. In the quality control, three sub-processes are included: gross quality control, channel selection, and spatial thinning. The bias correction process is divided into scan-bias correction and air-mass-bias correction. As input data used in DART, the observation errors are also estimated for the AMSU-A channels. In the trial experiments, a positive analysis impact is obtained by assimilating the AMSU-A observations on top of the DART data assimilation system that already makes use of the conventional measurements. In particular, the analysis errors are significantly reduced in the whole troposphere and lower stratosphere over the Northern Hemisphere. Overall, this study demonstrates a positive impact on the analysis when the AMSU-A observations are assimilated in the DART assimilation system.

Accelerated warming and a decline in sea ice coverage in the summertime Arctic Ocean can significantly affect the emissions of marine organic aerosols and biogenic volatile organic compounds. However, how these changes affect the characteristics of atmospheric water-soluble organic carbon (WSOC), which plays an important role in the climate system, remains unclear. Thus, to improve our understanding of WSOC characteristics, including its summertime fluorescence characteristics, in the rapidly changing Arctic Ocean, we simultaneously measured atmospheric concentrations of ionic species and WSOC, fluorescence excitation–emission matrix coupled with parallel factor (EEM–PARAFAC) analysis of WSOC, and marine biological parameters in surface seawaters of the western Arctic Ocean during the summer of 2016. WSOC was predominantly present as fine-mode aerosols (diameter < 2.5 μm) (median = 92 %) with the mean concentration being higher in the coastal water areas (462 ± 130 ngC m−3) than in the sea ice-covered areas (242 ± 88.4 ngC m−3). Moreover, the WSOC in the fine-mode aerosols was positively correlated with the methanesulfonic acid in the fine-mode aerosol samples collected over the sea ice-covered areas (r = 0.88, p < 0.01, n = 10), suggesting high sea–air gas exchange and emissions of aerosol precursor gases due to sea ice retreat and increasing available solar radiation during the Arctic summer. Two fluorescent components, humic-like C1 and protein-like C2, were identified by the PARAFAC modeling of fine-mode atmospheric WSOC. The two components varied regionally between coastal and sea ice-covered areas, with low and high fluorescence intensities observed over the coastal areas and sea ice-covered areas, respectively. Further, the humification index of WSOC was correlated with the fluorescence intensity ratio of the humic-like C1/protein-like C2 (r = 0.89, p < 0.01) and the WSOC concentration in the fine-mode aerosols (r = 0.66, p < 0.05), with the highest values observed in the coastal areas. Additionally, the WSOC concentration in the fine-mode aerosols was positively correlated with the fluorescence intensity ratio of the humic-like C1/protein-like C2 (r = 0.77, p < 0.01), but was negatively correlated to the biological index (r = −0.69, p < 0.01). Overall, these results suggested that the WSOC in the fine-mode aerosols in the coastal areas showed a higher degree of polycondensation and higher aromaticity compared that in the sea ice-covered areas, where WSOC in the fine-mode aerosols was associated with relatively new, less oxygenated, and biologically-derived secondary organic components. The findings can improve our understanding of the chemical and biological linkages of WSOC at the ocean–sea ice–atmosphere interface.

The purpose of this study is to examine the current trend of research on auditory training programs for the hearing impaired through a systematic literature review, and to provide fundamental information in terms of program design and intervention of 24 studies conducted from 1998 to 2020 were selected according to the Participants, Intervention, Control, Outcomes, and Study design (PICOS) criteria. The quality of the study was evaluated, and then a systematic review of the literature was conducted. First, as a result of examining the selected auditory training program of hearing-impaired target, it was conducted in various experimental design methods including location, personnel, age, and intervention method. Second, as a result of examining different methods of intervention on independent variables, in case of auditory training programs, the most common intervention was conducted by using speech. For the assisting devices, the most common intervention programs were conducted by using speech with wearing hearing aid. Third, as a result of examining the intervention method on dependent variables, it was found that the most frequent intervention programs were conducted by using speech. For the further research, the auditory program for the hearing impaired shoud be proceeded at any place in family-friendly environment, and in the form of intervention implemented by caregivers through parental education. In addition, another intervention technique might be applied at untact interveniton using the internet and digital devices.

