CCR Staff: Gerald A. Meehl, Senior Scientist
Major research tasks have involved two broad ongoing activities: (1) analysis and interpretation of results from various climate model experiments for past and future climate, and (2) analysis and interpretation of observed data, often attempting to relate the observed results to characteristics of model simulations. Recent research activities include the following:
- Collaborative work with Rebecca Morss on a study of impacts of heat extremes.
- Collaborative work with Harry van Loon (NCAR), Julie Arblaster (NCAR), addressed influences of solar forcing on observed 20th century climate. A similar signal to the anomalous high pressure area in the North Pacific has been discovered in the South Pacific in association with peaks in the 11 year solar cycle, along with a stronger Indian monsoon.
- Meehl collaborated with Aixue Hu to analyze processes associated with changes in the meridional overturning circulation (MOC) in the Atlantic in a future warmer climate, as well as the effects of Bering Strait throughflow on North Atlantic climate and effects of Greenland Ice Sheet melt on future climate.
- Meehl collaborated with Julie Arblaster to study the processes involved with time periods when the TBO was dominant versus when the ENSO timescale was more important, to determine what mechanisms produce more biennial versus less biennial conditions in the Asia-Pacific region.
- Meehl collaborated with Warren Washington, H. Teng, C. Tebaldi, A. Hu, W. Gary Strand, and Trey White to document future climate projections in CCSM4, and to quantify the effects of mitigation on temperature and sea level rise.
- Meehl collaborated with Julie Arblaster, Julie Caron, H. Annamalai, Markus Jochum, A. Chakraborty, Kerry Cook, and Raghu Murtugudde to document characteristics of the monsoon regimes in CCSM4.
- Meehl collaborated with Julie Arblaster, Aixue Hu, John Fasullo and Kevin Trenberth to identify where heat goes in the climate system during decades when globally averaged surface air temperatures are not increasing, and in contrasting so-called hiatus decades to other decades when there is an acceleration of global warming. These periods are associated with opposite patterns of SST trends in the Pacific, with hiatus decades showing the negative phase of the Interdecadal Pacific Oscillation (IPO, negative phase means relatively cool tropical Pacific SSTs on the decadal timescale), and accelerated warming decades showing the opposite pattern.
- Meehl collaborated with Haiyan Teng and Grant Branstator to quantify decadal predictability both for the North Pacific and globally, using versions of CCSM and the CMIP3 models.
- Meehl collaborated with H. Teng, H., W.M. Washington, G. Branstator, and J.-F. Lamarque to document remote effects over the U.S. in summertime due to increased black carbon aerosols over the south Asian monsoon region.
- Meehl collaborated with Julie Arblaster and David Karoly on addressing the relative influences of increasing GHGs and changes in stratospheric ozone on Southern Hemisphere climate associated with the SAM.
- Collaborations with Julie Arblaster and Grant Branstator produced results related to understanding the U.S. east-west differential of record temperatures and processes that are relevant to the lack of late 20th century warming in the southeastern U.S., referred to as the "warming hole".
- Meehl collaborated with H. Teng to analyze the decadal climate prediction experiments performed with CCSM4 for CMIP5. Two initialization schemes were used, and results show both methods can capture the mid-1970s climate shift when there was an acceleration of global warming, and the early 2000s hiatus when global temperatures showed little increase. Both these decades were associated with shifts in Pacific SSTs, with the mid-1970s shift transitioning from a negative to positive phase of the Interdecadal Pacific Oscillation (IPO), and the early 2000s hiatus showing the opposite shift of Pacific SSTs.
- Collaborative work with Julie Arblaster on the modulation of interannual variability associated with the Tropospheric Biennial Oscillation (TBO) and the Interdecadal Pacific Oscillation (IPO), whereby during negative phases of the IPO (relatively cool tropical Pacific SSTs), the TBO has larger amplitude, and vice versa for the positive phase of the IPO.