Shallow Component Research Articles

Spatial Distribution of Earthquake Occurrence for the New Zealand National Seismic Hazard Model 2022

ABSTRACT We develop candidate hybrid models representing the spatial distribution of earthquake occurrence in New Zealand over the next 100 yr. These models are used within the onshore/near-shore, shallow component of the distributed seismicity model within the New Zealand National Seismic Hazard Model 2022. They combine a variety of spatially gridded covariates based on smoothed seismicity, strain rates, and proximity to mapped faults and plate boundaries in both multiplicative and additive hybrids. They were optimized against a standardized catalog of New Zealand earthquakes with magnitude M ≥ 4.95 and hypocentral depth ≤40 km from 1951 to 2020. We extract smoothed seismicity covariates using three different methods. The additive models are linear combinations of earthquake likelihood models derived from individual covariates. We choose three preferred hybrid models based on the information gain statistics, consideration of the ongoing Canterbury sequence and regions of low seismicity, and inclusion of the most informative covariates. Since the hazard model is designed for the next 100 yr, the preferred hybrid models are also combined with 20-year earthquake forecasts from the “Every Earthquake a Precursor According to Scale” model. Thus, in total, six hybrid spatial distribution candidates are advanced for sensitivity analyses and expert elicitation for inclusion in the final logic tree for the New Zealand National Seismic Hazard Model.

Deep Attentive Interest Collaborative Filtering for Recommender Systems

Collaborative filtering (CF) is a pivotal building block in commercial recommender systems due to its strength and utility in user interest modeling. Recently, many researchers have turned to deep learning as a way to capture richer collaborative signals from user-item feature interactions. However, most deep-based methods only consider nonlinear, high-order interactions while ignoring the explicit collaborative signals in low-order interactions. They also typically ignore the quality of the user and item profiles. These are cornerstones in item recommendation that, we argue, must be considered for high-quality recommendations. Hence, we propose Deep Attentive Interest Collaborative Filtering (DAICF) to overcome these limitations. DAICF profiles users based on their interactive items, i.e., user neighborhood information. Similarly, item profiles are based on users who had interacted with it, i.e., item neighborhood information. Given a user's profile varies over different items, DAICF accurately models his attentive interests based on the specific target item. Low-order collaborative signals are captured by a shallow component, and high-order collaborative signals are captured by a deep component. These two complementary collaborative signals are then fused to provide rich recommendations that cut through today's information overload. By designing a personalized feature extraction method based on bilateral neighborhood information to solve the data sparsity problem in recommender systems, DAICF can dynamically distinguish the importance of a user's historical interaction items for predicting user preferences for a specific target item. A set of experiments against four real-world datasets validate that DAICF outperforms the most recent state-of-the-art recommendation algorithms and justifies the effectiveness and interpretability of our method.

A timeseries supervised learning framework for fault prediction in chiller systems

Chiller systems play a critical role in large-scale commercial buildings, providing air-conditioning to occupied spaces and possibly also providing cooling to other process equipment. When faults occur in these systems, significant energy can be wasted, and costly maintenance may be necessary to restore the equipment to working conditions. Meanwhile, occupant comfort or operational efficiency may be sacrificed due to the lost cooling capacity. To help avoid these issues, various fault detection and diagnosis (FDD) approaches have been proposed and developed to automatically detect and diagnose faulty conditions in chiller systems. Unfortunately, merely detecting faults may not be sufficient to fully mitigate the ill effects. If instead faults can be predicted ahead of time, then operators may be able to take corrective action to prevent the faults from occurring in the first place. Nevertheless, fault prediction has rarely been investigated, perhaps due to its inherent challenges compared to standard FDD. In this work, we develop a machine-learning-based modular framework to predict faults in chiller systems based on timeseries sensor data. Specifically, the overall model consists of autoencoder, classifier, and thresholder components, with multiple variants of each component type. These models undergo supervised training using labeled data containing both normal and faulty instances. To validate the proposed approach, we leverage various deep and shallow components (see the Terminology defined in Section 4) in the modular framework with data collected from multiple chillers over one or more years of operation. Sample results show the efficacy and applicability of the framework for fault prediction, thus illustrating the potential for real-world application.