The Makarov Basin halocline receives contributions from diverse water masses of Atlantic, Pacific, and East Siberian Sea origin. Changes in surface circulation (e.g., in the Transpolar Drift and Beaufort Gyre) have been documented since the 2000s, while the upper ocean column in the Makarov Basin has received little attention. The evolution of the upper and lower halocline in the Makarov Basin and along the East Siberian Sea slope was examined combining drifting platforms observations, shipborne hydrographic data, and modelled fields from a global operational physical model.In 2015, the upper halocline in the Makarov Basin was warmer, fresher, and thicker compared to 2008 and 2017, likely resulting from the particularly westward extension of the Beaufort Gyre that year. From 2012-onwards, cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian slope, with a sharp shift from 155 to 170°E above the 1000 m isobath in winter 2011-2012, followed by a progressive eastward motion after winter 2015-2016 and reached the western Chukchi Sea in 2017. In parallel, an active mixing between upwelled Atlantic water and shelf water along the slope, formed dense warm water which also supplied the Makarov Basin lower halocline.The progressive weakening of the halocline, together with shallower Atlantic Waters, is emblematic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime now may extend toward the Amerasian Basin.

In recent years, growing attentions have been paid to the potential benefit of extra observations over the data-sparse Arctic Ocean for weather forecasts. Here we also focus on such a case by targeting the inhabited land area, Alaska. During 2–18 August 2015, ship-borne radiosonde sounding observations were performed every 12 h (except 6-hourly from 12:00 UTC 11 August to 00:00 UTC 14 August) around the Chukchi Sea. To assess the impact of those extra radiosonde observations, two sets of ensemble forecast experiments (CTLf and OSE_Af) were produced, which were respectively initialized by atmospheric reanalysis data without (CTL) and with (OSE_A) additional assimilation of those data. The tropospheric circulation fields are compared to verify their differences in forecast performance. While two forecasts have similar performance in the earlier spin-up period of the analysis-forecast cycle (from 4 to 7 August), their performance tends to diverge in the later period (from 11 to 18 August) due to the accumulated influence on the error reduction in OSE_Af. Among the improved forecasts in OSE_Af, two most outperformed forecasts, each initialized on 00:00 UTC 12 and 00:00 UTC 14, show a notable improvement in predicting the developing trough over Alaska on 16–17 August by suppressing the development of erroneous high anomalies in CTLf. Though the positive impact of single-point observations is limited in a space, our results suggest that enhanced radiosonde profile observations in the data-sparse polar ocean could be beneficial for the forecasts beyond the observational area.

This study investigates the relationship of cloud properties and radiative effects with air mass origin during the winter (November–February, 2016–2020) at Ny-Ålesund, Svalbard, through a combination of cloud radar, ceilometer, and microwave radiometer measurements. The liquid cloud fraction (CF) was less than 2%, whereas the ice CF predominantly exceeded 10% below 6 km. The liquid water content (LWC) of mixed-phase clouds (LWCmix), which predominantly exist in the boundary layer (CFmix: 10–30%), was approximately four times higher than that of liquid clouds (LWCliq). Warm air mass advection (warmadv) cases were closely linked with strong southerly/southwesterly winds, whereas northerly winds brought cold and dry air masses (coldadv) to the study area. Elevated values of LWC and ice water content (IWC) during warmadv cases can be explained by the presence of mixed-phase clouds in the boundary layer and ice clouds in the middle troposphere. Consistently, the re of ice particles in warmadv cases was approximately 5–10 μm larger than that in coldadv cases at all altitudes. A high CF and cloud water content in warmadv cases contributed to a 33% (69 W m−2) increase in downward longwave (LW) fluxes compared to cloud-free conditions.

