A common goal of next-generation Global Circulation Models (GCMs) is that they should be “scale-aware”, which typically implies that such models should not be excessively sensitive to grid spacings, and that they should in some sense converge monotonically towards a result as grid spacings decrease. While both horizontal and vertical resolution have been treated in this manner, time resolution is typically viewed differently. Specifically, a decrease in time step size is often viewed as a “necessary evil”, being decreased only in cases where spatial resolution is also decreased, requiring a change to the time resolution to satisfy a CFL condition. Our experiments with the E3SM Atmosphere Model suggest that cloud physics and precipitation in GCMs is in fact quite sensitive to process coupling time step size, and that the biases affected by time integration error are independent from (and of comparable size to) biases due to other common sources of error, such as grid spacing and choice of sub-grid-scale physics parameterizations. This suggests that process coupling frequency is a key feature that should be adjusted for future models.

Understanding the contribution of the West Antarctic Ice Sheet (WAIS) to past and future sea level has emerged as a scientific priority over the last three decades. In recent years, observed thinning and ice-flow acceleration of the marine-based Pine Island Glacier has demonstrated that dynamic changes are central to the long-term stability of the WAIS. However, significantly less is known about the evolution of the catchment during the Holocene. Internal Reflecting Horizons (IRHs) provide a cumulative record of accumulation, basal melt and ice dynamics that, if dated, can be used to inform ice flow models to project spatial and temporal mass changes. Here, we use airborne radars to trace four consistent IRHs spanning the Holocene across the Pine Island Glacier catchment. We use the WAIS Divide ice-core chronology to assign discrete ages to three IRHs: 4.72 ± 0.08, 6.94 ± 0.11, and 16.50 ± 0.62 ka. We use a 1D model, constrained by observational and modelled accumulation rates, to produce an independent validation of our ice-core-derived ages and provide an age estimate for our shallowest IRH (2.31-2.92 ka). We find that significantly older ice is present below our deepest reflector, but the absence of continuous radar-observed reflectors at depth currently limits our understanding of pre-Holocene ice dynamical history. The clear correspondence between our IRH package and the one previously identified over Institute Ice Stream, altogether representing ~20% of the WAIS, suggests that a unique set of stratigraphic markers spanning the Holocene exist widely across West Antarctica.

With the rapid rise in flooding events induced by climate change across the globe, effective flood management strategies through modelling have garnered attention over the years. In the present study, we propose a holistic hydrodynamic flood modelling framework to derive the flooding extent. Various hydraulic scenarios are integrated into the framework which consider different combinations of cross-section and lining material options along the river channel for this purpose. A 3-way coupled flood model has been developed in MIKE FLOOD platform, over Mithi river catchment an extremely flood-prone area in Mumbai, the financial capital of India. Flood influencers such as precipitation, flows through the channel, overland, storm-water drains, and tidal influences are considered to generate flood inundation and hazard maps for the scenarios. The dearth of data in the model is met by implementing alternate robust procedures to compute the design values of the influencers. Subsequently, the maps are derived for different return periods of design precipitation, tidal elevation and streamflow values to identify the most desirable scenario. The proposed framework efficiently determines that the scenario having trapezoidal river cross-section with concrete lining material maximizes the decrease in spatial extent of flood in comparison to the other scenarios. This user-friendly generic approach can be potentially executed as an effective flood mitigation option in thickly populated and socially vulnerable regions where lack of space limit the implementation of structural measures for flood management. The framework can prove instrumental particularly for the developing and under-developed countries where application of these strategies is hindered by inadequacy of data.

