Middle Latitudes Research Articles

Fractional change of scattering and absorbing aerosols contributes to Northern Hemisphere Hadley circulation expansion

The relative amount of scattering and absorbing aerosols is essential in determining the aerosol radiative and climate effects. Using reanalysis datasets and climate simulations, here, we show that changes in the relative amount of scattering and absorbing aerosols in the Northern Hemisphere (NH) high latitudes, manifested as long-term decreasing trends in aerosol single-scattering albedo (SSA), have played an important role in driving the widening and weakening trends of the NH Hadley circulation (HC) since the early 1980s. Decreasing SSA in the NH middle and high latitudes can notably warm the troposphere there, thus reducing the equator-to-pole temperature gradient, increasing static stability in mid-latitude regions, and leading to the widening and weakening trends of NH HC. Further analysis of the Coupled Model Intercomparison Project Phase 6 (CMIP6) aerosol forcing–only simulations also supports the importance of SSA trends in perturbing NH HC through the above mechanism.

Improved convective cloud differential (CCD) tropospheric ozone from S5P-TROPOMI satellite data using local cloud fields

Abstract. We present the CHORA (Cloud Height Ozone Reference Algorithm) for retrieving tropospheric-ozone columns from S5P-TROPOMI (Sentinel-5 Precursor–TROPOspheric Monitoring Instrument). The method uses a local-cloud reference sector (CLC – CHORA Local Cloud) to determine the stratospheric (above-cloud) column, which is subtracted from the total column in clear-sky scenes in the same zonal band to retrieve the tropospheric column. The standard CCD (convective cloud differential) approach uses cloud data from the Pacific region (CPC – CHORA Pacific Cloud) instead. An important assumption for the standard method is the zonal invariance of stratospheric ozone. The local-cloud approach is the first step to diminish this constraint in order to extend the CCD method to mid-latitudes, where stratospheric-ozone variability is larger. An iterative approach has been developed for the automatic selection of an optimal local-cloud reference sector around each retrieval grid box varying latitudinally by ± 1° and longitudinally between ± 5 and ± 50°. The optimised CLCT (CHORA Local Cloud Theil–Sen) algorithm, a follow-up from the CLC, employs a homogeneity criterion for total ozone from the cloud reference sector in order to overcome the inhomogeneities in stratospheric ozone. It directly estimates the above-cloud column ozone for a common reference altitude of 270 hPa using the Theil–Sen regression. The latter allows for the combination of the CCD method with the cloud-slicing algorithm that retrieves upper-tropospheric ozone volume mixing ratios. Monthly averaged tropospheric-column ozone (TCO) using the Pacific cloud reference sector (CPC) and the local-cloud reference sector (CLC, CLCT) has been determined over the tropics and subtropics (26° S–22° N) using TROPOMI for the time period from 2018 to 2022. The accuracy of the various methods was investigated by means of comparisons with spatially collocated NASA/GSFC SHADOZ (Southern Hemisphere Additional Ozonesondes) measurements and the ESA TROPOMI level-2 tropospheric-ozone product. At eight out of nine tropical stations, tropospheric-ozone columns using the CLCT yield better agreement with ozonesondes than the CPC. In the tropical region (20° S–20° N), the CLCT shows a significantly lower overall mean bias and dispersion of 1 ± 7 %, outperforming both the CPC (12 ± 10 %) and CCD-ESA (22 ± 10 %). The CLCT surpasses the ESA operational product, providing more accurate tropospheric-ozone retrievals at eight out of nine stations in the tropics. For the Hilo station, with a larger stratospheric-ozone variability due to its proximity to the subtropics, the bias of +30 % (CPC) is effectively reduced to −5 % (CLCT). Similarly, in the subtropics (Reunion, Irene, Hanoi, and King's Park), the CLCT algorithm provides an overall bias and scatter of −11 ± 9 % with respect to sondes. The CLCT effectively reduces the impact of stratospheric-ozone inhomogeneity, typically at higher latitudes. These results demonstrate the advantage of the local-cloud reference sector in the subtropics. The algorithm is therefore an important basis for subsequent systematic applications in current and future missions of geostationary satellites, like GEMS (Geostationary Environment Monitoring Spectrometer, Korea), ESA Sentinel-4, and NASA TEMPO (Tropospheric Emissions: Monitoring of POllution), predominantly covering the middle latitudes.