In this study, we investigated the daily variability of PM

The harmony of the Southern Ocean and Antarctic terrain is the pacemaker of Antarctic climate change under global warming., Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although this asymmetric feature is well recognized, its origin remains poorly understood. Here, by analyzing observation data and multimodel results, we show that a west-east asymmetric internal mode amplified in austral winter originates from the harmony of the atmosphere-ocean coupled feedback off West Antarctica and the Antarctic terrain. The warmer ocean temperature over the West Antarctic sector has positive feedback, with an anomalous upper-tropospheric anticyclonic circulation response centered over West Antarctica, in which the strength of the feedback is controlled by the Antarctic topographic layout and the annual cycle. The current west-east asymmetry of Antarctic surface climate change is undoubtedly of natural origin because no external factors (e.g., orbital or anthropogenic factors) contribute to the asymmetric mode.

Arctic tundra is undergoing a rapid transition due to global warming and will be exposed to snow-free conditions for longer periods under projected climate scenarios. Regional climate modeling is useful for understanding and predicting climate change in the Arctic tundra, however, the lack of in-situ observations of surface energy fluxes and the planetary boundary layer (PBL) structure hinders accurate predictions of local and regional climate around the Arctic. In this study, we investigate the performance of the Polar-optimized version of the Weather Research and Forecasting model (PWRF) in the Arctic tundra on clear days in summer. Based on simultaneous observations of surface fluxes and the PBL structure in Cambridge Bay, Nunavut, Canada, our validation shows that the PWRF simulates a drier environment, leading to a larger Bowen ratio and a warmer atmosphere compared to observations. Further sensitivity analyses indicate that the model biases are mainly from the uncertainties in physical parameters such as surface albedo and emissivity, the solar constant, and the model top height, rather than structural flaws in the model physics. Importantly, the PWRF reproduces the observations more accurately when the observed soil moisture is fed into the simulation. This indicates that there must be improvements in simulations of the land-atmosphere interaction at the Arctic tundra, not only in the accuracy of the initial soil moisture conditions but also in soil hydraulic properties and drainage processes. The mixing diagram analysis also shows that the entrainment process between the PBL and the overlying atmosphere needs to be improved for better weather and climate simulation. Our findings shed light on modeling studies in the Arctic region by disentangling the model error sources from uncertainties by parameters and physics package options.

11 pages, 7 figures.-- Supplementary data to this article can be found online at https://doi.org/10.1016/j.atmosenv.2019.11723.-- Data will be made available on request, Arctic aerosol-climate interactions are controlled by multiple factors including sources, processes and removal mechanisms of particles. The Arctic is mostly ocean, surrounded by mostly land, and our understanding of Arctic aerosol processes is incomplete due to scarce measurements carried out in sea ice regions. In particular, it is currently not known if these particular regions are sources of aerosols of primary or secondary origin. We present new results from ship-based measurements illustrating that marine new particle production and growth events occur in open ocean and melting sea ice regions in the Chukchi and East Siberian Seas. We report two new particle formation events during which a recently formed nucleation mode (, This work was supported by a Korea Grant from the Korean Government (MSIP) (NRF- 2016M1A5A1901769) (KOPRI-PN19081), the KOPRI projects (PE17390, PE19130 and PE19140) and the K-AOOS (KOPRI, 20160245) funded by the MOF, Korea. The study was supported by the Spanish Ministry of Economy through project PI-ICE (CTM2017-89117-R) and the Ramon y Cajal fellowship (RYC-2012-11922), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Many general circulation models (GCMs) have difficulty simulating Arctic clouds and climate, causing substantial inter-model spread. To address this issue, two Atmospheric Model Intercomparison Project (AMIP) simulations from the Community Atmosphere Model version 5 (CAM5) and Seoul National University (SNU) Atmosphere Model version 0 (SAM0) with a unified convection scheme (UNICON) are employed to identify an effective mechanism for improving Arctic cloud and climate simulations. Over the Arctic, SAM0 produced a larger cloud fraction and cloud liquid mass than CAM5, reducing the negative Arctic cloud biases in CAM5. The analysis of cloud water condensation rates indicates that this improvement is associated with an enhanced net condensation rate of water vapor into the liquid condensate of Arctic low-level clouds, which in turn is driven by enhanced poleward transports of heat and moisture by the mean meridional circulation and transient eddies. The reduced Arctic cloud biases lead to improved simulations of surface radiation fluxes and near-surface air temperature over the Arctic throughout the year. The association between the enhanced poleward transports of heat and moisture and increase in liquid clouds over the Arctic is also evident not only in both models, but also in the multi-model analysis. Our study demonstrates that enhanced poleward heat and moisture transport in a model can improve simulations of Arctic clouds and climate.

