bluuebunny/crossref_metadata_2025_split huggingface dataset:
On North Pacific Multidecadal Climate Variability
Authors: Latif Mojib 
Published: June 2006

Abstract
The multidecadal climate variability in the North Pacific region is investigated by using a 2000-yr-long integration with a coupled ocean–atmosphere general circulation model. It is shown that the multidecadal variability evolves largely independent of the variations in the tropical Pacific, so that this kind of multidecadal variability may be regarded as internal to the North Pacific. The coupled model results suggest that the multidecadal variability can be explained by the dynamical ocean response to stochastic wind stress forcing. Superimposed on the red background variability, a multidecadal mode with a period of about 40 yr is simulated by the coupled model. This mode can be understood through the concept of spatial resonance between the ocean and the atmosphere.
An Improved Land Surface Emissivity Parameter for Land Surface Models Using Global Remote Sensing Observations
Authors: Jin Menglin , Liang Shunlin 
Published: June 2006

Abstract
Because land surface emissivity (ɛ) has not been reliably measured, global climate model (GCM) land surface schemes conventionally set this parameter as simply constant, for example, 1 as in the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction (NCEP) model, and 0.96 for bare soil as in the National Center for Atmospheric Research (NCAR) Community Land Model version 2 (CLM2). This is the so-called constant-emissivity assumption. Accurate broadband emissivity data are needed as model inputs to better simulate the land surface climate. It is demonstrated in this paper that the assumption of the constant emissivity induces errors in modeling the surface energy budget, especially over large arid and semiarid areas where ɛ is far smaller than unity. One feasible solution to this problem is to apply the satellite-based broadband emissivity into land surface models.
The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument has routinely measured spectral emissivities (ɛλ) in six thermal infrared bands. The empirical regression equations have been developed in this study to convert these spectral emissivities to broadband emissivity (ɛ) required by land surface models. The observed emissivity data show strong seasonality and land-cover dependence. Specifically, emissivity depends on surface-cover type, soil moisture content, soil organic composition, vegetation density, and structure. For example, broadband ɛ is usually around 0.96–0.98 for densely vegetated areas [(leaf area index) LAI &gt; 2], but it can be lower than 0.90 for bare soils (e.g., desert). To examine the impact of variable surface broadband emissivity, sensitivity studies were conducted using offline CLM2 and coupled NCAR Community Atmosphere Models, CAM2–CLM2. These sensitivity studies illustrate that large impacts of surface ɛ occur over deserts, with changes up to 1°–2°C in ground temperature, surface skin temperature, and 2-m surface air temperature, as well as evident changes in sensible and latent heat fluxes.
A Study of Historical Droughts in Southeastern Mexico
Authors: Mendoza Blanca , Velasco Victor , Jáuregui Ernesto 
Published: June 2006

AbstractA catalog containing an unprecedented amount of historical data in the southeastern part of Mexico covering almost four centuries (1502–1899) is used to construct a drought time series. The catalog records information of agricultural disasters and includes events associated with hydrometeorological phenomena or hazards whose effects were mainly felt in the agricultural sector, such as droughts. An analysis of the historical series of droughts in southeastern Mexico for the period 1502–1899 is performed. The highest drought frequency occurred around the years 1650, 1782, and 1884; no droughts were reported around 1540, between 1630 and 1640, along the largest time lapse of 1672–1714, and between 1740 and 1760. From 1760 until the end of the period of study droughts definitively occur more often than they did from ∼1550 to 1760. In addition, most droughts lasted for 1–2 yr. Analyzing the frequencies of the drought time series it is found that the most conspicuous cycles are ∼3–4 and 7 yr, although cycles of ∼12, 20, 43, and 70 yr are also evident. The relation between droughts and El Niño events indicates that 38% of droughts are associated with El Niño. Sea surface temperature changes, the Southern Oscillation index, and solar activity leave their signals in the southeastern part of Mexico, with the signs in Oaxaca clearer than in the Yucatan Peninsula. However, the dominance of some phenomena over others depends on the time scales considered.
Transient Climate Simulations with the HadGEM1 Climate Model: Causes of Past Warming and Future Climate Change
Authors: Stott Peter A. , Jones Gareth S. , Lowe Jason A. , Thorne Peter , Durman Chris , Johns Timothy C. , Thelen Jean-Claude 
Published: June 2006

