Nicole Feldl

Climate feedbacks

nicole — Thu, 04 Aug 2011 18:39:56 +0000

My current research focuses on how the energy balance of the atmosphere is amplified or damped due to changes in physical processes (such as clouds, water vapor, lapse rate, and ice albedo) that occur in a warming climate.

At the global scale, feedback analysis is a powerful tool for constraining climate sensitivity through understanding uncertainty in the component model physics. Our focus here is to evaluate the extent to which this framework can be applied to the question of regional climate predictability. We have developed a clean and clear approach to address these challenges. We employ the GFDL AM2 model in aquaplanet mode, coupled to simple ocean mixed-layer and sea-ice schemes, and run under perpetual equinox conditions. This simplified, aquaplanet simulation enables us to investigate the atmospheric response to carbon dioxide without the effects of a seasonal cycle or land-sea distribution, which can obscure the response. Further, we explicitly calculate radiative kernels (necessary to diagnose the feedbacks) for this precise model set-up, thus removing much of the ambiguity in the feedback approximation. We find that linking regional predictability and individual climate feedbacks depends on the balance between local radiative feedbacks and meridional energy transport in response to changes in climate forcing. An important aspect of this energy budget is the linearity of the kernel-calculated feedbacks, which we evaluate. Spatial patterns of these factors can be related to the basic structure of atmospheric circulation, and our results highlight regional differences in the effect of feedbacks on the regional climate response.

Extreme precipitation

nicole — Sat, 22 Jan 2011 12:51:57 +0000

Our ENSO work makes the New York Times! In the wake of heavy rains seen in southern California this winter (a La Nina year), Prof. David Battisti explains how a northward shift of the jet stream “makes the average number of storms go down, but it means the odds of having a really juicy storm go up.” These big La Nina storms can occur even though El Nino years are generally wetter on average in the American southwest.

The hydrological cycle, extreme precipitation, and synoptic variability. How are dynamical changes in the atmosphere manifest in the hydrological cycle? This work focuses on the relationship between large-scale circulation patterns and the frequency distribution of daily precipitation, using a case study of ENSO (El Niño Southern Oscillation) and the American West. A surprising and significant result is that intense rain is locally more intense (but not more frequent!) during La Niña winters in the southwest. Composite analyses show that intense precipitation events in the southwest arise from the presence of a persistent offshore trough and the simultaneous emplacement of a strong source of subtropical water vapor. The greater intensity of these big storms during La Niña is consistent with a deeper offshore trough leading to strengthened moisture fluxes.

The papers that have come out of this work include the following:

Feldl, N., and G. H. Roe (2011), Climate variability and the shape of daily precipitation: A case study of ENSO and the American West, Journal of Climate, 24, 2483-2499, doi: 10.1175/2010JCLI3555.1. [pdf]
Feldl, N., and G. H. Roe (2010), Synoptic weather patterns associated with intense ENSO rainfall in the southwest United States [color], Geophysical Research Letters, 37, L23803, doi:10.1029/2010GL045439. [B&W pdf]

Crustal deformation

nicole — Tue, 31 May 2005 12:00:35 +0000

In years past (2002-2007), I directed my geophysical efforts toward looking down at the Earth’s crust rather than up at the atmosphere. I conducted numerous field campaigns, modeled motions on the megathrust beneath the Himalaya mountains (India sliding under Asia), and thought about seismic hazard in this earthquake-prone part of the world. More information can be found on my C.V.

The publications that came out of this research include the following:

Feldl, N., and R. Bilham (2006), Great Himalayan earthquakes and the Tibetan Plateau, Nature, 444, 165-170. [Supplementary Materials]
Feldl, N. (2005), Crustal Deformation Across the Himalaya of Eastern and Central Nepal, M.S. Thesis, University of Colorado.
Bilham, R., E.R. Engdahl, N. Feldl, and S.P. Satyabala (2005), Partial and Complete Rupture of the Indo-Andaman Plate Boundary 1847-2004, Seismological Research Letters, 76, 299-311.
Hough, S.E., R. Bilham, N. Ambraseys, and N. Feldl (2005), The 1905 Kangra and Dehra Dun earthquakes, Geological Survey of India Special Publications, 85, 15-22.
Hough, S.E., R. Bilham, N. Ambraseys, and N. Feldl (2005), Revisiting the 1897 Shillong and 1905 Kangra earthquakes in northern India: Site response, Moho reflections and a triggered earthquake, Current Science, 88 (10), 1632-1638.