Seasonal and diurnal variability of atmospheric CO2 and its driving factors are studied using its continuous monitoring of concentration and isotopic ratios (δ13C-CO2 and δ18O-CO2) for the first time over Shadnagar, a sub-urban location of India with high precision in-situ data from November 2018 to October 2019. The annual averaged atmospheric CO2 concentrations, δ13C-CO2 and δ18O-CO2 are 414.76±4.26 ppm, -11.19±1.63 ‰ and 9.02 ±12.78 ‰. Maximum seasonal diurnal variability of atmospheric CO2 was observed in summer monsoon (17.30 ± 9.29 ppm) and the minimum was noticed in winter (7.19 ± 0.11 ppm) indicating strong seasonality at the study site. To characterize the atmospheric CO2 sources, an improved model of Miller and Tans was implemented by plotting DCO2 against D(CO2 ×δ13C) respectively during day and night. However, a strong source/sink signature of δ13C was observed during nighttime of summer monsoon with a slope of -37.42 ± 0.73 ‰, obtained using a reduced major axis (RMA) regression.The source identified is attributed to combustion and dominance of C3 ecosystem respiration respectively. The seasonal relationship between δ18O-CO2 and δ13C-CO2 is strongly correlated during pre-monsoon ( ‘r’ = 0.93-0.95) than post-monsoon (‘r’ = 0.07-0.13), which might be due to high vapour pressure deficit. A Lagrangian back-trajectory model confirms the influence of the Indian summer monsoon on the variability of atmospheric CO2 concentration during the summer monsoon season.

Fracture geometry, density, and distribution control fluid and thermal transport in low porosity rocks, as well as their seismic attributes. The creation of cracks throughout the matrix can result in large and disparate reductions in P- and S-wave velocities with negligible porosity development, which breaks the classic velocity-porosity relationship. Properly interpreting these signatures in seismic surveys from stimulated geothermal, oil, and gas reservoirs or seismogenic areas requires a rock physics model that uses realistic elastic properties of fractures. Conventional models for cracked rocks employ specific inclusion shapes such as spheroids with small aspect ratios. However, all these exhibit the same normal-to-shear compliance ratio -- regardless of aspect ratio -- and therefore impact the bulk and shear moduli in the same qualitative way. As such they are inadequate for describing many of the complementary evolutions of P- and S-wave velocities that transpire with the generation of cracks. Using a differential model of dimensionless compliances, we analyze published velocities for granite, basalt, and limestone to quantify typical compliance ratios and find that it is often different from that assumed in conventional crack models, which then affects crack density estimates. We also investigate how the total normal and shear compliances change due to certain thermo-hydro-chemo-mechanical processes that generate large crack densities, and conclude that the final ratios often still deviate from that of conventional models. Finally, we demonstrate how the model can be used to describe scatter in both P- and S-wave velocity-porosity trends. Implications for energy extraction and seismic monitoring are discussed.

With LOFAR we have been able to image the development of lightning flashes with meter-scale accuracy and unprecedented detail. We discuss the primary steps behind our most recent lightning mapping method. To demonstrate the capabilities of our technique we show and interpret images of the first few milliseconds of two intra-cloud flashes. In all our flashes the negative leaders propagate in the charge layer below the main negative charge. Among several interesting features we show that in about 2 ms after initiation the Primary Initial Leader triggers the formation of a multitude (more than ten) negative leaders in a rather confined area of the atmosphere. From these only one or two continue to propagate after about 30 ms to extend over kilometers horizontally while another may propagate back to the initiation point. We also show that normal negative leaders can transition into an initial-leader like state, potentially in the presence of strong electric fields. In addition, we show some initial breakdown pulses that occurred during the primary initial leader, and even during two “secondary” initial leaders that developed out of stepped leaders.

