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AGU Research Spotlight (Oct 06-Oct 12, 2016)

2016-10-13 15:27:24

I. Atmospheric Sciences

1.Simulating the Climate 145 Million Years Ago

A new model shows that the Intertropical Convergence Zone wasn't always a single band around the equator, which had drastic effects on climate.


2.Why 2015 Was a Big Hurricane Year for the Eastern North Pacific

Record-breaking oceanic and atmospheric conditions led to a remarkable season in a key Pacific hurricane development region.


II. Geology & Geophysics

1.Paden Receives 2016 Cryosphere Early Career Award

John Paden will receive the 2016 Cryosphere Early Career Award at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award is for "a significant contribution to cryospheric science and technology."


2.Marín-Spiotta Receives 2016 Sulzman Award for Excellence in Education and Mentoring

Erika Marín-Spiotta will receive the 2016 Sulzman Award for Excellence in Education and Mentoring at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award is given for "significant contributions by a mid-career female scientist as a role model and mentor for the next generation of biogeoscientists."


3.Scientists Spend Arctic Winter Adrift on Sea Ice

A hovercraft-based ice drift station gives researchers access to previously inaccessible regions of the changing Arctic sea ice cover off the coast of Greenland.


4.Hall, Jakob, Maloney, Scaife, and Van den Heever Receive 2016 Atmospheric Sciences Ascent Award

Alexander D. Hall, Christian Jakob, Eric Maloney, Adam Scaife, and Susan C. van den Heever will receive the 2016 Atmospheric Sciences Ascent Award at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award recognizes "research contributions by exceptional mid-career scientists in the fields of atmospheric and climate sciences."


5.Wang Receives 2016 James R. Holton Junior Scientist Award

Yuan Wang will receive the 2016 James R. Holton Junior Scientist Award at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award recognizes "outstanding research contributions by a junior atmospheric scientist within three years of his or her Ph.D."


6.Rosenlof Receives 2016 Yoram J. Kaufman Unselfish Cooperation in Research Award

Karen H. Rosenlof will receive the 2016 Yoram J. Kaufman Unselfish Cooperation in Research Award at the 2016 American Geophysical Union Fall Meeting, to be held 12–16 December in San Francisco, Calif. The award recognizes "broad influence in atmospheric science through exceptional creativity, inspiration of younger scientists, mentoring, international collaborations, and unselfish cooperation in research."


7.Climate-Driven Change in Ice-Free Areas of Greenland

KAIRN (Kangerlussuaq International Research Network) 2nd Annual Meeting; Acadia National Park, Maine, 4–7 May 2016


8.Cubans, Americans Bridge a Scientific Rift

Two scientific communities that evolved separately for more than 50 years reunited last week to share their findings and plan a more unified future.


III.Hazards & Disasters

1.Lab Experiment Tests What Triggers Massive Solar Eruptions

In a first-of-its-kind demonstration, scientists provide experimental support for a possible mechanism behind the formation of coronal mass ejections.


2.Tracking Landslide Hazards Around the World, Pixel by Pixel

Combining satellite precipitation measurements and remotely sensed environmental data, a new system aims to improve landslide awareness and preparedness in all corners of the globe.


IV. Climate Change

1.Europe to Push Paris Climate Accord over Brink to Take Effect

Enough member states in the European Union have already individually ratified the agreement to meet the emissions requirement for the agreement to go into force.


V.Earth and Space Science

1.Large precipitation events critical in replenishing groundwater resources

Large precipitation events that occur about every 10 years are a critical source of recharge for replenishing groundwater resources, according to a new study. Groundwater is a vital source of water in the western United States and will be increasingly important with continued population growth and climate variability. Understanding the role of these large recharge events in replenishing aquifers and sustaining water supplies is crucial for long-term groundwater management.


VI. Geophysical Research Letters

1. Aerosol optical depth distribution in extratropical cyclones over the Northern Hemisphere oceans

Using Moderate Resolution Imaging Spectroradiometer and an extratropical cyclone database, the climatological distribution of aerosol optical depth (AOD) in extratropical cyclones is explored based solely on observations. Cyclone-centered composites of aerosol optical depth are constructed for the Northern Hemisphere midlatitude ocean regions, and their seasonal variations are examined. These composites are found to be qualitatively stable when the impact of clouds and surface insolation or brightness is tested. The larger AODs occur in spring and summer and are preferentially found in the warm frontal and in the postcold frontal regions in all seasons. The fine mode aerosols dominate the cold sector AODs, but the coarse mode aerosols display large AODs in the warm sector. These differences between the aerosol modes are related to the varying source regions of the aerosols and could potentially have different impacts on cloud and precipitation within the cyclones.


