ALBERT

Description: Concurrent daytime and nighttime heat extremes (CHW) occur when both the daytime and nighttime temperatures during a heatwave are significantly higher than normal for an extended period of time. It means that not only are daytime temperatures reaching extreme levels, but nighttime temperatures are also remaining at high levels, providing little relief from the heat. CHW can be particularly dangerous as it can lead to extended periods of high heat stress, which can cause heat exhaustion, dehydration, and heat stroke, as well as other health problems. Those concurrent heat extremes recently increased over East Asia, especially in Korea. However, there are few previous studies examining CHW in Korea, and atmospheric circulation associated with CHW have not been investigated in previous studies. In this study, therefore, we tried to understand the characteristics of recently increased CHW by simply classifying it with the Self-Organizing Map clustering method. This study revealed large-scale atmospheric circulations associated with CHWs and patterns of increased clusters during recent periods. In addition, the effect of recently increased land-atmosphere interactions on CHW is examined. Due to global warming trends, we expect that CHW is favorable for more extreme increases in the future, occurring more robust and long-lived CHWs more likely.

Description: Heatwaves become more frequent over land, and their magnitude and duration also significantly increase, high impact on society and the economy in summer season. The climatic factors that affect the occurrence of heatwaves are very diverse, especially, the process of land plays an important role in extreme heatwave cases and understanding the role is associated with predictive performance. This study uses the Global Seasonal Forecast system version 6 to investigate the role of soil water content and the impact of multi-satellite soil moisture retrievals data assimilation to prediction skills for heatwave. The 2018 summer heatwave over Northern Europe and USA cases are examined which are combined with drought. Soil water content based on multi-satellite soil moisture retrievals data assimilation plays an important role of land-air interaction to intensify extreme temperature via positive feedback that dry soils contribute to decrease evaporation and to increase surface heating, more warm and dry air weakening cloud formation. This process is evident in the results of the forecasting model based on satellite data assimilation, which leads to improved predictability of heatwaves and stronger heatwave intensity. This study investigates the role of soil water content in heatwave forecasting and the impact of multi-satellite soil moisture retrievals data assimilation on sub-seasonal forecasting and land-air interaction in heatwaves.

Description: Observations often show that solar eruptive events involve interaction of two or more flux ropes. Although Lau and Finn (1996) has presented a quite thorough numerical study of interaction of two flux ropes, their flux ropes are located between two parallel planes and each end of them is anchored in either of the planes. Such a configuration is not suited for providing information on solar eruption because there is no preferable direction for an erupting structure, if any, to proceed. In this paper, we have investigated the interaction of flux ropes, both ends of which are rooted in one plane representing the solar photosphere. Our 3D magnetohydrodynamic (MHD) study has investigated the following four cases depending on the directions of axial fields and axial currents: (1) co-axial field and co-axial current (co-helicity), (2) counter-axial field and co-axial current (counter-helicity), (3) co-axial field and counter-axial current (counter-helicity), and (4) counter-axial field and counter-axial current (co-helicity). These cases are further subdivided depending on the presence or absence of overlying fields. In all cases, we have found certain eruptive behaviors but their natures are totally different. A remarkable case produces a self-closed magnetic structure detached from the bottom boundary, which drives eruption of the surrounding line-tied field. We have also constructed artificial emission measure images based on the simulations and compare them with real images of observed CMEs in order to tell what field configurations generate certain eruption features.

Description: Coronal magnetic fields are often approximated by force-free fields (FFFs). An FFF problem is well-posed when the boundary normal magnetic field and the boundary normal current density should both be prescribed under the condition that the divergence-freeness of magnetic field is guaranteed. In the vector potential formulation, which is divergence-free, the two boundary conditions cannot be prescribed by fixing the values of vector potentials at the boundary. In the poloidal-toroidal formulation, fixing the values of the poloidal and toroidal functions at the boundary prescribes the two boundary conditions once for all. We have devised a novel iteration scheme for FFFs using a poloidal-toroidal representation of magnetic field and developed a computational code based on it. The performance of this code is tested against Titov & Demoulin’s analytical FFF modes and compared with that of other existing codes. Our new code is found to excel others not only in figures of merits, but also in reproducing topological features of the Titov-Demoulin FFFs. We have also used the code to reconstruct time sequence of FFFs for AR 11974. This sequence reveals the changes of field connectivity, which are considered responsible for two flares and one CME that occurred in the active region.

