The land-sea breeze is resonant with the inertial response of the ocean at the critical latitude of 30°N/S. 1D-vertical numerical experiments were undertaken to study the key drivers of enhanced diapycnal mixing in coastal upwelling systems driven by diurnal-inertial resonance near the critical latitude. The effect of the land boundary was implicitly included in the model through the ‘Craig approximation’ for first order cross-shore surface elevation gradient response. The model indicates that for shallow water depths (<~100m), bottom shear stresses must be accounted for in the formulation of the ‘Craig approximation’, as they serve to enhance the cross-shore surface elevation gradient response, while reducing shear and mixing at the thermocline. The model was able to predict the observed temperature and current features during an upwelling/mixing event in 60m water depth in St Helena Bay (~32.5°S, southern Benguela), indicating that the locally forced response to the land-sea breeze is a key driver of diapycnal mixing over the event. Alignment of the sub-inertial Ekman transport with the surface inertial oscillation produces shear spikes at the diurnal-inertial frequency, however their impact on mixing is secondary when compared with the diurnal-inertial resonance phenomenon. The amplitude of the diurnal anticlockwise rotary component of the wind stress represents a good diagnostic for the prediction of diapycnal mixing due to diurnal-inertial resonance. The local enhancement of this quantity over St Helena Bay provides strong evidence for the importance of the land-sea breeze in contributing to primary production in this region through nutrient enrichment of the surface layer.

Mercury is valuable to us because we can see the interaction between the planet and its space environment. This research aims to clarify how Mercury’s neutral Na exosphere was produced. Data from MESSENGER/MASCS and model calculations that examine possible generation, transportation and dissipation processes will be compared. First, seasonal variability of the amount of Na exosphere is analyzed for each local time (LT) using MASCS data. Previous research has shown that the amount of Na above LT12 reaches its maximum at aphelion, and it is found that this maximum is recorded only at LT12. Following this result, we construct 3-D Na exosphere model to understand the key seasonal variability processes occurring around LT12. The numerical calculation produced results that are consistent with the MASCS observations regarding the vertical profile and the seasonal variability at LT06 and LT18. However, the peak that occurs around aphelion at LT12 could not be reproduced. Yet the model produced results suggesting that less than 10 kg particles of comet stream dust per Mercury year could be the local and short-term source of Na.

The empirical Bath’s law is derived from the statistical distribution in magnitude difference of pairs of earthquakes. It is shown that earthquake correlations can be expressed by means of the magnitude-difference distribution. We introduce a distinction between dynamical correlations, which imply an “earthquake interaction”, and purely statistical correlations, generated by other, unknown, causes. The distribution of dynamically correlated earthquakes is derived from the statistical fluctuations of the accumulation time, by means of the geometric-growth model of energy accumulation in the focal region. The derivation of the Gutenberg-Richter statistical distributions in energy and magnitude is presented, as resulting from this model. It is shown that the most suitable framework for understanding the origin of the Bath’s law is the extension of the statistical distributions to pairs of earthquakes, where the difference in magnitude is allowed to take negative values. The seismic activity which accompanies a main shock, including both the aftershocks and the foreshocks, can be viewed as fluctuations in magnitude. The extension of the magnitude difference to negative values leads to a vanishing mean value of the fluctuations and to the standard deviation as a measure of these fluctuations. It is suggested that the standard deviation of the magnitude difference is the average difference in magnitude between the main shock and its largest aftershock (foreshock), thus providing an insight into the nature and the origin of the Bath’s law. Time correlations of the accompanying seismic activity are also presented.