Abstract
The ability of climate models to simulate large-scale temperature changes during the twentieth century when they include both anthropogenic and natural forcings and their inability to account for warming over the last 50 yr when they exclude increasing greenhouse gas concentrations has been used as evidence for an anthropogenic influence on global warming. One criticism of the models used in many of these studies is that they exclude some forcings of potential importance, notably from fossil fuel black carbon, biomass smoke, and land use changes. Herein transient simulations with a new model, the Hadley Centre Global Environmental Model version 1 (HadGEM1), are described, which include these forcings in addition to other anthropogenic and natural forcings, and a fully interactive treatment of atmospheric sulfur and its effects on clouds. These new simulations support previous work by showing that there was a significant anthropogenic influence on near-surface temperature change over the last century. They demonstrate that black carbon and land use changes are relatively unimportant for explaining global mean near-surface temperature changes.
The pattern of warming in the troposphere and cooling in the stratosphere that has been observed in radiosonde data since 1958 can only be reproduced when the model includes anthropogenic forcings. However, there are some discrepancies between the model simulations and radiosonde data, which are largest where observational uncertainty is greatest in the Tropics and high latitudes.
Predictions of future warming have also been made using the new model. Twenty-first-century warming rates, following policy-relevant emissions scenarios, are slightly greater in HadGEM1 than in the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) as a result of the extra forcing in HadGEM1. An experiment in which greenhouse gases and other anthropogenic forcings are stabilized at 2100 levels and held constant until 2200 predicts a committed twenty-second-century warming of less than 1 K, whose spatial distribution resembles that of warming during the twenty-first century, implying that the local feedbacks that determine the pattern of warming do not change significantly.
Summer Moisture Variability across Europe
Authors: van der Schrier G. , Briffa K. R. , Jones P. D. , Osborn T. J. 
Published: June 2006

Abstract
Maps of monthly self-calibrating Palmer Drought Severity Index (SC-PDSI) have been calculated for the period of 1901–2002 for Europe (35°–70°N, 10°W–60°E) with a spatial resolution of 0.5° × 0.5°. The recently introduced SC-PDSI is a convenient means of describing the spatial and temporal variability of moisture availability and is based on the more common Palmer Drought Severity Index. The SC-PDSI improves upon the PDSI by maintaining consistent behavior of the index over diverse climatological regions. This makes spatial comparisons of SC-PDSI values on continental scales more meaningful.
Over the region as a whole, the mid-1940s to early 1950s stand out as a persistent and exceptionally dry period, whereas the mid-1910s and late 1970s to early 1980s were very wet. The driest and wettest summers on record, in terms of the amplitude of the index averaged over Europe, were 1947 and 1915, respectively, while the years 1921 and 1981 saw over 11% and over 7% of Europe suffering from extreme dry or wet conditions, respectively.
Trends in summer moisture availability over Europe for the 1901–2002 period fail to be statistically significant, both in terms of spatial means of the drought index and in the area affected by drought. Moreover, evidence for widespread and unusual drying in European regions over the last few decades is not supported by the current work.
Tropical Intraseasonal Variability in 14 IPCC AR4 Climate Models. Part I: Convective Signals
Authors: Lin Jia-Lin , Kiladis George N. , Mapes Brian E. , Weickmann Klaus M. , Sperber Kenneth R. , Lin Wuyin , Wheeler Matthew C. , Schubert Siegfried D. , Del Genio Anthony , Donner Leo J. , Emori Seita , Gueremy Jean-Francois , Hourdin Frederic , Rasch Philip J. , Roeckner Erich , Scinocca John F. 
Published: June 2006

Abstract
This study evaluates the tropical intraseasonal variability, especially the fidelity of Madden–Julian oscillation (MJO) simulations, in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of daily precipitation from each model’s twentieth-century climate simulation are analyzed and compared with daily satellite-retrieved precipitation. Space–time spectral analysis is used to obtain the variance and phase speed of dominant convectively coupled equatorial waves, including the MJO, Kelvin, equatorial Rossby (ER), mixed Rossby–gravity (MRG), and eastward inertio–gravity (EIG) and westward inertio–gravity (WIG) waves. The variance and propagation of the MJO, defined as the eastward wavenumbers 1–6, 30–70-day mode, are examined in detail.
The results show that current state-of-the-art GCMs still have significant problems and display a wide range of skill in simulating the tropical intraseasonal variability. The total intraseasonal (2–128 day) variance of precipitation is too weak in most of the models. About half of the models have signals of convectively coupled equatorial waves, with Kelvin and MRG–EIG waves especially prominent. However, the variances are generally too weak for all wave modes except the EIG wave, and the phase speeds are generally too fast, being scaled to excessively deep equivalent depths. An interesting result is that this scaling is consistent within a given model across modes, in that both the symmetric and antisymmetric modes scale similarly to a certain equivalent depth. Excessively deep equivalent depths suggest that these models may not have a large enough reduction in their “effective static stability” by diabatic heating.
The MJO variance approaches the observed value in only 2 of the 14 models, but is less than half of the observed value in the other 12 models. The ratio between the eastward MJO variance and the variance of its westward counterpart is too small in most of the models, which is consistent with the lack of highly coherent eastward propagation of the MJO in many models. Moreover, the MJO variance in 13 of the 14 models does not come from a pronounced spectral peak, but usually comes from part of an overreddened spectrum, which in turn is associated with too strong persistence of equatorial precipitation. The two models that arguably do best at simulating the MJO are the only ones having convective closures/triggers linked in some way to moisture convergence.
Weak Simulated Extratropical Responses to Complete Tropical Deforestation
Authors: Findell Kirsten L. , Knutson Thomas R. , Milly P. C. D. 
Published: June 2006

