
NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
Recipient: |
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Initial Amendment Date: | April 19, 2016 |
Latest Amendment Date: | April 19, 2016 |
Award Number: | 1545675 |
Award Instrument: | Standard Grant |
Program Manager: |
Eric DeWeaver
edeweave@nsf.gov (703)292-8527 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
Start Date: | May 1, 2016 |
End Date: | April 30, 2020 (Estimated) |
Total Intended Award Amount: | $599,693.00 |
Total Awarded Amount to Date: | $599,693.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
601 S HOWES ST FORT COLLINS CO US 80521-2807 (970)491-6355 |
Sponsor Congressional District: |
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Primary Place of Performance: |
200 W. Lake St Fort Collins CO US 80521-4593 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): | Climate & Large-Scale Dynamics |
Primary Program Source: |
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Program Reference Code(s): | |
Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.050 |
ABSTRACT
The climate change induced by increases in greenhouse gas concentrations is generally characterized as an increase in globally averaged temperature, but the climate impacts experienced locally will be determined in part by the changes in atmospheric circulation that are induced by global warming. In particular, climate model simulations suggest that the westerly jet streams found at upper levels in the middle latitudes will shift towards the poles, so that the mean Northern Hemisphere jet stream will migrate northward, with a corresponding southward shift for its the Southern Hemisphere counterpart. These shifts are small but consequential, as patterns of rainfall and storminess in the middle latitudes are determined in large part by the positions of the jet streams.
The poleward shift of jet streams as a consequence of greenhouse warming is a robust feature of global warming simulations and has been a research topic since at least 2005, but the seasonality and geography of the response has not yet been fully explored. Preliminary work for this project shows that in the Southern Hemisphere the largest shift is in the Fall (March to May), followed by Summer (December to February), Winter (June to August), and Spring (September to November). In the North Atlantic the order is, from largest to smallest, Fall (September to November), Summer (June to August), Spring (March to May), and Winter (December to February). The ordering is again different in the North Pacific, with Fall leading by a large margin followed by Winter, Spring, and Summer. By now several theories have been proposed to explain why the jets shift poleward in an year-round, longitudinally averaged sense, but none of these theories provides a clear intuition for the seasonality (i.e. why the shift is largest in Fall) or the regional variations.
Research under this award consists of analysis of observational data from reanalysis products and simulations of future climate from the Coupled Model Intercomparison Project and the Large Ensemble archive of simulations using the Community Earth System Model. This analysis is followed by numerical experiments using models of varying levels of complexity, intended to isolate and study possibly physical mechanisms leading seasonally and geographically varying jet shifts. One issue to be considered is that the pattern of greenhouse warming generally includes a deep tropospheric warming maximum in the tropics together with surface trapped warming near the poles (referred to as polar amplification). The jet shifts can be regarded as a combined response to the tropical and polar influences, which are likely to have opposing effects and very different seasonalities.
The work is of societal as well as scientific interest due to the strong impacts of jet shifts on local climate, for instance a northward shift of jet streams could cause drying in the region downwind of the present-day jet location accompanied by excessive rain and snow to the north. In addition, the project will support and train two students, thereby contributing to the future workforce in this research area. The PI and her students will also organize a special session at an annual geosciences meeting to publicize results of the study and encourage further investigation of the topic.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The jet-streams and storm-tracks comprise a major portion of the large-scale, atmospheric circulation in midlatitudes, bringing stormy days or clear skies while playing a critical role in maintaining earth’s climate. How the storm tracks will change as anthropogenic greenhouse gas concentrations continue to rise is of vital importance to policy makers and city planners who must prepare for future extreme events. However, given that weather extremes and their impacts are a strong function of the time-of-year, that is, heat waves and drought typically occur in summer while heavy snow-falls and flooding typically occur in winter, it is not enough to only understand the annual-mean changes in the circulation. Instead, we must also understand the dynamics behind the seasonal to sub-seasonal responses. This project focused on understanding the seasonal response of the storm tracks to climate warming.
The key outcomes of the intellectual meric portion of the work are presented in 13 published peer reviewed journal articles, with 1 still under review (total of 14 peer reviewed articles). Within these articles, we detail many results and highlight some of the key findings/outcomes here:
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The response of the jet-streams to climate warming changes across seasons and regions of the globe. These differences can be explained, in part, by fundamental theories of the atmospheric circulation, and suggest a simple dynamical mechanism for why the storm tracks respond to melting Arctic sea ice.
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Climate model differences in the climatological jet stream position to differences in the jet stream position’s sensitivity to Arctic warming, explaining, in part, the large disagreement in response across climate models.
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Statistical methods that help identify causal connections provide insights into the relationship between melting Arctic sea ice and the midlatitude storm tracks. We find that the midlatitude regions that have a substantial impact on Arctic climate (e.g., Siberia, the North Pacific) are not the regions that are the most heavily influenced by the Arctic.
In terms of broader impacts, the project supported three scientists from underrepresented groups within STEM: two female PhD students and an early-career female faculty member. It also supported the PI and one of the PhD students to closely collaborate with two other female researchers at CSU and another female colleague at NCAR, further supporting female scientists in STEM. Over half of the 14 scientific articles were led by graduate students, and the award supported travel for students to scientific conferences and workshops, where they met colleagues in the field and gave oral and poster presentations, supporting their professional development.
Last Modified: 06/15/2020
Modified by: Elizabeth Barnes
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