However, despite the evidence of similar events from many places around the world, the occurrence of the LIA cannot be assumed synchronous in time and uniform across space.
#GLIMS OVER A TOPIC SERIES#
įollowing the warm period of the ‘Medieval Climatic Optimum’, a dramatic series of glacier advances and retreats symbolized the cooling events of the LIA. The term has now been more formally and widely adopted to describe the period approximately from AD 1300 to 1850, characterized by lower temperature over most of the globe and growth of glaciers to a more advanced extent than that of prior and post the period. Although his original term to describe ‘an epoch of renewed but moderate glaciation that already has lasted about 4000 years’ has been overtaken as ‘ neoglacial’, in this report, it was noted that ‘… the glacier-oscillations of the last few centuries have been among the greatest that have occurred during the 4000-year period…’. The term ‘Little Ice Age’ was first introduced by Matthes in 1939 in Report of Committee on Glacierspublished on Eos. Prior to the twentieth century warming, the cold extremes of the Little Ice Age (LIA) appeared to be remote in human’s memory and often easily ignored. The findings of glacier size and elevation as key local factors are representative and consistent with other studies.Įxtending the timescale of climate variations from the past century to the past millennium allows us to see the broader context of the unprecedented global warming today. With data sets of the Glacier Inventory of China and the presumed LIA glacial extents, we applied statistical models in a case study of the eastern Tian Shan to examine the impact of local topographic and geometric factors on glacier area changes.
Here we present an overview of topics recently studied on the modern and LIA glaciers in the Tian Shan of the central Asia. As the most recent glacial event, the Little Ice Age (LIA, approximately AD 1300–1850) signifies the cold periods prior to the warming trend in the twentieth century. Documenting glacier distribution and research on glacier changes can provide insights and scientific support for water management in central Asia. High concentration of glaciers and meltwater from the Tian Shan contribute considerably to the freshwater resource in Xinjiang (China), Kyrgyzstan and nearby countries. The importance of mountain glaciers is best reflected in regions with limited precipitation, such as arid and semi-arid central Asia. Then, the occurrence number of both IC and CG discharges can be used for calculating a more accurate estimation of the total lightning currents in the global electric circuit.Mountain glaciers are a reliable and unequivocal indicator of climate change due to their sensitive response to changes in temperature and precipitation. The regional dependence of Z-ratio derived from this study can be combined with the CG lightning data provided by the ground-based lightning detection networks to estimate the occurrence number of IC discharges.
The estimated Z-ratio varies from 2.9–0.29 from the equator to 50° latitude, and the global mean value is 1.6. We also found that the Z-ratio significantly decreases with the latitude, which is generally comparable to the results shown in the previous studies. It is found that the Z-ratio over the continental area is larger than the oceanic area. From this result, we calculated the Z-ratio over many regions around the world and estimated its latitudinal and regional dependences. We analyzed 8,354 lightning events that obtained by JEM-GLIMS observation and succeeded in identifying 4,431 IC discharges, 597 +CG discharges, and 3,326 −CG discharges. Therefore, using optical data obtained by the Global Lightning and Sprite Measurements on Japanese Experiment Module (JEM-GLIMS), we distinguished the lightning discharge type, that is, IC, positive CG (+CG), and negative CG (−CG) discharges, and statistically estimated the Z-ratio. However, the latitudinal and regional dependences of Z-ratio are not fully clarified. The occurrence ratio of intracloud (IC) to cloud-to-ground (CG) discharges, which is denoted by Z-ratio, is the crucial parameter for the studies on the global electric circuit.
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