Warm Phase Research Articles

Ionospheric quasi-biennial oscillation of the TEC amplitude of the equatorial ionization anomaly crests from continuous GPS data in the Southeast Asian region

The quasi-biennial oscillation (QBO) signals at two Equatorial ionization anomaly (EIA) crests of the ionosphere have been studied using the continuous GNSS network data in Vietnam and adjacent regions during the 2008- 2021 period. The monthly mean EIA crests amplitudes are calculated. The Lomb-Scargle periodogram method was applied to the residuals of the EIA crests magnitudes, DTEC, which are obtained from subtracting the fittings with solar index, F10.7. The Lomb-Scargle spectrum shows the quasi-biennial component in the residuals DTEC with the picks at 18, 25, and 29-30 months. The ionosphere QBO at two EIA crests was found out by the band-pass filter centered at 25 months with haft-power points at 17 and 33 months. The zonal wind data at 50 hPa (~ 20 km) of the tropical equatorial stratosphere is used as the stratosphere QBO (SQBO) to consider the relationship between the SQBO and the obtained ionosphere QBO. The direct comparison and the cross wavelet transform of the SQBO and ionosphere QBO data series show that during 2008-2009, the ionosphere QBO signal is low, the SQBO and ionosphere QBO are in phase during the 2010-2013 and 2018-2021 periods, but anti-phase during the 2014-2017 period. For the 2010-2013, 2014-2017 and 2018-2021 periods, the correlation coefficients are 0.623, 0.637, -0.646 in the northern crest, and 0.571, 0.53, -0.530 in the southern crest, respectively. Furthermore, we also observed that the SQBO and the ionosphere QBO signals were shortened during the 2015-2016 period, approximately 1.5 years. Previous studies showed that the ENSO (El Niño - Southern Oscillation) warm phase, also known as El-Niño existed during 2015-2016. The results of this study allow us to assume that the SQBO influences the ionosphere QBO. Our results show that the SQBO is the main factor affecting the ionospheric QBO at two EIA crests. However, the physical theoretical interpretation of the mechanisms of action is a challenge for scientists and requires further research.

Role of solar activity and Pacific decadal oscillation in the hydroclimatic patterns of eastern China over the past millennium

The hydroclimatic patterns in eastern China (EC) over the past millennium, both influenced by solar activity and Pacific decadal oscillation (PDO), are presented based on the climatic reconstructions and simulations. For strong solar activity, a consistent pattern exists where drought appears in the majority of EC initialized from the cold PDO phase, which is related to less moisture caused by the negative East Asia/Pacific-like (EAP-like) pattern and the enhanced western Pacific subtropical high (WPSH). When the initial condition with a neutral or warm PDO phase is set up, there is a tripole-like pattern from north to south, i.e., drought–flood–drought for the neutral PDO phase and flood–drought–flood for the warm PDO phase, which is related to the positive EAP-like pattern with various moisture transportation paths. For weak solar activity, there are dipole-like patterns where drought occurs in the northern part of the Yangtze River and flood appears in the southern part initialized from the cold or warm PDO phase, which is possibly related to the influence of the weakened WPSH. When the initial condition is the neutral PDO phase, there is a tripole-like pattern from north to south (flood–drought–flood) in EC affected by the weakened WPSH and the intensive India–Burma trough. Notably, the vertical velocity anomalies of airflow, representing the vertical moisture transportations, correspond well with the hydroclimatic patterns in EC whenever the various initialization strategies of PDO phases are employed. • Hydroclimatic patterns in eastern China (EC) are related to solar activity and PDO. • A consistent pattern in EC for strong solar period (SS) and cold PDO initial phase. • The tripole-like patterns for SS and the neutral or warm PDO initial phase. • A tripole-like pattern for weak solar period (WS) and neutral PDO initial phase. • The dipole-like patterns for WS and the cold or warm PDO initial phase.