The rivers in the Peruvian Amazon basin are the veins that feed the largest rainforest on the planet. They connect habitats and ecosystems and are considered a source of high biodiversity. Since before the conquest, many indigenous peoples have settled along riverbanks to be supplied with water, food, and many other ecosystem services. Furthermore, the Amazonian rivers have been the basis for the sociability of those population groups. For many years, the indigenous riverine people, such as the Kukama and the Shipibo-Conibo, have developed an empirical knowledge about the rivers from their coexistence and lifestyle. Therefore, indigenous communities have learned how to be adapted under the physical dynamics by shaping their culture. It evidenced the great understanding of rivers that communities developed over the years, endowed with affective and spiritual links, which has allowed them to be preserved for many years. As part of a scientific study of the hydrogeomorphological characteristics of the main Peruvian Amazonian rivers, it was considered important to involve indigenous perceptions and knowledge. Recognizing these views is necessary for a holistic understanding of rivers; however, these have been absent from the plans and projects developed by government institutions. “River Stories” (https://www.historiasdelrio.com) is a digital storytelling platform that supports the dissemination of indigenous cosmovision in terms of experiences, in which the knowledge, memory and spirituality are displayed. It hosts more than 100 stories from indigenous people (including children and teenagers), students, local authorities, and scientists that reveal the importance of rivers in their daily life. In this way, different perspectives of the rivers from science, civil society, and the indigenous worldview are exchanged. Integrating this knowledge is essential to highlight the vital role that rivers play at the social, cultural and environmental areas. This, especially in the current context, where multiple threats, such as infrastructure and energy projects, put Amazonian rivers at risk.

Gas transport in dominantly microporous rocks such as coal, shale is significantly controlled by Klinkenberg or slippage effect at low reservoir pressures. Pore size fractions of the concerned reservoir rock control the degree of Klingenberg effect. This study tries to assess the differences in Klinkenberg effect in dissimilar coals owing to their difference in pore-size distributions. We report apparent permeabilities of three Gondowana coal samples from the Bokaro, Jharia, and Bansgara coalfields at room temperature and constant isostatic stress (6.2 MPa). The linear plots of apparent permeability versus inverse pore pressure were modelled using the Klinkenberg equation, and non-linear plots by the Ashrafi equation to determine the slippage coefficient and intrinsic permeabilities. Ashrafi model reports lower values of slippage corrected permeability compared to the Klinkenberg model. The slippage coefficient and intrinsic permeability obtained from N2 and CO2 is different for the Bansgara sample. The trends between transport parameters and pore-size parameters were examined. The slippage coefficient decreased with interconnected porosity and total specific pore volume. Intrinsic permeabilities showed an opposite trend to that of the slippage coefficient. The Bansgara sample having larger volumetric proportion of micropores in the pore volume gamut with open ended interconnected pore network resulted in the lowest slippage coefficient and highest intrinsic permeabiliity. Reporting the slippage coefficients and intrinsic permeabilities with corresponding pore size distributions of coal samples from different global basins will lead to statistically significant empirical relationships between pore size parameters and slippage coefficients.

Understanding the effect of different landscapes on local temperature is important for understanding land-atmospheric interactions, and is a critical step toward an informed urban design under a changing climate. This presentation considers Lake Memphremagog, a transboundary water body between Quebec and Vermont, along with one of its adjacent wetlands as a test bed to study the impact of different water bodies on regulating the local temperature. We use the data from two identical climate stations to study hourly temperature, absolute and relative humidity as well as incoming and outgoing radiation components along with vapour pressure deficit at the lake and wetland. We benchmark the temperature measurements in these two sites with the data gauged in an Environment and Climate Change Canada’s weather station located between the two sites. Using a systematic analysis, we account for the cooling and heating impacts of the lake and the wetland and demonstrate their underlying causes. We show that during the growing season and at the daily scale, the cooling impacts of the wetland can cancel out the heating impacts of the lake. This is not the case during day times, in which the lake acts as a sink of heat, while the wetland is the source. We show that the cooling and heating effects of the considered lake-wetland duo can be described by the daily temperature statistics (i.e. average, minimum, maximum and range) at the benchmark weather station. This provides an opportunity to create stochastic models for retrospective and prospective projections of cooling and heating impacts of this lake-wetland duo under current and future climate.

In Peru, a group of scientists are investigating the main Amazonian rivers to understand all those physical variables that define their behavior and ecological importance throughout the Amazon basin. But what happens with this information? How does it connect with the citizens and become mechanisms of valorization and conservation? “Science for Rivers” is a comprehensive educational initiative that seeks to channel all the scientific knowledge generated regarding rivers towards different actors who are linked to them. The communication strategies implemented have translated complex information in a way that is accessible and useful to all audiences. Therefore, many specialized courses and workshops have been developed for different government institutions in order to incorporate this type of knowledge into their development plans. Also, two free access web pages have been developed that show in an interactive way the multiple technical and social variables when intervening in rivers. Likewise, an educational graphic proposal was implemented through social media where information about the rivers is shared with a simple and playful language. Appropriating this knowledge at different levels is fundamental to guarantee policies coherent with this ecosystem, as well as to forge a citizenry that knows, values and cares for its rivers.

