We present an investigation of polar cap plasma structure lifetimes. We analyze both simulated data from ionospheric models (International Reference Ionosphere model and Mass Spectrometer Incoherent Scatter model) and in-situ data from the Swarm satellite mission (the 16 Hz Advanced Plasma Density data set). We find that the theoretical prediction that E-region conductance is a predictor of F-region polar cap plasma structure lifetimes is indeed supported by both in-situ-based observations and by ionospheric models. In-situ plasma structure lifetimes correlate well with the ratio of F- to E-region conductance. We present explicit predictions of small scale (~1 km) structure lifetimes, which range from less than 1 hour during local summer to around 3 hours during local winter. We highlight a large discrepancy between the observational and theoretical scale-dependency of decay due to diffusion.

Familiarity with the use of face coverings to reduce the risk of respiratory disease has increased during the coronavirus pandemic; however, recommendations for their use outside of the pandemic remains limited. Here, we develop a modeling framework to quantify the potential health benefits of wearing a face covering or respirator to mitigate exposure to severe air pollution. This framework accounts for the wide range of available face coverings and respirators, fit factors and efficacy, air pollution characteristics, and exposure-response data. Our modeling shows that N95 respirators offer robust protection against different sources of air pollution, reducing exposure by more than a factor of 14 when worn with a leak rate of 5%. Synthetic-fiber masks offer less protection with a strong dependence on aerosol size distribution (protection factors ranging from 4.4 to 2.2.), while natural-fiber and surgical masks offer reductions in exposure of 1.9 and 1.7, respectively. To assess the ability of face coverings to provide population-level health benefits to wildfire smoke, we perform a case study for the 2012 Washington state fire season. Our models suggest that although natural-fiber masks offer minor reductions in respiratory hospitalizations attributable to smoke (2-11%) due to limited filtration efficiency, N95 respirators and to a lesser extent surgical and synthetic-fiber masks may lead to notable reductions in smoke-attributable hospitalizations (22-39%, 9-24%, and 7-18%, respectively). The filtration efficiency, bypass rate, compliance rate (fraction of time and population wearing the device) are the key factors governing exposure reduction potential and health benefits during severe air pollution events.

The evolution of anvil clouds detrained from deep convective systems has important implications for the tropical energy balance and is thought to be shaped by radiative heating. We use combined radar-lidar observations and a radiative transfer model to investigate the influence of radiative heating on anvil cloud altitude, thickness, and microphysical structure. We find that high clouds with an optical depth between 1 and 2 are prevalent in tropical convective regions and can persist far from any convective source. These clouds are generally located at higher altitudes than optically thicker clouds, experience strong radiative heating, and contain high concentrations of ice crystals indicative of turbulence. These findings support the hypothesis that anvil clouds are driven towards and maintained at a preferred optical thickness that corresponds to a positive cloud radiative effect. Comparison of daytime and nighttime observations suggests that anvil thinning proceeds more rapidly at night, when net radiative cooling promotes the sinking of cloud top. It is hypothesized that the properties of aged anvil clouds and their susceptibility to radiative destabilization are shaped by the time of day at which the cloud was detrained. These results underscore the importance of small-scale processes in determining the radiative effect of tropical convection.

The Monsoon Asia region is home to ten of the world’s biggest rivers, supporting the lives of 1.7 billion people who rely on streamflow for water, energy, and food. Yet, a synthesized understanding of multi-centennial streamflow variability for this region is lacking. To fill this gap, we produce the first large scale streamflow reconstruction over Monsoon Asia (62 stations in 16 countries, 813 years of mean annual flow). In making this reconstruction, we develop a novel, automated, climate-informed, and dynamic reconstruction framework that is skillful over most of the region. We show that streamflow in Monsoon Asia is spatially coherent, owing to common drivers from the Pacific, Indian, and Atlantic Oceans. We also show how these oceanic teleconnections change over space and time. By characterizing past and present hydroclimatic variability, we provide a platform for assessing the impact of future climatic changes and informing water management decisions.

