Middle Latitudes Research Articles

Accuracy Evaluation of Ocean Wave Spectra from Sentinel-1 SAR Based on Buoy Observations and ERA5 Data

Doppler mis-registrations in azimuth can lead to ocean waves shorter than a specific wavelength being undetectable by SAR. In order to evaluate the actual ocean wave observation ability, the accuracy of Sentinel-1 SAR ocean wave spectra from January 2016 to December 2021 is evaluated by comparisons to NDBC buoys, ERA5 wave height, and CMEMS buoys. The results compared with NDBC show that the spectral shape of Sentinel-1 SAR ocean wave spectra is accurate, while the spectral values need to be improved. The wave spectra of Sentinel-1 have the best observations in season autumn. The comparison results of total wave height show the RMSE and bias are 0.91 m and −0.52 m for the comparisons to NDBC buoy wave spectra data, 0.93 m and −0.68 m for the comparison to ERA5 wave height data, and 0.9 m and −0.35 m for the comparisons to CMEMS buoy data. The comparison results of wave height in different wind speeds and areas shows that the accuracy of Sentinel-1 wave mode data is relatively good in the open ocean located in middle and low latitude area under the medium wind speed, while those are relatively poor in high latitude areas or the areas with excessively high or low wind speed.

Global characteristics of cloud macro-physical properties from active satellite remote sensing

Based on the products of joint CloudSat and CALIPSO observations from 2006 to 2017, this study investigates the global cloud macro-physical characteristics, including the spatial differences in cloud height, cloud thickness, cloud type, and cloud phase, along with the spatial-temporal variations and the land-sea discrepancy of the cloud vertical structure variables according to the study areas. The results show that the cloud frequency is higher over oceans than over land globally, but the opposite is true for cloud systems with more than two layers. Seasonal variability of global-average total cloud fraction is small, but large among different latitudinal bands. The global spatial distributions of cloud top height (CTH) and cloud base height (CBH) are similar, showing larger cloud heights over the land than over the ocean. The low clouds are mostly located in the central subtropical region, with CTH among 2.5–7.5 km, While the high clouds are mainly distributed in the equatorial region with CTH about 10–15 km. Meanwhile, the regional and seasonal variability of cloud geometric thickness (CGT) in all study areas are small, and the average thickness of higher clouds is slightly larger than that of lower clouds. By categorizing the clouds into eight types, it was found that the frequency of cirrus (Ci) and stratocumulus (Sc) is higher, followed by altocumulus (Ac), altostratus (As), nimbostratus (Ns) and cumulus (Cu), and the frequency of stratus (St) and deep convective clouds (DC) is the lowest. In addition, the occurrence frequency of clouds in phases was ranked from high to low as ice clouds, liquid clouds and mixed-phase clouds. Ice clouds are concentrated in the tropics and mid-latitudes, and located almost symmetrically around the equator during Mar-Apr-May (MAM) and Sep-Oct-Nov (SON). Liquid clouds are mainly distributed around 30°S and 30°N with large seasonal variability, and their frequency is higher over the ocean than over the land. Mixed-phase clouds are concentrated in the middle and high latitudes, with much less occurring in the equatorial regions.

Calibration of Swarm Ion Density, Drift, and Effective Mass Measurements

AbstractWe calibrate the Swarm Langmuir Probe Ion Drift, Density and Effective Mass (SLIDEM) products using the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC‐1) electron density measurements. SLIDEM combines electric current measurements from the Electric Field Instrument faceplate (situated on the ram‐facing side of the satellite) with ion admittance measurements from a spherical Langmuir probe to estimate ionospheric ion density, bulk ion drift parallel to the satellite trajectory in the polar regions, and effective ion mass at low and middle latitudes. SLIDEM processing includes an eight‐parameter empirical geometry model that expresses the corrections to the effective faceplate area and spherical probe radius arising from satellite‐plasma interactions. Validation of SLIDEM density by conjunctions with COSMIC density altitude profiles reveals systematic errors, with SLIDEM underestimating corresponding COSMIC data by around 10%. Using the same conjunctions to calibrate the SLIDEM density processor, a simple one‐parameter geometry model is obtained, which significantly reduces bias in ion density. This leads to reduced bias in the ion ram speed and in the effective mass, both of which are more consistent with empirical ionospheric models. We examined three models characterizing the variation of probe effective electrode current collection areas. Faceplate geometries are statistically indistinguishable from the physical faceplate cross section. Spherical Langmuir probe radius is effectively reduced by about 10% due to satellite‐plasma interactions. We recommend updating the SLIDEM processor to use a smaller value for the spherical probe's radius.

