A global climatology of extreme rainfall rates in the inner core of intense tropical cyclones

The localized rain rate maxima (R_M) of the inner core region of intense tropical cyclones (TCs) are investigated using Version 6 of the Tropical Rainfall Measuring Mission Multi-satellite Precipitation Analysis data-set from 1998 to 2010. Specifically, this study examines the probabilities of R_M exceeding 25 mm h^?1 (P25) in intense TCs. The 25 mm h^?1 R_M is the 90th percentile of all R_M observations during the study period. The descending order of P25 observed from intense TCs for the six major ocean basins is: the North Indian Ocean, the Atlantic Ocean, the Northwest Pacific Ocean, the South Pacific Ocean, the South Indian Ocean, and the East-central Pacific Ocean. The six major basins have been subdivided into 29 sub-basins to discern regional variability of R_M. P25 increases with increasing TC category in all major basins, except for the South Pacific. Sub-basins with intense TCs that produce extreme rainfall rate maxima include the Bay of Bengal, the South Philippine Sea, the East China Sea, the north coast of Australia, southeast Melanesia, and the Northwest Atlantic. Sub-basins with a higher proportion of category 5 (CAT5) observations than category 3 (CAT3) observations tend to have a greater P25 beyond 60 km from the storm center.     

Interannual variations in the local spatial autocorrelation of tropospheric temperatures

Many dimensions of the global temperature pattern have been explored intensely over the past few decades. In this investigation, we explore the underlying spatial autoregressiveness of annual tropospheric temperature anomalies measured by polar-orbiting satellites. We found that the percent of the Earth covered by areas of significantly high local autocorrelation ranged from 11.92% to 25.90% over the 1979 to 2008 study period. We gathered 13 different teleconnection indices that have been linked to regional to global temperatures and found two (Polar/Eurasia pattern and North Atlantic Oscillation) that were positively correlated to the percent area with high local spatial autocorrelation. The magnitude but not the sign of the El Ni?o Southern Oscillation is also an important factor in the variation of spatial autocorrelation. The physical mechanism driving high local spatial autocorrelation is thought to be zonal and hemispheric flow governed by the subtropical and polar jet streams.     

Spatial analysis of variations in precipitation intensity in the USA

In this study, we used various spatial analytical methods to examine variations and trends in precipitation intensity in the conterminous USA. We found that three different measures of precipitation intensity were highly correlated; intensity increased in a spatially coherent fashion in the northeastern quarter of the USA and generally decreased in the center portion of the western USA. Evidence is presented that spatial and temporal patterns in the trends of precipitation intensity are related to the Atlantic multidecadal oscillation. Our results are generally in agreement with others who are reporting an upward trend in precipitation intensity during a period when the planet appears to have warmed.     

North Atlantic sea surface temperatures and their relation to the North Atlantic Oscillation during the last 230?years

August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated with 2?year average resolution from a 230-year-long sediment core (Rapid 21-12B), from the Reykjanes Ridge in the subpolar North Atlantic. The results indicate a warming trend of ~0.5°C of the surface waters at the Reykjanes Ridge for the last 230?years. Superimposed on this warming trend there is a multidecadal to decadal aSST variability of up to 1°C. The interval from the 1770s to the 1830s represents the coldest period, whereas ~1860?C1880 represents the warmest period during the last 230?years. The last 25?years is characterized by a warming trend showing strong decadal aSST variability with several warm years, but also the coldest years since the 1820s. The time of these cold years in the mid-1970s, -1980s and -1990s correspond with the documented great salinity anomalies (GSA) in the North Atlantic suggesting increased fluxes of cold, low-salinity waters from the Arctic during the last decades. The aSST record and the August North Atlantic Oscillation (aNAO) index show similar multidecadal-scale variability indicating a close coupling between the oceanic and atmospheric patterns. The aSST record shows a negative correlation with the aNAO indicating cold aSST during the positive aNAO trend and vice versa. Results suggest that the wind driven variation in volume fluxes of the North Atlantic surface waters could be the major mechanism behind the observed relationship.     

Climate entropy budget of the HadCM3 atmosphere–ocean general circulation model and of FAMOUS, its low-resolution version

The entropy budget is calculated of the coupled atmosphere–ocean general circulation model HadCM3. Estimates of the different entropy sources and sinks of the climate system are obtained directly from the diabatic heating terms, and an approximate estimate of the planetary entropy production is also provided. The rate of material entropy production of the climate system is found to be ～50 mW m^?2 K^?1, a value intermediate in the range 30–70 mW m^?2 K^?1 previously reported from different models. The largest part of this is due to sensible and latent heat transport (～38 mW m^?2 K^?1). Another 13 mW m^?2 K^?1 is due to dissipation of kinetic energy in the atmosphere by friction and Reynolds stresses. Numerical entropy production in the atmosphere dynamical core is found to be about 0.7 mW m^?2 K^?1. The material entropy production within the ocean due to turbulent mixing is ～1 mW m^?2 K^?1, a very small contribution to the material entropy production of the climate system. The rate of change of entropy of the model climate system is about 1 mW m^?2 K^?1 or less, which is comparable with the typical size of the fluctuations of the entropy sources due to interannual variability, and a more accurate closure of the budget than achieved by previous analyses. Results are similar for FAMOUS, which has a lower spatial resolution but similar formulation to HadCM3, while more substantial differences are found with respect to other models, suggesting that the formulation of the model has an important influence on the climate entropy budget. Since this is the first diagnosis of the entropy budget in a climate model of the type and complexity used for projection of twenty-first century climate change, it would be valuable if similar analyses were carried out for other such models.     