Cosmic rays and thermal instability in self-regulating cooling flows of massive galaxy clusters

One of the key physical processes that helps prevent strong cooling flows in galaxy clusters is the continued energy input from the central active galactic nucleus (AGN) of the cluster. However, it remains unclear how this energy is thermalised so that it can effectively prevent global thermal instability. One possible option is that a fraction of the AGN energy is converted into cosmic rays (CRs), which provide non-thermal pressure support, and can retain energy even as thermal energy is radiated away. By means of magneto-hydrodynamical simulations, we investigate how CR injected by the AGN jet influence cooling flows of a massive galaxy cluster. We conclude that converting a fraction of the AGN luminosity as low as 10% into CR energy prevents cooling flows on timescales of billion years, without significant changes in the structure of the multi-phase intra-cluster medium. CR-dominated jets, by contrast, lead to the formation of an extended, warm central nebula that is supported by CR pressure. We report that the presence of CRs is not able to suppress the onset of thermal instability in massive galaxy clusters, but CR-dominated jets do significantly change the continued evolution of gas as it continues to cool from isobaric to isochoric. The CR redistribution in the cluster is dominated by advection rather than diffusion or streaming, but the heating by CR streaming helps maintain gas in the hot and warm phase. Observationally, self-regulating, CR-dominated jets produce a γ-ray flux in excess of current observational limits, but low CR fractions in the jet are not ruled out.

Deoxygenation and organic carbon sequestration in the Tethyan realm associated with the middle Eocene climatic optimum

The middle Eocene climatic optimum (ca. 40 Ma) stands out as a transient global warming phase of ∼400 k.y. duration that interrupted long-term Eocene cooling; it has been associated with a rise in atmospheric CO2 concentrations that has been linked to a flare-up in Arabia-Eurasia continental arc volcanism. Increased organic carbon burial in the Tethys Ocean has been proposed as a carbon sequestration mechanism to bring the middle Eocene climatic optimum to an end. To further test these hypotheses, we assessed the sedimentary and geochemical expression of the middle Eocene climatic optimum in the northern Peri-Tethys, specifically, the organic-rich Kuma Formation of the Belaya River section, located on the edge of the Scythian Platform in the North Caucasus, Russia. We constructed an age-depth model using nannofossil chronobiostratigraphy. Throughout the studied middle Eocene interval (41.2−39.9 Ma), we documented sea-surface temperatures of 32−36 °C based on the tetraether index of tetraethers consisting of 86 carbons (TEX86), depending on proxy calibration, and during the early middle Eocene climatic optimum, we observed sea-surface warming of 2−3 °C. Despite the proximity of the section to the Arabia-Eurasia volcanic arc, the hypothesized source of volcanic CO2, we found no evidence for enhanced regional volcanism in sedimentary mercury concentrations. Sedimentary trace-element concentrations and iron speciation indicate reducing bottom waters throughout the middle Eocene, but the most reducing, even euxinic, conditions were reached during late middle Eocene climatic optimum cooling. This apparent regional decoupling between ocean warming and deoxygenation hints at a role for regional tectonics in causing basin restriction and anoxia. Associated excess organic carbon burial, extrapolated to the entire regional Kuma Formation, may have been ∼8.1 Tg C yr−1, comprising ∼450 Pg C over this ∼55 k.y. interval. Combined with evidence for enhanced organic carbon drawdown in the western Peri-Tethys, this supports a quantitatively significant role for the basin in the termination of the middle Eocene climatic optimum by acting as a large organic carbon sink, and these results collectively illustrate that the closing Tethys Ocean might have affected global Paleogene climate. Moreover, this study highlights the importance of the interplay between global climate and regional oceanic gateway evolution in determining local climate and oceanographic change.