On 16 December 2017 a chain mass movement, started as a rockslide, produced a debris and mud flow which channelized in the Burritos River. The flow reached and flooded the Santa Lucia village (-43.41°/-72.37°) destroying 50% of the urban area and killing 22 people. This fatal event resulted as a conjunction of geologic, meteorological and glaciological variables: Highly altered volcanic rocks with deep vertical fractures and steep slopes in the Yelcho Range; an intense precipitation event 30 hours prior the rockslide of up to 124.8 mm in one day with a high zero-degree isotherm elevation; an ice-cored lateral moraine deposit under the headwall plus hyper saturated soils downhill near the Burritos River. The role of a proglacial lake has been discussed, nonetheless, current studies argue that the main liquid inputs could have been pre-existing water in saturated soil. In this study we analyzed satellite imagery available on the web, including Sentinel 2 and Landsat scenes. Based on the Public Chilean Glacier Inventory, we quantify the retreat of glaciers laying on the eastern flank of the Yelcho Range, west of the Santa Lucía village. On a time-span of 33 years (1987 to 2020), we estimate over 650 m of glacial retreat plus an accelerated retreat rate up to 30 m/yr for the last decade. Such glacier shrinkage coupled with increasing local temperatures may lead to the genesis of more proglacial lakes, enhancing the odds of chain mass movements, favoring the interaction between rockslides and glacial lakes. Our results show an example of a relatively simple analysis that can be performed with basic tools and with no further expenses. The proper understanding of glacial landscape evolution with time and its response to extreme climatic events is essential to prevent human loses, as these events will be more frequent due to the current climate change context. For that purpose, further work aims to clarify more hidden variables in the region, such as the number of proglacial lakes, steep slopes on headwalls, highly eroded slopes, among others, in order to enlarge the local knowledge linked to one of many components involved on a natural disaster, thus, increasing the resilience of communities whom are still occupying the affected area after the Santa Lucía landslide disaster.

One key question about Mars is whether life has been or still is present on or beneath its surface. For life to flourish, it requires a habitable environment with the appropriate physical and chemical regolith parameters. To better understand the parameters that constitute a habitable environment, leachates of three martian simulants (JSC Mars-1, MMS-1 fine, and MGS-1) were analyzed for their soluble ionic composition, pH, and conductivity in order to determine the presence of any beneficial or toxic elements and their effects on the two bacteria E. coli and Eucapsis. E.coli was cultured in minimal media where acetic acid was the only organic source, and tested its requirements for a carbon source (acetic acid), nitrogen source ((NH4)2SO4) as well as trace elements (Ca, Mn, Zn, Cu, Fe, Co, Mo). In minimal culture media with all nutrients available for healthy growth, E. coli showed substantial growth. In the case of a carbon-only source or nitrogen-only source in MMS-1 soil leachate, E. coli showed limited growth compared to that observed in the full minimal culture media. Assessing Eucapsis growth, among the three leachates tested MMS-1 displayed the best growth. Additionally, we observed that MMS-1+Allen’s minimal and full Allen’s medium groups displayed similar growth curves, indicating that MMS-1 can provide all the trace elements needed for Eucapsis growth. Among all the leachates, MMS-1 showed the most promising results. MMS-1 + Allen’s medium provided the highest Eucapsis growth. MGS-1 + Allen’s minimal media also showed significantly higher growth than MGS-1 alone. However, JSC and JSC + Allen’s minimal did not show any significant difference regarding Eucapsis growth. The results indicated that Eucapsis grew best in both MMS-1 F leachate only and MMS-1 F leachate with Allen’s minimal medium.