Convection Self‐Aggregation in CNRM‐CM6‐1: Equilibrium and Transition Sensitivity to Surface Temperature

AbstractThis study investigates the spontaneous self‐aggregation of convection in non‐rotating Radiative‐Convective Equilibrium (RCE) simulations performed by the CNRM‐CM6‐1 General Circulation Model within the framework of the RCE Model Intercomparison Project (RCEMIP). In this model, the level of convection self‐aggregation at equilibrium, as quantified by metrics based on moisture or moist static energy, strongly increases with sea surface temperature (SST). As it gets warmer, the troposphere gets drier, high cloud cover diminishes in dry regions, the top of high cloud rises and their thickness increases in moist regions, and low‐cloud cover increases. At high SSTs, the large‐scale circulation exhibits a shallow component, stronger than its deep counterpart. The transition toward self‐aggregation has a similar first 20‐day phase for all SSTs within the 295–305 K range. It primarily involves radiative positive feedback processes. Then, for SSTs above approximately 298 K, a new, slower, transition toward higher levels of self‐aggregation occurs. It is concomitant with a shift from a top‐heavy to a more bottom‐heavy large‐scale circulation, a strengthening of the shallow circulation and a reduced mobility of convective aggregates. This second transition is mostly driven by the dry regions, still involves longwave radiative positive feedbacks, but also advective positive feedbacks in the driest regions. It is argued that boundary‐layer radiative cooling difference between moist and dry regions, which is stronger at high SSTs, is instrumental in this second phase of self‐aggregation. The sensitivity of deep convection to environmental dry air also likely acts as a positive feedback on the system.

Click-Through Rate Prediction Algorithm Based on Modeling of Implicit High-Order Feature Importance

<p>Click-through rate (CTR) prediction plays a central role in online advertising and recommendation systems. In recent years, with the successful application of deep neural networks (DNNs) in many fields, researchers have integrated deep learning into CTR prediction algorithms to model implicit high-order features. However, most of these existing methods unify the weights of implicit higher-order features to predict user behaviors. The importance of such features of different dimensions for predicting user click behaviors are different. Base on this, we propose a prediction method that dynamically learns the importance of implicit high-order features. Specifically, we integrate the output features of deep and shallow components, and adaptively learn the weights of implicit high-order features from among all features through the designed attention network, which effectively capturing the deep interests of users. In addition, this framework has strong versatility and can be combined with shallow models such as Logistic Regression (LR) and Factorization Machines (FMs) to form different models and achieve optimal performance. The extended experiment is conducted on two large-scale datasets, AVAZU and SafeDrive, and the experimental results show that the performance of the proposed model is superior to that of existing baseline models.</p> <p> </p>

An extended period of extremely weak geomagnetic field suggested by palaeointensities from the Ediacaran Grenville dykes (SE Canada)

Long-term variations of the geomagnetic field, observed in the palaeomagnetic record, have the potential to shed much light on the evolution of Earth's deep interior. With a geomagnetic field characterised by anomalous directions and ultra-low intensities, the Ediacaran period (635-538 Ma) is a time of special interest. Steep and shallow directions, leading to virtual geomagnetic poles (VGPs) separated by angles of up to 90° and very close in age could have recorded a geomagnetic field switching between axial and equatorial dipole-dominated states. Alternatively, the field may simply have been highly nondipolar and subject to rapid reversals. Palaeointensity determinations of units that record the anomalous directions could potentially help to discriminate between morphologies but the spatial and temporal distribution of palaeomagnetic data require improvement. Here we present new palaeointensities from 6 dykes from the western end of the Grenville Dyke swarm that recorded directionally anomalous geomagnetic fields around ∼585 Ma. Results from double-heating Thellier experiments failed to satisfy the used selection criteria, but successful microwave Thellier, Shaw and pseudo-Thellier experiments lead to palaeointensities that show field strength values of 2.9 ± 2.2 μT and corresponding virtual dipole moments of 0.3-1.7×1022 Am2. These field strengths are an order of magnitude weaker than the present-day field. VGPs grouping in two distinct clusters with almost identical angular dispersions of VGPs (SB=18.5° and 18.9°) may argue for the presence of an equatorial dipole. In contrast, the palaeointensities associated with the steep and shallow components are indistinguishable. Although based on a low number of results, this observation, together with the overall very large VGP dispersion may rather support that the Grenville Dykes have recorded enhanced secular variation linked to a highly unstable and rapidly reversing field.