The Ninth Symposium on Polar Science/Ordinary sessions: [OM] Polar meteorology and glaciology, Wed. 5 Dec. / 3F Multipurpose Conference room, National Institute of Polar Research

The thermal evolution of melt ponds on Arctic sea ice was investigated through a combination of autonomous observations and two-dimensional high-resolution fluid dynamics simulations. We observed one relatively fresh pond and one saline pond on the same ice floe, with similar depth. The comparison of observations and simulations indicates that thermal convection dominates in relatively fresh ponds, but conductive heat transfer dominates in salt-stratified ponds. Using a parameterized surface energy balance, we estimate that the heat flux to the ice is larger under the saline pond than the freshwater pond when averaged over the observational period. The deviation is sensitive to assumed wind, varying between 3 and 14 W/m(2) for winds from 0 to 5 m/s. If this effect persists as conditions evolve through the melt season, our results suggest that this imbalance potentially has a climatologically significant impact on sea-ice evolution. Plain Language Summary Sea ice provides key feedbacks on polar and global climate, with melt ponds being particularly significant. Melt ponds darken the ice surface, thereby increasing the absorption of sunlight and accelerating ice melt. This study provides a new perspective on melt-pond salinity, its previously unrecognized significance in controlling the thermal properties of ponds, and the potential impact on ice melting as we transition toward a younger sea ice cover. Many state-of-the-art sea ice models represent melt ponds as a freshwater layer with a surface temperature of 0 degrees C, consistent with a past Arctic ocean dominated by desalinated perennial ice and relatively fresh ponds. However, perennial ice has diminished in recent decades, with increasing prevalence of young saline ice. This leads to ponds with a wider range of salinities and temperatures. We show that salinity strongly impacts pond temperatures, using observations of adjacent freshwater and saline melt ponds on Arctic sea ice. Combining this data with model simulations, we find that melt-pond salinity impacts heat transfer to the ice below and the resulting melting rate. Our study reveals that melt-pond salinity and salt stratification are key variables influencing heat transfer in melt ponds, which need to be considered in future model development.

This study examined the quiescence of Asian dust events in South Korea and Japan during the spring of 2012, presenting a synoptic characterization and suggesting possible causes. Synoptic observation reports from the two countries confirmed that spring 2012 had the lowest number of dust events in 2000–2012. The monthly dust frequency (DF) in March 2012 over the dust source regions, i.e., deserts in northern China and Mongolia, indicated a significant decrease compared to the 12 year (2000–2011) March climatology. The DF in April 2012 was comparable to the 12 year climatology values, but in May 2012 it was slightly lower. The daily Ozone Monitoring Instrument Aerosol Index and the Navy Aerosol Analysis and Prediction System simulations revealed stagnant dust movement in March and May 2012. Anomalous anticyclones north of the source regions decreased the dust outbreaks and enhanced the southeasterly winds, resulting in few dust events over the downwind countries (i.e., South Korea and Japan). By contrast, in April 2012, a strong anomalous cyclone east of Lake Baikal slightly increased the dust outbreaks over northeastern China. However, the major dust outbreaks were not transported downwind because of exceptional dust pathways, i.e., the southeastward pathway of dust transport was unusually blocked by the expansion of an anomalous anticyclonic circulation over the Sea of Okhotsk, with dust being transported northeast.