In previous work (Hairston et al., GRL doi 10.1029/2018GL077381, 2018) we showed the topside F-layer (~850 km) electron temperatures measured by two DMSP spacecraft as they flew through the Moon’s shadow during the 21 August 2017 eclipse exhibited a series of non-uniform, banded decreases rather than a broad and smooth temperature decrease. We found that making a “mask” of the shadow of the Moon eclipsing the existing active regions on the sun’s surface created a pattern on the ionosphere showing where the gradient of the EUV from the active regions was greatest. The complex pattern of these areas from the mask at the F-peak altitude at 300 km corresponded to the areas in the topside F-layer where the DMSP observed the bands of cooled electrons. We have expanded this work to examine about a dozen other eclipses including the most recent 21 June 2020 eclipse. We repeatedly observed the same banded pattern in the electron temperatures in almost all the DMSP eclipse passes, thus demonstrating this is a repeatable phenomenon. Since the DMSP series of spacecraft form a constellation of four operational satellites with the same plasma instrument package making multiple measurements of the shadow at different local times, and sometimes within 10-15 minutes of each other, we can use these observations to map the shape and evolution of these cooling band patterns as the eclipse’s shadow passes over the Earth’s ionosphere. Here we will present our first detailed analysis of the two eclipses that occurred on 20-21 May 2012 and 2 July 2019. Both these eclipses have passes through the duskside by two spacecraft within a few minutes of each other, thus allowing us to examine the evolution of the pattern. We are using these events to determine the empirical patterns seen in the electron temperature decreases during eclipses and to explore the mechanism causing the cooling of the plasma and how it is transported from the F-peak region to the topside ionosphere.

Shallow glacial aquifers systems are the primary source of drinking water for millions of residents in the upper Midwest and Great Lakes regions of the United States. Studies show that a significant number of municipal and private groundwater wells in these regions are impacted by high nitrate concentrations, which can have negative health impacts for humans. Reducing nitrate contamination through good land management practices will reduce the need for costly nitrate treatment systems and help mitigate other ecological concerns related to nutrient pollution of groundwater. This study presents a Python-based modelling tool that uses a local groundwater flow model and historical land use data (USDA CropScape) to estimate nitrate concentrations at a high-capacity pumping well. Nitrate concentrations predicted by this model are within 5% of median annual values observed at a study site in Waupaca, WI. The model is user-friendly and can easily be adapted to other locations, where it has the potential to help local and state agencies, landowners, and growers make cost-effective decisions about land-use and agricultural practices.

The extent to which terrestrial weather below 30 km in altitude can influence the dynamics and mean state of the thermosphere (ca., 100-500 km) is a fascinating discovery of the last two decades or so. Waves that are excited by deep convection in the tropical troposphere and propagate vertically into the thermosphere are responsible for much of this influence. Tropospheric convection associated with the Madden JulianOscillation(MJO), the dominant mode of intra-seasonal variability in tropical convection and circulation, has been known to modulate the intensity of upward propagating gravity waves and Kelvin waves. An MJO impact on tides was already proposed over two decades ago, but only recent gains in satellite observational capabilities allows one to quantify their effect from observations. Previous work by Gasperini et al. [2017a] demonstrate that a 90-day oscillation in tropospheric convection during 2009-2010 is imprinted on both thermospheric mean winds and the eastward propagating wavenumber 3 diurnal (DE3) tidal amplitudes observed by the GOCE and CHAMP satellites and modeled with the TIME-GCM. In a follow-on modeling-based study, Gasperini at al. [2020] present statistical evidence for a strong connection (+/-12%) between the phase of the tropospheric MJO and the amplitudes of the thermospheric DE3 and 3-day ultra-fast Kelvin wave (UFKW), two of the most prominent and well-established waves from the tropical wave spectrum that preferentially propagate into the thermosphere. These recent studies demonstrate that strong coupling between the troposphere and the thermosphere occurs on intra-seasonal timescales, raising important questions that have implications for the whole atmosphere system. In this work, we present evidence for a strong quasi-60 day oscillation in GOLD column-integrated O/N2 and Swarm-C total mass density during 2018-2019. A similar and concurrent oscillation is observed in the DE3 and SE2 tidal amplitudes derived from SD/WACCM-X. Spectral analysis of OLR reveals a similar oscillation in tropical tropospheric convection that is shown to be eastward propagating with s=-1 and is thus consistent with an MJO event.