Animal migrations mark the largest daily movement of biomass on Earth today, but who performed the first diurnal migration? Extant benthic microbial mats inhabiting Lake Huro’s low-oxygen, high-sulfur submerged sinkholes that resemble life on early Earth, may offer some answers. Herein, mats are dominated by motile filaments of purple-pigmented cyanobacteria capable of oxygenic and anoxygenic photosynthesis, and pigment-free chemosynthetic sulfur-oxidizing bacteria. We captured time-lapse images of diurnal vertical migration between phototactic cyanobacteria and chemotactic sulfur-oxidizing bacteria – dramatically turning the mat surface purple at dawn and white at dusk. Alternating waves of vertically migrating photosynthetic and chemosynthetic filaments rapidly tracked diurnally fluctuating light; observations corroborated with intact mats under simulated day-night conditions. Both types of filaments increased in surface coverage non-linearly, albeit at different rates. During their respective surface takeovers, maximum nightly rate of movement for white chemosynthetic filaments occurred an hour before that of purple cyanobacteria during the day. However, though slow to start at dawn, the cyanobacteria’s maximum rate of movement was double that of the chemosynthetic bacteria, leading to greater total coverage over the span of the day. Such synchronized diurnal “tango” might have been the largest daily mass movement of life during the long Archean and Proterozoic eras, when the biosphere was mostly benthic, and played a critical role in optimizing photosynthesis, chemosynthesis, carbon burial, and oxygenation. Further studies of extant microbial “mat worlds” will add to the expanding knowledge of Earth’s biodiversity and physiologies, and may aid our ongoing search for life in extraterrestrial waters.

Ion temperature is a key parameter that influences dynamics in the magnetosphere, such as particle transport and wave-particle interactions. Measurements of ion heating and energization yields information about phenomena such as magnetic reconnection, bursty bulk flows, and ion injections. Taking advantage of the global view provided by energetic neutral atom imaging, a database of ion temperature maps during geomagnetic storms occurring throughout the NASA TWINS mission has been created. These ion temperature maps and relevant metadata are publicly available on CDAWeb to facilitate comparison to in situ measurements and model output, for use as boundary conditions for simulations, and for other relevant studies. A preliminary study of average plasma sheet ion temperatures calculated from these maps has revealed a common occurrence of decreasing ion temperature concurrent with a sharp negative gradient in the IMF B. Two case studies are presented, supporting a hypothesis that substorm activity results in injection of high temperature ions, leaving behind an interval of lower plasma sheet temperatures.

In this paper extreme value theory (EVT) has been used to estimate the return levels for geomagnetic activity based on the aa index. The aa index is the longest, continuously recorded, geomagnetic dataset (from 1868 - Present). This long, 150 year, dataset is an ideal candidate for extreme value analysis. However the data are not independent and identically distributed as required for EVT since they are impacted by the approximately 11 year solar cycle. The Hilbert-Huang Transform has been used to identify the solar cycle component in the data and the data has been split into solar maximum and minimum times. In these two regimes the generalised extreme value distribution has been fit to the datasets. These have also been combined for an estimate of the overall return times. The results suggest that the largest event in the database (March 1989) is a one in 25 year event. However, considering separate solar maximum and minimum times has a large impact on the return times. During solar minimum conditions the return time of the March 1989 event is 130 years. This suggests that the occurrence of extreme space weather events is conditionally dependent on where in the Solar Cycle we are.

We report the radiocarbon age, chemistry, and mineralogy of sinter deposits from Castle and Giant Geyser in the Upper Geyser Basin of Yellowstone National Park. At each geyser, we sampled following the stratigraphy of the older terrace and younger cone. We analyzed 15 samples with x-ray diffraction, x-ray tomography, x-ray fluorescence, scanning electron microscopy, thin section microscopy, 3D imaging, and loss on ignition. Castle Geyser's terrace and Giant Geyser's cone are composed of more increasingly more mature sinter. The concentrations of Na, K, Cs, and Ga decrease in the sinter with decreasing H2O and increasing SiO2, therefore water and trace element concentrations correlate with stratigraphic position, and sinters exhibit progressive dehydration with increasing age. However, radiocarbon dates resulted in stratigraphically out-of-sequence ages. This suggests both physical mixing and the influence of magmatically dead carbon. By isolating and dating individual pieces of externally sourced organic material, we report ages as upper bounds---increasing the known age of Castle Geyser cone to 2,000 yr BP. Additionally, we demonstrate that Castle Geyser's shield is mineralogically distinct from and at least 1,000 years older than it's cone.