Different Earth orientation parameter (EOP) time series are publicly available that typically arise from the combination of individual space geodetic technique solutions. The applied processing strategies and choices lead to systematically differing signal and noise characteristics particularly at the shortest periods between 2 and 8 days. We investigate the consequences of typical choices by introducing new experimental EOP solutions obtained from combinations at either normal equation level processed by DGFI-TUM and BKG, or observation level processed by ESA. All those experiments contribute to an effort initiated by ESA to develop an independent capacity for routine EOP processing and prediction in Europe. Results are benchmarked against geophysical model-based effective angular momentum functions processed by ESMGFZ. We find, that a multi-technique combination at normal equation level that explicitly aligns a priori station coordinates to the ITRF2014 frequently outperforms the current IERS standard solution 14C04. A multi-GNSS-only solution already provides very competitive accuracies for the equatorial components. Quite similar results are also obtained from a short combination at observation level experiment using multi-GNSS solutions and SLR from Sentinel-3A and -3B to realize space links. For ΔUT1, however, VLBI information is known to be critically important so that experiments combining only GNSS and possibly SLR at observation level perform worse than combinations of all techniques at normal equation level. The low noise floor and smooth spectra obtained from the multi-GNSS solution nevertheless illustrates the potential of this most rigorous combination approach so that further efforts to include in particular VLBI are strongly recommended.

The formation of platelet ice is well known to occur under Antarctic sea ice, where sub-ice platelet layers form from supercooled ice shelf water. In the Arctic however, platelet ice formation has not been extensively observed and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long-term in situ observations of a decimeter thick sub-ice platelet layer under free-drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition, provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth.

Recently, there has been renewed interest in the performance and functionality of traditional small-scale storage interventions (check dams, farm bunds and tanks) used across India for the improvement of local water security. The Central Groundwater Board of India is encouraging the construction of such interventions for the alleviation of water scarcity. It is of critical importance to understand the hydrological effect of these interventions at basin scales to maximise their effectiveness. The quantification of small-scale interventions in hydrological modelling is often neglected, especially in large-scale modelling exercises. A bespoke version of the GWAVA model was developed to assess the impact of interventions on the water balance of the Cauvery Basin and two smaller sub-catchments. Model results demonstrate that farm bunds appear to have a negligible effect on the estimated average annual streamflow at the outlets of the two sub-catchments and the basin whereas tanks and check dams have a more significant effect. Interventions generally were found to increase evaporation losses across the catchment. The model adaption used in this study provides a step-change in the conceptualisation and quantification of the consequences of small-scale storage interventions in large- or basin-scale hydrological models.

This study considers 28 geomagnetic storms with Dst $\leq-50$ nT driven by high-speed streams (HSSs) and associated stream interaction regions (SIRs) during 2010-2017. Their impact on ionospheric horizontal and field-aligned currents (FACs) have been investigated using superposed epoch analysis of SuperMAG and AMPERE data, respectively. The zero epoch ($t_0$) was set to the onset of the storm main phase. Storms begin in the SIR with enhanced solar wind density and compressed southward oriented magnetic field. The integrated FAC and equivalent currents maximise 40 and 58 min after $t_0$, respectively, followed by a small peak in the middle of the main phase ($t_0$+4h), and a slightly larger peak just before the Dst minimum ($t_0$+5.3h). The currents are strongly driven by the solar wind, and the correlation between the Akasofu $\varepsilon$ and integrated FAC is $0.90$. The number of substorm onsets maximises near $t_0$. The storms were also separated into two groups based on the solar wind dynamic pressure p_dyn in the vicinity of the SIR. High p_dyn storms reach solar wind velocity maxima earlier and have shorter lead times from the HSS arrival to storm onset compared with low p_dyn events. The high p_dyn events also have sudden storm commencements, stronger solar wind driving and ionospheric response at $t_0$, and are primarily responsible for the first peak in the currents after $t_0$. After $t_0+2$ days, the currents and number of substorm onsets become higher for low compared with high p_dyn events, which may be related to higher solar wind speed.