Deep hydrothermal and shallow groundwater borne lithium and boron loadings to a mega brine lake in Qinghai Tibet Plateau based on multi-tracer models

Brine lakes are good natural laboratories to investigate groundwater influences on the hydrologic and chemical evolutions in arid environments, and the mineralization processes under intensive evaporation. Lacustrine groundwater discharge (LGD) is the vital conveyor for the loadings of resource elements in the brine lakes. Da Qaidam Lake, located in the Qaidam basin of the Qinghai–Tibet Plateau (QTP), is one of the largest brine lakes for boron and lithium resources in China. Lithium and boron in the lake are considered to be dominantly sourced from deep hydrothermal groundwater and shallow groundwater, but the partitioning of deep and shallow components to the lake and the derived lithium and boron loadings remain unknown, LGD derived boron and lithium provide the primary source of the salt lake. vitally regulates the formation, evolution and mineralization of Li and B resources in the brine lake. This study performs systematical investigations of radium isotopes (226Ra, 228Ra, 224Ra and 223Ra), lithium, boron, and other hydrogeochemical parameters in different water endmembers around the brine lake. The results indicate that radium isotopes are significantly enriched in the hydrothermal groundwater and will be removed by co-precipitation with barite precipitates in the lake water. The multi-tracer models coupled radium bass balance, conservative tracer buildup and water budget were deployed to precisely constrain radium co-precipitation rates, and to quantify the deep and shallow LGD (total LGD = LGDD + LGDS) and the derived lithium and boron loadings. Radium co-precipitation coefficient is obtained to be 4.7–6.1 y−1. LGDD and total LGD are estimated to be 8.8 × 106 and 3.3 × 107 m3 y−1, respectively, which account for 11.9% and 57.2% of the total water input. LGDD and total LGD derived lithium/boron loadings constitute up to 70.2/60.1%, and 79.0/77.7% of the total loadings, respectively, indicating the significance of disproportionate LGDD in delivering resource elements into the brine lake. This study presents the first attempt to partition the deep hydrothermal and shallow LGD to a mega the QTP brine lake by multi-tracer models and the findings contribute to the understanding of lithium and boron budgets in the brine lakes of the QTP and worldwide.

Fe and As geochemical self-removal dynamics in mineral waters: evidence from the Ferrarelle groundwater system (Riardo Plain, Southern Italy).

A theoretical pattern for Fe and As co-precipitation was tested directly in a groundwater natural system. Several monitoring wells were sampled to identify the different endmembers that govern the hydrodynamics of the Ferrarelle Groundwater System in the Riardo Plain (Southern Italy). In agreement with recent investigations, we found a mix of a deep and a shallow component in different proportions, resulting in a specific chemical composition of groundwater in each well depending on the percentages of each component. The shallow component was characterized by EC ~ 430 µS/cm, Eh ~ 300 mV, Fe ~ 0.06 µmol/L and As ~ 0.01–0.12 µmol/L, while the deep component was characterized by EC ~ 3400 µS/cm, Eh ~ 170 mV, Fe ~ 140 µmol/L and As ~ 0.59 µmol/L. A general attenuation of As and Fe concentration that was not due to a simple dilution effect was observed in the mixing process. The oxidation of Fe(II) to Fe(III) produces solid precipitates which adsorb As from solution and then co-precipitate. The reactions pattern of Fe(II) oxidation and As adsorption gave a linear function between [As] and [Fe], where the angular coefficient depends on the [O2]/[H+] ratio. Chemical data obtained from our samples showed a very good agreement with this theoretical relationship. The investigated geochemical dynamics represented a natural process of attenuation of Fe and As, two undesirable elements that usually affect groundwater quality in volcanic aquifers in central-southern Italy, which are exploited to supply drinking water.Graphic abstract

Revisiting the seismogenic characteristics of stable continental interiors: The case of three Indian events