A model study of factors influencing projected changes in regional sea level over the twenty-first century

In addition to projected increases in global mean sea level over the 21st century, model simulations suggest there will also be changes in the regional distribution of sea level relative to the global mean. There is a considerable spread in the projected patterns of these changes by current models, as shown by the recent Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (AR4). This spread has not reduced from that given by the Third Assessment models. Comparison with projections by ensembles of models based on a single structure supports an earlier suggestion that models of similar formulation give more similar patterns of sea level change. Analysing an AR4 ensemble of model projections under a business-as-usual scenario shows that steric changes (associated with subsurface ocean density changes) largely dominate the sea level pattern changes. The relative importance of subsurface temperature or salinity changes in contributing to this differs from region to region and, to an extent, from model-to-model. In general, thermosteric changes give the spatial variations in the Southern Ocean, halosteric changes dominate in the Arctic and strong compensation between thermosteric and halosteric changes characterises the Atlantic. The magnitude of sea level and component changes in the Atlantic appear to be linked to the amount of Atlantic meridional overturning circulation (MOC) weakening. When the MOC weakening is substantial, the Atlantic thermosteric patterns of change arise from a dominant role of ocean advective heat flux changes.     

SiB3对不同下垫面的模拟试验与验证

首先介绍简单生物圈模式版本3(Simple Biosphere Model 3,SiB3)相比SiB2的改进之处以及相应的参数化方案。为了检验SiB3模式能否模拟不同下垫面的地气之间水分和能量交换,本文在全球选择3个代表高、中、低纬度的典型实验站点(青藏高原安多站点、亚马逊流域的Km34站点和美国中西部的WLEF站点),利用SiB3进行模拟分析和实验验证。研究结果表明,SiB3能够较好地模拟出不同下垫面的地表感热通量、潜热通量和净辐射通量随时间的变化率以及变化趋势,模式模拟值和测量值的相关系数达到080左右。但与实测相比,SiB3模拟的感热通量值仍偏高。在安多站点,模式模拟的地表土壤水分比较干燥,且模拟的地表温度较测量值偏高。     

Dependence of ground-based Pc5 ULF wave power on F10.7 solar radio flux and solar cycle phase

Utilising fifteen (1990–2005) years of ground-based magnetometer data from four magnetometer stations, we characterise the statistical dependence of the Pc5 ULF wave power spectra on variations in F10.7 solar radio flux and on solar cycle phase. We show that the median Pc5 ULF wave power spectra can be characterised as a power-law with a localised Gaussian centred at a specific frequency superimposed on the power-law spectrum. Further, we demonstrate that the location of the Gaussian in frequency systematically varies with both solar cycle phase and F10.7 and is more pronounced during high-speed solar wind intervals. We postulate that the localised power spectrum enhancement (or Gaussian) is a manifestation of the local eigenfrequency of field line resonances in the Earth's magnetosphere and that the variation in the location of the Gaussian occurs as a result of increased ionospheric outflow during periods of enhanced F10.7 and active solar activity.     

A field study of mean and turbulent flow characteristics upwind,over and downwind of barchan dunes

Field‐measured patterns of mean velocity and turbulent airflow are reported for isolated barchan dunes. Turbulence was sampled using a high frequency sonic anemometer, deriving near‐surface Reynolds shear and normal stresses. Measurements upwind of and over a crest‐brink separated barchan indicated that shear stress was sustained despite a velocity reduction at the dune toe. The mapped streamline angles and enhanced turbulent intensities suggest the effects of positive streamline curvature are responsible for this maintenance of shear stress. This field evidence supports an existing model for dune morphodynamics based on wind tunnel turbulence measurements. Downwind, the effect of different dune profiles on flow re‐attachment and recovery was apparent. With transverse incident flow, a re‐attachment length between 2·3 and 5·0h (h is dune brink height) existed for a crest‐brink separated dune and 6·5 to 8·6h for a crest‐brink coincident dune. The lee side shear layer produced elevated turbulent stresses immediately downwind of both dunes, and a decrease in turbulence with distance characterized flow recovery. Recovery of mean velocity for the crest‐brink separated dune occurred over a distance 6·5h shorter than the crest‐brink coincident form. As the application of sonic anemometers in aeolian geomorphology is relatively new, there is debate concerning the suitability of processing their data in relation to dune surface and streamline angle. This paper demonstrates the effect on Reynolds stresses of mathematically correcting data to the local streamline over varying dune slope. Where the streamline angle was closely related to the surface (windward slope), time‐averaged shear stress agreed best with previous wind tunnel findings when data were rotated along streamlines. In the close lee, however, the angle of downwardly projected (separated) flow was not aligned with the flat ground surface. Here, shear stress appeared to be underestimated by streamline correction, and corrected shear stress values were less than half of those uncorrected. Copyright © 2011 John Wiley & Sons, Ltd.     

Paleogene carbon isotope excursions in the Bunkers Hill borehole: Hampshire Basin, UK

This study demonstrates that the Bunkers Hill borehole, which is located within the Hampshire Basin, contains a carbon isotope excursion (CIE) in the Upnor Formation followed by a positive recovery from another CIE within the overlying Reading Formation. This study has also shown that the CIE in the Upnor Formation predates the Paleocene/Eocene Thermal Maximum (PETM), while the carbon isotope recovery at the base of the Reading Formation is most likely related to it. The positive carbon isotope trend, before a return to more negative values, seen throughout the majority of the Reading Formation can also be seen in coeval deposits in the Jubilee 404T borehole in the London Basin and in the Tienen Formation in the Doel and Kallo boreholes from the Belgium Basin. This indicates that this post-PETM carbon isotope signal may, therefore, be regional if not global in nature.