Drought forecasts, particularly at seasonal scales, offer great potential for managing climate risk in water resources and agricultural systems. In this context, the importance of assessing the economic value of such forecasts and determining whether a decision-maker should adopt them cannot be overstated. Value-assessment studies often, however, ignore the dynamic aspects of forecast adoption, despite evidence from field-based studies suggesting that farmers’ forecast-adoption behavior fits the general framework of innovation diffusion, i.e. that forecast adoption is a dynamic learning process that takes place over time. In this study, we develop an agent-based model of drought forecast adoption to study the role played by heterogeneous economic and behavioral factors (i.e. risk aversion, wealth, learning rates), forecast characteristics (i.e. accuracy), and the social network structure (i.e. inter- and intra-county ties, change agents, self-reliance) in the process of forecast adoption and diffusion. We consider two learning mechanisms: learning by doing, represented by a reinforcement-learning mechanism, and learning from others, represented by a DeGroot-style opinion-aggregation model. Results show that, when social interactions between agents occur, forecast adoption follows a typical S-shaped diffusion curve. By contrast, when agents rely only on their own experience, the adoption pattern is close to linear. Our numerical experiment shows additionally that forecasts are never adopted if forecast accuracy drops below 65 percent. Finally, the proposed model also provides a flexible tool with which to test the effectiveness of extension targeting strategies in facilitating the diffusion of forecasts.

This technical report summarizes the GLOBE Observer dataset from 1 April 2016 to 1 December 2019. GLOBE Observer is an ongoing NASA-sponsored international citizen science project that is part of the Global Learning & Observations to Benefit the Environment (GLOBE) Program. GLOBE Observer is the largest citizen science project in the Earth Science Division at NASA. Participants use the GLOBE Observer mobile app (launched in 2016) to collect atmospheric, hydrologic, and terrestrial observations. 38,000 participants have contributed 320,000 observations worldwide, including 1,000,000 geotagged photographs. It would take an individual more than 13 years to replicate this effort. Comparing the same data types between the GLOBE Observer app and the formal GLOBE Program, the app doubled data volume and substantially increased geographic coverage over the study period. GLOBE Observer data are publicly available at observer.globe.gov.

This chapter describes the two major types of impulsive magnetic energy release on the sun: flares and coronal mass ejections (CMEs). The sections include a brief historical overview, a description of observational signature and detection properties, a section on theoretical considerations and outstanding problems, and a final brief section on the field of space weather and anticipated future developments in the field.

We propose a semi-quantitative model of the initiation and early evolution of a mud volcano. Basin modeling was calibrated against our previous seismic interpretation of the Absheron mud volcano and surroundings in the South Caspian Basin on the one hand, analysis of geological samples from seabed and two exploration boreholes on the other. Some input parameters of the model were derived from laboratory testing of samples from the mud volcano and we used a constitutive law obtained from a previous laboratory study showing the extent to which gas exsolution may damage host sediments, eventually leading to mud generation from compacted sediments. The study identified key geological and physical conditions that led to mud volcano formation: coupling diffusion processes with hydrofracturing and fluid advection, we were able to simulate conditions required to generate mud 3.5 km below the Absheron mud volcano. We also modeled mud remobilization up to the seabed using Navier-Stokes equations modified to account for the impact of gas expansion on mud density. Considering density inversion only, simulations indicate that mud would be extruded at the seabed 100 years after its generation, an ascent rate similar to extrusion rates measured at some active mud volcanoes in Azerbaijan, e.g. the Kotyrdag mud volcano. These models considering eruption dynamics provide semi-quantitative support to purely conceptual formation models based on seismic interpretation of subvolcanic stratal geometry.

The interaction between two complex systems, turbulent flow and multi-sized bed sediment causes considerable fluctuations in sediment transport rates and displays different characteristics depending on the scale of the observation. To explore this phenomenon, we measured grain-size specific transport rates in a flume experiment at 1 s resolution. The analysis of the time series of these transport rates reveals either individual or collective transport regimes at different sampling intervals. We compare the sampling intervals of these regimes for differently sized particles with the time scales of turbulent structure formation. This comparison informs the presentation of a heuristic model, in which small suspended particles swirl in the wake vortices of keystones until large to very-large-scale coherent structures transport those suspended particles downstream. Keystones consequently destabilize and in turn, collectively entrain another group of sheltered particles. We suggest that interactive cascades, such as this one, should be incorporated in sediment transport models.

