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L'Heureux M.L.,5830 University Research Court | Lee S.,Pennsylvania State University | Lyon B.,International Research Institute for Climate and Society
Nature Climate Change | Year: 2013

The Pacific Walker circulation is a large overturning cell that spans the tropical Pacific Ocean, characterized by rising motion (lower sea-level pressure) over Indonesia and sinking motion (higher sea level-pressure) over the eastern Pacific. Fluctuations in the Walker circulation reflect changes in the location and strength of tropical heating, so related circulation anomalies have global impacts. On interannual timescales, the El Niño/Southern Oscillation accounts for much of the variability in the Walker circulation, but there is considerable interest in longer-term trends and their drivers, including anthropogenic climate change. Here, we examine sea-level pressure trends in ten different data sets drawn from reanalysis, reconstructions and in situ measurements for 1900-2011. We show that periods with fewer in situ measurements result in lower signal-to-noise ratios, making assessments of sea-level pressure trends largely unsuitable before about the 1950s. Multidecadal trends evaluated since 1950 reveal statistically significant, negative values over the Indonesian region, with weaker, positive trends over the eastern Pacific. The overall trend towards a stronger, La Niña-like Walker circulation is nearly concurrent with the observed increase in global average temperatures, thereby justifying closer scrutiny of how the Pacific climate system has changed in the historical record. © 2013 Macmillan Publishers Limited. All rights reserved. Source

Kumar A.,5830 University Research Court | Murtugudde R.,University of Maryland University College
Current Opinion in Environmental Sustainability | Year: 2013

In this essay, the common thread of limits of predictability and uncertainty that permeate across weather and climate prediction and projections is discussed in the context of developing a strategy for 'seamless' communication and utilization of uncertain information in decision making. In understanding why uncertainty is an unavoidable trait of predictions in the first place, a useful concept is the separation of the Earth System (ES) into internal and external components. This separation allows one to first, recognize that for prediction at all time-scales, the inherent source for limits on predictability is due to the divergence of forecasts from a cloud of initial conditions, and second, thereby recognize that the fundamental source of uncertainty (or unpredictability) is limited by our ability to specify initial conditions for the internal component with perfect accuracy.The unavoidability of uncertainty in predictions, and accepting this fact could be advantageous in the ongoing discussions on how to communicate climate projections and the associated uncertainties by learning from the knowledge base that exists for communicating similar information on weather and seasonal predictions that are generated on a much more frequent basis. Similarly, decision-support systems for developing adaptation and mitigation strategies can use predictions on shorter range as a test-bed to hone their strategies to incorporate predictive uncertainty when dealing with longer-range projections. By practicing the use of decision making tools and the incorporation of uncertain predictions on weather and seasonal time scale, decision makers can improve their level of comfort in accepting uncertainty inherent in longer range predictions and projections on a much less infrequent basis. In this paradigm, evolving strategy for seamless predictions can be blended with a strategy for seamless communication of uncertain information and also with seamless application of decision support systems. © 2013. Source

The Suomi National Polar-orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) sensor data record (SDR) product achieved validated maturity status in March 2014 after roughly two years of on-orbit characterization (S-NPP spacecraft launched on 28 October 2011). During post-launch analysis the VIIRS Sea Surface Temperature (SST) Environmental Data Record (EDR) team observed an anomalous striping pattern in the daytime SST data. Daytime SST retrievals use the two VIIRS long-wave infrared bands: M15 (10.7 μm) and M16 (11.8 μm). To assess possible root causes due to detector-level spectral response function (SRF) effects, a study was conducted to compare the radiometric response of the detector-level and operationalband averaged SRFs of VIIRS bands M15 and M16. The study used simulated hyperspectral blackbody radiance data and clear-sky ocean hyperspectral radiances under different atmospheric conditions. It was concluded that the SST product is likely impacted by small differences in detector-level SRFs and that if users require optimal radiometric performance, detector-level processing is recommended for both SDR and EDR products. Future work should investigate potential SDR product improvements through detector-level processing in support of the generation of Suomi NPP VIIRS climate quality SDRs. © 2015 Optical Society of America. Source

Zhu T.,Colorado State University | Zhu T.,5830 University Research Court | Weng F.,College Park
Geophysical Research Letters | Year: 2013

The warm-core structures of Hurricane Sandy and other nine tropical cyclones (TCs) are studied using the temperatures retrieved from Advanced Technology Microwave Sounder (ATMS). A new algorithm is developed for the retrieval of atmospheric temperature profiles from the ATMS radiances. Since ATMS observation has a higher spatial resolution and better coverage than its predecessor, Advanced Microwave Sounding Unit-A, the retrieved temperature field explicitly resolves TC warm core throughout troposphere and depicts the cold temperature anomalies in the eyewall and spiral rainbands. Unlike a typical TC, the height of maximum warm core of Hurricane Sandy is very low, but the storm size is quite large. Based on the analysis of 10 TCs in 2012, close correlations are found between ATMS-derived warm core and the TC maximum sustained wind (MSW) or minimum sea level pressure (MSLP). The estimation errors of MSW and MSLP from ATMS-retrieved warm core are 13.5 mph and 13.1 hPa, respectively. Key Points A new algorithm was developed to retrieve atmospheric temperatures from ATMS We studied Hurricane Sandy warm cores, including that of Hurricane Sandy Tropical cyclone intensity was estimated using retrieved temperature anomaly ©2013. American Geophysical Union. All Rights Reserved. Source

Liu R.-F.,Central Weather Bureau CWB | Wang W.,5830 University Research Court
Climate Dynamics | Year: 2015

In this paper we analyze the multi-week prediction bias and skill from the National Centers for Environment Prediction (NCEP) Climate Forecast System version 2 (CFSv2) based on its hindcasts for 1999–2012. The analyses focus on the prediction of the rainfall variability over South-East Asia during boreal warm seasons and the dependence of the prediction on the activity of intrasesaonal leading modes. It is shown that the prediction skill measured by anomaly correlation is comparable between the total anomalies and intraseasonal anomalies during the first 2 weeks. After week 2, the prediction skill drops substantially and the skill for total anomalies is largely from the prediction for the interannual variability. Moreover, the forecast skill tends to be higher when the amplitude of the Madden–Julian Oscillation and the Boreal Summer Intraseasonal Oscillation (BSISO) is larger, especially for the BSISO. It is noted that the prediction skill over South-East Asia depends on the phase of the BSISO. One deficiency in the CFSv2 is that the northward propagation of the forecast BSISO is generally slower than the observed. © 2014, Springer-Verlag (outside the USA). Source

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