Response of planktonic foraminifera to seasonal and interannual hydrographic changes: Sediment trap record from the northern South China Sea

Foraminifera play an important role in the organic and inorganic carbon pumps of the ocean. Understanding their responses in seasonal and interannual time scales to the climate and seawater chemistry changes is important for studying carbon cycles and paleoclimatology. This study examined about 5.1-year continuous mass fluxes in 2013/9-2019/8 and 1.8-year planktonic foraminiferal shell fluxes in 2016/8-2019/8 census from ten and four sets of sediment traps, respectively, moored at the South East Asia Time-series Study (SEATS) site in the northern South China Sea (SCS), the world’s largest marginal sea. A total of four sets of sediment trap mooring with 11 common species were identified, spanning from August 2016 to August 2019 with 8-day and 16-day collecting periods, which provided access to evaluate the impact of the prevailing monsoon system and interannual climatic conditions. Our results show that the winter monsoon enhances the nutrient inventories in the euphotic zone, supporting the productivity and the mass and shell fluxes. In addition to seasonal cycles, the variation of chlorophyll-a concentration in the SCS shows a strong response to wind speed under the influence of El Niño–Southern Oscillation (ENSO). The reduction in wind speed and the intensification of Kuroshio intrusion during the ENSO warm phases reduces the productivity and mass and shell fluxes, and vice versa in the case of the ENSO cold phases. The imprint of an ENSO cold phase (La Niña event) in 2017 was signified by 2–3-fold higher values than the 3-year average of total mass and foraminiferal shell fluxes. Instead of the common dominance of Trilobatus sacculifer and Globigerinoides ruber among species composition, Neogloboquadrina dutertrei was the predominant species comprising over 40%–60% of total shells greater than 212 μm. Furthermore, the interval with an elevated abundance of N. dutertrei lasted throughout January 2018 (four collecting intervals). Foraminifera shell fluxes were the lowest during warm months (March-August) in 2019, which was coeval with the increase in proportions of Orbulina universa and Globigerinella calida. The unusual species composition might signify a weak ENSO warm phase (A weak El Niño event) between September 2018 and August 2019.

Modulation of the Predictability of the East Asian Summer Monsoon by the Interdecadal Pacific Oscillation

AbstractWe identified an interdecadal modulation of the potential predictability (measured by the signal‐to‐noise ratio) of the East Asian summer monsoon (EASM) by the interdecadal Pacific oscillation (IPO). The EASM potential predictability is relatively high during the warm phase of the IPO, but relatively low during the cold phase. The IPO has been in a cold phase since the late 1990s and this has coincided with a decrease in the potential predictability of the EASM, which has posed a severe challenge to the seasonal forecasting of the EASM in recent decades. The El Niño‐Southern Oscillation (ENSO)‐EASM relationship is stronger in the warm phase of the IPO than in the cold phase, resulting in an enhanced influence of the ENSO on the EASM and a stronger external signal of predictability for the EASM in the warm phase of the IPO. Changes in the ENSO‐EASM relationship can be attributed to a significant difference in the amplitude of the variability of the ENSO during the IPO cold and warm phase. The latter was found to have contributions from the modulation of the IPO on the El Niño and La Niña frequency asymmetry. These results imply that the phase of the IPO should be considered when assessing the prediction skill of the EASM.

Interpreting Sentinel-1 SAR Backscatter Signals of Snowpack Surface Melt/Freeze, Warming, and Ripening, through Field Measurements and Physically-Based SnowModel

The transition of a cold winter snowpack to one that is ripe and contributing to runoff is crucial to gauge for water resource management, but is highly variable in space and time. Snow surface melt/freeze cycles, associated with diurnal fluctuations in radiative inputs, are hallmarks of this transition. C-band synthetic aperture radar (SAR) reliably detects meltwater in the snowpack. Sentinel-1 (S1) C-band SAR offers consistent acquisition patterns that allow for diurnal investigations of melting snow. We used over 50 snow pit observations from 2020 in Grand Mesa, Colorado, USA, to track temperature and wetness in the snowpack as a function of depth and time during snowpack phases of warming, ripening, and runoff. We also ran the physically-based SnowModel, which provided a spatially and temporally continuous independent indication of snowpack conditions. Snowpack phases were identified and corroborated by comparing field measurements with SnowModel outputs. Knowledge of snowpack warming, ripening, and runoff phases was used to interpret diurnal changes in S1 backscatter values. Both field measurements and SnowModel simulations suggested that S1 SAR was not sensitive to the initial snowpack warming phase on Grand Mesa. In the ripening and runoff phases, the diurnal cycle in S1 SAR co-polarized backscatter was affected by both surface melt/freeze as well as the conditions of the snowpack underneath (ripening or ripe). The ripening phase was associated with significant increases in morning backscatter values, likely due to volume scattering from surface melt/freeze crusts, as well as significant decreases in evening backscatter values associated with snowmelt. During the runoff phase, both morning and evening backscatter decreased compared to reference values. These unique S1 diurnal signatures, and their interpretations using field measurements and SnowModel outputs, highlight the capacities and limitations of S1 SAR to understand snow surface states and bulk phases, which may offer runoff forecasting or energy balance model validation or parameterization, especially useful in remote or sparsely-gauged alpine basins.