Linking Vegetation Phenology to Net Ecosystem Productivity: Climate Change Impacts in the Northern Hemisphere Using Satellite Data

With global climate change, linking vegetation phenology with net ecosystem productivity (NEP) is crucial for assessing vegetation carbon storage capacity and predicting terrestrial ecosystem changes. However, there have been few studies investigating the relationship between vegetation phenology and NEP in the middle and high latitudes of the Northern Hemisphere. This study comprehensively analyzed vegetation phenological changes and their climate drivers using satellite data. It also investigated the spatial distribution and climate drivers of NEP and further analyzed the sensitivity of NEP to vegetation phenology. The results indicated that the average land surface phenology (LSP) was dominated by a monotonic trend in the study area. LSP derived from different satellite products and retrieval methods exhibited relatively consistent responses to climate. The average SOS and POS for different retrieval methods showed a higher negative correlation with nighttime temperatures compared to daytime temperatures. The average EOS exhibited a higher negative correlation with daytime temperatures than a positive correlation. The correlations between VPD and the average SOS, POS, and EOS showed that the proportion of negative correlations was higher than that of positive correlations. The average annual NEP ranged from 0 to 1000 gC·m−2. The cumulative trends of NEP were mainly monotonically increasing, accounting for 61.04%, followed by monotonically decreasing trends, which accounted for 17.95%. In high-latitude regions, the proportion of positive correlation between VPD and NEP was predominant, while the proportion of negative correlation was predominant in middle-latitude regions. The positive and negative correlations between soil moisture and NEP (48.08% vs. 51.92%) were basically consistent in the study area. The correlation between SOS and POS with NEP was predominantly negative. The correlation between EOS and NEP was overall characterized by a greater proportion of negative correlations than positive correlations. The correlation between LOS and NEP exhibited a positive relationship in most areas. The sensitivity of NEP to vegetation phenological parameters (SOS, POS, and EOS) was negative, while the sensitivity of NEP to LOS was positive (0.75 gC·m−2/d for EVI vs. 0.63 gC·m−2/d for LAI vs. 0.30 gC·m−2/d for SIF). This study provides new insights and a theoretical basis for exploring the relationship between vegetation phenology and NEP under global climate change.

Dominant spring precipitation anomaly modes and circulation characteristics in the Tarim Basin, Central Asia

Recently, extreme precipitation has occurred frequently in the Tarim Basin, which has a fragile ecological environment, arousing widespread concern. Using daily precipitation observations from 42 stations in the Tarim Basin during the spring of 1980–2021 and monthly circulation reanalysis data from the European Center for Medium-Range Weather Forecasts Reanalysis v5, as well as statistical analyses and physical diagnostic methods, this study investigated the abnormal modes and the evolution characteristics and differences in atmospheric circulation. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first (EOF1) is a precipitation pattern that is uniform throughout the region and the second (EOF2) is an east–west inverse pattern. Thus, there are distinct differences in the atmospheric circulation characteristics responsible for abnormal spring precipitation modes in the basin. When the precipitation across the entire basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation related circulation, and the 700 hPa wind field is controlled by abnormal southwesterly winds. Water vapor transport is mainly driven by anomalous water vapor uplift along the terrain in the middle latitudes west of the Atlantic Ocean and south of the Arabian Sea. This leaves the Tarim Basin with a net water vapor budget and abnormally high atmospheric precipitable water. The opposite situation occurs when the precipitation across the entire basin is consistently lower than normal. When there is a west-to-east precipitation gradient, The western region of the Tarim Basin is dominated by upward airflow, whereas the eastern region is dominated by downward airflow, providing dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, water vapor conditions favorable for precipitation can occur. The net water vapor in the basin also exhibited an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water demonstrated an inverse phase distribution under the EOF2 atmospheric precipitation mode in the Tarim Basin.