Geomagnetic Disturbances Due To Neutral‐Wind‐Driven Ionospheric Currents

AbstractPrevious simulation efforts on geomagnetic disturbances (GMDs) and geomagnetically induced currents (GICs) mostly rely on global magnetohydrodynamics models, which explicitly calculate the magnetospheric currents and carry certain assumptions about the ionosphere currents. Therefore, the role of ionospheric and thermospheric processes to GMDs has not been fully evaluated. In this study, Global Ionosphere Thermosphere Model simulations for an idealized storm event have been conducted. Simply, the high‐latitude electrodynamic forcing (potential pattern and particle precipitation) has been specified by empirical models. GMDs due to neutral‐wind driven currents have been compared to those caused by magnetospheric convection driven currents during both the main and recovery phases. At locations where the high‐latitude electric potential is dominant, neutral‐wind driven currents are found to contribute to about 10%–30% of the total GMDs. During the recovery phase when the ion‐convection pattern retreats to high latitudes, neutral‐wind driven currents become the primary sources for GMDs at middle latitudes on the dayside due to the “flywheel” effect and the large dayside conductance. Our result strongly suggests that ionospheric and thermospheric processes should not be neglected when estimating GMDs and therefore GICs.

Climatic interactions between cold surges in the South China Sea and North Pacific extratropical cyclones

AbstractCold surge events in the South China Sea (over 110–117.5° E longitude at 15° N latitude) from 1979 to 2019 are divided into four types depending on their correlation with North Pacific extratropical cyclones (ECs). Climatologic relationships between the two phenomena reveal that 92% (39%) of all cold surges are accompanied by ECs (explosive extratropical cyclones, abbreviated as EC‐E), while 31% of ECs are accompanied by cold surges. The occurrence and development of ECs favour eruptions of cold air from higher latitudes, which in turn produce conditions conducive to cold surges. In the North Pacific, ECs travel in a northeastward direction, ultimately contributing to the Aleutian low. Meanwhile, the westerly jet is observed to strengthen following cold surge events. Both actions drive further EC activity, which in turn facilitates subsequent cold surges. Therefore, when ECs occur before and after cold surges, the cold surge event itself tends to be relatively strong and long lived. The transmission of energy by ECs is a primary link between the high and middle latitudes and contributes to the impact of cold surges on low latitudes. This study also explores the respective influences of the Siberia High and Aleutian Low on cold surges. The majority of cold surges that do not involve ECs occur in the context of the weaker Siberia High and Aleutian Low. Cold surges accompanied with ECs can be even stronger and longer lasting when the Siberia High and Aleutian Low strengthen.

Latitude Variation of the Post‐Sunset Plasma Density Enhancement During the Minor Geomagnetic Storm on 27 May 2021

AbstractIn this study, multiple instrumental observations including Global Navigation Satellite System total electron content (TEC), plasma drift velocity measured by Sanya (18.3°N, 109.6°E, dip latitude 12.6°N) Incoherent Scatter Radar (SYISR) and F2‐layer peak electron density (NmF2) and peak height (hmF2) from ionosonde and SYISR have been used to investigate ionospheric responses during a minor yet highly geo‐effective geomagnetic storm on 26–27 May 2021. Our findings revealed a significant time delay in the post‐sunset plasma density enhancement peak across different latitudes over East Asia, that is, the lower the geographic latitude, the earlier the peak appeared. The plasma density enhancement was accompanied by a decrease in hmF2 prior to NmF2 peak around sunset. The newly built SYISR measurements around sunset verified that the field‐aligned drift decreased the ionosphere with a notable time delay at latitude, beneficial to electron density enhancements at lower altitudes within the 16–30°N latitudinal band but a small TEC change. While at 30–50°N, it is possible that the competition between storm‐induced equatorward winds and downward field‐aligned drift depressed hmF2 decline and the buildup increased both NmF2 and TEC. The ICON observations suggested that the meridional wind during this minor storm event modulated the direction of plasma transport near sunset, playing a dominant role in post‐sunset plasma density enhancement from low to middle latitudes. These results provide fresh insight into the electrodynamic mechanisms of post‐sunset enhancements at middle and low latitudes over East Asia, and also enhance our understanding of the intricate behaviors within the ionosphere‐thermosphere system in response to a minor storm.