On the Korean Peninsula (KP), heavy rainfall often precedes the landfall of a tropical cyclone (TC). This rainfall is called antecedent indirect precipitation (AIP), because it occurs well beyond the effective radius of the TC. The present study examines the statistical characteristics and physical mechanism of the AIP produced by TCs that influenced the KP during the period 1993–2004. Composite analyses demonstrate that the AIP events were accompanied by midtropospheric frontogenesis due to the TC-mid-latitude environment interaction. When an approaching TC encountered an approaching mid-latitude upper-level trough, this encounter resulted in confluent and deformed flows at the mid-level by the combination of westerlies from the trough and southerlies from the TC. The delicate balance of horizontal winds related to the two systems at the mid-level led to the midtropospheric frontogenesis to the north of the KP. The frontogenetic feature related to the AIP was in marked contrast to those of the remote rainfall event over the KP and the predecessor rainfall event over the United States suggested by previous studies. Quasi-geostrophic analysis demonstrates that the midtropospheric front induced thermally direct circulation, which led to ascending motion over the KP. Consequently, the midtropospheric front helped to intensify the AIP, together with the convective instability that was amplified by the transport of warm and moist air along the conduit between the TC and subtropical high. Keywords: tropical cyclone, antecedent indirect precipitation, TC–mid-latitude interaction, QG frontogenesis, remote rainfall, predecessor rainfall event (Published: 20 June 2015) Citation: Tellus A 2015, 67, 27476, http://dx.doi.org/10.3402/tellusa.v67.27476

Recent research has demonstrated that additional winter radiosonde observations in Arctic regions enhance the predictability of mid-latitude weather extremes by reducing uncertainty in the flow of localised tropopause polar vortices. The impacts of additional Arctic observations during summer are usually confined to high latitudes and they are difficult to realize at mid-latitudes because of the limited scale of localised tropopause polar vortices. However, in certain climatic states, the jet stream can intrude remarkably into the mid-latitudes, even in summer; thus, additional Arctic observations might improve analysis validity and forecast skill for summer atmospheric circulations over the Northern Hemisphere. This study examined such cases that occurred in 2016 by focusing on the prediction of the intensity and track of tropical cyclones (TCs) over the North Atlantic and North Pacific, because TCs are representative of extreme weather in summer. The predictabilities of three TCs were found influenced by additional Arctic observations. Comparisons with ensemble reanalysis data revealed that large errors propagate from the data-sparse Arctic into the mid-latitudes, together with high-potential-vorticity air. Ensemble forecast experiments with different reanalysis data confirmed that additional Arctic observations sometimes improve the initial conditions of upper-level troposphere circulations.

In the Pacific sector of the Arctic, a noticeable dipole pattern of the sea ice concentration (SIC) between the Sea of Okhotsk and the Bering Sea has been reported on timescales of weeks to months. The dipole pattern owes its existence to the large-scale circulation variability across the North Pacific. Meanwhile, it is well known that eastward propagating tropical convection on an intraseasonal timescale, the Madden&ndash, Julian Oscillation (MJO), forms large-scale circulation anomalies in the North Pacific through the poleward-propagating Rossby waves that are stimulated by MJO-related tropical convection, which is often manifested as a Pacific&ndash, North American teleconnection pattern. Few studies, however, have focused on the lagged MJO influence on the SIC change in the high-latitude North Pacific by poleward-propagating waves. Thus, herein, we investigated the intraseasonal SIC variations associated with the MJO phases by considering the lagged circulation response. The dipole pattern in the composite daily SIC change map between the two seas becomes apparent after approximately one week of MJO phases 3 and 7. In the Bering Sea (the Sea of Okhotsk), the SIC increases after MJO phase 3 (phase 7), while it decreases in phase 7 (phase 3). The lagged anomalous circulation pattern in the North Pacific associated with the MJO leads to SIC changes primarily through the dynamic response in 10 m winds and the resultant sea ice motion.