2. A drought index based on actual evapotranspiration from the Bouchet hypothesis

Global drought assessment has mainly depended on precipitation-based drought indices that may also take into account potential evapotranspiration (ETp). In this study, we combined the actual evapotranspiration (ETa) estimated from the Bouchet hypothesis and the structure of the Standardized Precipitation-Evapotranspiration Index to develop a fully ET-based drought index, the Standardized Evapotranspiration Deficit Index (SEDI). We found that SEDI, without using precipitation data, produces results that are consistent with the Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Index (SPI) for drought identification in the South-Central United States. We also found a competitive performance of SEDI through comparisons between the Vegetation Health Index with SEDI, PDSI, and SPI. We suggest the high applicability of the SEDI based on the Bouchet hypothesis as an independent drought index for regions with strong land-atmosphere coupling or as an alternative drought index to fully precipitation-dependent indices for assessing agricultural droughts.


3. Far-field pressurization likely caused one of the largest injection induced earthquakes by reactivating a large preexisting basement fault structure

The Mw5.1 Fairview, Oklahoma, earthquake on 13 February 2016 and its associated seismicity produced the largest moment release in the central and eastern United States since the 2011 Mw5.7 Prague, Oklahoma, earthquake sequence and is one of the largest earthquakes potentially linked to wastewater injection. This energetic sequence has produced five earthquakes with Mw4.4 or larger. Almost all of these earthquakes occur in Precambrian basement on a partially unmapped 14?km long fault. Regional injection into the Arbuckle Group increased approximately sevenfold in the 36?months prior to the start of the sequence (January 2015). We suggest far-field pressurization from clustered, high-rate wells greater than 12?km from this sequence induced these earthquakes. As compared to the Fairview sequence, seismicity is diffuse near high-rate wells, where pressure changes are expected to be largest. This points to the critical role that preexisting faults play in the occurrence of large induced earthquakes.


4. Contrasting upper and lower atmospheric metrics of tropical expansion in the Southern Hemisphere

Observational studies suggest that the tropics are expanding, but a wide range of expansion rates have been reported (from 0.2° to 2° of latitude per decade). This is due, in part, to the great variety of metrics used to define the tropical width. Here we ask whether these metrics are measuring tropical width consistently, focusing on the Southern Hemisphere, where the circulation is better approximated by the zonally symmetric component. Analyzing output from the Community Earth System Model (CESM) Large Ensemble Project, we show that tropical expansion robustly occurs in the model in response to forcings. In addition, we find that whereas the width of the Hadley circulation is strongly correlated with the midlatitude jet, from interannual to decadal time scales, it is essentially uncorrelated with upper atmospheric metrics, e.g., the maximum gradient of tropopause height, both in terms of variability and of response to forcings.


5. Low stress drop earthquakes in the rupture zone of the 1992 Nicaragua tsunami earthquake

Tsunami earthquakes, events that generate larger than expected tsunami and are deficient in high-frequency seismic radiation, are rare but hazardous to coastal populations. One model for these events is shallow rupture through low-strength materials. We calculate seismic moment, corner frequency, and stress drop for 216 earthquakes (2.1?<Mw< ?4.7, november 2005 to june 2006) within and external to the 1992 nicaragua tsunami earthquake rupture zone to test the hypothesis that differences in fault zone properties defined the limits of the 1992 tsunami rupture zone and continue to produce spatial variations in earthquake source properties. mean stress drop of events within the rupture area is 1.2?mpa, and 5.5?mpa for events just outside of the rupture zone, with similar magnitude earthquakes in each group. our results demonstrate different source parameter characteristics for microseismicity in the region of a past tsunami earthquake.