Understanding the origin of seismic swarms can be controversial, especially when they occur near volcanic areas. Here, we investigate a seismic sequence which is steadily active in a non-volcanic area close by the volcanic field of Harrat Lunayyir in the western shield of Arabia. Our results unveil a planar zone of seismicity with ~5 km long E-W, sub-vertically ~9 km south-dipping structure, which is characterized by a dominant tensional focal mechanism. Independent evidence for the tectonic style dominance came from assessing the ground deformation images using the InSAR technique. This local seismicity might be attributed to a reactivated structure along a regional weakness zone of the Najd Fault System, which dominates the Precambrian structure of our area. Comparing the effects of high- and low-frequency datasets for the moment tensor inversion conclude a consistency of our solution. The frequency index analysis for P- and S- waves spectral datasets, does not suggest fluid-driven processes. We observe average stress drop of ~5.40 MPa with corner frequency of ~2.75 Hz. Our study confirms a localized reactivation of a brittle crustal seismogenic zone in the area of interest. This interpretation relies on the integration of several analysis methods, including spatial and magnitude-frequency distributions statistics.

Cirrus control the longwave radiative budget of the tropics. For the first time, we quantify the variability in cirrus properties and longwave cloud radiative effects (CREs) that arises from using different bulk ice microphysical parameterizations within a single global storm-resolving model. We run five-day meteorologically-nudged simulations with four commonly-used microphysics schemes (M2005, Thompson, P3 and SAM1MOM) and evaluate them with satellite products and in situ observations. Tropical average longwave CRE varies over 20 W m$^{-2}$ between schemes. Within the Thompson scheme, rapid autoconversion of cloud ice to snow leads to deficient anvil cirrus even with radiatively active snow. SAM1MOM, which uses saturation adjustment for cloud ice, also has deficient anvil cirrus. M2005 and P3 simulate cirrus with realistic frozen water path, and P3 best reproduces observed longwave CRE. Even in those schemes, ice crystal number concentrations commonly hit limiters and lack the observed variability and dependence on frozen water content.

This paper examines the response of the upper atmosphere to equatorial Kelvin waves with a period of ~3 days, also known as ultra-fast Kelvin waves (UFKWs). The whole atmosphere model GAIA is used to simulate the UFKW events in the late summer of 2010 and 2011 as well as in the boreal winter of 2012/2013. When the lower layers of the model below 30 km altitude are constrained with meteorological data, GAIA is able to reproduce salient features of the UFKW in the mesosphere and lower thermosphere as observed by the Aura Microwave Limb Sounder. The model also reproduces ionospheric response, as validated through comparisons with total electron content data from the GOCE satellite as well as with earlier observations. Model results suggest that the UFKW produces eastward-propagating ~3-day variations with zonal wavenumber 1 in the equatorial zonal electric field and F-region plasma density. Model results also suggest that for a ground observer, identifying ionospheric signatures of the UFKW is a challenge because of ~3-day variations due to other sources. This issue can be overcome by combining ground-based measurements from different longitudes. As a demonstration, we analyze ground-based magnetometer data from equatorial stations during the 2011 event. It is shown that wavelet spectra of the magnetic data at different longitudes are only in partial agreement, with or without a ~3-day peak, but a spectrum analysis based on multipoint observations reveals the presence of the UFKW.

Based on 16-year MODIS-Aqua (MODISA) satellite products, a new method is used to derive vertical Chl distributions in the equatorial and North Indian Oceans. The Chl seasonal and interannual variabilities are examined. The Bay of Bengal (BoB) experiences summer surface Chl (SChl) increases in the areas south and east of Sri Lanka, and SChl increases in the southwestern bay during the winter monsoon. The SChl high in the Sri Lanka Dome (SLD) exists as an annual feature along the time series. SeasonalSChl variance is characterized by a distinct vertical evolution of the mixed layer depth (MLD), with the SChl increase appearing with a shallow MLD in the SLD, while SChl increase with MLD deepens in the southwestern bay in winter. The less productive southern equatorial region explains most of the interannual anomalies with diploe structures present in both the physical fields and Chl. We observed a close correlation between the Indian Ocean dipole (IOD) and the physical field anomalies, such that the wind stress curl is positively correlated with IOD in the easternequatorial India Oceanand negatively correlated in the south, with the opposite pattern observed in sea surface height (SSH) with IOD. Both surface and subsurface Chl anomalies are closely related to IOD, suggesting the bottom-up transition of thermocline feedback to biology under the remote and local influence of IOD. The advent of depth-resolved satellite Chl improves the understanding of the Chl response to changes in the environment under potential climatic feedbacks in the North Indian Ocean.