Decadal Variability of Rainfall in Senegal: Beyond the Total Seasonal Amount

Abstract Rainfall characteristics are crucial in monsoon regions, in particular for agriculture. Crop yields indeed depend on the rainfall seasonal amounts, but also on other rainfall characteristics such as the onset of the rainy season or the distribution of rainy days. In the Sahel region, while the average amount of seasonal rainfall has been shown to be marked by strong decadal variability, the modulation of rainfall characteristics has received less attention in the literature so far. In this study, we show that the frequency of light, heavy, and extreme rainfall events and the mean intensity of rainfall events in Senegal exhibit a marked decadal variability over the 1918–2000 period, strongly similar to that of the mean seasonal rainfall. The decadal modulations of these events show a strong and positive link with the Atlantic multidecadal variability (AMV). Indeed, positive sea surface temperature anomalies over the North Atlantic and Mediterranean related to a warm AMV phase are associated with negative sea level pressure anomalies over the northern Atlantic and a northward shift of the intertropical convergence zone. We also find that the onset and cessation dates as well as the length of the rainy season show relatively less decadal variability, which is more related to the interdecadal Pacific oscillation (IPO), a positive phase of the latter leading to a late onset, an early cessation, and an overall shorter rainy season in Senegal.

Investigation on the MLT tidal variability during September 2019 minor sudden stratospheric warming

Tidal variability in the mesosphere and lower thermosphere (MLT) during September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing ground-based meteor radar wind observations from the equatorial, extratropical, middle, and high latitude stations and global reanalysis dataset. The polar warming is found to move from the mesosphere to the stratosphere until the peak warming day (PWD) of the SSW. The diurnal and semidiurnal tides at individual observational sites do not exhibit any consistent response during the observational interval, but a notable and consistent variability in some specific zonal wavenumber components, i. e., DW1 (migrating diurnal tide), DE3 (nonmigrating eastward wavenumber 3 diurnal tide), and SW2 (migrating semidiurnal tide) is found in the global reanalysis dataset. Incidentally, the warming event occurs during Spring equinox when a dominant seasonal change in the tidal activities generally takes place and hence seasonal variability is also looked into while identifying the SSW impact during the observational interval. It is found that the seasonal broad changes in the DW1, DE3, and SW2 amplitudes can be explained by the variability in the tidal sources, i.e., water vapor, convective activity, ozone, etc during the observational period. However, the extracted short-term variability in the global tidal modes on removing seasonal trend reveals noticeable response in connection with the warming event. The deseasoned amplitude of the DW1 significantly enhances around the PWD at most of the present latitudes. The deseasoned DE3 amplitude responds significantly in the middle atmosphere at low latitudes during the warming phase. The deseasoned SW2 exhibit clear enhancement around the PWD at all the latitudes. However, the deseasoned tidal features do not seem to correlate well with that of the source species unlike the seasonal ones that imply involvement of complex processes during the warming event, seeking further future investigations in this regard.