6. Linked trends in the South Pacific sea ice edge and Southern Oscillation Index

Previous work have shown that sea ice variability in the South Pacific is associated with extratropical atmospheric anomalies linked to the Southern Oscillation (SO). Over a 32?year period (1982–2013), our study shows that the trend in Southern Oscillation Index (SOI) is also able to quantitatively explain the trends in sea ice edge, drift, and surface winds in this region. On average two thirds of the winter ice edge trend in this sector, linked to ice drift and surface winds, could be explained by the positive SOI trend, thus subjecting the ice edge to strong decadal SO variability. If this relationship holds, the negative SOI trend prior to the recent satellite era suggests that ice edge trends opposite to that of the recent record over a similar time scale. Significant low-frequency ice edge trends, linked to the natural variability of SO, are superimposed upon any trends expected of anthropogenic forcing.


7. The Northern Appalachian Anomaly: A modern asthenospheric upwelling

The Northern Appalachian Anomaly (NAA) is an intense, laterally localized (400?km diameter) low-velocity anomaly centered in the asthenosphere beneath southern New England. Its maximum shear velocity contrast, at 200?km depth, is about 10%, and its compressional-to-shear velocity perturbation ratio is about unity, values compatible with it being a modern thermal anomaly. Although centered close to the track of the Great Meteor hot spot, it is not elongated parallel to it and does not crosscut the cratonic margin. In contrast to previous explanations, we argue that the NAA's spatial association with the hot spot track is coincidental and that it is caused by small-scale upwelling associated with an eddy in the asthenospheric flow field at the continental margin. That the NAA is just one of several low-velocity features along the eastern margin of North America suggests that this process may be globally ubiquitous.


8. Convective moisture adjustment time scale as a key factor in regulating model amplitude of the Madden-Julian Oscillation

Despite its pronounced impacts on weather extremes worldwide, the Madden-Julian Oscillation (MJO) remains poorly represented in climate models. Here we present findings that point to some necessary ingredients to produce a strong MJO amplitude in a large set of model simulations from a recent model intercomparison project. While surface flux and radiative heating anomalies are considered important for amplifying the MJO, their strength per unit MJO precipitation anomaly is found to be negatively correlated to MJO amplitude across these multimodel simulations. However, model MJO amplitude is found to be closely tied to a model's convective moisture adjustment time scale, a measure of how rapidly precipitation must increase to remove excess column water vapor, or alternately the efficiency of surface precipitation generation per unit column water vapor anomaly. These findings provide critical insights into key model processes for the MJO and pinpoint a direction for improved model representation of the MJO.


9. High atmospheric horizontal resolution eliminates the wind-driven coastal warm bias in the southeastern tropical Atlantic

We investigate the strong warm bias in sea surface temperatures (SST) of the southeastern tropical Atlantic that occurs in most of the current global climate models. We analyze this bias in the Max Planck Institute Earth System Model at different horizontal resolutions ranging from 0.1° to 0.4° in the ocean and 0.5° to 1.8° in the atmosphere. High atmospheric horizontal resolution eliminates the SST bias close to the African coast, due to an improved representation of surface wind stress near the coast. This improvement affects coastal upwelling and horizontal ocean circulation, as confirmed with dedicated sensitivity experiments. The wind stress improvements are partly caused by the better represented orography at higher horizontal resolution in the spectral atmospheric model. The reductions of the coastal SST bias obtained through higher horizontal resolution do not, however, translate to a reduction of the large-scale bias extending westward from the African coast into the southeastern tropical Atlantic.


10. Prolonged El Ni?o conditions in 2014–2015 and the rapid intensification of Hurricane Patricia in the eastern Pacific

Hurricane Patricia was the most intense tropical cyclone on record in the eastern North Pacific or Atlantic, reaching a peak intensity of 95 m s?1 only 30 h after attaining hurricane status (33 m s?1). Here it is shown that exceptionally warm sea surface temperatures (SSTs), a deeper than normal thermocline, and strong near-surface salinity stratification all aided Patricia's rapid intensification, combining to increase its Potential Intensity by 1–14 m s?1. Anomalous surface warming and thermocline deepening along Patricia's track were driven by prolonged El Ni?o conditions during 2014–2015 and punctuated by the buildup to the extreme El Ni?o of 2015–2016. In the region where Patricia intensified, SST was 1.5° C higher and sea surface height was 10 cm higher compared to conditions during the last extreme El Ni?o in 1997, emphasizing the extraordinary nature of the 2015 anomalies.




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