Abstract
The Geophysical Fluid Dynamics Laboratory atmosphere–land model version 2 (AM2/LM2) coupled to a 50-m-thick slab ocean model has been used to investigate remote responses to tropical deforestation. Magnitudes and significance of differences between a control run and a deforested run are assessed through comparisons of 50-yr time series, accounting for autocorrelation and field significance. Complete conversion of the broadleaf evergreen forests of South America, central Africa, and the islands of Oceania to grasslands leads to highly significant local responses. In addition, a broad but mild warming is seen throughout the tropical troposphere (&lt;0.2°C between 700 and 150 mb), significant in northern spring and summer. However, the simulation results show very little statistically significant response beyond the Tropics. There are no significant differences in any hydroclimatic variables (e.g., precipitation, soil moisture, evaporation) in either the northern or the southern extratropics. Small but statistically significant local differences in some geopotential height and wind fields are present in the southeastern Pacific Ocean. Use of the same statistical tests on two 50-yr segments of the control run show that the small but significant extratropical differences between the deforested run and the control run are similar in magnitude and area to the differences between nonoverlapping segments of the control run. These simulations suggest that extratropical responses to complete tropical deforestation are unlikely to be distinguishable from natural climate variability.
Great Plains Hydroclimate Variability: The View from North American Regional Reanalysis
Authors: Ruiz-Barradas Alfredo , Nigam Sumant 
Published: June 2006

Abstract
Interannual variability of warm-season rainfall over the Great Plains is analyzed using the recently released North American Regional Reanalysis (NARR). The new dataset differs from its global counterparts in the additional assimilation of precipitation and radiances. This along with the use of a more comprehensive land surface model in generation of NARR offers the prospect of obtaining improved estimates of surface hydrologic and near-surface meteorological fields.
NARR’s representation of hydroclimate is used to weigh in on the authors’ recent finding of the dominance of large-scale moisture flux convergence over evaporation in accounting for Great Plains precipitation variations. Evaporation estimates are notoriously uncertain and, while the NARR ones are not assured to be realistic, they are more constrained than those diagnosed before from inline and offline assessments.
NARR’s portrayal of warm-season hydroclimate variability corroborates the importance of remote water sources in generation of Great Plains precipitation variability and supports the authors’ claim that some state-of-the-art atmosphere/land surface models vigorously recycle precipitation, erroneously, at least in context of Great Plains interannual variability. These very models have been key to recent claims of strong coupling between soil moisture and precipitation.
Influences of the Atlantic Warm Pool on Western Hemisphere Summer Rainfall and Atlantic Hurricanes
Authors: Wang Chunzai , Enfield David B. , Lee Sang-ki , Landsea Christopher W. 
Published: June 2006

Abstract
The Atlantic warm pool (AWP) of water warmer than 28.5°C comprises the Gulf of Mexico, the Caribbean Sea, and the western tropical North Atlantic (TNA). The AWP reaches its maximum size around September, with large AWPs being almost 3 times larger than small ones. Although ENSO teleconnections are influential on the AWP, about two-thirds of the large and small AWP variability appears unrelated to ENSO. The AWP is usually geographically different from the TNA; however, the AWP size is correlated with the TNA SST anomalies. During August to October, large AWPs and warm TNA are associated with increased rainfall over the Caribbean, Mexico, the eastern subtropical Atlantic, and the southeast Pacific, and decreased rainfall in the northwest United States, Great Plains, and eastern South America. In particular, rainfall in the Caribbean, Central America, and eastern South America from August to October is mainly related to the size of the AWP. Large (small) AWPs and warm (cold) TNA correspond to a weakening (strengthening) of the northward surface winds from the AWP to the Great Plains that disfavors (favors) moisture transport for rainfall over the Great Plains. On the other hand, large (small) AWPs and warm (cold) TNA strengthen (weaken) the summer regional Atlantic Hadley circulation that emanates from the warm pool region into the southeast Pacific, changing the subsidence over the southeast Pacific and thus the stratus cloud and drizzle there. The large AWP, associated with a decrease in sea level pressure and an increase in atmospheric convection and cloudiness, corresponds to a weak tropospheric vertical wind shear and a deep warm upper ocean, and thus increases Atlantic hurricane activity.
Seasonality of Decadal Sea Surface Temperature Anomalies in the Northwestern Pacific
Authors: Mochizuki Takashi , Kida Hideji 
Published: June 2006