Interaction between the Westerlies and Asian Monsoons in the Middle Latitudes of China: Review and Prospect

The westerly circulation and the monsoon circulation are the two major atmospheric circulation systems affecting the middle latitudes of the Northern Hemisphere (NH), which have significant impacts on climate and environmental changes in the middle latitudes. However, until now, people’s understanding of the long-term paleoenvironmental changes in the westerly- and monsoon-controlled areas in China’s middle latitudes is not uniform, and the phase relationship between the two at different time scales is also controversial, especially the exception to the “dry gets drier, wet gets wetter” paradigm in global warming between the two. Based on the existing literature data published, integrated paleoenvironmental records, and comprehensive simulation results in recent years, this study systematically reviews the climate and environmental changes in the two major circulation regions in the mid-latitudes of China since the Middle Pleistocene, with a focus on exploring the phase relationship between the two systems at different time scales and its influencing mechanism. Through the reanalysis and comparative analysis of the existing data, we conclude that the interaction and relationship between the two circulation systems are relatively strong and close during the warm periods, but relatively weak during the cold periods. From the perspective of orbital, suborbital, and millennium time scales, the phase relationship between the westerly and Asian summer monsoon (ASM) circulations shows roughly in-phase, out-of-phase, and anti-phase transitions, respectively. There are significant differences between the impacts of the westerly and ASM circulations on the middle-latitude regions of northwest China, the Qinghai–Tibet Plateau, and eastern China. However, under the combined influence of varied environmental factors such as BHLSR (boreal high-latitude solar radiation), SST (sea surface temperature), AMOC (north Atlantic meridional overturning circulation), NHI (Northern Hemisphere ice volume), NAO (North Atlantic Oscillation), ITCZ (intertropical convergence zone), WPSH (western Pacific subtropical high), TIOA (tropical Indian Ocean anomaly), ENSO (El Niño/Southern Oscillation), CGT/SRP (global teleconnection/Silk Road pattern), etc., there is a complex and close coupling relationship between the two, and it is necessary to comprehensively consider their “multi-factor’s joint-action” mechanism and impact, while, in general, the dynamic mechanisms driving the changes of the westerly and ASM circulations are not the same at different time scales, such as orbital, suborbital, centennial to millennium, and decadal to interannual, which also leads to the formation of different types of phase relationships between the two at different time scales. Future studies need to focus on the impact of this “multi-factor linkage mechanism” and “multi-phase relationship” in distinguishing the interaction between the westerly and ASM circulation systems in terms of orbital, suborbital, millennium, and sub-millennium time scales.

Solar Spectrum Reflectometer Measurements on Profiled and Small Samples: Design and Testing of Adapters

AbstractTesting solar reflective building materials is mainly performed in laboratories using Solar Spectrum Reflectometer (SSR) or spectrophotometry. To obtain aged materials values, after exposing materials in test farms for natural ageing or applying ASTM-D7897, treated samples shall be tested again using SSR. On-site measurements of new and aged surfaces is allowed using pyranometers or albedometers, which present issues caused both by high-pitched roof and by solar and sky requirements in several locations such as at southern and middle Europe latitudes, where clay tiles are a typical coverage of roof surfaces. The use of battery-powered SSR offsite could be a solution to obtain reliable measurements in every climate, lighting, and slope condition. However, the shape of roof surfaces remains an issue since most of the tiles are characterized by elaborated morphologies that cannot fit the measurement head of the SSR. In this study, two sets of cylindrical adapters for SSR, made via Fused Deposition Modeling and coated with solar reflective white diffuse paint or specular reflective coating were produced and tested to overcome this problem. The adapters were attached to the top of the measurement head and measurements were performed according to ASTM-C1549. These adapters were tested with samples characterized by ASTM-C1549, analyzing the output from all 6 detectors of SSR, and by spectrophotometry according to ASTM-E903, using both AM1GH and ASTM E891-87 irradiance spectra. Aluminum-coated adapters proved ideal due to non-impact on measurements. Solar reflectance showed strong linear correlation for 30–50 mm adapter lengths, indicating minimal signal damping. They will allow testing most of the samples that cannot be tested with standard methods, especially aged ones, without altering their surface.