Sporadic E Layer Intensification in the Winter of 2009 Examined by FORMOSAT‐3/COSMIC RO Data and GAIA Model

AbstractThis study examines the role of winds in wintertime sporadic E layer intensification (WEsLI) in 2009 from a global viewpoint. Previous studies showed that sporadic E layer (EsL) intensity had increased for 20–30 days in some winters, although intense EsLs do not form generally in winter. A recent study found that vertical ion convergence (VIC) driven by intensified migrating semidiurnal (SW2) tides caused WEsLI at middle latitudes in 2009. However, no studies have investigated the global distributions and generation mechanisms of WEsLI in 2009. Herein, we employed FORMOSAT‐3/COSMIC radio occultations to investigate the global distributions of WEsLI in 2009. Distributions of VIC driven by winds obtained from the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy were compared with global WEsLI distributions to elucidate the role of winds in WEsLI. We found that WEsLI in 2009 occurred at geomagnetic low/middle latitudes except between W and E. WEsLI was observed below 120 km altitudes, especially at 12–17 local times. WEsLI was attributable to VIC driven by SW2 tides, migrating diurnal tides, and eastward propagating diurnal tides with wavenumber 3. Tidal amplifications were possibly related to mesospheric/stratospheric atmospheric variations such as sudden stratospheric warming, zonal mean zonal winds, and quasi‐biennial oscillations. WEsLI in 2009 is further evidence of the coupling between EsLs and mesospheric/stratospheric atmospheric variations through tidal modifications.

Eco-physiological approach to assessing the functional state of workers in geological prospecting expeditions during meridian movement between mid-latitudes and the Arctic region

BACKGROUND: The current challenge lies in defining the unique characteristics of compensatory and adaptive mechanisms formation, as well as the development of healthcare technologies for various forms of work in Arctic region conditions. AIM: To study associations between climate patterns and physiological responses to daily fluctuations in meteorological factors. Specifically, we aimed to investigate how these factors impact the cardiovascular system and psychophysiological well-being of workers during geological prospecting expeditions along the meridian travel between Tyumen (57° 09’ N) and Yamal (71° 11ʹ N). MATERIAL AND METHODS: A total of 115 men aged 20–40 years in mid-latitude conditions (baseline data) and during occupational relocation to the Arctic region comprised the sample. The examination included recording key indicators of the cardiovascular system (heart rate, blood pressure, mean arterial pressure, pulse pressure), ECG in standard unipolar and augmented leads, and psychophysiological assessments (evaluation of trait and state anxiety, stress diagnostics, regulation of self-control, and emotional lability). Additionally, to calculate the natural and climatic contrast of regions in Western Siberia, meteorological data and geomagnetic activity indicators were analyzed based on eight daily measurements over 12 months across 11 years using a unified system of meteorological station indicators in Tyumen and Kharasavey. RESULTS: The cardiovascular system experiences desynchronosis during meridian movement from middle latitudes to the Arctic region. This condition is influenced by the interregional climatic contrast and the differences in daily rhythm characteristics of meteorological data between the initial and final destinations. The interaction within the system of meteorological rhythms plays an important role in these variations. CONCLUSION: The established associations within the ‘meteorhythms–biorhythms’ system underscore the necessity for developing regional norms for chronophysiological parameters of a healthy individual under specific environmental and climatic conditions. It also highlights the importance of dynamic monitoring of deviations in these parameters during occupational relocations between mid-latitudes and the Arctic region across different seasons. This approach is essential for the effective monitoring of maladaptive disorders and for predicting the potential development of pathologies.

Long-term (2010–2021) lidar observations of stratospheric aerosols in Wuhan, China

Abstract. This study analyzes the vertical distribution, optical properties, radiative forcing, and several perturbation events of stratospheric aerosols using observations from a ground-based polarization lidar in Wuhan (30.5° N, 114.4° E) from 2010 to 2021. The background stratospheric aerosol optical depth (sAOD) was 0.0044 ± 0.0019 at 532 nm, as calculated during a stratosphere-quiescent period from January 2013 to August 2017. In addition, several cases of volcanic aerosol and wildfire-induced smoke were observed. Volcanic aerosols from the Nabro (2011) and Raikoke (2019) eruptions (both in boreal summer) increased the sAOD to 2.9 times the background level. Tracers of smoke from the Canadian wildfire in the summer of 2017 were observed twice, at 19–21 km on 14–17 September and at 20–23 km on 28–31 October, with a plume-isolated aerosol optical depth (AOD) of 0.002–0.010 and a particle linear depolarization ratio δp of 0.14–0.18, indicating the dominance of non-aged smoke particles. During these summertime events, the injected stratospheric aerosols were captured by the large-scale Asian monsoon anticyclone (AMA), confining the transport pathway to mid-latitude Asia. On 8–9 November 2020, smoke plumes originating from the California wildfire in October 2020 appeared at 16–17 km, with a mean δp of 0.13. Regarding seasonal variation, the sAOD in the cold half-year (0.0054) is 69 % larger than in the warm half-year (0.0032) due to stronger meridional transport of stratospheric aerosols from the tropics to middle latitudes. The stratospheric radiative forcing was −0.11 W m−2 during the stratosphere-quiescent period and increased to −0.31 W m−2 when volcanic aerosols were largely injected. These findings contribute to our understanding of the sources and transport patterns of stratospheric aerosols over mid-latitude Asia and serve as an important database for the validation of model outputs.