The equatorial region of the slow-spreading Mid-Atlantic Ridge is characterized by several major transform faults, which are some of the longest on Earth. Among them, the St. Paul Transform system (SPTS) is a complex group of four transform faults, bounding three short intra-transform segments with total offset of 630 km. The northernmost transform is the 200 km-long, 30 km-wide Atoba Ridge, which represents a major topographic feature that rises above sea level at the St. Peter and St. Paul islands (SPSPA). This push-up ridge formed from transpressive stresses along several transform fault step-overs and restraining bends, uplifting mantle rocks at a rate of ~1.5 mm/yr. Moderate-sized earthquakes (>4.0 Mw) have been located by global teleseismic networks along the SPTS and near region. These earthquakes are recorded at large epicentral distances, and include raypaths that travel within the upper mantle (Pn and Sn phases). Pn velocity estimates can help to understand the dynamics of upper mantle structure around of the transform faults. Here, waveforms recorded over ~6 months of 2012 by two autonomous hydrophones moored north and south of SPTS (EA-2 and EA-8), and a seismographic station installed on SPSPA island (ASPSP station) are examined. These data allow us to make Pn velocity estimates from 32 earthquakes that occurred in the SPTS region from 1.5º S to 4.5º N. Pn wave velocities are typically thought to be 8.0–8.2 km/s in upper mantle, however we identify Pn velocities ranging from 7.5 to 9.0 km/s. The slower velocities (7.5-8.0 km/s) are from ray paths oriented parallel to the ridge axis and could be explained by elevated mantle potential temperature and the presence of melt. Ray paths passing through the transform fault system have Pn velocities from 8.1 to 9.0 km/s, indicating that upper mantle conditions are strongly affected by the presence of the crustal fault system. We will also compare our velocity estimates to global shear-wave tomographic models of the upper mantle. Hence it is our goal to show that the availability of autonomous hydrophones and a single island seismic station can be used to make rare estimates of Pn velocities, as well as provide insights into upper mantle structure, in this remote part of the Atlantic Ocean.

The subducting slab morphology in the mantle transition zone (MTZ) is strongly affected by the mantle viscosity and density variations at the 660-km discontinuity (D660). Besides the negative Clapeyron slope of phase transition and the viscosity increase, a possible thin weak layer at around D660 is proposed to play a key role in the slab stagnation, which is however not well constrained. In this study, a series of numerical models are systematically conducted, which reveal that a weak layer beneath D660 does not change the slab mode selection (penetration versus stagnation). However, it will contribute to longer slab flattening at the bottom of the MTZ, when slab sinking is strongly resisted by either the viscosity increase or a large Clapeyron slope at D660. The role of a weak layer on slab flattening is dependent on the lubrication effect that promotes sub-horizontal slab movement at the bottom of the MTZ.

The aerodynamic roughness length is a crucial parameter that controls surface variables including the horizontal wind, surface temperature, and heat fluxes. Despite its importance, in the Weather Research and Forecasting (WRF) model, this parameter is typically assigned a predefined value, mostly based on the dominant land-use type. In this work, the roughness length is first estimated from eddy-covariance measurements at Al Ain in the United Arab Emirates (UAE), a hyper-arid region, and then ingested into WRF. The estimated roughness length is in the range 1.3 to 2.2 mm, one order smaller than the default value used in WRF. In line with previous studies, and from WRF model simulations during the warm and cold seasons, it is concluded that, when the roughness length is decreased by an order of magnitude, the horizontal wind speed increases by up to 1 m s, the surface temperature rises by up to 2.5ºC, and the sensible heat flux decreases by as much as 10 W m. In comparison with in situ station and eddy covariance data, and when forced with the updated roughness length, WRF gives more accurate 2-m air temperature and sensible heat flux predictions. For prevailing wind speeds > 6 m s, the model underestimates the strength of the near-surface wind, a tendency that can be partially corrected, typically by 1-3 m s, when the updated roughness length is considered. For low wind speeds (< 4 m s), however, WRF generally overestimates the strength of the wind.