This study examines antecedent mid-tropospheric frontogenesis (AMF) resulting from the interaction between Typhoon Rusa (2002) and a midlatitude trough over the Korean Peninsula. In this event, the AMF contributed to the first peak in the time series of rainfall in Gangneung (37.75°N, 128.90°E), occurring about 12 h before the time of the extratropical transition (ET) process of the tropical cyclone (TC). Using observations and high-resolution model outputs, we showed that the AMF contributed to the antecedent rainfall in Gangneung during the first rainfall period when Gangneung was located outside of Rusa's sphere of direct influence. A Weather Research Forecasting (WRF) model experiment was conducted to diagnose the frontogenetical features and associated precipitation processes in detail. The experiment revealed that the AMF was mainly forced by the horizontal deformation forcing (HDF). The direction of the HDF was oriented from southwest to northeast in the middle part of the peninsula. The HDF increased positively due to the confluence of the southeasterlies from the TC and the northwesterlies emanating from the midlatitude trough. The experiment also suggested that the mid-tropospheric moisture originated from the subtropical ocean and deposited into the frontal region by the southerlies on the eastern periphery of the TC, which enhanced the convergence of moisture flux in the frontal region during the first rainfall period. The thermally direct circulation associated with the AMF lead to the mid-tropospheric saturation, which enhanced the precipitation of the first rainfall event together with the orographically forced convection at the low level above Gangneung.

Recently, the National Typhoon Center (NTC) at the Korea Meteorological Administration launched a track-pattern-based model that predicts the horizontal distribution of tropical cyclone (TC) track density from June to October. This model is the first approach to target seasonal TC track clusters covering the entire western North Pacific (WNP) basin, and may represent a milestone for seasonal TC forecasting, using a simple statistical method that can be applied at weather operation centers. In this note, we describe the procedure of the track-pattern-based model with brief technical background to provide practical information on the use and operation of the model. The model comprises three major steps. First, long-term data of WNP TC tracks reveal seven climatological track clusters. Second, the TC counts for each cluster are predicted using a hybrid statistical-dynamical method, using the seasonal prediction of large-scale environments. Third, the final forecast map of track density is constructed by merging the spatial probabilities of the seven clusters and applying necessary bias corrections. Although the model is developed to issue the seasonal forecast in mid-May, it can be applied to alternative dates and target seasons following the procedure described in this note. Work continues on establishing an automatic system for this model at the NTC.

The spatial distribution of trends in tropical cyclone (TC) intensity over the western North Pacific Ocean (WNP) during the period 1977–2010 was examined using five TC datasets. The spatial distribution of the TC intensity was expressed by seasonally averaged maximum wind speeds in 5° × 5° horizontal grids. The trends showed a spatial inhomogeneity, with a weakening in the tropical Philippine Sea (TP) and a strengthening in southern Japan and its southeastern ocean (SJ). This distribution could be described by TC intensification rate and genesis frequency, with the aid of the climatological direction of TC movement. The increasing intensification rate around the center of the WNP could mostly account for the increasing intensity over the SJ region, while the influence of both intensification rate and local genesis frequency mattered in the TP region because of the effect of the newly generated and less-developed weak TCs on the TC intensity. Thermodynamic variables (e.g., sea surface temperature, potential intensity, and 26°C isotherm depth) showed almost homogeneous changes in space, possibly favoring intensification rate and genesis frequency over the entire WNP. However, the decreasing intensification rate and genesis frequency in some tropical regions conflicted with the impact of thermodynamic variables; rather, they were in accord with the impact of dynamic variables (i.e., vorticity and wind shear). In conclusion, the spatially inhomogeneous trends in TC intensity could be explained by considering the thermodynamic and dynamic aspects in combination through intensification rate and genesis frequency.