Storms and convection on Uranus and Neptune: Impact of methane abundance revealed by a 3D cloud-resolving model

Context. Uranus and Neptune have atmospheres dominated by molecular hydrogen and helium. In the upper troposphere (between 0.1 and 10 bar), methane is the third main molecule, and it condenses, yielding a vertical gradient in CH4 . As this condensable species is heavier than H2 and He, the resulting change in mean molecular weight due to condensation serves as a factor countering convection, which is traditionally considered as governed by temperature only. This change in mean molecular weight makes both dry and moist convection more difficult to start. As observations also show latitudinal variations in methane abundance, one can expect different vertical gradients from one latitude to another. Aims. In this paper, we investigate the impact of this vertical gradient of methane and the different shapes it can take, including on the atmospheric regimes and especially on the formation and inhibition of moist convective storms in the troposphere of ice giants. Methods. We developed a 3D cloud-resolving model to simulate convective processes at the required scale. This model is nonhydrostatic and includes the effect of the mean molecular weight variations associated with condensation. Results. Using our simulations, we conclude that typical velocities of dry convection in the deep atmosphere are rather low (on the order of 1 m/s) but sufficient to sustain upward methane transport and that moist convection at the methane condensation level is strongly inhibited. Previous studies derived an analytical criterion on the methane vapor amount above which moist convection should be inhibited in saturated environments. In ice giants, this criterion yields a critical methane abundance of 1.2% at 80 K (this corresponds approximately to the 1 bar level). We first validated this analytical criterion numerically. We then showed that this critical methane abundance governs the inhibition and formation of moist convective storms, and we conclude that the intensity and intermittency of these storms should depend on the methane abundance and saturation. In the regions where CH4 exceeds this critical abundance in the deep atmosphere (at the equator and the middle latitudes on Uranus and at all latitudes on Neptune), a stable layer almost entirely saturated with methane develops at the condensation level. In this layer, moist convection is inhibited, ensuring stability. Only weak moist convective events can occur above this layer, where methane abundance becomes lower than the critical value. The inhibition of moist convection prevents strong drying and maintains high relative humidity, which favors the frequency of these events. In the regions where CH4 remains below this critical abundance in the deep atmosphere (possibly at the poles on Uranus), there is no such layer. More powerful storms can form, but they are also a bit rarer. Conclusions. In ice giants, dry convection is weak, and moist convection is strongly inhibited. However, when enough methane is transported upward, through dry convection and turbulent diffusion, sporadic moist convective storms can form. These storms should be more frequent on Neptune than on Uranus because of Neptune’s internal heat flow and larger methane abundance. Our results can explain the observed sporadicity of clouds in ice giants and help guide future observations that can test the conclusions of this work.

Global integrated navigation position correction algorithm and virtual polar region technology based on normal vector

To achieve the inherent uniformity of all-earth navigation for autonomous underwater vehicles (AUV), a global integrated navigation position correction algorithm based on the normal vector (n-vector) is proposed. First, a four-element vector comprising the non-singular n-vector and height represents the carrier’s position in the Earth-centered Earth-fixed (ECEF) frame. The integrated navigation systems are designed with the strapdown inertial navigation system (SINS), Doppler velocity log (DVL), and other equipment. Secondly, the reverse navigation algorithm in the ECEF mechanization is derived, and the results of forward and reverse navigation are fused to correct the AUV’s underwater position. Additionally, a virtual polar region technology based on the ECEF attitude, velocity, and height invariant method (E-AVHIM) is proposed to convert the actual test data obtained at low and middle latitudes into high latitudes for more convincing polar region algorithm verification. Simulations and lake trial demonstrated the excellence and efficiency of the proposed algorithm.

