Plain Language Summaries are published alongside a paper’s scientific abstract, and are a great way to communicate your work to a broader audience. Submitting a Plain Language Summary is now an option across all AGU Journals. We showcase some good examples here. Find out more about how to write a good Plain Language Summary.
Large tabular icebergs break away from ice shelves around Antarctica, and drift into the ocean. As the icebergs move, they melt, which injects freshwater into the ocean. This freshwater can promote sea-ice growth, affect deep-water formation and alter ocean temperatures and salinities. In this way icebergs play an important part in the climate system, and need to be modeled accurately. However, the current generation of iceberg models is unable to model large tabular icebergs. In this paper, we develop a new model which can simulate the movement of large tabular icebergs drifting in the ocean. Most previous iceberg models treat iceberg as point particles which do not occupy any physical space. In our model, we represent iceberg using element which do occupy physical space, and can interact with the ocean and other elements more realistically. We then create large tabular icebergs by bonding together many smaller elements to form large structures. This allows us to simulate the movement of larger tabular icebergs in the ocean. An advantage of this approach is that by breaking the bonds between elements, we can simulate an iceberg calving away from an ice shelf, or an iceberg breaking into two or more parts.
Magnetic storms can pose significant risks to critical technology infrastructure such as the electric power grids. Real-time estimation of geoelectric fields can give the grid operators an opportunity for prompt intervention that would mitigate the long-term consequences. We develop and validate a method to efficiently and accurately (to within 85–90%) “nowcast” storm time geoelectric fields in close to real time in places where both geomagnetic field data are collected or estimated, and a magnetotelluric impedance has been previously measured. This method can be applied in all regions where magnetotelluric data have been collected, including in the United States, where USArray magnetotelluric data survey is ongoing and by 2018 will cover about two thirds of the country. In this work, we focus on the algorithm development only.
Although the last decade is the warmest decade in the instrumental record and CO2 continues to rise, global surface air temperature has not increased as much as before over the last 10–15 years, leading to the so-called hiatus or slowdown of the global warming. This is a key event which has still not received any definitive explanation, although many possible causes have already been adduced. Here we take into account the almost simultaneous phenomena which arose at the beginning of the 21st century: acceleration in the disappearance of the summer arctic sea ice, increase of the rate of ice sheets and glacier melting and of seal-level rise, and the appearance of a decrease of the warming trend of the atmosphere. Our calculations based on three climate records show that the energy left in the atmosphere by the slowdown of the global warming is pretty similar to the energy requested to melt the ice over the same period. While the heat content of the atmosphere alone shows a leveling off after 2002, no such behavior is observed when the heat of ice melting is added, suggesting a redistribution of heat within the atmosphere–cryosphere system.
Along the west coast of North America, intense rain storms that produce extreme and impactful weather occasionally happen. These rain storms are called “atmospheric rivers.” Atmospheric rivers cause considerable mayhem – delivering flooding rains when they occur and desiccating droughts during their absence. Because their impacts are so extreme, it would be beneficial to have as much forewarning as possible about when and where they will occur. Unfortunately, modern-day weather models are unable to forecast atmospheric rivers beyond two weeks in advance. However, we find that the potential exists to improve forecasts of atmospheric rivers by using knowledge of the current weather in the tropics. The weather in the tropics foretells many weeks in advance when and where atmospheric rivers will impact the west coast of North America. Our findings offer an opportunity to improve weather forecasts and thereby provide more forewarning for atmospheric rivers and their extreme impacts.
Sediments accumulating at the bottom of Bainbridge Crater Lake have provided a record of Galapagos climate and the frequency of El Niño events over the past ~6000 years. Motivated by the importance of this lake for our understanding of climate in the tropical Pacific Ocean, we have been monitoring the link between climate, lake conditions and the physical and chemical properties of the lake sediments since 2009. Based on this long-term monitoring, we find that the Bainbridge sediment record preserves both El Niño and La Niña events. This makes Bainbridge a particularly valuable archive of past climate, as most sediment-based records typically preserve only one or the other key phase of tropical Pacific climate.
