Simulated shifts in the mid-latitude storm tracks over the western US detected through isotopes in precipitation and vapor
Abstract
One of the most robust features of climate model projections for the 21st century includes a poleward shift of middle latitude storm tracks in response to enhanced radiative forcing. This study evaluates how shifts in the middle latitude storm tracks over the North Pacific has been expressed in the stable isotopic composition of atmospheric vapor and precipitation in the past 60 years. Previous work has demonstrated how the isotopic composition of precipitation (δ18Op) in the Pacific Northwest and in atmospheric vapor (δ18Ov) across the western US reflects the large-scale atmospheric circulation. Thus, it is possible to use the isotopic composition of water in these regions to detect shifts in mid-latitude storm tracks. Results from the Isotope-incorporated Global Spectral Model (IsoGSM) are presented to better understand the recent low frequency variations in δ18O values over the western US. The IsoGSM simulations presented here were spectrally nudged every six hours to the NCEP/NCAR Reanalysis wind and temperature fields. The spectral nudging technique allows for realistic isotopic simulations that are consistent with observed large-scale mid-latitude storm systems. Model results suggest that δ18Op has risen over the Pacific Northwest and δ18Ov has increased across the western US since the 1950s (see Figure), an indication of more moisture advection from the tropics and less moisture transported from the middle latitudes. Water tagging simulations reveal that as δ18Ov increased in the western US, the fraction of vapor from the subtropics had also increased, while the fraction from the middle latitudes had decreased. Similarly, the tagging simulations resulted in increased subtropical precipitation falling in the Pacific Northwest and decreased precipitation from the middle latitudes. These model simulations suggest that a northward shift in storm tracks has already taken place over the last 60 years in the western US. Furthermore, the results underscore the potential of using isotopes in vapor and precipitation in certain regions of western North America to monitor middle latitude storm behavior as the climate warms.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMGC23E..07B
- Keywords:
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- 1655 GLOBAL CHANGE Water cycles;
- 3305 ATMOSPHERIC PROCESSES Climate change and variability;
- 3337 ATMOSPHERIC PROCESSES Global climate models;
- 1620 GLOBAL CHANGE Climate dynamics