Pacific Decadal Oscillation modulates the Arctic sea-ice loss influence on the midlatitude atmospheric circulation in winter

Abstract. The modulation of the winter impacts of Arctic sea-ice loss by the Pacific Decadal Oscillation (PDO) is investigated in the IPSL-CM6A-LR ocean–atmosphere general circulation model. Ensembles of simulations are performed with constrained sea-ice concentration following the Polar Amplification Model Intercomparison Project (PAMIP) and initial conditions sampling warm and cold phases of the PDO. Using a general linear model, we estimate the simulated winter impact of sea-ice loss, PDO and their combined effects. On the one hand, a negative North Atlantic Oscillation (NAO)-like pattern appears in response to sea-ice loss together with a modest deepening of the Aleutian Low. On the other hand, a warm PDO phase induces a large positive Pacific–North America pattern, as well as a small negative Arctic Oscillation pattern. Both sea-ice loss and warm PDO responses are associated with a weakening of the poleward flank of the eddy-driven jet, an intensification of the subtropical jet and a weakening of the stratospheric polar vortex. These effects are partly additive; the warm PDO phase therefore enhances the response to sea-ice loss, while the cold PDO phase reduces it. However, the effects of PDO and sea-ice loss are also partly non-additive, with the interaction between both signals being slightly destructive. This results in small damping of the PDO teleconnections under sea-ice loss conditions, especially in the stratosphere. The sea-ice loss responses are compared to those obtained with the same model in atmosphere-only simulations, where sea-ice loss does not significantly alter the stratospheric polar vortex.

Gas distribution from clusters to filaments in IllustrisTNG

Matter distribution in the environment of galaxy clusters, from their cores to their connected cosmic filaments, must in principle be related to the underlying cluster physics and its evolutionary state. We aim to investigate how radial and azimuthal distribution of gas is affected by cluster environments and how it can be related to cluster-mass assembly history. We first analysed the radial physical properties of gas (velocity, temperature, and density) around 415 galaxy cluster environments from IllustrisTNG simulations at z = 0 (TNG300-1). Whereas hot plasma is virialised inside clusters (< R200), the dynamics of a warm, hot, intergalactic medium (WHIM) can be separated in two regimes: accumulating and slowly infalling gas at cluster peripheries (∼R200) and fast infalling motions outside clusters (> 1.5 R200). The azimuthal distribution of dark matter (DM), hot, and warm gas phases is secondly statistically probed by decomposing their 2D distribution in harmonic space. Inside clusters, the azimuthal symmetries of DM and hot gas trace cluster structural properties well. These include their centre offsets, substructure fractions, and elliptical shapes. Beyond cluster-virialised regions, we find that WHIM gas follows the azimuthal distribution of DM, thus tracing cosmic filament patterns. Azimuthal symmetries of hot and warm gas distribution are finally shown to be imprints of cluster mass assembly history, strongly correlated with the formation time, mass accretion rate, and dynamical state of clusters. The azimuthal mode decomposition of 2D gas distribution is a promising probe to assess the 3D physical and dynamical cluster properties up to their connected cosmic filaments.

Coupling Warm Rain With an Eddy Diffusivity/Mass Flux Parameterization: 1. Model Description and Validation

AbstractA new version of the stochastic multiplume Jet Propulsion Laboratory Eddy‐Diffusivity/Mass‐Flux (JPL‐EDMF) parameterization which consistently couples the simplified Khairoutdinov and Kogan (2000), https://doi.org/10.1175/1520-0493(2000)128<0229:ANCPPI>2.0.CO;2, warm phase cloud microphysical parameterization with the parameterization of cloud macrophysical and subgrid scale dynamical processes is described. The new parameterization combines the EDMF approach with an assumed shape of a joint probability density function of thermodynamic and kinematic variables which provide the basis for the computation of all parameterized processes. As far as we are aware this is the first attempt to consistently couple all of these parameterized processes in the EDMF framework. This paper is part one of a two paper series. Here, the JPL‐EDMF parameterization is described and benchmark simulations of precipitating stratocumulus and cumulus convection are performed in a single‐column‐model framework. The parameterization results compare favorably to the reference large‐eddy‐simulation results. In the second part (Smalley et al., 2022, https://doi.org/10.1029/2021MS002729) the JPL‐EDMF parameterization is validated for a wide range of observation‐based scenarios covering the continuous transition from subtropical stratocumulus to cumulus convection derived from global reanalysis, and parameterization uncertainties are studied in detail.