Kinematic source process models using tele-seismic waveform inversion of three stable continental region (SCR) earthquakes from India (1993 Mw 6.2 Latur, 1997 Mw 5.8 Jabalpur and 2001 Mw 7.6 Bhuj) are presented in this paper to demonstrate the slip evolution and stress drop. These finite-fault models are methodologically unique to constrain the source dimensions, compared with assumptions and quasi-observations around blind faults. Our results show that these events do have a compact zone of singular asperity breakage within the Indian crust. Whereas the Bhuj and Jabalpur events have their rupture majorly restricted within the lower crustal regions. The Latur event ruptured a very shallow crustal asperity. The estimated rupture velocities are in the range of 2.6–3.2 km/s, Bhuj event the slowest and lengthiest. Our results do not favour an updip shallow component of asperity breakage for the Bhuj earthquake, as evident from lack of surface ruptures. Study also indicates that the 1993 Latur event occurred on a fault with high stress concentration which indicates stronger fault asperities or slip within a newer fault. Models on 1997 Jabalpur event imply higher frictional strength and very brittle nature at the lower crustal regions of the Indian slab, indicating a mechanically very strong lower crust. We conclude that an event like Latur can occur anywhere within continental interiors of Indian SCR, or elsewhere globally, and is an underestimated seismic hazard.

No Evidence for [C ii] Halos or High-velocity Outflows in z ≳ 6 Quasar Host Galaxies

Abstract We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z ≳ 6, using the [C ii] 158 μm emission line and the underlying dust continuum observed at ∼1 kpc resolution with Atacama Large Millimeter Array. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [C ii] and the dust continuum emission can be described by a steep component within a radius of 2 kpc and a shallower component with a scale length of 2 kpc, detected up to ∼10 kpc. The surface brightness of the extended emission drops below ∼1% of the peak at radius of ∼5 kpc, beyond which it constitutes 10%–20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [C ii] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [C ii] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [C ii] broad-line emission (velocities in excess of ≳500 km s−1), which would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10 kpc, whereas we find no evidence for halos or outflows.

The Dragonfly Edge-on Galaxies Survey: Shaping the Outer disk of NGC 4565 via Accretion

Abstract We present deep g- and r-band imaging of the well-known edge-on galaxy NGC 4565 (the “Needle Galaxy”), observed as part of the Dragonfly Edge-on Galaxies Survey. The 3σ local surface brightness contrast limit on 10″ scales is 28.616 ± 0.005 mag arcsec−2 for the r-band image and 28.936 ± 0.005 mag arcsec−2 for the g-band image. We trace the galaxy’s starlight in narrow slice profiles spanning over 90 kpc along the major axis (with bin sizes ranging from 1.7 × 0.5 to 1.7 × 7.8 kpc) to surface brightnesses below 29 mag arcsec−2. We confirm the previously observed asymmetric disk truncation in NGC 4565. In addition, the sharp northwest truncation turns over to a shallower component that coincides with a fan-like feature seen to wrap around the northwest disk limb. We propose that the fan may be a tidal ribbon and qualitatively replicate the fan with simple simulations, although alternative explanations of the fan and the disk’s asymmetry are shown to be possible. In any case, we conclude that there is strong evidence for accretion-based outer disk growth in NGC 4565.

Observing the Tropical Atmosphere in Moisture Space

Measurements from the Barbados Cloud Observatory are analyzed to identify the processes influencing the distribution of moist static energy and the large-scale organization of tropical convection. Five years of water vapor and cloud profiles from a Raman lidar and cloud radar are composed to construct the structure of the observed atmosphere in moisture space. The large-scale structure of the atmosphere is similar to that now familiar from idealized studies of convective self-aggregation, with shallow clouds prevailing over a moist marine layer in regions of low-rank humidity, and deep convection in a nearly saturated atmosphere in regions of high-rank humidity. With supplementary reanalysis datasets the overall circulation pattern is reconstructed in moisture space, and shows evidence of a substantial lower-tropospheric component to the circulation. This shallow component of the circulation helps support the differentiation between the moist and dry columns, similar to what is found in simulations of convective self-aggregation. Radiative calculations show that clear-sky radiative differences can explain a substantial part of this circulation, with further contributions expected from cloud radiative effects. The shallow component appears to be important for maintaining the low gross moist stability of the convecting column. A positive feedback between a shallow circulation driven by differential radiative cooling and the low-level moisture gradients that help support it is hypothesized to play an important role in conditioning the atmosphere for deep convection. The analysis suggests that the radiatively driven shallow circulations identified by modeling studies as contributing to the self-aggregation of convection in radiative–convective equilibrium similarly play a role in shaping the intertropical convergence zone and, hence, the large-scale structure of the tropical atmosphere.

