A Study of the Earth-Affecting CMEs of Solar Cycle 24     

Phillip Hess  Jie Zhang 《Solar physics》2017,292(6):80

Using in situ observations from the Advanced Composition Explorer (ACE), we have identified 70 Earth-affecting interplanetary coronal mass ejections (ICMEs) in Solar Cycle 24. Because of the unprecedented extent of heliospheric observations in Cycle 24 that has been achieved thanks to the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instruments onboard the Solar Terrestrial Relations Observatory (STEREO), we observe these events throughout the heliosphere from the Sun to the Earth, and we can relate these in situ signatures to remote sensing data. This allows us to completely track the event back to the source of the eruption in the low corona. We present a summary of the Earth-affecting CMEs in Solar Cycle 24 and a statistical study of the properties of these events including the source region. We examine the characteristics of CMEs that are more likely to be strongly geoeffective and examine the effect of the flare strength on in situ properties. We find that Earth-affecting CMEs in the first half of Cycle 24 are more likely to come from the northern hemisphere, but after April 2012, this reverses, and these events are more likely to originate in the southern hemisphere, following the observed magnetic asymmetry in the two hemispheres. We also find that as in past solar cycles, CMEs from the western hemisphere are more likely to reach Earth. We find that Cycle 24 lacks in events driving extreme geomagnetic storms compared to past solar cycles.  相似文献   

The Effects of Quality Control on Decreasing Error Propagation in the LandScan USA Population Distribution Model: A Case Study of Philadelphia County     

Lauren Patterson  Marie Urban  Aaron Myers  Budhendra Bhaduri  Eddie Bright  Phillip Coleman 《Transactions in GIS》2009,13(2):215-228

LandScan USA is a 90 m population distribution model that is used for a variety of applications, including emergency management. Models should have a measure of accuracy; however, the accuracy of population distribution models is difficult to determine due to the inclusion of multiple input datasets and the lack of quantifiable, observable (validated) data to confirm model output. Validated data enables quantification of: (1) overall model accuracy and (2) changes in model output at different levels of quality control. This article examines the effect of quality control for two national school datasets incorporated as input in LandScan USA for Philadelphia County, Pennsylvania; which had a local, validated school dataset available. The effect of each stage of quality control efforts utilized throughout the LandScan USA process were assessed to determine what level of quality control was required to have a statistically significant change of the model's population distribution. The typical level of quality control for LandScan USA resulted in 36% of schools being moved to the correct location and 20% of missing student enrollments were found, compared to 87% and 98% respectively for the validated dataset. The costs of increasing quality control resulted in a six-fold increase in labor time; however, the additional quality control did not produce statistically significant improvements in the LandScan USA model. Thus, typical quality control efforts for schools in LandScan USA produced a population distribution similar to the validated level of quality control, and can be applied with confidence for policy, planning, and emergency situations.  相似文献   

An organic geochemical investigation of the practice of manuring at a Minoan site on Pseira Island,Crete     

Ian D. Bull  Richard P. Evershed  Phillip P. Betancourt 《Geoarchaeology》2001,16(2):223-242

Lipid components in a soil profile developed in an agricultural terrace at a Minoan site on Pseira Island, Crete, were analyzed to determine whether the practice of manuring in antiquity, as inferred by distributional and temporal sherd scatter, could be confirmed through the use of biomarker compounds as proxies for manuring. Analysis of total organic carbon and the abundance of n‐alkyl lipids (n‐alkanols and fatty acids) demonstrated that while the upper part of the soil profile had received more recent inputs of vegetation‐derived organic matter, the deeper archaeological strata remained essentially undisturbed. Further analysis of 5β‐stanols, sterol components which may be utilized as fecal biomarkers, revealed a signal indicative of manuring, with human or porcine‐derived fecal material, in the lower 15 cm of the profile. Additional appraisal of epicoprostanol abundance inferred the possible practice of composting in later periods. This study represents a detection of manuring, in the oldest samples to date, using organic geochemical methods. © 2001 John Wiley & Sons, Inc.  相似文献