Observational records reveal that the number of tropical cyclones (TCs) approaching East Asia in July–October is positively correlated with sea surface temperatures (SSTs) in the equatorial and northern off-equatorial central Pacific (CP) oceans, indicating the significant impact of CP El Niño (CP-EN). Through experiments using a Weather Research and Forecast (WRF) model–based regional climate model, this study demonstrates that it is northern off-equatorial CP warming, rather than equatorial CP warming, that effectively induces local anomalous steering flows pertinent to the observed increase in TC activity over East Asia during CP-EN. Sensitivity experiments, in which the prescribed CP-EN-related SST anomaly is confined near the equator, do not capture the observed TC increase over East Asia, whereas those including the off-equatorial region successfully reproduce observed atmospheric and TC variabilities. The off-equatorial CP SST anomaly acts to expand the anomalous cyclonic response in the Philippine Sea farther northward. This produces a tunnel effect in the East China Sea, by which more TCs move to East Asian coastal regions (e.g., east China, Taiwan, Korea, and Japan).

Recent improvements in the theoretical understanding of the relationship between tropical cyclones (TCs) and their large-scale environments have resulted in significant improvements in the skill for forecasting TC activity at daily and seasonal time-scales. However, future changes in TC activity under a warmer climate remain uncertain, particularly in terms of TC genesis locations and subsequent pathways. Applying a track-pattern-based statistical model to 22 Coupled Model Intercomparison Project Phase 5 (CMIP5) model runs for the historical period and the future period corresponding to the Representative Concentration Pathway 8.5 emissions scenarios, this study shows that in future climate conditions, TC passage frequency will decrease over the North Atlantic, particularly in the Gulf of Mexico, but will increase over the western North Pacific, especially that hits Korea and Japan. Unlike previous studies based on fine-resolution models, an ensemble mean of CMIP5 models projects an increase in TC activity in the western North Pacific, which is owing to enhanced subtropical deep convection and favorable dynamic conditions therein in conjunction with the expansion of the tropics and vice versa for the North Atlantic. Our results suggest that North America will experience less TC landfalls, while northeast Asia will experience more TCs than in the present-day climate.

In January 2016, the Arctic experienced an extremely anomalous warming event after an extraordinary increase in air temperature at the end of 2015. During this event, a strong intrusion of warm and moist air and an increase in downward longwave radiation, as well as a loss of sea ice in the Barents and Kara seas, were observed. Observational analyses revealed that the abrupt warming was triggered by the entry of a strong Atlantic windstorm into the Arctic in late December 2015, which brought enormous moist and warm air masses to the Arctic. Although the storm terminated at the eastern coast of Greenland in late December, it was followed by a prolonged blocking period in early 2016 that sustained the extreme Arctic warming. Numerical experiments indicate that the warming effect of sea ice loss and associated upward turbulent heat fluxes are relatively minor in this event. This result suggests the importance of the synoptically driven warm and moist air intrusion into the Arctic as a primary contributing factor of this extreme Arctic warming event.

Recent cold winter extremes over Eurasia and North America have been considered to be a consequence of a warming Arctic. More accurate weather forecasts are required to reduce human and socioeconomic damages associated with severe winters. However, the sparse observing network over the Arctic brings errors in initializing a weather prediction model, which might impact accuracy of prediction results at midlatitudes. Here we show that additional Arctic radiosonde observations from the Norwegian young sea ICE cruise project 2015 drifting ice camps and existing land stations during winter improved forecast skill and reduced uncertainties of weather extremes at midlatitudes of the Northern Hemisphere. For two winter storms over East Asia and North America in February 2015, ensemble forecast experiments were performed with initial conditions taken from an ensemble atmospheric reanalysis in which the observation data were assimilated. The observations reduced errors in initial conditions in the upper troposphere over the Arctic region, yielding more precise prediction of the locations and strengths of upper troughs and surface synoptic disturbances. Errors and uncertainties of predicted upper troughs at midlatitudes would be brought with upper level high potential vorticity (PV) intruding southward from the observed Arctic region. This is because the PV contained a ‘‘signal’’ of the additional Arctic observations as it moved along an isentropic surface. This suggests that a coordinated sustainable Arctic observing network would be effective not only for regional weather services but also for reducing weather risks in locations distant from the Arctic.

The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively “clear” and “opaque” atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Alesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Alesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Alesund generate great differences below. The long-term radiosonde record (1993–2014) from Ny-Alesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1–3∘C warmer than the climatology during winter.