| 1. |
- Chen, Deliang, 1961, et al.
(författare)
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Recent Recovery of the Siberian High Intensity
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116
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Tidskriftsartikel (refereegranskat)abstract
- This study highlights the fast recovery of the wintertime Siberian High intensity (SHI) over the last two decades. The SHI showed a marked weakening trend from the 1970s to 1980s, leading to unprecedented low SHI in the early 1990s according to most observational data sets. This salient declining SHI trend, however, was sharply replaced by a fast recovery over the last two decades. Since the declining SHI trend has been considered as one of the plausible consequences of climate warming, the recent SHI recovery seemingly contradicts the continuous progression of climate warming in the Northern Hemisphere. We suggest that alleviated surface warming and decreased atmospheric stability in the central Siberia region, associated with an increase in Eurasian snow cover, in the recent two decades contributed to this rather unexpected SHI recovery. The prominent SHI change, however, is not reproduced by general circulation model (GCM) simulations used in the IPCC AR4. The GCMs indicate the steady weakening of the SHI for the entire 21st century, which is found to be associated with a decreasing Eurasian snow cover in the simulations. An improvement in predicting the future climate change in regional scale is desirable.
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| 2. |
- Chen, Deliang, 1961, et al.
(författare)
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Spatial Interpolation of Daily Precipitation in China : 1951-2005
- 2010
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Ingår i: Advances in Atmospheric Sciences. - : Springer Science and Business Media LLC. - 0256-1530 .- 1861-9533. ; 27:6, s. 1221-1232
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Tidskriftsartikel (refereegranskat)abstract
- Climate research relies heavily on good quality instrumental data; for modeling efforts gridded data are needed. So far, relatively little effort has been made to create gridded climate data for China. This is especially true for high-resolution daily data. This work, focuses on identifying an accurate method to produce gridded daily precipitation in China based on the observed data at 753 stations for the period 1951-2005. Five interpolation methods, including ordinary nearest neighbor, local polynomial, radial basis function, inverse distance weighting, and ordinary kriging, have been used and compared. Cross-validation shows that the ordinary kriging based on seasonal semi-variograms gives the best performance, closely followed by the inverse distance weighting with a power of 2. Finally the ordinary kriging is chosen to interpolate the station data to a 18 kmx 18 km grid system covering the whole country. Precipitation for each 0.5A degrees x 0.5A degrees latitude-longitude block is then obtained by averaging the values at the grid nodes within the block. Owing to the higher station density in the eastern part of the country, the interpolation errors are much smaller than those in the west (west of 100A degrees E). Excluding 145 stations in the western region, the daily, monthly, and annual relative mean absolute errors of the interpolation for the remaining 608 stations are 74%, 29%, and 16%, respectively. The interpolated daily precipitation has been made available on the internet for the scientific community.
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| 3. |
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| 4. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Exploring teleconnections between the summer NAO (SNAO) and climate in East Asia over the last four centuries – a tree-ring perspective
- 2013
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Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 31:4, s. 297-310
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Tidskriftsartikel (refereegranskat)abstract
- The summer North Atlantic Oscillation (SNAO), derived from the first EOF of mean sea level pressure over the extratropical North Atlantic in July and August, has a close association with climate variability over the North Atlantic region, and beyond, on both short and long time scales. Recent findings suggested a teleconnection, through the SNAO, linking climate variability over Northern Europe with that of East Asia in the latter part of the twentieth century. Here we investigate the temporal stability of that teleconnection for the last four centuries using 4261 tree-ring width series from 106 sites and, additionally, ten climate reconstructions from East Asia. Our results showed a great potential in using tree-ring width (TRW) data to extend analyses of the SNAO influence on East Asian climate beyond the instrumental period, but preferably with a denser network. The strongest SNAO-TRW associations were found in central East Asia (in and around Mongolia) and on the eastern edge of the Tibetan Plateau. In addition, the analysis showed that the association between the SNAO and East Asian climate over the last 400 years has been variable, both among regions and at specific sites. Moreover, a clear difference in the SNAO-TRW associations was found on two examined time scales, being stronger on longer timescales. Our results indicate that TRW data can be a useful tool to explore the remote influence of the SNAO on East Asian climate in the past.
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| 5. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Influences of large- and regional-scale climate on fish recruitment in the Skagerrak-Kattegat over the last century
- 2014
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 134, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Dynamics of commercial fish stocks are generally associated with fishing pressure and climate variability. Due to short time series, past studies of the relationships between fish stock dynamics and climate have mainly been restricted to the last few decades. Here we analyzed a century-long time series of plaice, cod and haddock from the Skagerrak-Kattegat, to assess the long-term influence of climate on recruitment. Recruitment success (R-s) was compared against sea-surface temperature (SST) and atmospheric circulation indices on large (North Atlantic) and regional (Skagerrak-Kattegat) scales. Our results show that the influence of climate on R-s was more pronounced on longer, than on shorter timescales. Over the century-long period, a shift from low to high climate sensitivity was seen from the early to the late part for plaice and cod, while the opposite was found for haddock. This shift suggests that the increasing fishing pressure and the climate change in the Skagerrak-Kattegat have resulted in an increased sensitivity of R-s to climate for plaice and cod. The diminishing of climate sensitivity in haddock R-s, on the other hand, may be linked to the early twentieth century collapse of the stock in the region. While no long-term relationship between R-s and the Atlantic Multidecadal Oscillation (AMO) could be found, large R-s fluctuations during the positive phase of the AMO (1935-1960), relative to the cold phases, suggests a changed pattern in recruitment during warm periods. On the other hand, this could be due to the increased fishing pressure in the area. Thus, reported correlations between climate and fish may be caused by strong trends in climate in the late-twentieth century, and coincident reduction in fish stocks caused by intense fishing, rather than a stable relationship between climate and fish recruitment per se. (C) 2014 Elsevier B.V. All rights reserved.