Joint Pattern Analysis of Forest Fire and Drought Indicators in Southeast Asia Associated with ENSO and IOD

Land and forest fires in Southeast Asia often coincide with severe dry seasons in the specific region caused by the warm phase of an El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). This research aims to identify and quantify the ENSO–IOD effect on a joint pattern between the dry season and land and forest fires in Southeast Asia. This research provides a quantitative result which represents the ENSO–IOD’s impact in Southeast Asia for hotspots, dry spells, and precipitation anomalies. The methods used in this research are singular value decomposition, probability density skill score, and coherence analysis. Cambodia, Myanmar, and Thailand gave a similar result with less than a 25% increasing severity in the hotspots from normal to either El Niño, positive IOD, or El Niño–positive IOD years. The maximum increase in hotspot severity in North Sumatra was 13.06% and happened during a weak El Niño and positive IOD. Meanwhile, South Sumatra had a maximum accumulation of more than 89% and Kalimantan had more than a 72% increase during the strong El Niño in 2015. Even though the relationship between the ENSO and IOD was inconsistent, the occurrence of both phenomena in the same year can lead to fires and need to be considered.

Interdecadal wind stress variability over the tropical Pacific causes ENSO diversity in an intermediate coupled model

The role of interdecadal wind stress variability in the genesis of ENSO diversity is examined by using an intermediate coupled model (ICM) in the tropical Pacific; two types of experiments are performed, one with the original ICM, and the other with interdecadal wind stress ( $${\uptau }_{interde}$$ ) effect being explicitly represented. The $${\uptau }_{interde}$$ component is derived from NCEP/NCAR reanalysis dataset as follows. First, the ensemble empirical mode decomposition (EEMD) is used to extract the interdecadal component of wind stress anomalies on about a 10–40 yr timescale. Next, an idealized interdecadal cycle of $${\uptau }_{interde}$$ is reconstructed by a principal oscillation pattern (POP) analysis based on the EEMD-extracted interdecadal wind component. A 110-yr model integration is then performed by explicitly incorporating the reconstructed $${\uptau }_{interde}$$ cycle into the ICM. Compared with the regular interannual oscillation in the original ICM, the simulated ENSO events become highly irregular with interdecadal variations in the amplitude and asymmetry when the $${\uptau }_{interde}$$ effect is included. Especially, the model reproduces two types of El Niño with different spatial distribution and temporal evolution of SST anomalies, namely Eastern-Pacific (EP) and Central-Pacific (CP) types. Further attribution analyses are performed to understand the modulating effects of $${\uptau }_{interde}$$ in the tropical Pacific using the ocean component of the ICM, forced by the added $${\uptau }_{interde}$$ effect. Two different roles of the Interdecadal Pacific Oscillation (IPO) in modulating different types of El Niño are illustrated. On the one hand, the warm phase of IPO favors for the emergence of EP-El Niño events, in association with the initial warming signals occurring in the eastern equatorial Pacific, which are absent in the original ICM. On the other hand, the cold phase of IPO tends to shift the El Niño (i.e., the single type of El Niño in the original ICM) to an CP type, with which the SST anomalies propagate eastward along the equator but cannot extend into the eastern boundary. This simple modeling study highlights the significant contributions of interdecadal wind variability to the genesis of ENSO irregularity and diversity theoretically.

