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Application of MJO simulation diagnostics to climate model simulations
Daehyun Kim,D. E. Waliser,K. R. Sperber,L Donner,J. Gottschalck,H. H. Hendon,W. Higgins,I.-S. Kang,E. D. Maloney,M. W. Moncrieff,S. Schubert,W. Stern,F. Vitart,B. Wang,W. Wang,K. M. Weickmann,M. C. Wh 한국기상학회 2008 한국기상학회 학술대회 논문집 Vol.2008 No.-
서기원,Duane E. Waliser,Baijun Tian,김백민,박성찬,Steve Cocke,손병주,Masayoshi Ishii 한국기상학회 2012 Asia-Pacific Journal of Atmospheric Sciences Vol.48 No.2
Variations of global evapotranspiration (ET) and fresh water discharge from land to oceans (D) are important components of global climate change, but have not been well monitored. In this study, we present an estimate of twenty years (1989 to 2008) variations of global D and ET derived from satellite remote-sensed measurements and recent reanalysis products, ERA-Interim and CFSR, by using a novel application of the water balance equations separately over land and over oceans. Time series of annual mean global D and ET from both satellite observations and reanalyses show clear positive and negative trends, respectively, as a result of modest increase of oceanic evaporation (Eo). The inter-annual variations of D are similar to the in-situ-based observations, and the negative trend of ET supports the previous result that relative humidity has decreased while temperature has increased on land. The results suggest considerable sensitivity of the terrestrial hydrological cycles (e.g., D and ET) to small changes in precipitation and oceanic evaporation.
Seo, K.W.,Waliser, D.E.,Lee, C.K.,Tian, B.,Scambos, T.,Kim, B.M.,van Angelen, J.H.,van den Broeke, M.R. Elsevier 2015 Global and planetary change Vol.128 No.-
Understanding the mechanisms that drive the mass imbalance of the Greenland ice sheet (GrIS) is critical to the accurate projection of its contribution to future sea level rise. Greenland's ice mass loss has been accelerating recently. Using satellite Earth-gravity and regional climate model data, we show that the acceleration rate of Greenland ice mass loss from 2003 to 2012 is -13.9+/-2.0Gt/yr<SUP>2</SUP>, which results mainly from an increase of meltwater runoff (-6.3+/-1.1Gt/yr<SUP>2</SUP>) and a decrease of precipitation (-4.8+/-1.1Gt/yr<SUP>2</SUP>). Before the extreme surface melting in the summers of 2010 and 2012, the decrease of precipitation (-9.7+/-2.5Gt/yr<SUP>2</SUP>) was a larger contributor to the ice mass loss acceleration than the increase of runoff (-2.1+/-2.2Gt/yr<SUP>2</SUP>). Furthermore, we show that the North Atlantic Oscillation (NAO) is linked to the precipitation decrease during summer, and its recent influence to Greenland is anomalously large possibly due to the change in atmospheric circulation in the North Atlantic. These results indicate that inter-annual climate variability is playing a significant role in the recently observed Greenland ice mass loss acceleration, underscoring the difficulty of projecting future sea level rise based on the recent observations of GrIS mass loss.
Neena, J.M.,Lee, J.Y.,Waliser, D.,Wang, B.,Jiang, X. AMERICAN METEOROLOGICAL SOCIETY 2014 Journal of climate Vol.27 No.12
The Madden-Julian oscillation (MJO) represents a primary source of predictability on the intraseasonal time scales and its influence extends from seasonal variations to weather and extreme events. While the last decade has witnessed marked improvement in dynamical MJO prediction, an updated estimate of MJO predictability from a contemporary suite of dynamic models, in conjunction with an estimate of their corresponding prediction skill, is crucial for guiding future research and development priorities. In this study, the predictability of the boreal winter MJO is revisited based on the Intraseasonal Variability Hindcast Experiment (ISVHE), a set of dedicated extended-range hindcasts from eight different coupled models. Two estimates of MJO predictability are made, based on single-member and ensemble-mean hindcasts, giving values of 20-30 days and 35-45 days, respectively. Exploring the dependence of predictability on the phase of MJO during hindcast initiation reveals a slightly higher predictability for hindcasts initiated from MJO phases 2, 3, 6, or 7 in three of the models with higher prediction skill. The estimated predictability of MJO initiated in phases 2 and 3 (i.e., convection in Indian Ocean with subsequent propagation across Maritime Continent) being equal to or higher than other MJO phases implies that the so-called Maritime Continent prediction barrier may not actually be an intrinsic predictability limitation. For most of the models, the skill for single-member (ensemble mean) hindcasts is less than the estimated predictability limit by about 5-10 days (15-25 days), implying that significantly more skillful MJO forecasts can be afforded through further improvements of dynamical models and ensemble prediction systems (EPS).
GRACE's spatial aliasing error
Seo, Ki-Weon,Wilson, Clark R.,Chen, Jianli,Waliser, Duane E. Blackwell Publishing Ltd 2008 Geophysical journal international Vol.172 No.1
<P>SUMMARY</P><P>The GRACE satellite mission provides a near-continuous sequence of approximately 30-d gravity field solutions in the form of spherical harmonics (SH). Because SH functions are global while GRACE measurements are sensitive mainly to variations along the ground-track, undersampling (alias contamination) occurs. Here we investigate how geophysical signals are likely to cause alias error in GRACE gravity fields. We use actual GRACE orbits and systematically sample several types of time-varying signals that might represent either errors in geophysical models such as tide models, or unmodelled geophysical signals. We show how error in semi-diurnal tides like <I>S</I><SUB>2</SUB> can alias into long period variations in particular harmonics, particularly as a possible error source in the degree 2, order 0 term (<I>C</I><SUB>20</SUB>) of GRACE fields. We also show that aliasing associated with non-tidal geophysical model errors is significant at order 15 or multiples of 15, due to the GRACE ground track spacing in longitude. This can be predicted from Kaula's resonance formula and might be reduced by suppressing amplitudes of affected harmonics.</P>