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| 6. |
- Linderholm, Hans W., 1968, et al.
(författare)
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Interannual teleconnections between the summer North Atlantic Oscillation and the East Asian summer monsoon
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116:D13
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a study of the relationship between July–August (JA) mean climate over China, which is strongly linked to the East Asian summer monsoon (EASM), and the summer (JA) North Atlantic Oscillation (SNAO). The variations of temperature, precipitation, and cloud cover related to the SNAO were analyzed for the period 1951–2002 using gridded data sets as well as instrumental data from 160 stations in China. It was shown that the major patterns of summer climate over China are highly connected with the interannual variation of the SNAO, supporting a teleconnection between the North Atlantic region and East Asia. Based on the analyses of the daily and monthly reanalysis data sets, we propose possible mechanisms of this teleconnection. Changes in the position of the North Atlantic storm tracks and transient eddy activity associated with the positive (negative) SNAO phase contribute downstream to negative (positive) sea level pressure anomalies in northeastern East Asia. In negative SNAO years, a stationary wave pattern is excited from the southern SNAO center over northwestern Europe to northeastern East Asia. However, during positive SNAO years, a stationary wave pattern is excited extending from the SNAO center across the central Eurasian continent at around 40°N and downstream to the southeast. This may explain a connection between the positive SNAO and atmospheric circulation in middle and southeastern China.
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| 7. |
- Ou, Tinghai, et al.
(författare)
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Evaluation of global climate models in simulating extreme precipitation in China
- 2013
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 65
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Tidskriftsartikel (refereegranskat)abstract
- Variations in extreme precipitation can be described by various indices. In order to evaluate a climate model’s ability to simulate extreme precipitation, gridded extreme precipitation indices from observations are needed. There are two ways to obtain gridded extreme precipitation indices from station-based observations: either through interpolation of station-based extreme indices (EISTA) or estimated from gridded precipitation datasets (EIGRID). In this work, we evaluated these two methods and compared observational extreme precipitation indices in China to those obtained from a set of widely used global climate models. Results show that the difference between the two methods is quite large; and in some cases it is even larger than the difference between model simulations and observed gridded EISTA. Based on the sensitivity of the indices to horizontal resolution, it was suggested that EIGRID is more appropriate for evaluating extreme indices simulated by models. Subsequently, historic simulations of extreme precipitation from 21 CMIP5 (Coupled Model Intercomparison Project Phase 5) global climate models were evaluated against two reanalysis datasets during 1961-2000. It was found that most models overestimate extreme precipitation in the mountain regions in western China and northern China and underestimate extreme precipitation in southern China. In eastern China, these models simulate mean extreme precipitation fairly well. Despite this bias, the temporal trend in extreme precipitation for western China is well captured by most models. However, in eastern China, the trend of extreme precipitation is poorly captured by most models, especially for the so-called southern flood and northern drought pattern. Overall, our results suggest that the dynamics of inter-decadal summer monsoon variability should be improved for better prediction of extreme precipitation by the global climate models
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| 8. |
- Ou, Tinghai
(författare)
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Observed and simulated changes in extreme precipitation and cold surges in China: 1961–2005
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present work, precipitation and temperature related climate extremes are examined, with a focus on Mainland China. The objectives of this study are a) to identify targeted climate extremes and their changes during the last decades, and b) to examine the ability of current global climate models to reproduce identified patterns of change. The observed change in extreme precipitation from 1961 to 2000 is investigated using a set of indices, and the change simulated by global climate models is evaluated. In order to find an appropriate gridding method for the extreme indices in model evaluations, the effects of two different methods for estimating indices from station data are examined: one set interpolated from indices at stations (EISTA) and the other calculated from gridded precipitation (EIGRID). Results show that there is a large difference between the two, especially at coarser resolution, and suggests that EIGRID indices are more appropriate to evaluate model simulated precipitation extremes. During the period in question, observed extreme precipitation amounts increased in most parts of China, the only exception being northern China, where there was a decreasing trend. The trend of consecutive dry days (CDD) observed there is generally opposite to that of extreme precipitation elsewhere in China, except in southeast China, where both extreme precipitation and CDD increased. Most of the studied global climate models tend to overestimate extreme precipitation amounts but underestimate CDD. The pattern of precipitation extremes is generally well captured in western China, while in eastern China, where the combination of the monsoon system and human activities (e.g., anthropogenic changes in land use and aerosols) affects climate variation, with the result that climate patterns are reproduced poorly by comparison. In regard to temperature-related extremes, the variation in the occurrence of winter cold surges in southeast China for the period from 1961 to 2005 is investigated. The identified cold surges are divided into 5 different groups based on the evolution pattern of the Siberian High (SH). Associated evolutions of the large-scale atmospheric circulation are investigated. Results suggest the importance of a SH amplification and pre-existing specific synoptic systems to the occurrence of cold surges. Investigating the long-term changes in cold surges of different groups, it is found that the SH-related cold surges (33%) have decreased in the last 20 years, while cold surges more closely associated with background atmospheric circulation systems, which often have a larger impact area (i.e., stronger cold air outbreak) than the SH-related ones, have increased since the early 1980s. Although the intensity of SH was relatively weak with warmer surface air temperatures over China during the period from 1980 to 2005, the total number of cold surges in this period was nearly identical to that of previous decades. This implies that future occurrences of cold surges in southeast China may remain at current levels, provided that the contribution from the SH-related surges does not change dramatically.
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| 9. |
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