Description: The 2018 summer heatwaves over Northern Europe and USA were unexpected extreme and complex cases combined with droughts. To investigate the compound heatwave cases and the role of land-air interaction with progress in soil water content and air temperature, ERA5 reanalysis data, CPC temperature, GLEAM, and ESA-CCI datasets are examined. Also, Global Seasonal Forecasting System is used to validate predictive performance in summer 2018. Based on observational and reanalysis datasets, the model performance of the water-limited regime and energy-limited regime is spatially verified over Northern Europe and USA. A combination of drought and heatwave occurred, and the breakpoint, which is the basis for the phase in which land-atmosphere feedback is placed in positive and as the threshold value of soil water content that daily maximum temperature becoming more sensitive with soil water declining, is established at each grid points for both forecasting model, observational and reanalysis data. When the dry side of the soil water content is well simulated in the forecast model, the heat wave forecasting skill score is improved. Even in the coupled forecasting model, there is a regime in which the daily maximum temperature is hyper-sensitive with decreasing in soil water content and, when the soil water content is well simulated, land-air positive feedback is well expressed within dry regime. This study estimates the improvement of heatwave prediction skills by simulating soil water and daily maximum temperature relationship in hyper-sensitive regimes and land-air interaction plays an important role as sources in extreme heat events cases.

Description: Different synoptic weather systems have been linked in previous studies to the occurrence of clear air turbulence (CAT), an aviation hazard and indication of turbulent processes near the tropopause. While the jet stream is the most studied weather system concerning CAT, tropopause folds, upper-level fronts, and moist convection associated with extratropical cyclones are also suggested to be possible causes of CAT. However, most of these studies are restricted by the limited availability of observation from pilot reports, and the linkages between weather systems and CAT can thus only be established through individual events. With the introduction of automated measurement of eddy dissipation rate (EDR), which is a metric inferring turbulence intensity, on commercial aircraft recently, more and objective CAT observations are available for a systematic review of the previous results. In this study, a multi-year EDR measurement archive (2019-2022) is used as the observational CAT database and compared to weather systems identified with feature-based methods in the ERA5 reanalysis. More than 5000 severe turbulence events are identified from the EDR measurements and the frequencies of the co-occurrence of different weather systems in the neighbourhood are assessed. Apart from confirming the important role of the jet stream in the occurrence of CAT, preliminary results also suggest that linkages to CAT potentially exist for Rossby wave breaking (using potential vorticity streamers as a proxy) and warm conveyor belts. The categorization of the 5000 CAT events will reveal to which degree different weather systems are linked to turbulent processes in the atmosphere.

Description: In support of the first Tropospheric Ozone Assessment Report (TOAR) a relational database of global surface ozone observations has been developed and populated with hourly measurement data and enhanced metadata. A comprehensive suite of ozone data products including standard statistics, health and vegetation impact metrics, and trend information, are made available through a common data portal and a web interface. These data form the basis of the TOAR analyses focusing on human health, vegetation, and climate relevant ozone issues, which are part of this special feature.Cooperation among many data centers and individual researchers worldwide made it possible to build the world's largest collection of in-situ hourly surface ozone data covering the period from 1970 to 2015. By combining the data from almost 10,000 measurement sites around the world with global metadata information, new analyses of surface ozone have become possible, such as the first globally consistent characterisations of measurement sites as either urban or rural/remote. Exploitation of these global metadata allows for new insights into the global distribution, and seasonal and long-term changes of tropospheric ozone and they enable TOAR to perform the first, globally consistent analysis of present-day ozone concentrations and recent ozone changes with relevance to health, agriculture, and climate.Considerable effort was made to harmonize and synthesize data formats and metadata information from various networks and individual data submissions. Extensive quality control was applied to identify questionable and erroneous data, including changes in apparent instrument offsets or calibrations. Such data were excluded from TOAR data products. Limitations of a posteriori data quality assurance are discussed. As a result of the work presented here, global coverage of surface ozone data for scientific analysis has been significantly extended. Yet, large gaps remain in the surface observation network both in terms of regions without monitoring, and in terms of regions that have monitoring programs but no public access to the data archive. Therefore future improvements to the database will require not only improved data harmonization, but also expanded data sharing and increased monitoring in data-sparse regions.