The Moho discontinuity plays an important role in crustal growth and evolution. In this study, we delineate the Moho geometry in southern California by jointly using local Moho-reflected waves PmP and teleseismic Moho-converted waves Ps. To well constrain the Moho geometry, we have developed a two-stage process to pick PmP waves and have created a reliable PmP travel time data set with a total of 10,192 picks. We have also extracted 38,648 high-quality P-wave receiver functions (RFs). The Moho depth is initially estimated via the common conversion point (CCP) stacking of RFs and then refined by inverting the PmP travel time data in a community velocity model (CVM-H, version 15.1.1). The newly built Moho geometry is generally consistent with the California Moho Model version 1.0 (CMM-1.0), that is, a shallow Moho beneath the Salton Trough (23 km), a uniformly shallow Moho beneath the Mojave Desert and the Basin and Range (<29 km), and a sliver of deep Moho under the western Peninsular Ranges, the eastern Transverse Ranges, and the western Sierra Nevada (>34 km). However, our Moho model reveals some new features different from the CMM–1.0, such as a deep Moho (∼34 km) beneath the northern end of the central and western Transverse Ranges, consistent with the observation of deep seismicities due to a thick brittle crust there. We also find a gradual transition from the lower crust to the uppermost mantle beneath the western Peninsular Ranges, leading to the rareness of pickable PmP waves as well as weak Moho-converted signals there.

Projections of the winter North Atlantic circulation exhibit large spread. Coupled Model Intercomparison Project archives typically provide only a few ensemble members per model, rendering it difficult to quantify reducible model structural uncertainty and irreducible internal variability (IV) in projections. We estimate using the Multi-Model Large Ensemble Archive that model structural differences explain two-thirds of the spread in late 21st century (2080-2099) projections of the winter North Atlantic Oscillation (NAO). This estimate is biased by systematic model errors in the forced NAO response and IV. Across the North Atlantic, the NAO explains a substantial fraction of the spread in mean sea level pressure (MSLP) projections due to IV, except in the central North Atlantic. Conversely, the spread in North Atlantic MSLP projections associated with model differences is largely unexplained by the NAO. Therefore, improving understanding of the NAO alone may not constrain the reducible uncertainty in North Atlantic MSLP projections.

High-resolution microstructural analysis of porphyroblast inclusion trails integrated with Sm-Nd garnet geochronology has provided new insight into the tectonic history of the Betic-Rif orogen. Three principal age groups of porphyroblast are demonstrated with distinctly oriented inclusion-trails. Inclusion-trail curvature axes or ‘FIA’ (Foliation Inflexion/Intersection Axes) are shown to represent ‘fossilized’ crenulation axes from which a succession of different crustal shortening directions can be deduced. The regional consistency of inclusion-trail orientations and their geometric relationship with several sets of macroscopic folds reveal the composite character of the Gibraltar Arc formed by a superposition of different folding directions and associated lineations. Bulk-garnet ages of 35-22Ma obtained from 5 micaschist samples of the Alpujarride-Sebtide complex (ASC) and of 35-13Ma from 4 micaschists of the Nevado-Filabride complex (NFC) allow to deduce NNE-SSW directed shortening in the Late Eocene changing to NW-SE shortening in the early Oligocene, alternating with suborthogonal NE-SW shortening during the Miocene. These directions can be related to a major swing in the direction of relative Africa-Iberia plate-motion known from kinematic modeling of magnetic seafloor anomalies, and dynamic interference between plate convergence and suborthogonal ‘tectonic escape’ of the Alboran Domain thereafter. Coupled to previously established P-T-t paths, the new garnet ages support a common tectono-metamorphic evolution of the ASC and NFC since the Late Eocene. However, while the first became exhumed in the Middle-Miocene (15Ma), the second experienced a re-subduction prior to being exhumed itself about 5 Myr later.

Uncertainty exists in the time-mean total transport of the Antarctic Circumpolar Current (ACC), the world’s strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12 global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, i.e. approximately the average of the cDrake and DRAKE estimates, is actually representative of the time-mean ACC transport through the Drake Passage. The cDrake experiment overestimated the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near-surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated, thus monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.

Whole plant chlorophyll fluorescence imaging is a powerful tool for non-destructive analysis of photosynthesis. Analysis of such images requires software that is able to process and calculate photosynthetic parameters per plant pixel. PlantCV is an open-source, Python-based library of image analysis tools for plant science. Previous versions of PlantCV included tools to analyze photosynthetic efficiency data, but recent developments to the photosynthesis subpackage have expanded to include more photosynthetic parameters based on chlorophyll fluorescence and spectral indices. This paper highlights the newest updates to the photosynthesis package of PlantCV and discusses applications of these tools on a sorghum dataset that was imaged with a PhenoVation CropReporter system.