Detection of lunar water, hydroxyl ion and their diurnal changes from CHACE-2 orbiter observation

This work reports the spatial and diurnal variations of the number densities of lunar molecular water (H2O), atomic mass unit (amu) 18 and hydroxyl (OH), amu 17 over low (0° to 30°), middle (31° to 60°) and high (61° to 80°) latitudinal regions of the lunar exosphere during the pre-sunrise, noon, sunset and midnight periods using the mass spectrometric data of CHandra's Atmospheric Composition Explorer-2 (CHACE-2) on board Chandrayaan-2, the second lunar mission developed in India. Both H2O and OH exhibit, particularly in the low latitude regions, a trend of increasing number density after the sunrise and up to noon, followed by a decrease till sunset. An overall higher density of H2O is obtained compared to the previous reports. The findings are justified in terms of the polar orbital height of the instrument and the duration of data procurement. The maximum number density for the low, middle and high latitudes reaches 5225 cm−3, 5135 cm−3 and 3747 cm−3, respectively. The corresponding OH abundances are found to be 5079 cm−3, 5565 cm−3 and 5720 cm−3. The diurnal variations of H2O and OH and their comparisons, similar to those of the present report may provide suitable means for tracing the lunar water cycle. The CHACE-2 observations imply that the influence of magnetotail passage on volatiles like water is to be further quantified in future missions with other sensors.

Latitudinal Characteristics of the Post‐Sunset Enhancements in Ionospheric Electron Density During the Geomagnetic Quiet Period in May 2021 Over East‐Asian Region

AbstractThis study investigated the latitudinal variations of post‐sunset enhancements in the ionospheric electron density during the geomagnetic quiet period in May 2021 with a combination of high‐precision ionospheric parameters obtained from four ionosondes, Beidou geostationary satellite (BD‐GEO) receiver network and Sanya incoherent scatter radar (SYISR). We identified four categories of post‐sunset enhancement phenomena (Types 1–4), each with unique spatial and temporal evolutions, yet uniformly accompanied by a decrease in hmF2. Measurements of plasma drift vector velocities from SYISR and hmF2 gradients across various latitudes provided pivotal insights, confirming that the ionospheric post‐sunset enhancements can result from downward plasma motion due to westward electric field, downward field‐aligned drift, or a combination of both. For Type 1, dominated by field‐aligned drift, plasma density enhancements not only intensify at low latitudes but may also extend to mid‐latitudes, exhibiting a distinct temporal delay with increasing latitude. In contrast, Type 4, primarily driven by the westward electric field, is characterized by modest increases in plasma density confined to localized low‐latitude regions, with no observable latitudinal time delay in the peak of enhancements. Types 2 and 3, which are subject to the combined influence of the westward electric field and field‐aligned drift, exhibit plasma density increases at certain low‐latitude areas, with Type 2 presenting a delayed pattern and Type 3 showing none with rising latitude. Meanwhile, neutral winds can partially account for the observed post‐sunset enhancement from low to middle latitudes. These findings offer new insights into the factors influencing ionospheric behavior after sunset.

10Be chronology of the Last Glacial Maximum and Termination in the Andes of central Chile: The record of the Universidad Glacier (34° S)

Reconstructing mid-latitude glacier variations is a prerequisite for unveiling the interhemispheric climate linkages and atmospheric-ocean forcings that triggered those changes during the last glacial cycle. Nonetheless, the timing, magnitude, and structure of glacier fluctuations in the southern mid-latitudes remain incomplete. Here, we present a new 10Be chronology of the Universidad Glacier in the Andes of central Chile (34° S, 70° W; ∼2500 m a.s.l.) based on 21 cosmogenic-exposure ages of boulders on discrete moraine ridges defining former ice margins. Our findings include the mapping and dating of three moraines, UNI I, UNI II, and UNI III, located ∼20 km, 15 km, and 10 km down-valley from the present-day glacier front, respectively. The 10Be exposure ages of the UNI I moraine range from 135.9 ± 7.1 to 51.4 ± 2.7 ka (n = 3). The UNI II moraine gave a mean age of 18.0 ± 0.9 (n = 15) and the UNI III moraine yielded a mean age of 13.9 ± 0.8 ka (n = 3). The UNI I moraine implies the largest ice extent during a pre-Last Glacial Maximum (pre-LGM) period, including the penultimate glaciation. The UNI II is a moraine complex that represents cold and humid conditions in central Chile at the end of the LGM, which we attribute to the northward-shift of the Southern Westerly Winds (SWW). The UNI III moraine represents a return to glacial conditions interrupting the Termination, evidencing both a double-step deglacial trend observed through the southern middle and high latitudes at the end of the last ice age. The Andes at this subtropical latitude record a global signal of glacial and climate change.