Abstract
The seasonality of the decadal sea surface temperature (SST) anomalies and the related physical processes in the northwestern Pacific were investigated using a three-dimensional bulk mixed layer model. In the Kuroshio–Oyashio Extension (KOE) region, the strongest decadal SST anomaly was observed during December–February, while that of the central North Pacific occurred during February–April. From an examination of the seasonal heat budget of the ocean mixed layer, it was revealed that the seasonal-scale enhancement of the decadal SST anomaly in the KOE region was controlled by horizontal Ekman temperature transport in early winter and by vertical entrainment in autumn. The temperature transport by the geostrophic current made only a slight contribution to the seasonal variation of the decadal SST anomaly, despite controlling the upper-ocean thermal conditions on decadal time scales through the slow Rossby wave adjustment to the wind stress curl.
When averaging over the entire KOE region, the contribution from the net sea surface heat flux was also no longer significantly detected. By examining the horizontal distributions of the local thermal damping rate, however, it was concluded that the wintertime decadal SST anomaly in the eastern KOE region was rather damped by the net sea surface heat flux. It was due to the fact that the anomalous local thermal damping of the SST anomaly resulting from the vertical entrainment in autumn was considerably strong enough to suppress the anomalous local atmospheric thermal forcing that acted to enhance the decadal SST anomaly.
Recent Trends in Land Surface Temperature on the Tibetan Plateau
Authors: Oku Yuichiro , Ishikawa Hirohiko , Haginoya Shigenori , Ma Yaoming 
Published: June 2006

Abstract
The diurnal, seasonal, and interannual variations in land surface temperature (LST) on the Tibetan Plateau from 1996 to 2002 are analyzed using the hourly LST dataset obtained by Japanese Geostationary Meteorological Satellite 5 (GMS-5) observations. Comparing LST retrieved from GMS-5 with independent precipitation amount data demonstrates the consistent and complementary relationship between them. The results indicate an increase in the LST over this period. The daily minimum has risen faster than the daily maximum, resulting in a narrowing of the diurnal range of LST. This is in agreement with the observed trends in both global and plateau near-surface air temperature. Since the near-surface air temperature is mainly controlled by LST, this result ensures a warming trend in near-surface air temperature.
Modeling the Hydrological Effect on Local Gravity at Moxa, Germany
Authors: Hasan Shaakeel , Troch Peter A. , Boll J. , Kroner C. 
Published: June 2006

Abstract
A superconducting gravimeter has observed with high accuracy (to within a few nm s−2) and high frequency (1 Hz) the temporal variations in the earth’s gravity field near Moxa, Germany, since 1999. Hourly gravity residuals are obtained by time averaging and correcting for earth tides, polar motion, barometric pressure variations, and instrumental drift. These gravity residuals are significantly affected by hydrological processes (interception, infiltration, surface runoff, and subsurface redistribution) in the vicinity of the observatory. In this study time series analysis and distributed hydrological modeling techniques are applied to understand the effect of these hydrological processes on observed gravity residuals. It is shown that the short-term response of gravity residuals to medium- to high-rainfall events can be efficiently modeled by means of a linear transfer function. This transfer function exhibits an oscillatory behavior that indicates fast redistribution of stored water in the upper layers (interception store, root zone) of the catchment surrounding the instrument. The relation between groundwater storage and gravity residuals is less clear and varies according to the season. High positive correlation between groundwater and gravity exists during winter months when the freezing of the upper soil layers immobilizes water stored in the unsaturated zone of the catchment. To further explore the spatiotemporal dynamics of the relevant hydrological processes and their relation to observed gravity residuals, a GIS-based distributed hydrological model is applied for the Silberleite catchment. Driven by observed atmospheric forcings (precipitation and potential evapotranspiration), the model allows the authors to compute the variation of water storage in three different layers: the interception store, the snow cover store, and the soil moisture store. These water storage dynamics are then converted to predicted gravity variation at the location of the superconducting gravimeter and compared to observed gravity residuals. During most of the investigated period (January 2000 to January 2004) predictions are in good agreement with the observed patterns of gravity dynamics. However, during some winter months the distributed hydrological model fails to explain the observations, which supports the authors’ conclusion that groundwater variability dominates the hydrological gravity signal in the winter. More hydrogeological research is needed to include groundwater dynamics in the hydrological model.