Due to the complex physical and biogeochemical conditions, the adjacent South Yellow Sea (SYS) and East China Sea (ECS) are ideal sites for studying different carbonate characteristics in marginal seas. The distributions of carbonate system parameters were investigated in this region in early spring and summer. Overall, dissolved inorganic carbon (DIC) and alkalinity concentrations in the SYS were higher than those in the ECS due to the Yellow River runoff which was featured with intensive carbonate weathering and erosion. Low DIC, alkalinity and high pH values were observed in the Zhe-Min Coastal Current with intensive primary production in spring caused by the Changjiang River and Taiwan Warm Current. Temperature and biological activities were the primary drivers in controlling the partial pressure of CO2 (pCO2) variability in the SYS, whereas temperature was the only dominant factor in the outer shelf of the ECS, which was heavily impacted by the Kuroshio Current. The pCO2 dynamics was controlled by primary production and physical mixing in the Changjiang River plume and the inner and middle shelves of the ECS, due to the influence of the Changjiang River with high nutrient supply. Overall, strong CO2 sinks (-4.11 ± 5.28 mmol m-2d-1) turned into weak sources (0.88 ± 5.09 mmol m-2d-1) in the entire study area from spring to summer. Specifically, the SYS and ECS offshore waters changed from CO2 sinks in spring to sources in summer, while the Changjiang River plume always served as a CO2 sink.

We propose a novel and accurate calibration method for short-time waveform signals passed through a linear time-invariant (LTI) system that has a non-negligible group delay. Typically, the calibration process of waveform data is expressed by the Fourier transform and is performed in the frequency domain. If the short-time Fourier transform is applied to the waveform data in the calibration process, multiplying the data by a window function is highly recommended to reduce side-lobe effects. However, the multiplied window function is also modified in the calibration process. We analyzed the modification mathematically and derived a novel method to eliminate the modification of the multiplied window function. In the novel method, calibrated data in the frequency domain are inverse-transformed into waveform data at each frequency, divided by a modified window function at each frequency, and accumulated over the frequencies. The principle of this method derived quantitatively indicates that the calibration accuracy depends on the transfer function of the system, frequency resolution of the Fourier transform, type of the window function, and typical frequency of the waveform data. Compared with conventional calibration methods, the proposed method provides more accurate results in various cases. This method is useful for calibration of general radio wave signals through passed LTI systems as well as for calibration of plasma waves observed in space.

The high sensitivity of tropical hydro-climate to the mean position of the intertropical convergence zone (ITCZ) at different time scales is well known. However, recent research suggests a more complex behaviour of the northern hemispheric tropical rain belts in the western tropical Atlantic. Here we present a precisely dated speleothem multi-proxy record from a well-monitored cave from Puerto Rico, covering the period between 46.2 and 15.4 ka BP in unprecedented resolution. This allows the investigation of multi-decadal to millennial-scale climate variability. The proxy records document a pronounced response of regional rainfall to abrupt centennial to millennial-scale climatic excursions in the North Atlantic across the Last Glacial (i.e., Heinrich Stadials and Dansgaard/Oeschger events). In particular, we observe a strong agreement between the speleothem proxy data and the strength of the Atlantic meridional overturning circulation, supporting a persistent link of regional precipitation to oceanic forcing. Spectral analysis suggests that multi-decadal to centennial variability persisted in the regional hydro-climate not only during stadial and interstadial conditions, but also during the Last Glacial Maximum, supporting the hypothesis that the Atlantic low-latitude regions respond to internal modes of climate variability on these time scales regardless of the global climate state. The compilation with other paleo-precipitation records enables the reconstruction of past changes in position, strength and extent of the ITCZ in the western tropical Atlantic in response to millennial and orbital global climate change.