On the Response of Shallow-water Tidal Regime by Geological Characteristic of Waterway and Man-made Structures in a Macrotidal Estuary: Han River Estuary (Korea)

Yoon, B.I. and Woo, S.-B., 2018. On the response of shallow-water tidal regime by geological characteristic of waterway and man-made structures in a macrotidal estuary: Han River estuary (Korea). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 16–20. Coconut Creek (Florida), ISSN 0749-0208.To understanding shallow-water (short- and long-term period than semidiurnal tide) tidal regime in a macrotidal estuary, Han River estuary (HRE), located on the west coast of South Korea, tidal harmonic constituents of 20 stations were analysed. The semidiurnal tide dominated HRE consists of two main waterways, which have complex geological characteristics. The shallow and narrow characteristics of waterway transform propagating astronomical tides from the open-sea to shallow tidal components such as overtides and compound tides. The shallow tide (e.g., M4, MS4, and MSf) is important factors, which is determined water and mass circulation in a macrotidal estuary. To find shallow-water tidal regime characteristic in this study, we suggest short- and long-term period of tidal form number using shallow tidal constituents. The short-term period of tidal form number covers a range from 0.02 to 0.43, and it increase 10 times larger in the upstream estuary than the open-sea. The long-period of tidal form number is small in the open-sea, but going upward to the estuary, the value increases by 10 times, and it shows 100 times greater than that of the open-sea at the upper region of Han River. Due to complex geological characteristics of waterway, the amplitude of astronomical tidal constituent rapidly decrease and shallow water tidal constituent sharply increase. The other rapid change of tidal constituent is caused by the influence of man-made structures (Singok underwater dam) in the lower tidal river. It is apparent that regional characteristic of tidal regime caused by geological effect and influence of man-made structure.

Coastal ocean acidification and increasing total alkalinity in the northwestern Mediterranean Sea

Abstract. Coastal time series of ocean carbonate chemistry are critical for understanding how global anthropogenic change manifests in near-shore ecosystems. Yet, they are few and have low temporal resolution. At the time series station Point B in the northwestern Mediterranean Sea, seawater was sampled weekly from 2007 through 2015, at 1 and 50 m, and analyzed for total dissolved inorganic carbon (CT) and total alkalinity (AT). Parameters of the carbonate system such as pH (pHT, total hydrogen ion scale) were calculated and a deconvolution analysis was performed to identify drivers of change. The rate of surface ocean acidification was −0.0028 ± 0.0003 units pHT yr−1. This rate is larger than previously identified open-ocean trends due to rapid warming that occurred over the study period (0.072 ± 0.022 °C yr−1). The total pHT change over the study period was of similar magnitude as the diel pHT variability at this site. The acidification trend can be attributed to atmospheric carbon dioxide (CO2) forcing (59 %, 2.08 ± 0.01 ppm CO2 yr−1) and warming (41 %). Similar trends were observed at 50 m but rates were generally slower. At 1 m depth, the increase in atmospheric CO2 accounted for approximately 40 % of the observed increase in CT (2.97 ± 0.20 µmol kg−1 yr−1). The remaining increase in CT may have been driven by the same unidentified process that caused an increase in AT (2.08 ± 0.19 µmol kg−1 yr−1). Based on the analysis of monthly trends, synchronous increases in CT and AT were fastest in the spring–summer transition. The driving process of the interannual increase in AT has a seasonal and shallow component, which may indicate riverine or groundwater influence. This study exemplifies the importance of understanding changes in coastal carbonate chemistry through the lens of biogeochemical cycling at the land–sea interface. This is the first coastal acidification time series providing multiyear data at high temporal resolution. The data confirm rapid warming in the Mediterranean Sea and demonstrate coastal acidification with a synchronous increase in total alkalinity.