The clear-sky and all-sky global mean energy flow system of the Earth as the solution of four radiative transfer constraint equations were presented in Zagoni (CERES STM 2020). These equations have their theoretical origin in the concept of radiative equilibrium for stratified atmospheres (Schwarzschild 1906, Eq. 11; Milne 1930, Eq. 93-95; Goody 1964, Chamberlain 1978, Eq. 1.2.29-1.2.30; Eq. 2.115; Goody and Yung 1989, Eq. 2.146 and Eq. 9.5; Houghton 2002, Eq. 2.13; Andrews 2010, Eq. 3.50-3.51; Pierrehumbert 2010, Eq. 4.44-4.45, etc.). We showed that each of the equations is justified by 19 years of CERES data within ±3 Wm-2 and the all-sky equations by the IPCC-AR5 (2013) Fig. 2.11 global energy budget estimate within ±2 Wm-2. The individual flux components, both for clear-sky and all-sky are valid within ± 1 Wm-2 at the TOA and within ± 4 Wm-2 at the surface. A fifth equation was introduced in Zagoni (EGU 2020) showing the place of a non-observable flux component (atmospheric window radiation) in the theoretical system; and a sixth equation allowed to extend the arithmetic structure to total solar irradiance. The set of these equations has a solution for LWCRE = 1 as unit flux, and the whole system of the global mean atmospheric energy flows can be described by small integers, in their own units, separately for the clear-sky, the cloudy sky and (as their weighted sum) for the all-sky case. OLR(all) = 9, OLR(clear) = 10, ULW = 15, G(all) = 6, G(clear) = 5 units = 133.40 Wm-2 with TSI = 51 units = 1360.68 Wm-2. Here we introduce the cloudy versions of the examined classic radiative transfer constraint equations and present the all-sky global mean energy budget as the weighted sum of the clear-sky and cloudy-sky energy flow system. “Clouds” are regarded as a single IR-opaque layer, represented by an effective cloud area fraction. Essential characteristics of the climate (like the clear-cloudy energy exchange; the surface, TOA, in-atmosphere and net CREs; and the greenhouse effect) are explained as the cooperation of the clear-sky and cloudy-sky geometric arrangements expressed in the transfer equations. This way, the theoretical description of the Earth’s global mean energy budget is complete.

We perform 3D simulations of seismic wavefields to clarify effects of strong reductions of shallow velocities on long-period seismic waves. The simulations use a reference community velocity model of Southern California and a modified version with strong velocity reductions in the top 500 m of the Los Angeles basin. Differences between wavefields generated by ten earthquakes in the reference and perturbed models are analyzed. Velocity changes are estimated by measuring relative time shifts between reference and perturbed seismograms using wavelet cross-correlation spectra. The results indicate that strong localized temporal velocity drops near the surface, such as those observed during strong ground motions, may generate regional perturbations of wavefields at periods up to 20 s. These perturbations may be misinterpreted as generated by temporal changes at seismogenic depths. The results also have important implications for waveform tomography studies.

One possible human response to climate change and other environmental stresses is migration. However, migration is complex, multi-causal phenomenon, and the complexity of human migration poses a challenge for researchers who aim to study the effects of environmental changes on population mobility. This project aims to understand how changing environmental conditions and livelihood opportunities impact migration decisions in coastal Bangladesh. We are developing an original agent-based model (ABM) that combines stylized environmental change dynamics with livelihood to understand how these dynamics impact migration decisions as well as what feedbacks may exist between them. The ABM uses agents to represent households, which consist of individuals, within a single origin community. At each step of the model, the household assesses the expected utility of different livelihood options within the community for each of its members, including agricultural work on the household’s land (if any), seeking paid employment within the community, and pursuing non-agricultural livelihood activities. After assessing opportunities within the community, households will decide whether or not a household member should seek opportunities outside the community. The model imposes stochastic droughts that impact crop yields. We report preliminary results from this model, comparing simulated migration patterns to empirical observations. Future work will incorporate more complex and psychologically realistic decision-making heuristics, as well as diverse destination locations and the possibility of return migration.

Underwater bedforms in a flow have been shown to cast free-surface signatures that carry important information about these bedforms thus allowing for a novel non-intrusive methodology for bedform inference through measurement of these signatures (Gakhar et al. 2020, J. Fluid Mech. vol.900, A41). We present a method (Polarimetric Height Sensing or PHS) for spatiotemporally reconstructing the two-dimensional height field of a (water) free surface, thereby allowing for characterization of the free-surface signatures of submerged bedforms. The instrumentation for PHS comprises a small, easily portable polarimetric camera. PHS, which incorporates more than just the intensity of the light as in a regular digital image, works as follows. When light is reflected from the water surface, it acquires a polarization that depends on the polarization state of the incident beam, the indices of refraction of the surface and air, and most importantly the angle and plane of incidence. Given that we already know the refractive indices and the incident light’s polarization, using measurements of the polarization of the reflected light, we can quantify the geometric properties of the water surface. We illustrate the technique via laboratory experiments using imaging of the water in an open-channel recirculating water flume.