Modulation of western North Pacific tropical cyclone formation by central Pacific El Niño–Southern Oscillation on decadal and interannual timescales

AbstractThis study investigates the impact of central Pacific (CP) El Niño–Southern Oscillation (ENSO) on tropical cyclone (TC) frequency over the western North Pacific (WNP) on decadal and interannual timescales. The CP ENSO‐TC frequency relationship is strong and significant only on decadal timescales, with enhanced TC formation over most of the WNP associated with warm CP ENSO phases. TC formation changes, driven by CP ENSO, exhibit a southeast–northwest dipole pattern on interannual timescales, similar to the typical pattern induced by eastern Pacific ENSO. Associated with warm CP ENSO phases on decadal timescales are increases in TC formation east of 125°E, while increases in TC formation east of 140°E are observed with warm CP ENSO phases on interannual timescales. These increases in TC activity are primarily caused by favourable dynamic conditions, including increased 850‐hPa relative vorticity and 200‐hPa divergence and decreased 850–200‐hPa vertical wind shear. The main TC formation difference on decadal and interannual timescales is concentrated over the longitudinal band of 125°–140°E, where reduced TC formation is observed on interannual timescales during CP El Niño years, predominately due to suppressed thermodynamic factors, for example, reduced maximum potential intensity and 700–500‐hPa relative humidity. We find insignificant (significant) changes in thermodynamic conditions between 125°E and 140°E due to weak (strong) descending motion in the western cell of the anomalous Walker circulation on decadal (interannual) timescales. This can be explained by different patterns of CP ENSO‐induced sea surface temperature anomalies on different timescales.

Temperature variability interacts with mean temperature to influence the predictability of microbial phenotypes.

Despite their relatively high thermal optima (T opt), tropical taxa may be particularly vulnerable to a rising baseline and increased temperature variation because they live in relatively stable temperatures closer to their T opt. We examined how microbial eukaryotes with differing thermal histories responded to temperature fluctuations of different amplitudes (0 control, ±2, ±4°C) around mean temperatures below or above their T opt. Cosmopolitan dinoflagellates were selected based on their distinct thermal traits and included two species of the same genus (tropical and temperate Coolia spp.), and two strains of the same species maintained at different temperatures for >500 generations (tropical Amphidinium massartii control temperature and high temperature, CT and HT, respectively). There was a universal decline in population growth rate under temperature fluctuations, but strains with narrower thermal niche breadth (temperate Coolia and HT) showed ~10% greater reduction in growth. At suboptimal mean temperatures, cells in the cool phase of the fluctuation stopped dividing, fixed less carbon (C) and had enlarged cell volumes that scaled positively with elemental C, N, and P and C:Chlorophyll‐a. However, at a supra‐optimal mean temperature, fixed C was directed away from cell division and novel trait combinations developed, leading to greater phenotypic diversity. At the molecular level, heat‐shock proteins, and chaperones, in addition to transcripts involving genome rearrangements, were upregulated in CT and HT during the warm phase of the supra‐optimal fluctuation (30 ± 4°C), a stress response indicating protection. In contrast, the tropical Coolia species upregulated major energy pathways in the warm phase of its supra‐optimal fluctuation (25 ± 4°C), indicating a broadscale shift in metabolism. Our results demonstrate divergent effects between taxa and that temporal variability in environmental conditions interacts with changes in the thermal mean to mediate microbial responses to global change, with implications for biogeochemical cycling.

Climate-Induced Fire Hazard in Forests in the Volga Federal District of European Russia during 1992–2020

This paper shows the relevance of the problem of fire hazard in the forests of the Volga Federal District (VFD) of European Russia. The Nesterov index and the Selyaninov hydrothermal coefficient (HTC) are considered as indicators of fire hazard. The changes in climatic conditions in the VFD during 1955–2018 are shown; a trend towards warming and an increase in aridity in the study region were revealed. The repeatability of various fire hazard classes from May to September was calculated using the Nesterov method. It is shown that in July, the most dangerous situation was in the south of the VFD, where the repeatability of class IV fire hazard reached 27%. Using the HTC index, the degree of aridity of the district in the summer period was estimated. The frequency of the most arid conditions (HTC < 0.5) increases from the north to the south of the district, from 6% (Kirov Region) to 47% (Orenburg Region). Using the TT index, the potential thunderstorm danger in the VFD was assessed. With the help of the constructed maps, the hotspots of the most probable occurrence of thunderstorms were detected. The use of Rosstat data on the number of forest fires from 1992 to 2020 made it possible to consider the spatiotemporal distribution of forest fires in 14 administrative regions of the VFD. The distribution of the number of fires by the regions is shown depending on their forest cover and season. The peak of the number of fires was revealed in 2010, when the entire territory of the study region was covered by a severe drought, as a result of which the area of forests covered by fire increased many times over. In recent years (since 2017), there has been an increase in the area of burned forest due to the active phase of climate warming.