Ductile fracture modelling and J-Q fracture mechanics: a constraint based fracture assessment approach

The reduced state of stress triaxiality observed in shallow cracked components allows an increased capacity to resist crack propagation compared to that observed in deeply cracked specimens. This may be regarded as a higher fracture toughness value which allows a reduction in the inherent conservatism when assessing components in low constraint conditions. This study uses a two-parameter fracture mechanics approach (JQ) to quantify the level of constraint in a component (e.g. a pipe with a surface crack) and in fracture test specimens, i.e. single edge tension [SE(T]) and compact tension [C(T)] specimens, of varying constraint level. The level of constraint of the component is matched to a specific test specimen and therefore the ability of the structure to resist fracture is given by the fracture toughness of the test specimen with a similar J-Q response. Fracture toughness values for different specimens have been obtained from tearing resistance curves (J-R curves) constructed by means of a virtual testing framework. The proposed engineering approach shows that the combination of a local approach and two-parameter fracture mechanics can be used as a platform to perform more accurate fracture assessments of defects in structures with reduced constraint conditions. KEYWORDS. Crack tip constraint; Ductile fracture modelling; J-Q fracture mechanics.

Roles of deep and shallow convection and microphysics in the MJO simulated by the Model for Prediction Across Scales

AbstractThe November event of the Madden‐Julian oscillation (MJO) during the Dynamics of North Atlantic Models (DYNAMO) field campaign was simulated using the global compressible nonhydrostatic Model for Prediction Across Scales with global coarse (60 and 15 km) and regional (the Indian Ocean) cloud‐permitting (3 km) meshes. The purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in MJO simulations. Two cumulus schemes were used: Tiedtke and Grell‐Freitas. The deep and shallow components of Tiedtke scheme can be turned on and off individually. The results reveal that microphysics alone (without cumulus parameterization) is able to produce strong signals of the MJO in precipitation with 3 km mesh and weak MJO signals with 15 km mesh. A shallow scheme (Tiedtke) along with microphysics strengthens the MJO signals but makes them less well organized on large scales. A deep cumulus scheme can either improve the large‐scale organization of MJO precipitation produced by microphysics and shallow convection (Tiedtke) or impair them (Grell‐Freitas). The deep scheme of Tiedtke cannot reproduce the MJO well without its shallow counterpart. The main role of shallow convection in the model is to transport moisture upward to the lower to middle troposphere. By doing so, it removes dry biases in the lower to middle troposphere, a distinct feature in simulations with weak or no MJO signals, and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes. Changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the MJO. All roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection. Results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving MJO simulations. In other words, a holistic approach should be taken that consider parameterization of shallow cumulus, microphysics, boundary layer, and deep cumulus as a whole for model improvement.

Radiative driving of shallow return flows from the ITCZ

AbstractThe tropical overturning circulation over the central‐east Pacific not only extends through the troposphere but also includes a shallow component outflowing from the ITCZ near the planetary boundary layer (PBL) top, the Shallow Meridional Circulation (SMC). Idealized simulations with the Weather Research and Forecasting (WRF) model, which qualitatively reproduce this two‐component circulation, are used to investigate the mechanism driving the SMC by altering model parameterization schemes (PBL, cumulus and radiation), the solar heating rate, and the SST gradient. A radiative‐driving model for subsidence is tested and found to quantitatively predict the altitude and strength of the SMC in all experiments. This includes experiments with a changed SST gradient, in which the changes in temperature profile and clouds near PBL top in the subsiding region altered radiative cooling so as to make the SMC vary in proportion to the SST gradient. These results indicate that the SMC is strongly controlled by radiative cooling rather than independently by SST patterns or convective processes, at least in this model setup. Experiments with altered solar heating of the atmosphere affected the strength of the SMC strongly, while changes in cumulus parameterization had a weaker effect. Parameterization changes influenced the SMC mainly by altering shallow cloud amount and humidity in subsidence regions, but vertical gradients of temperature also affect the radiative driving of the SMC in at least one case. The results highlight that atmospheric radiative heating is of prime importance for determining the character of deep and shallow overturning.