Characteristic analysis of the differences between total electron content (TEC) values in global ionosphere map (GIM) grids

Abstract. Using total electron content (TEC) from a global ionosphere map (GIM) for ionospheric delay correction is a common method of eliminating ionospheric errors in satellite navigation and positioning. On this basis, the TEC of a puncture point can be obtained by GIM grid TEC interpolation. However, in terms of grid, only few studies have analyzed the TEC value size characteristics of its four grid points, that is, the TEC difference characteristics among them. In view of this, by utilizing the GIM data from high solar-activity years (2014) and low solar-activity years (2021) provided by CODE (Center for Orbit Determination in Europe), this paper proposes the grid TEC difference as a way of analyzing TEC variation characteristics within the grid, which is conducive to exploring and analyzing the variation characteristics of the ionosphere TEC in the single-station area. The value is larger in high solar-activity years and generally small in low solar-activity years, and the value of high-latitude areas is always smaller than that of low-latitude areas. Specifically, in high solar-activity years, most of the GIM grid TEC internal differences are within 4 TECu (1 TECu = 1016 electrons m−2) in high-latitude and midlatitude regions, while only 78.17 % are in low-latitude regions. In low solar-activity years, the TEC difference values within a GIM grid are mostly less than 2 TECu, and most of them in the high and middle latitudes are within 1 TECu. The main finding of this analysis is that the grid TEC differences are small for most GIM grids, especially in the midlatitudes to high latitudes of low solar years. This means that relevant extraction methods and processes can be simplified when TEC within these GIM grids is needed.

Impact Analysis of H2O Fluxes and High-Frequency Meteorology–Water Quality: Multivariate Constrained Evaporation Modelling in Lake Wuliangsuhai, China

It is imperative to elucidate the process of evaporation in lakes, particularly those that are freshwater and are situated in middle and high latitudes. Based on one-year evaporation and high-frequency meteorological–water quality data of Lake Wuliangsuhai, this study analyzed the applicability and driving mechanism of the evaporation model. These dynamics are elucidated by the vorticity covariance method combined with the multivariate constrained evaporation Modelling method. The findings of this study revealed that (1) Lake evaporation (ET) is affected by multiple meteorological–water quality constraints, and the water quality indicators significantly related to ET are also affected by lake stratification. The coupled meteorological–water quality evaporation model can explain 93% of the evaporation change, which is 20% higher than the traditional meteorological Modelling evaporation model. (2) The nighttime ET is mainly affected by the thermal inertia lag, and the nighttime ET loss in Lake Wuliangsuhai accounts for 37.34% of the total evaporation, which cannot be ignored. (3) The actual water surface evaporation of the lake is much smaller than that measured by the pan conversion method and the regional empirical C formula method. The cumulative evaporation of Lake Wuliangsuhai from the non-freezing period to the early glacial period converted from meteorological station data is 1333.5 mm. The total evaporation in the non-freezing period is 2.77~3.68 × 108 m3, calculated by the lake area of 325 km2, while the evaporation calculated by the eddy station is 1.91 × 108 m3. In addition, the ET value measured by the cumulative C formula method was 424.2% higher than that of the model method and exceeded the storage capacity. Low-frequency and limited environmental index observations may lead to an overestimation of the real lake evaporation. Therefore, in situ, high-frequency meteorological–water quality monitoring and the eddy method deserve more consideration in future research on lake evaporation.

Connection of Summer Surface Temperature Anomalies between the East European Plain–West Siberian Plain and North America on the Interannual Time Scale

Abstract This study identifies a significantly positive relationship between summer surface air temperature (SAT) anomalies over two remote regions in the Eurasian continent and North America during the period 1979–2021 on the interannual time scale. The former region includes the East European Plain and the West Siberian Plain, and the latter region includes central and eastern North America. The regionally averaged summer SAT anomalies show a correlation coefficient of 0.66 between these two regions, which is significant at the 99% confidence level. This intercontinental SAT relationship can be explained by a wavelike pattern of circulation anomalies, which is the leading mode of upper-tropospheric circulation anomalies over the middle and high latitudes of the Northern Hemisphere in summer. Further analysis suggests that the sea surface temperature (SST) anomalies over the Pacific and North Atlantic in the preceding spring, being coupled with the leading mode of atmospheric circulation anomalies over the Pacific–Atlantic sector, persist into summer and affect the SATs in the two remote regions, resulting in the intercontinental SAT connection. Significance Statement Summer surface air temperature (SAT) has profound effects on public health and agricultural production. Here we find a significantly positive relationship between interannual variations of summer SATs over two remote regions, one in the Eurasian continent and the other in North America. This intercontinental relationship in SATs can be explained as a result of atmosphere–ocean coupling over the Pacific and North Atlantic in the preceding spring. The result is likely to be a critical implication for the seasonal forecast of SAT variations over the two regions. In addition, the concurrence of higher or lower temperatures in these two regions may have impacts on global grain production, since these two regions include many major grain-producing areas in the world.