Slovakia is located within the Central Western Carpathians (CWC), one of many connected curved mountain belts prominent throughout the Mediterranean area and Europe. It is divided into tectonic domains considered “superunits,” termed the Gemeric, Veporic, and Tatric that correlate to the lower, middle, and upper Austoalpine nappes. For example, granite bodies exposed in the unit (termed apophyses) yield a wide range of zircon ages from 310±21 Ma to 87±4 Ma. This range of ages leads to problems in deciphering where the Gemeric unit was located in global plate reconstructions of eastern Europe and the western Carpathians specifically. This case study involves U-Pb dating of magmatic and detrital zircons from the Gemeric tectonic unit. This area records the Variscan orogeny that formed the CWC, rifting, and opening of the Meliata Ocean. This ocean was created due to the formation of a back-arc basin during closing/subduction of the Paleo-Tethys Ocean. We aim to constrain the timing of rifting and identify the provenance of Meliata Ocean radiolarian sediments collected from an obducted Meliata ophiolite suite (Dobsina, Slovakia). The relative age of the Variscan orogeny extends from the late Devonian to early Permian and was followed by rifting throughout the Mesozoic within the CWC. Eventually, the Meliata Ocean closed during the Cretaceous. Zircons from several S-type granites were collected throughout the Gemeric tectonic unit; they were dated using Laser Ablation Inductively Coupled Plasma Mass Spectrometry and imaged using cathodoluminescence. Rim crystallization ages from the granites are 295.8±3.4 Ma (2σ, 238U-206Pb) to 213.1±4.4 Ma. Ages from the detrital zircons are 346.4±4.5 Ma to 263.9±2.7 Ma, indicating that sediments overlying the Meliata Ocean ophiolite contain remnants of both the Variscan orogeny and Gemeric granites.

The rise of the ecosystem services concept has brought some characteristics of the water cycle to the attention of a broader audience who are not necessarily intrinsically familiar with hydrological processes. When referring to water supply, the term “hydrological regulation” (or streamflow buffering) is frequently used by non-hydrologists, yet they are often lost in the intricacies of the processes that drive it leading to confusion and misunderstandings. It is not uncommon that several water security challenges that require the conservation or enhancement of hydrological regulation end up prioritizing actions that aim at increasing water yield instead. Here, I present a simple index named “baseflow yield coefficient” (BYC), which is calculated as the ratio between baseflow (or dry season flow) and precipitation for a given period of time. Although quite simple, this might be a powerful tool to quantify both water yield and hydrological regulation and to provide an accessible and transparent variable that addresses the aforementioned issue. By using this index, I aim to guide the conversation to achieving more effective water security investments while, at the same time, seek to prevent having to revive the misunderstanding between water yield and hydrological regulation, so that we can move directly on to more relevant matters.

An obvious interdecadal change is measured in the super cyclones (SCs, categories 4 and 5) that occur from Oct-Nov over the Bay of Bengal (BoB). This change may be modulated by the interdecadal Pacific oscillation (IPO). A La Niña-like difference between the 1977–1998 (IP1) and 1999–2014 (IP2) periods forces a local Hadley circulation in the eastern tropical Indian Ocean by strengthening the Walker circulation, causing a plummeting upper-level temperatures and ultimately creating favorable thermodynamic conditions to enhance the cyclone intensity. Meanwhile, an equatorial downwelling Kelvin wave caused by heating and westerly wind differences enters the BoB rim along the coast and aptly intensifies the cyclone such that the downwelling Kevin wave and Rossby wave generated by its reflection deepen the thermocline in the BoB. The favorable atmospheric and oceanic conditions in IP2 jointly and preferentially form far more SC activities from Oct-Nov over the BoB compared to IP1.