Parametric study of a physically-based, plot-scale hillslope hydrological model through virtual experiments

A physically-based hillslope hydrological model with shallow overland flow and rapid subsurface stormflow components was developed and calibrated using field experiments conducted on a preferential path nested hillslope in northeast India. Virtual experiments were carried out to perform sensitivity analysis of the model using the automated parameter estimation (PEST) algorithm. Different physical parameters of the model were varied to study the resulting effects on overland flow and subsurface stormflow responses from the theoretical hillslopes. It was observed that topographical shapes had significant effects on overland flow hydrographs. The slope profiles, surface storage, relief, rainfall intensity and infiltration rates primarily controlled the overland flow response of the hillslopes. Prompt subsurface stormflow responses were mainly dominated by lateral preferential flow, as soil matrix flow rates were very slow. Rainfall intensity and soil macropore structures were the most influential parameters on subsurface stormflow. The number of connected soil macropores was a more sensitive parameter than the size of macropores. In hillslopes with highly active vertical and lateral preferential pathways, saturation excess overland flow was not evident. However, saturation excess overland flow was generated if the lateral macropores were disconnected. Under such conditions, rainfall intensity, duration and preferential flow rate governed the process of saturation excess overland flow generation from hillslopes.Editor D. Koutsoyiannis; Associate editor C. Perrin

DISCOVERY OF CARBON RADIO RECOMBINATION LINES IN M82

Carbon radio recombination lines (RRLs) at low frequencies (<=500 MHz) trace the cold, diffuse phase of the interstellar medium, which is otherwise difficult to observe. We present the detection of carbon RRLs in absorption in M82 with LOFAR in the frequency range of 48-64 MHz. This is the first extragalactic detection of RRLs from a species other than hydrogen, and below 1 GHz. Since the carbon RRLs are not detected individually, we cross-correlated the observed spectrum with a template spectrum of carbon RRLs to determine a radial velocity of 219 +- 9 km/s . Using this radial velocity, we stack 22 carbon-{\alpha} transitions from quantum levels n = 468-508 to achieve an 8.5 sigma detection. The absorption line profile exhibits a narrow feature with peak optical depth of 0.003 and FWHM of 31 km/s. Closer inspection suggests that the narrow feature is superimposed on a broad, shallow component. The total line profile appears to be correlated with the 21 cm H I line profile reconstructed from H I absorption in the direction of supernova remnants in the nucleus. The narrow width and centroid velocity of the feature suggests that it is associated with the nuclear starburst region. It is therefore likely that the carbon RRLs are associated with cold atomic gas in the direction of the nucleus of M82.

Abrupt changes in deep Atlantic circulation during the transition to full glacial conditions

Six Ocean Drilling Program (ODP) sites, in the Northwest Atlantic have been used to investigate kinematic and chemical changes in the “Western Boundary Undercurrent” (WBUC) during the development of full glacial conditions across the Marine Isotope Stage 5a/4 boundary (~70,000 years ago). Sortable silt mean grain size measurements are employed to examine changes in near bottom flow speeds, together with carbon isotopes measured in benthic foraminifera and % planktic foraminiferal fragmentation as proxies for changes in water‐mass chemistry. A depth transect of cores, spanning 1.8–4.6 km depth, allows changes in both the strength and depth of the WBUC to be constrained across millennial scale events. measurements reveal that the flow speed structure of the WBUC during warm intervals (“interstadials”) was comparable to modern (Holocene) conditions. However, significant differences are observed during cold intervals, with higher relative flow speeds inferred for the shallow component of the WBUC (~2 km depth) during all cold “stadial” intervals (including Heinrich Stadial 6), and a substantial weakening of the deep component (~3–4 km) during full glacial conditions. Our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation (involving Glacial North Atlantic Intermediate Water) that was quantitatively distinct from preceding cold stadial events. Furthermore, our chemical proxy data show that the physical response of the WBUC during the last glacial inception was probably coupled to basin‐wide changes in the water‐mass composition of the deep Northwest Atlantic.