Localized Plasma Density Peak at Middle Latitudes During the April 2023 Geomagnetic Storm

AbstractThis paper conducts a multi‐instrument analysis of a latitudinal plasma density peak at the middle latitudes during the early recovery phase of the April 2023 geomagnetic storm. The total electron content (TEC), peak density of the F layer, and the in situ plasma density from Swarm and Defense Meteorological Satellite Program (DMSP) satellites all capture this peak feature. This narrow latitudinal peak structure appeared around 50°N and extended from 40°E to 150°E in longitude with a prolonged duration of about 8 hr from sunset to midnight. This mid‐latitude peak reveals a noticeable equatorward motion and a slight westward shift. According to the plasma composition observations from DMSP satellites, this peak structure shows an O+ ions dominance, which means that this peak is more likely to be formed by an internal rather than an external source from the plasmasphere. Meanwhile, the middle latitude Fabry–Perot interferometer (FPI) observed strong equatorward thermospheric winds, and the peak height of the F layer presented a visible elevation, which suggests that the equatorward wind lifting caused the plasma density enhancement. Besides, the O/N2 ratio significantly decreased at lower and middle latitudes, and ion drift observations showed a distinct subauroral westward channel. Based on these simultaneous measurements, this structure's sharp equatorward and poleward boundaries might be related to the O/N2 ratio change and the subauroral polarization stream (SAPS) flow separately.

Seasonal and Interannual Variations of Global Tides in the Mesosphere and Lower Thermosphere Neutral Winds: II. Semidiurnal and Terdiurnal Tides

AbstractIn the mesosphere and lower thermosphere (MLT) region, semidiurnal and terdiurnal tides are dominant at middle and high latitudes and are important for the dynamics and structures. Using the global neutral horizontal wind data in the MLT region observed by TIMED Doppler interferometer from 2002 to 2021, the seasonal and interannual variations of six semidiurnal and terdiurnal tidal components (SW2, SW3, SW4, TW3, TW2 and TW4) are investigated. Particularly, the responses of these tidal components to the stratospheric quasi‐biennial oscillation (SQBO) and the solar cycle are presented. The results indicate that: (a) seasonal and interannual variations of these tidal components are pronounced in their peak regions. The peak region is defined as the region where the ratio of the annual mean amplitude to the maximum annual mean amplitude is larger than 0.8. (b) In their peak regions, migrating tidal components exhibit strong seasonal variations at annual (annual oscillations (AO)), semiannual (semiannual oscillations (SAO)) and terannual (terannual oscillations (TAO)) periods, whereas nonmigrating tidal components only exhibit prominent AO and SAO. (c) In their peak regions, the responses of the annual mean amplitudes of these tidal components to SQBO are negative; the responses of migrating tidal components to solar cycle are negative whereas those of nonmigrating tidal components are positive. (d) For these tidal components, the responses of the amplitudes of seasonal variations to SQBO and solar cycle are weaker than their annual mean amplitudes, and the latitude × altitude response patterns are not always consistent with those of the annual mean amplitudes.

Relativistic Electron Precipitation Driven by Mesoscale Transients, Inferred From Ground and Multi‐Spacecraft Platforms