For over a decade there has been a discrepancy in the observed variability of the size and strength of the subpolar gyre: satellite estimates based on the height of the sea-surface were interpreted as showing a rapid decline in the gyre since the early 1990s, while direct measurements from ships and moorings showed the gyre to be quite stable over the same time period. In this work, we reconcile these two measurement techniques by subtracting the long-term sea level rise from the satellite altimetry. Changes to ocean circulation require changes to the slope of the sea-surface, so sea-surface height variability that is present across the gyre can obscure variability in the ocean circulation. Our new measures of the size and strength of the gyre indicate a weakening, but at about 1/4 the rate of previous estimates, and a stable gyre size over the study period. Both of these are consistent with the direct measurements. In addition, we find that the eastern boundary of the gyre does not have large coherent excursions to the east and west, and we find that it most likely does not control the temperature and salinity the eastern subpolar region as has been previously theorized.
Solar storms are formed by incredibly powerful explosions on the Sun, and travel as clouds of plasma threaded by magnetic fields through the solar system. Depending on their propagation direction, they may impact planets such as Earth, where they elicit colorful aurorae or, in very seldom cases, can lead to power failures with potentially tremendous economical and societal effects, thus posing a serious natural hazard.In this work, we have shown how well the solar storm impact can be forecasted when using a special type of instrument that can actually image the solar storms as they propagate towards the planets and even as they sweep over them. Our analysis includes two thirds of a solar cycle with 8 years of data, and spacecraft at Mercury, Venus, Earth and in the solar wind to check on the correctness of our predictions. We could forecast the arrival time within +/- 16 hours, and for 1 correct impact there are 2 to 3 false alarms. This forms a new baseline for the science of space weather prediction. Clearly the modeling should be further improved to be used on a daily basis for a space weather mission to the Sun-Earth L5 point.
Numerical simulations of the general ocean circulation resemble reality only up to a limited degree. Therefore, numerical models are often combined with actual observations to improve the reliability of computational results. In this study, we investigate the usage of a novel set of observations, namely satellite measurements of ocean-induced magnetic signals. Seawater is a highly conductive medium. By moving through the magnetic core field of the Earth, ocean flow generates characteristic magnetic signals, which are emitted outside of the ocean into space. Satellite observations of these ocean-induced magnetic signals could be used as a measure of oceanic transports of water, heat, and salinity. In this study, we investigate the benefits and challenges of using satellite observations of the ocean-induced magnetic field to correct a global ocean model. The results show that simulated large-scale ocean currents can be corrected with this technique, if high-quality satellite observations are provided and if the uncertainties of the ocean model can be estimated accurately.
There are large differences in mass balance estimates (the net loss or gain of ice mass) from independent techniques for glaciers draining into the Abbot and Getz Ice Shelves of West Antarctica. This is believed to be primarily due to previous uncertainties in the knowledge of ice thickness in these regions at the grounding line (the point where the ice sheet detaches from the bedrock and begins to float). We use new higher accuracy ice thickness measurements derived from ESA’s CryoSat-2 satellite to reassess the mass balance for these regions for the 2006-2008 period. Our results provide better agreement with other techniques and resolve outstanding discrepancies over the Abbot region in particular. We also find that grounding line retreat, a key indicator of ice sheet imbalance, has likely to have been occurring over the Getz region since this period. Our results demonstrate the ability for the satellite to more accurately calculate the mass loss from these regions and better constrain their subsequent contribution to sea level rise.
The Curiosity rover, which is exploring the Gale crater on Mars, has been investigating a dune field. This is the first time an active and extensive dune field is explored by a rover on Mars, and therefore Curiosity used all the instruments onboard in order to better understand how the dunes can form and with what processes, and also to assess their chemistry. This in situ investigation was a great opportunity to compare with orbital data. Our work is focusing on chemical data from the ChemCam instrument, as well as on grain size distributions from the image analyses of two cameras. We show that overall the dunes are similar in chemistry to the soils analyzed along the traverse, but they are depleted in H, Cl, S suggesting they contain less fine-grained particles, or less amorphous component (which is known to be enriched in such elements). This could be due to several processes that we try to investigate. Also, we show that the coarser grains of the dunes (150-250 microns) are enriched in Fe and Mn, probably due to an enrichment in olivine.