Multi-scale temporal analysis of evaporation on a saline lake in the Atacama Desert

Abstract. We investigate how evaporation changes depending on the scales in the Altiplano region of the Atacama Desert. More specifically, we focus on the temporal evolution from the climatological to the sub-diurnal scales on a high-altitude saline lake ecosystem. We analyze the evaporation trends over 70 years (1950–2020) at a high-spatial resolution. The method is based on the downscaling of 30 km ERA5 reanalysis data at hourly resolution to 0.1 km spatial resolution data, using artificial neural networks to analyze the main drivers of evaporation. To this end, we use the Penman open-water evaporation equation, modified to compensate for the energy balance non-closure and the ice cover formation on the lake during the night. Our estimation of the hourly climatology of evaporation shows a consistent agreement with eddy-covariance (EC) measurements and reveals that evaporation is controlled by different drivers depending on the time scale. At the sub-diurnal scale, mechanical turbulence is the primary driver of evaporation, and at this scale, it is not radiation-limited. At the seasonal scale, more than 70 % of the evaporation variability is explained by the radiative contribution term. At the same scale, and using a large-scale moisture tracking model, we identify the main sources of moisture to the Chilean Altiplano. In all cases, our regime of precipitation is controlled by large-scale weather patterns closely linked to climatological fluctuations. Moreover, seasonal evaporation significantly influences the saline lake surface spatial changes. From an interannual scale perspective, evaporation increased by 2.1 mm yr−1 during the entire study period, according to global temperature increases. Finally, we find that yearly evaporation depends on the El Niño–Southern Oscillation (ENSO), where warm and cool ENSO phases are associated with higher evaporation and precipitation rates, respectively. Our results show that warm ENSO phases increase evaporation rates by 15 %, whereas cold phases decrease it by 2 %.

Long-Term Warm–Cold Phase Shifts in the Gerlache Strait, Western Antarctic Peninsula

The Gerlache Strait plays an important role for the transports of heat, nutrients, and primary producers between the northern West Antarctic Peninsula (WAP) and the continental shelf in the southern WAP. The means, seasonal variations, and long-term trends of currents in the Gerlache Strait are analyzed based on Acoustic Doppler Current Profiler (ADCP) data between 1999 and 2016 available from the Joint Archive for Shipboard ADCP (JASADCP) dataset. The results revealed that the mean currents between the sea surface and 300 m in the Gerlache Strait (known as the Gerlache Strait Current) were predominantly northeastward, associated with the northeastward intrusion of Modified Circumpolar Deep Water (MCDW). The variance ellipses of currents were in parallel to the principal axis of the strait. The currents reached the maximum during austral spring and summer and were minimum during austral winter. The long-term trends revealed that the mean currents were southwestward during austral fall or winter before 2005, and the northeastward currents increased between 1999 and 2011, weakened, and reversed between 2011 and 2016. The long-term shifts between warm and cold phases in the Gerlache Strait were associated with shifts between the dominance of northeastward and southwestward currents in the strait, which are respectively associated with the intrusion of warm MCDW in the south and the transport of cold water from the Bransfield Strait in the north.

MONITORING OF FOREST FIRES IN THE TERRITORY OF THE VOLGA FEDERAL DISTRICT IN RECENT DECADES

The distribution of forest fires across the territory of the Volga Federal District (VFD) in the period 1992-2020 is considered. The distribution of the number of fires in the subjects of the Volga Federal District is shown depending on their forest cover and season. The peak of the number of fires was revealed in 2010, when the entire territory of the region was covered by a severe drought, which led to a multiple increase in the area of forests covered by fire. An increase in the number of forest fires in recent years due to the active phase of climate warming has been noted.