Nighttime ionospheric irregularity during intense geomagnetic storm events over the Europe-African longitudinal sector

Radio communication and navigation systems can be severely impacted by irregularities in the ionosphere. There is still much to learn about how geomagnetic storms affect the occurrence of these irregularities. Ionosphere studies in different regions, particularly the equatorial and low-latitudes, are necessary to enhance the forecasting of this phenomenon. This study investigates the effect of intense geomagnetic storm events of August 27, October 7 and December 22, 2015, on nighttime ionospheric irregularities. Data collected from the receivers of the Global Navigation Satellite Systems (GNSS) in specific longitudinal sector of 15∘W – 0∘, 0∘ – 15∘E, 15∘E – 30∘E and 30∘E – 45∘E, as well as from the Swarm constellations in the longitude range of 30∘W – 70∘E and the latitude range of 50∘S – 50∘N, have been used. The rate of change of the total electron content (TEC) index (ROTI) and the rate of change of the electron density index (RODI) were analyzed. In the main phases of the storms, at equatorial and low-latitude regions we observed ionospheric irregularities in the African longitudinal sectors of 15∘W – 0∘, 0∘ – 15∘E and 30∘E – 45∘E in the three storm events. The observed ionospheric irregularities were more pronounced in the western than eastern regions. These irregularities were possibly driven by the Prompt Penetration Electric Fields (PPEFs) that point east to west during nighttime. Ionospheric irregularities were inhibited in the selected storm periods over the middle latitudes in the African sector. In the longitudinal sector of 15∘E – 30∘E, we obtained inhibition of irregularity in the study periods. In the case of the top-side ionosphere, we observed enhanced and depleted electron density during the storm in the low latitude and equatorial regions. In the low latitude and equatorial regions, there were electron density fluctuations within the range of 15∘N and 15∘S, indicating significant top-side irregularities.

Relationship between interannual variability of the north edge of the East Asian summer monsoon and extreme precipitation in North China

The north edge of the East Asian summer monsoon (EASM) is defined by using the isoline with average total column water vapor (TCWV) equal to 25 mm, and the relationship between the north edge of the EASM and summer extreme precipitation in North China (NC) from 1961 to 2020 is discussed. Self-Organizing Maps (SOM) method is used to cluster extreme precipitation in the abnormal years of the north edge in NC, and the circulation characteristics of different types of extreme precipitation are discussed. The results show that the north edge of the EASM is closely related to extreme precipitation in NC. When the north edge is northerly, both the frequency and total amount of extreme precipitation increase significantly in the monsoon marginal zone. Based on different monsoon circulation background, summer extreme precipitation events in NC are divided into four categories, namely, the central type and southern type in the northerly years of north edge, and the central type and eastern type in the southerly years of north edge. The occurrence of different types of extreme precipitation is closely related to the different characteristics of local trough, the western Pacific subtropical high (WPSH), and wave trains in the middle and high latitudes. Specifically, the central type extreme precipitation is affected by the mid-latitude wave train in the northerly years of north edge. As for the central type extreme precipitation in the southerly years of north edge, both high-latitude and mid-latitude wave trains transfer from west to east and converge over NC. However, the wave disturbance energy is relatively weak, leading to the extreme precipitation with weak intensity.

Genetic diversity, population structure, and phylogenetic relationships of a widespread East Asia herb, Cryptotaenia japonica Hassk. (Apiaceae) based on genomic SNP data generated by dd-RAD sequencing.