Most particle motions on Earth's surface are fundamentally stochastic and often occur under rarefied transport conditions. Every particle makes a unique path along the bed, similar but distinct from the paths of all other particles in motion, until it loses enough kinetic energy to become disentrained. The details of a particle's motion are determined by the amount of energy added and extracted during each moment of travel. Thus, particle motions physically reflect the complex energy dynamics at play and are a building block of morphodynamic theory. A full appreciation of this energy balance is needed to properly describe the motion of particles and associated disentrainment under different transport conditions. Often multidimensional behaviors occur during transport as both a result of and influence on these particle scale energy dynamics. One such phenomenon is that of particle-scale random walking during transport which results in diffusion over short timescales in both the downstream and transverse directions. We have adopted the Galton board as the fundamental conceptual model on which to create a mechanistic yet probabilistic formulation of particle diffusion. Here we provide a data set of two-dimensional particle travel distances supplemented with high-speed videos of particle-surface collisions collected during laboratory experiments to characterize the influence of shedding fluid vortices and angularity on collisional distances and two-dimensional travel for particles at low Reynolds numbers. Such a description is consistent with diffusion from the top-down and may be distinct from the bottom-up, or surface roughness, controlled random walking that other studies have explored. Preliminary analysis shows that spherical particles experience jiggling motions resulting in transverse displacement in the absence of surface roughness and this behavior is further exaggerated for particles of natural angularity. We hope to clarify the influence of the particle Reynolds number in top-down and bottom-up spreading.

Abstract Based on the round-trip intelligent sounding system, we used the structure function and spectrum analysis method to analyze the interaction between the small-scale gravity wave and turbulence in the middle stratosphere. The result showed that the generation of turbulence was closely related to the Kelvin-Helmholtz(KH) billows. An upscale energy cascade occurred on the spatial scale of KH billows, while a downscale energy cascade occurred on a larger spatial scale (gravity wave scale), which resulted in the breaking of the gravity wave and turbulence. Obvious two-dimensional turbulence that the inverse energy cascade in 2D exists simultaneously with a direct enstrophy cascade to the small scales was found, which is considered to be the first-hand observation result of relevant height.

Based on the round-trip intelligent sounding system, we used the structure function and spectrum analysis method to analyze the interaction between the small-scale gravity wave and turbulence in the middle stratosphere. The result showed that the generation of turbulence was closely related to the Kelvin-Helmholtz(KH) billows. An upscale energy cascade occurred on the spatial scale of KH billows, while a downscale energy cascade occurred on a larger spatial scale (gravity wave scale), which resulted in the breaking of the gravity wave and turbulence. Obvious two-dimensional turbulence that the inverse energy cascade in 2D exists simultaneously with a direct enstrophy cascade to the small scales was found, which is considered to be the first-hand observation result of relevant height.

With a linear theoretical model, we have investigated the properties of whistler waves excited by anisotropic hot electrons with a drift velocity, which is usually neglected in previous studies. It is found that a finite drift velocity can significantly change the properties of excited whistler waves, resulting in distinct properties for parallel and antiparallel propagating waves. In the high-beta regime, as the drift velocity increases, the frequency of parallel propagating whistler waves increases, while that of antiparallel propagating waves is found to decline. So parallel and antiparallel propagating whistler waves appear in different frequency bands. However, the growth rate of parallel wave is always smaller than that of antiparallel wave, and falls below 10Ω for large drift velocities (v/v>1.5), in which case the parallel wave may be too weak to be observed. Generally, the growth rate of whistler waves in both directions is enhanced with the increasing anisotropy or proportion of hot electrons. In the low-beta regime, the trends of the frequency and linear growth rate of excited whistler waves are quite similar to those in the high-beta regime. But, with the increase of the drift velocity, the wave normal angle of parallel propagating whistler waves gradually declines until reaching zero, while that of antiparallel propagating waves continues to increase. Our study may help people to better understand various whistler-mode spectra observed in the Earth’s magnetosphere.

