2011 - Cooperative Institute for Research in Environmental Sciences ...

tolysis) and global warming potential (GWP) of approximately
1. Hydrolysis is slow and produces HFC-227ea as
the only gas phase product, a long-lived and potent greenhouse
gas. Another co-product was C2F5COOH, which was
highly soluble and did not show up in the gas phase. HFC-
227ea has an atmospheric lifetime of 38.9 years and a GWP
of 3580 (on a 100-year time horizon). Preliminary estimates
indicate that although both the Henry’s law constant and
the hydrolysis rate are small, loss via hydrolysis in clouds
and oceanic uptake can increase the effective climate forcing
of PFMP significantly. Detailed measurements are in
progress with other molecules of atmospheric interest. This
project is scheduled to be completed and a paper to be submitted
during the next year of this milestone.
Figure 1: Hydrolysis rate coefficient (in units of per second) at two temperatures,
273 and 293 K in the buffer solutions of varying pH (acidity)
relevant to tropospheric conditions.
PSD-01ModelingofSeasonal
toInterannualVariability
FEDERAL LEADS: RANDALL DOLE AND MARTIN HOERLING
CIRES LEAD: PRASHANT SARDESHMUKH
NOAA Goal 2: Climate
Project Goal: Understand how much predictability, especially
outside the tropics, exists on seasonal to inter-annual timescales
beyond that associated with linear El Niño–Southern
Oscillation (ENSO) signals, and what additional useful predictive
information can be extracted by making large ensembles
of nonlinear General Circulation Model (GCM) integrations.
Milestone 1. Determine the sensitivity of North American
drought to tropical sea surface temperature (SST) changes
at different locations, and identify the optimal anomalous
tropical SST pattern for maximizing drought.
In a recently published study (Shin, Sardeshmukh, and
Webb, Journal of Climate, 2010), the optimal anomalous
sea surface temperature (SST) pattern for forcing North
American drought was identified through atmospheric
general circulation model integrations in which the
response of the Palmer drought severity index (PDSI)
was determined for each of 43 prescribed localized SST
anomaly ‘‘patches’’ in a regular array over the tropical
oceans. The robustness and relevance of the optimal pat-
112 CIRES Annual Report 2011
tern were established through the consistency of results
obtained using two different models, and also by the good
correspondence of the projection time series of historical
tropical SST anomaly fields on the optimal pattern with
the time series of the simulated PDSI in separate model
integrations with prescribed time-varying observed global
SST fields for 1920–2005. It was stressed that this optimal
drought-forcing pattern differs markedly in the Pacific
Ocean from the dominant SST pattern associated with
El Niño–Southern Oscillation (ENSO), and also shows a
large sensitivity of North American drought to Indian and
Atlantic Ocean SSTs.
Product: Shin, SI, PD Sardeshmukh, and RS Webb
(2010), Optimal sea surface temperature forcing of
North American drought, J. Clim., 23, 3907-3916, DOI:
10.1175/2010JCLI3360.1.
PSD-02 Understanding and Predicting
Subseasonal Variations and Their Implications
for Longer-Term Climate Variability
FEDERAL LEADS: JEFFREY WHITAKER AND RANDALL DOLE
CIRES LEAD: PRASHANT SARDESHMUKH
NOAA Goal 2: Climate
Project Goal: Investigate the variability and predictability of
weekly averages of the atmospheric circulation through modeling
and diagnosis of the observed statistics, and also through detailed
analysis of numerical weather forecast ensembles for week two.
Milestone 1. Compare the week two and week three atmospheric
circulation forecast skill of state-of-the-art global
atmosphere-ocean coupled models with that of simple Linear
Inverse Models (LIMs) based on lag-correlations of the
northern hemispheric circulation and tropical convection
fields. Assess the prospects for further skill improvement
by performing a predictability analysis based on the relative
magnitudes of the forecast signal and forecast noise.
Extending atmospheric prediction skill beyond the
predictability limit of about 10 days for daily weather rests
on the hope that some time-averaged aspects of anomalous
circulations remain predictable at longer forecast lead
times, both due to the existence of natural low-frequency
modes of atmospheric variability and coupling to a medium
with larger thermal inertia. In a recent study (Pegion and
Sardeshmukh, 2011), the week two and week three forecast
skill of two global coupled atmosphere-ocean models recently
developed at NASA and NOAA was compared with
that of much simpler Linear Inverse Models (LIMs) derived
from observed time-lag correlations of atmospheric circulation
anomalies in the northern hemisphere and outgoing
long-wave radiation (OLR) anomalies in the tropics. The
coupled models were found to beat the LIMs only slightly,
and only if an ensemble prediction methodology was employed.
To assess the potential for further skill improvement,
a predictability analysis based on the relative magnitudes
of forecast signal and forecast noise in the LIM framework
was conducted. Estimating potential skill by such a method
was argued to be superior to using the ensemble-mean and
ensemble-spread information in the coupled-model ensemble
prediction system. The LIM-based predictability analysis
yielded relatively conservative estimates of the potential
skill, and suggested that outside the tropics, the average
coupled-model skill may already be close to the potential