In Canada, winter wheat must survive air temperatures as low as -30oC. Snow cover acts as a thermal blanket reducing the direct exposure to chilling air temperatures. In a joint Can/UK wheat project we measured vegetative cover (VC) on 88 different winter wheat varieties in the fall up to snow cover and directly after the snow melted in the spring. Comparing the VC pre- and post-winter provided a direct measure of winter hardiness. While the majority of the wheat cultivars from the UK experienced greater winter kill than the Canadian lines, there were still some with comparable hardiness. Fall and spring growth rates were determined and the UK lines had similar or greater fall growth rates than Canadian lines but lower spring growth rates. Phenomic determined hardiness was correlated to visual ratings and harvest yield.

While the Madden Julian Oscillation (MJO) is known to influence the midlatitude circulation and its predictability on subseasonal-to-seasonal (S2S) timescales, little is known how this connection may change with anthropogenic warming. This study investigates changes in the causal pathways between the MJO and the North Atlantic Oscillation (NAO) within historical and SSP585 simulations of the CESM2-WACCM coupled climate model. Two data-driven approaches are employed, namely, the STRIPES index and graphical causal models. These approaches collectively indicate that the MJO’s influence on the North Atlantic strengthens in the future, consistent with an extended jet-stream. In addition, the graphical causal models allow us to distinguish the causal pathways associated with the teleconnections. While both a stratospheric and tropospheric pathway connect the MJO to the North Atlantic in CESM2-WACCM, the strengthening of the MJO-NAO causal connection over the 21st century is shown to be due exclusively to teleconnections via the tropospheric pathway.

The loss of autocorrelations of tropical sea surface temperatures (SST) during late spring, also called the spring predictability barrier (SPB), is a factor that strongly limits the predictability of El Nino Southern Oscillation (ENSO), and especially the statistical SST-based ENSO forecasts starting from the winter-spring season. Recent studies show that Pacific atmospheric circulation anomalies in winter-spring may have a long-term impact on the summer tropical climate via the SST footprint. Here, we infer an index based on sea level pressure (SLP) data from February-March in a single area surrounding Hawaii, and show that this area is the most informative part of the large SLP pattern initiating the SST footprinting mechanism. We then construct a statistically optimal linear model of the Nino 3.4 index taking this atmospheric index as a forcing. We find that this forcing efficiently lowers the SPB and provides significant improvements of interseasonal Nino 3.4 forecasts.

Surface meltwater accumulating on Antarctic ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to increased ice discharge from the continent. Implications of increasing surface melt for future ice shelf stability are inadequately understood. The southern Amery Ice Shelf has an extensive surface hydrological system, and we present data from satellite imagery and ICESat-2 showing a rapid surface disruption there in winter 2019, covering ~60 km2. We interpret this as an ice-covered lake draining through the ice shelf, forming an ice doline with a central depression reaching 80 m depth, amidst uplift reaching 36 m. Flexural rebound modelling suggests 0.75 km3 of water was lost. We observed transient refilling of the doline the following summer with rapid incision of a narrow meltwater channel (20 m wide and 3 m deep). This study demonstrates how high-resolution geodetic measurements can explore critical fine-scale ice shelf processes.

In this study, we find significant sensitivity to the choice of time step for the Energy Exascale Earth System Model's atmospheric component, leading to large decreases in the magnitude of cloud forcing when the time step is reduced to 10 seconds. Reducing the time step size for the microphysics increases precipitation, leading to a drying of the atmosphere and an increase in surface evaporation. This effect is amplified when the microphysics is substepped together with other cloud physics processes. Coupling the model's dynamics and physics more frequently reduces cloud fraction at lower altitudes, while producing more cloud liquid at higher altitudes. Reducing the deep convection time step also reduces low cloud mass and cloud fraction. Together, these results suggest that cloud physics in a global circulation model can depend strongly on time step, and in particular on the frequency with which cloud-related processes are coupled with each other and with the model dynamics.