The Orinoco low-level jet (OLLJ) is characterized using finer horizontal, vertical, and temporal resolution than possible in previous studies via dynamical downscaling. The investigation relies on a 5-month-long simulation (November 2013-March 2014) performed with the WRF model, with initial and boundary conditions provided by the GFS analysis. Dynamical downscaling is demonstrated to be an effective method not only to better resolve the horizontal and vertical characteristics of the Orinoco low-level jet but also to determine the mechanisms leading to its formation. The OLLJ is a single stream tube over Colombia and Venezuela with wind speeds greater than 8 m s-1 , and four distinctive cores of higher wind speeds varying in height under the influence of sloping terrain. It is an austral summer phenomenon that exhibits its seasonal maximum wind speed and largest spatial extent (2100 km × 450 km) in January. The maxima diurnal mean wind speeds (13–17 m s-1) at each core location occur at different times during the night (2300–0900 LST). The momentum balance analysis in a natural coordinate system reveals that the OLLJ results from four phenomena acting together to accelerate the wind: a sea-breeze penetration, katabatic flow, three expansion fans, and diurnal variation of turbulent diffusivity. The latter, in contrast to the heavily studied nocturnal low-level jet in the U.S. Great Plains region, plays a secondary role in OLLJ acceleration. These results imply that LLJs near the equator may originate from processes other than the inertial oscillation and topographic thermal forcing.

The predicted increasing ground temperatures in the Arctic results in the deepening of the active layer and intensification of geochemical processes, which could affect the geochemical composition of surface waters. Determining the responses of the riparian soil systems to surrounding hydrological flows under changing climate conditions is important for understanding the seasonal changes in hydrological processes. Therefore, in this study, one soil core from the study area polygon rim (close to the Taz River, TA) and two soil cores from the riverain terrace (close to the Syoyakha River, SY and Murtyyakha River, MU) in Russian Western Siberia and their supra-permafrost water, adjacent stream flows and river water were sampled for analysis of geochemical elements. The results showed that most elements above their respective detection limits (Mn, Sr, Fe, Mg, Cr, Co, V, Pb, Al and Ca) started to accumulate in the downwards gleyed layer during September–October in response to the deepest thaw in the active layer. This study focused on the highly mobile elements, i.e., Mn, Ca, Mg, Al and Ti, in the deepest layer; and found the transport of organic matter in the upper layer carried these elements to both surface water ponds/flows and supra-permafrost water, and further, to the rivers. The best linear correlation for both stream flows and river water were Mn, which may be a proxy for predicting the processes occurring within the active layer during the annual summer-autumn thaw. Finally, landscapes with different ice contents may experience changes in the elements transported to surface waters.

Many studies have documented the trends in the latitudinal position and strength of the midlatitude westerly jet in the Southern Hemisphere. However, very little attention has been paid to the longitudinal variations of these trends. Here, we specifically focus on the zonal asymmetries in the southern jet trends between 1980-2018. Meteorological reanalyses show a robust strengthening and an equatorward shift of the annual-mean and springtime jet over the Pacific sector, in contrast to a weaker strengthening and poleward shift over the Atlantic and Indian Ocean sectors. The reanalysis trends fall within the ensemble spread for historical climate model simulations, showing that climate models are able to capture the observed trends. Climate model simulations indicate that the differential movement of the jet is a manifestation of internal variability and is not a forced response. Implications of these asymmetries for other components of the climate system are discussed.

This study investigates the impacts of wildfire aerosols (primary organic carbon, black carbon and sulfate) on the Northern hemispheric boreal winter climate. We found that wildfire aerosols emitted from equatorial Africa result in two mid-high latitude Rossby wave trains. One is from subtropical Atlantic propagating northward across Europe to Siberia, and the other one propagates eastward from Mid-East across Asia to Northwest Pacific. The maximum positive height anomaly locates in Europe, concurrent with a greater-than-2K surface warming. These Rossby wave trains are excited by the atmospheric heating in equatorial Africa and propagate into extratropics with the help of the westerly jet. Through the heat budget analysis, the source of the Rossby wave is primarily due to the solar absorption of black carbon in Africa. The present study emphasize that aerosols especial the absorbing aerosols would have profound thermo-dynamic effects on remote regions and need more attentions.