Single-nucleotide polymorphisms (SNPs) represent the most prevalent form of genomic polymorphism and are extensively used in population genetics research. Using dd-RAD sequencing, a high-throughput sequencing method, we investigated the genome-level diversity, population structure, and phylogenetic relationships among three morphological forms of the widely distributed taxon Cryptotaenia japonica Hassk., which is native to East Asia. Our study aimed to assess the species status of C. japonica according to its genetic structure and genetic diversity patterns among 66 naturally distributed populations, comprising 26C. japonica f. japonica, 36C. japonica f. dissecta (Y. Yabe) Hara and 4C. japonica f. pinnatisecta S. L. Liou accessions. Based on genomic SNP data generated by dd-RAD sequencing, we conducted genetic diversity, principal component, neighbor-joining (NJ) phylogenetic, admixture clustering, and population differentiation analyses. The findings revealed the following: (1) 5,39,946 unlinked, high-quality SNPs, with mean π, H O, H E and F IS values of 0.062, 0.066, 0.043 and -0.014, respectively, were generated; (2) population divergence was unaffected by isolation through distance; (3) six main distinct regions corresponding to geographic locations and exhibiting various levels of genetic diversity were identified; (4) pairwise F ST analysis showed significant (P < 0.05) population differentiation in 0%-14% of populations among the six regions after sequential Bonferroni correction; and (5) three migration events (historical gene flow) indicated east‒west directionality. Moreover, contemporary gene flow analysis using Jost's D, Nei's G ST, and Nm values highlighted the middle latitude area of East Asia as a significant contributor to genetic structuring in C. japonica. Overall, our study elucidates the relatively low genetic differentiation and population structure of C. japonica across East Asia, further enhancing our understanding of plant lineage diversification in the Sino-Japanese Floristic Region.

Diurnal Variation in Summer Precipitation and the Characteristics of Precipitation Events in the Western Tarim Basin, China

The Tarim Basin in the western part of Northwest China (NWC) is the largest inland basin in the world and one of the most arid regions in the middle latitudes. In recent years, heavy precipitation events have occurred frequently in this region, especially in the western Tarim Basin (WTB), due to the climate change. Based on the hourly precipitation data from 2010 to 2022, the diurnal variation in summer precipitation and the characteristics of precipitation events with different durations in WTB have been analyzed. The results mainly show that (1) the diurnal variations in the precipitation amount (PA), precipitation frequency (PF) and precipitation intensity (PI) mainly present a unimodal pattern, but the times of maximum value do not coincide. The peak value of PA and PF appears between 01:00 and 03:00 BJT (Beijing Time), while the valley value appears around 18:00 BJT, yet the peak value of PI appears between 20:00 and 23:00 BJT with no obvious valley value. (2) There are some differences in the diurnal variation characteristics of precipitation among different summer months and different regions. (3) During the past decade, the precipitation structure in WTB has been continuously adjusted, and short-duration- and long-duration-precipitation-dominant periods appear alternately. On the whole, short-duration precipitation has been more frequent in summer, accounting for 70% of the total precipitation events and 40% of the total accumulated precipitation amount. These results can help us to better understand the refined physical characteristics of precipitation events and enhance our understanding of the local climate in the WTB under the background of climate change.

Patterns and Trends in Northern Hemisphere River Ice Phenology from 2000 to 2021

River ice plays a crucial role in hydrology, ecosystems, and socio-economic systems in mid-to-high latitude regions. However, there is a notable gap in the analysis of patterns and trends in river ice phenologies and their influence factors at the river level. In this study, we developed a practical method to identify river ice phenologies by leveraging Landsat observations from 2000 to 2021, and established a comprehensive dataset encompassing 7970 river segments across the entire Northern Hemisphere. Our results revealed that the mean freeze-up date, break-up date, and ice duration for these river segments were October 24, May 4, and 192.1 days, respectively. Notably, 56% of the river segments exhibited a warming trend, with the average freeze-up date delayed by 2.7 days per decade, break-up date advanced by 2.5 days per decade, and ice duration shortened by 5.5 days per decade—nearly five times the documented decrease rate over the past 150 years. Furthermore, high-latitude polar regions and the Qinghai-Tibet Plateau demonstrated the most pronounced decreases in ice duration, exceeding 7.0 days per decade on average. We observed a substantial relative contribution, reaching up to 70%, of surface air temperature (SAT) in middle and low latitude regions characterized by relatively high winter temperatures. However, as winter temperatures decrease, the relative influence of SAT diminishes, while the contributions of precipitation, solar radiation, and residuals increase. Our dataset provided essential baseline for further understanding the fundamental physical processes within river systems, offering crucial insights for river management, hydrological disaster risk control, climate change research, and ecosystem conservation efforts.