Emergency Action Plan for Flash Flood Due to Dambreak - Case study: Shahrchai Dam, Urmia (Iran) Seyed M. Heidaria, Seyed Jalal Heidarib a Department of Civil Engineering, Sharif University of Technology, Tehran, Iran. (SeyedMHeidari@gmail.com) b Department of Civil Engineering, Betasaze Corporation, Mashhad, Iran. (j.heidari37@gmail.com) Abstract: A large number of dams have been built on the upstream of residential regions. Flash flood from these dams’ failure is a constant threat to the thousands of lives and million-dollar municipal facilities in downstream. Therefore, it is crucial to identify potentially flooded areas and develop an early warning system for downstream cities to mitigate the loss of life and financial damages. We prepared an emergency action plan (EAP) for flash floods in Iran for the first time in this work. Shahrchai Dam was selected as the case study since it is a large dam with a 220 million m2 capacity reservoir and is located close to a large city, Urmia, with 667,000 population and more than 197,000 households. We used HEC-RAS to model dambreak for two scenarios, piping and overtopping. ArcGIS was employed to identify flooded regions in downstream. The escape time was estimated based on the time that first waves reach residential zones. Time was 170 and 140 minutes for the piping and overtopping scenario, respectively. Water depth and water velocity were mapped for each scenario for flooded areas in downstream to identify secure shelters. EAP was developed for residential, commercial, and municipal buildings located in the flooded areas. Nine hospitals, four hotels, six mosques, more than ten municipal buildings, 54 public, and private schools, and five universities are determined within the flooded regions and considered in the EAP. We divided these regions into five categories, with three to five subcategories based on population and building types. For each subcategory, we identified an evacuation plan with detailed guidelines for residents and involved municipal organizations to avoid chaotic behaviors, which usually happens during flash floods. Results from this study are useful for educating people to be prepared for disasters like flash floods. Municipal policymakers can also use the findings to legislate required rules to protect urban areas from future floods and reduce associated fatality and financial costs. Acknowledgment: Authors would like to appreciate Sharif University of Technology and Dr. Fardin Jafarzadeh for their supports.

Declining sea ice in the Arctic Ocean is exposing its coasts to more frequent and intense forms of wave energy and storm surge. As a result, erosion rates along some stretches of coastline in the Alaskan Arctic have doubled since the middle of the 20th century and now rank among the highest in the world. People concentrated near the coast are being heavily impacted by erosion, with some facing relocation. Coastal erosion is projected to increase the cost of maintaining infrastructure by billions of dollars in the coming decades. The financial impact of enhanced erosion will likely be further exacerbated by emerging geopolitical pressures, including the discovery of natural resources, opening of new shipping routes, and construction of support facilities in the Arctic. Scientific knowledge and engineering tools for predicting coastal erosion and guiding land-use decision are not well-suited for the ice-bonded bluffs of the Alaskan Arctic. Investigation of the oceanographic, thermal, and mechanical processes that are relevant to permafrost bluff failure along Arctic coastlines is thus needed. We introduce a geomechanical simulation framework, informed by field observation and laboratory testing, that focuses on the impact of bluff geometry and material variability on permafrost bluff stress states associated with a 9-km stretch of Alaskan Arctic coastline fronting the Beaufort Sea that is prone to toppling-mode block failure. Our approach is advantageous in that it is based on measurable physical properties (e.g., the bluff geometry, permafrost bulk density, Young’s Modulus, and Poisson’s Ratio) and does not require the potential failure to be defined a priori, but rather, the failure area can be interpreted from the multidimensional patterns of stress produced by the model. Our findings highlight how (1) block failure characteristics could be tied to variations in the intensity and duration of the storm energy that intersects the coastline and (2) how deformation processes that create non-uniform patterns of displacement may play a role in localizing block failure. We propose that this kind of physics-based simulation approach can facilitate hypothesis testing regarding the prediction of decadal-scale erosion rates for increasingly dynamic coastal permafrost systems.