AbstractPrecipitation of relativistic electrons into the Earth's atmosphere regulates the outer radiation belt fluxes and contributes to magnetosphere‐atmosphere coupling. One of the main drivers of such precipitation is electron scattering by whistler‐mode waves. Such waves typically originate at the equator, where they can resonate with and scatter sub‐relativistic (tens to a few hundred keV) electrons. However, they can occasionally propagate far away from the equator along field lines, reaching middle latitudes, where they can resonate with and scatter relativistic (>500 keV) electrons. Such a propagation is typical for the dayside, but statistically has not been found on the nightside where the waves are quickly damped along their propagation due to Landau damping. Here we explore two events of relativistic electron precipitation from low‐altitude observations on the nightside. Combining measurements of whistler‐mode waves from ground observatories, relativistic electron precipitation from low‐altitude satellites, total electron content maps from GPS receivers, and magnetic field and electron flux from equatorial satellites, we show wave ducting by plasma density gradients is the possible channel that allows the waves to reach middle latitudes and scatter relativistic electrons. We suggest that both whistler‐mode wave generation and ducting can be driven by equatorial mesoscale (with spatial scales of about one Earth radius) transient structures during nightside injections. We also compare these nightside events with observations of ducted waves and relativistic electron precipitation at the dayside, where wave generation and ducting are driven by ultra‐low‐frequency waves. This study demonstrates the potential importance of mesoscale transients in relativistic electron precipitation, but does not however unequivocally establish that ducted whistler‐mode waves are the primary cause of the observed electron precipitation.

Time Variability Correction of CMIP6 Climate Change Projections

AbstractAccurate projections of climate change and associated extreme events under differing emission scenarios are linked to realistic representations of the temporal variability of the atmosphere at a variety of time scales, for example, annual, seasonal, synoptic, and daily. Here a new method is employed to explicitly quantify a model's ability to accurately represent covariance at and between differing time scales. From our global‐scale analysis, on average, raw Coupled Model Intercomparison Project Phase 6 (CMIP6) models misrepresent temporal variances at differing time scales for maximum temperature (tasmax) by a considerable margin, particularly at 183‐, 92‐ and 46‐day time scales. To ameliorate such variability errors, we propose a novel Time Variability Correction (TVC) method that corrects temporal covariances while preserving the essential time‐event sequence of the model simulations. We adopt a model‐as‐truth framework to evaluate the effectiveness of the TVC method under future forcing conditions when applied to daily tasmax simulations from 23 CMIP6 models for 1% of the global grid cells. TVC‐corrected temperatures generally show improved matching of temporal variance and lag correlations in the out‐of‐sample projection period compared to simple mean‐corrected projections. By imparting more realistic temporal‐correlations to model series, TVC is expected to improve the projections of extreme events associated with persistent heat, such as heatwaves. Applying TVC to future temperature projections using actual observations significantly increases the temperature variance in most middle to high latitude land regions in the Northern Hemisphere, while decreasing it in most low to middle latitude land regions, compared to simple mean‐corrected projections.

Analysis of Sprite Activity in Middle Latitudes

Sprite activity in the middle latitudes of the Northern Hemisphere is analyzed, with the example of the territory of Russia, aiming to facilitate the planning of observational campaigns in the region. The global model previously proposed by the authors is applied, using data from the WWLLN lightning detection network for 2015–2021. It is shown that the total number of sprites per year varies widely, from 394 in 2019 to 2354 in 2015. The most intense sprite activity almost always occurs in July, but in some years, there may be a shift to June (2015) and August (2021). The highest frequency of sprite initiation is observed in the Krasnodar Territory, Altai, and the Far East. Altai shows a high intensity of sprite activity every year, which is caused by the relief and underlying surface, while Krasnodar Territory and the Far East demonstrate sprites developed by incoming convective systems, which leads to high year-to-year variability.

Springtime Southern Hemisphere Quasi‐Stationary Planetary Wave Activities Associated With ENSO/IOD

AbstractThe tropical climate variabilities, such as Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO), are accompanied by changes in the tropical deep convection which can influence the atmospheric circulation in the Southern Hemisphere (SH). To investigate each role of IOD and ENSO in the September‐November (SON) circulation, we examine teleconnection patterns associated with IOD and ENSO events using the ERA5 monthly averaged data from 1979 to 2020. Our approach is to calculate the power spectral density (PSD) of the sea level pressure (SLP) and meridional wind and geopotential height at 300 hPa that are decomposed by zonal wave numbers (ZWNs), and to compute their correlations with IOD and ENSO at each latitudinal band. The main results are that IOD (ENSO) is negatively (positively) correlated with PSDs of ZWN2 and ZWN3 (ZWN1) at 300 hPa in the SH middle latitudes. Considering the Rossby wave train, IOD (ENSO) considerably affects the variability of the ZWN3 (ZWN1) pattern, which influences the meridional exchange of momentum. Additionally, the relationship between IOD and ZWN3 has become tighter in recent years, which is not seen in that with ENSO. The IOD and ENSO events also modify the SLP patterns and meridional surface winds, modulating the sea ice extent in the Southern Ocean. During the highly positive 2019 IOD event, the variability of the middle latitudes atmospheric circulation was considerably larger than climatology, suggesting a higher chance of more extreme weather patterns associated with more frequent intense IOD events in the warming climate.