The Global Airglow (GLOW) model has been updated and extended to calculate ultraviolet light emitted by the upper atmosphere, including during the day, during the night, and in the aurora. It can be run using inputs from standard climatological models of the upper atmosphere and ionosphere, or from complex computer models that describe the dynamics of the ionosphere. It computes energetic electron fluxes from both solar and auroral sources, and it contains a chemistry module that calculates the densities of excited and ionized atoms and molecules, and the resulting airglow emission rates. This paper describes the inputs, algorithms, and code structure of the model, and demonstrates example outputs for daytime and the aurora. Simulations of ultraviolet emissions by atomic oxygen and molecular nitrogen, as viewed from geostationary orbit, are shown, and model calculations are compared to observations by the Global Ultraviolet Imager on the TIMED satellite. The GLOW model code is provided to the community through an open-source academic research license.
The geolocation of radio signal sources that have traversed a strongly refracting medium is a complex mathematical and computational problem. A new ionospheric data assimilation method is introduced that has the capability to resolve wave structures known as travelling ionospheric disturbances (TIDs). TIDs are important because they cause strong delay and refraction to radio signals that are highly detrimental to the accuracy of high frequency (HF) geolocation systems. The new algorithms are demonstrated on a dataset from an experiment at White Sands Missile Range and show a significant improvement over previous methods. The assimilative approach in the new algorithm is extendable to include other types of ionospheric measurements.
Understanding the processes that lead to the organization of tropical rainstorms is an important challenge for weather forecasters and climate scientists. Over the last 20 years, idealized models of the tropical atmosphere have shown that tropical rainstorms can spontaneously clump together. These studies have linked this spontaneous organization to processes related to the interaction between the rainstorms, atmospheric water vapor, clouds, radiation, surface evaporation, and circulations. The present study shows that there are some similarities in how organization of rainfall in more realistic computer model simulations interacts with these processes (particularly radiation). This provides some evidence that the work in the idealized model studies is relevant to the organization of tropical rainstorms in the real world.
We describe a new analysis of sea level accelerations derived from tide-gauge data along the East Coast of North America. Previous analyses of acceleration in this region have focused on ocean dynamics as the cause of recent rapid sea level changes. We have included a number of sources of sea level acceleration, including not only ocean dynamics but also ice-mass loss from Greenland and Antarctica and atmospheric pressure. By focusing on accelerations we are able to remove one of the greatest sources of uncertainty in the sea level budget, postglacial rebound. We have devised an approach wherein data from previous decades (during which the long-term variation is assumed linear) are included, thereby improving the accuracy of estimated post-1990 accelerations by a factor of 3. We conclude that the spatial variability of sea level acceleration is well modeled using these multiple processes. The results indicate that multiple physical processes must be considered to understand changing sea level. We also conclude that the acceleration from Antarctic and Greenland ice loss alone is equivalent to a sea level rise in one century of 0.2 m in the north and 0.75 m in the south of this region.
Nutrient pollution from intensive fertilizer use and farming operations poses an increasing threat to water quality worldwide. Lakes, streams, and wetlands restrict the movement of nutrients, and thus protect downstream waters. We have a limited understanding, however, of how removal processes are affected by the size and type of the water body. Based on a synthesis of data from lakes, reservoirs, and wetlands worldwide, we found that smaller water bodies tend to have higher nutrient removal rates. We upscaled our results to the landscape scale and found that for the same wetland area loss, the loss of small wetlands corresponds to a greater loss in wetland nutrient removal potential. Such findings are significant to wetland protection and restoration efforts, which have historically focused maximizing total wetland area rather than on preserving a distribution of different wetlands sizes within a landscape.
Initially, polluted clouds can slowly transform into clean clouds when there is no significant source of aerosol particles. The rate at which this aerosol removal occurs, which can be thought of as cloud cleansing, undergoes a sudden acceleration when a cloud becomes sufficiently clean. Cloud chamber experiments show that random, turbulent fluctuations become large when a cloud becomes sufficiently clean, and these large fluctuations in temperature and the concentration of water vapor cause rapid activation of aerosol particles and rapid growth of cloud droplets. In the atmosphere these large droplets would be expected to aid in initiating the formation of precipitation by collisions and coalescence of droplets.