Transition of the Sun to a Regime of High Activity: Implications for the Earth Climate and Role of Atmospheric Chemistry

AbstractIt was recently suggested that the Sun could switch to a high‐activity regime which would lead to a rise of ultraviolet radiation with an amplitude of about four times larger than the amplitude of an average solar activity cycle and a simultaneous drop in total solar irradiance. Here, we applied the SOCOLv3‐MPIOM model with an interacting ocean to simulate the response of chemistry, dynamics, and temperature of Earth's atmosphere to such a change in solar irradiance. We studied the effect of high activity regime on the atmosphere investigating the influence of the chemical and radiative processes on the climate, and chemistry of NOx, HOx, and O3. We find a climate cooling by up to 1K and a substantial increase in stratospheric ozone (up to 14%) and total ozone (up to 8%). To understand the role of the different processes we performed simulations with two sets of forcing accounting separately for the influence on chemical processes and for direct radiation energy balance. Our calculations show that the stratospheric O3 response is almost fully driven by the chemical processes. We also found that the direct radiation processes lead to near‐surface cooling that results in the suppression of the Brewer‐Dobson circulation. This, in turn, leads to the reduction of H2O influx from the low layers of the troposphere and to less intensive transport of ozone from the tropics to the middle latitudes. The surface climate response is dominated by direct radiation influence with only a small contribution from chemical processes.

Observations and Model of Subauroral Sporadic E Layer Irregularities Driven by Turning Shears and Dynamic Instability

AbstractObservations of coherent scatter from patchy sporadic E layers in the subauroral zone made with a 30‐MHz coherent scatter radar imager are presented. The quasiperiodic (QP) echoes are similar to what has been observed at middle latitudes but with some differences. The echoes arise from bands of scatterers aligned mainly northwest to southeast and propagating to the southwest. A notable difference from observations at middle latitudes is the appearance of secondary irregularities or braids oriented obliquely to the primary bands and propagating mainly northward along them. We present a spectral simulation of the patchy layers that describes neutral atmospheric dynamics with the incompressible Navier Stokes equations and plasma dynamics with an extended MHD model. The simulation is initialized with turning shears in the form of an Ekman spiral. Ekman‐type instability deforms the sporadic E layer through compressible and incompressible motion. The layer ultimately exhibits both the QP bands and the braids, consequences mainly of primary and secondary neutral dynamic instability. Vorticity due to dynamic instability is an important source of structuring in the sporadic E layer.

Horizontal Scales of Small‐ and Meso‐Scale Field‐Aligned Current Structures at Middle and Low Latitudes

AbstractBy utilizing the close orbital separation between Swarm A and C during the Counter Rotation Orbit phase, we check the agreement and stationarity between the FAC‐associated magnetic signatures at the two spacecraft through cross‐correlation analysis. When the agreement and stationarity are passed, the magnetic signature is considered suitable for small and meso‐scale Field‐aligned currents (FAC) estimates with dual‐spacecraft technique. It is found that at low and middle latitudes the dayside wave structure with apparent periods of about 10–60s can be observed around 90% of the time during all seasons. From those 90% can be identified as quasi‐static current structures. On the nightside, the shorter period signatures dominate the apparent period spectrum. At about 30% of the time structures with 1–7s periods are observed. For the longer period signals the proportion is reduced greatly. About 80% of these signatures with periods longer than 3s are identified as quasi‐static current structures. By taking advantage of the constantly changing longitudinal orbit separation during the considered time intervals, we can determine the mean separation at which the correlation breaks down. This provides FAC scale sizes in east‐west direction separately for FACs of various latitudinal wavelengths. The result shows that typical east‐west scale sizes of FAC structures with latitudinal wavelength of 10–400 km range from 10 to 60 km, respectively. FAC‐related structures on the nightside have been associated with medium‐scale traveling ionospheric disturbances and structures on the dayside primarily with FACs driven by atmospheric gravity waves.