Triggers of present-day rockfalls in the zone of sporadic permafrost in non-glaciated mountain region: the case study of Turnia Kurczaba (the Tatra Mts., Poland)

In recent decades there has been growing evidence of the impact of ongoing climate warming on the frequency of rockfalls. However, these are not adequately documented, especially in non-glaciated, high mountain regions of middle latitude. This study comprehensively documents the Turnia Kurczaba rockfall, one of the most significant rockfalls recorded in recent decades in the Tatra Mountains. The precise projections of the volumes and distribution of rock losses and deposits, the determination of the trajectories, modes and speeds of movement of rock material, as well as information on the geological, morphological, and meteorological conditions behind the Turnia Kurczaba rockfall form a unique dataset. The data documents a spectacular episode in the contemporary development of a complex slope system in the Tatras in an all-encompassing way and can be used to validate and calibrate existing models and improve numerical simulations of other rockfalls, both for hazard and risk assessment and slope evolution studies. Moreover, in the context of archival data, they demonstrate that in the Tatra sporadic permafrost zone, only relatively small rockfalls have been recorded in recent decades. Their cause was not the degradation of permafrost but freeze-thaw processes with the co-participation of rainwater and meltwater. The largest of these occur within densely fractured cataclysites, mylonites, and fault breccias. The impact of rockfalls on the morphodynamics of talus slopes is uneven in the storied arranged rock-talus slope systems. Even colluviums belonging to the same slope system can differ in their development rate and regime, and different thermal and wetness drivers can control their evolution.

Evaluation of TIEGCM based on GOCE neutral density

The Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM), as one of the most advanced physical models of the Earth’s thermosphere and ionosphere, is not only widely used in scientific research, but also has essential reference value in aerospace operations. In this study, we use Gravity field and steady-state Ocean Circulation Explorer (GOCE) neutral density to evaluate the accuracy of the TIEGCM. The assessment is performed on both time and spatial scales. The time scales are conducted annually, monthly, and daily, while the spatial scales are carried out in terms of altitude, latitude, and local time. On the time scales, the performance of the TIEGCM on the monthly time scale is better than that on the annual time scale. Also, the performance on the daily time scale is better than that on the monthly time scale. The relative deviation shows a significant seasonal variation, that is, larger in winter and summer and smaller in spring and autumn. In addition, the relative deviation shows a negative correlation with F10.7 and Ap. On the spatial scale, with the increase in altitude, the average relative deviation of the model becomes larger in general. The relative deviation is usually larger at middle latitudes in the Northern Hemisphere and high latitudes in the Southern Hemisphere. Finally, on the scale of local time, the relative deviation changes more dramatically in local morning than at dusk.

Low latitude mesospheric clouds in a warmer climate

AbstractObservations show that mesospheric clouds (MCs) have been increasing in recent decades, presumably due to increased mesospheric water vapor which is mainly caused by greater methane (CH4) oxidation in the middle atmosphere. Past warm climates such as those of the early Cretaceous and Paleogene periods are thought to have had higher CH4 concentrations than present day, and future CH4 concentrations will also likely continue to rise. Here, idealized atmosphere chemistry‐climate model experiments forced with strong polar‐amplified sea‐surface temperatures and elevated carbon dioxide (CO2) and CH4 concentrations predict a substantial spreading of MCs to middle and low latitudes, well beyond regions where they are currently found. Sensitivity tests show that increased water vapor from CH4 oxidation and cooling from increased CO2 and CH4 concentrations create favorable conditions for cloud formation, producing MC fractions of 0.02 in the low latitudes and 0.1 in the mid‐latitudes in the Northern Hemisphere when CH4 concentration is 16× higher than pre‐industrial. Further increases in CH4 result in a monotonic increase in low‐ and mid‐latitude MCs. A uniform surface ocean warming, changes in polar amplification, or the solar constant do not significantly affect our results. While the appearance of these clouds is interesting, their ice and liquid water content is not sufficient to cause a significant radiative effect. On the other hand, dehydration of the mesosphere due to these low‐ and mid‐latitude MCs could potentially lead to a reduction in atomic hydrogen, thereby affecting mesospheric ozone concentration, although further study is required to confirm this.