Rotated Empirical Orthogonal Function Research Articles

The spring relationship between the Pacific-North American pattern and the North Atlantic Oscillation

The Pacific-North American pattern (PNA) and North Atlantic Oscillation (NAO) are two dominant modes of low-frequency variability in the Northern Hemisphere winter. Generally these two patterns are separable and uncorrelated in both space and time. However, dating back to the 1970s there have been studies which have linked the Aleutian and Icelandic low intensities, and shown that a significant temporal correlation does, on occasion, occur. Each of these semi-permanent low pressure systems is a part of the PNA and NAO patterns, respectively, and therefore, given a link between the two semi-permanent low pressure systems, we explore whether a link between the PNA and NAO also appears. Recently studies have found such a link during the winters of certain decades. The present study, documents an observed relationship between the PNA and NAO which is consistently present during the spring and early summer. This relationship is shown to be due to the fact that the PNA and NAO are spatially overlapping projections of the same pattern of variability, given by the first EOF of 500 hPa geopotential height. Both the PNA and NAO patterns correlate more strongly to the first EOF’s spatial pattern, resembling the Aleutian low-Icelandic low seesaw pattern, than the rotated EOF (REOF) loading patterns used to compute their respective indices. Furthermore, when the two patterns are correlated, the effect of El-Nino on the Northern Hemisphere is separate from the pattern associated with the PNA. Finally, we examine a 21-year period in the winter for which the PNA and NAO are significantly correlated, and find that the conclusions drawn from the spring hold true. The results presented herein demonstrate that defining the PNA and NAO based upon typical loading patterns may not be the ideal approach; especially given that the patterns are spatially similar and covary in time.

Investigation of medium-term barred beach behavior using 28-year beach profile data and Rotated Empirical Orthogonal Function analysis

A 28-year beach profile dataset for a stretch of the Hasaki coast in Japan was examined using Rotated Empirical Orthogonal Function (REOF) analysis to investigate the cross-shore variation in the characteristics of beach profile change. The data were obtained weekly, on a micro-tidal wave-dominated intermediate beach, along a survey line extending from the backshore to a water depth of approximately 5m. REOF analysis using the first eight empirical orthogonal functions led to the study area being divided into five unique zones based on beach profile change patterns, namely the backshore, the foreshore, the inner and outer transition zones and the bar-trough zone. Although these zones were notably distinct from one another, the profiles in foreshore and the shoreward part of the inner transition zone changed in the same way over periods of 6 and 12months.

Austral winter external and internal atmospheric variability between 1980 and 2014

AbstractWe examine the interannual variability of the seasonal mean atmospheric circulation in the Southern Hemisphere during austral winter. The three major modes are identified by rotated empirical orthogonal function (REOF) analysis. As expected, REOF1 is associated with the Southern Annular Mode which is dominated by internal atmospheric dynamics. REOF2 displays a wave train, linked to the western North Pacific monsoon and the Pacific‐Japan pattern in East Asia in the same season; REOF3 resembles the Pacific‐South American pattern. Externally forced variability strongly projects on both REOF2 and REOF3 so that in the ensemble mean, an atmospheric model with prescribed observed sea surface temperature captures considerable parts of the time evolution of REOF2 (50%) and REOF3 (25%), suggesting a potential predictability for the two modes.

Regionalization of precipitation and the spatiotemporal distribution of extreme precipitation in southwestern China

Daily precipitation data from 1951 to 2010 at 33 meteorological stations in five provinces/cities, including Sichuan Province, Yunnan Province, the Guangxi Zhuang Autonomous Region, Guizhou Province and Chongqing City, are used to partition the study area based on precipitation and analyze the spatiotemporal distribution of extreme precipitation. The rotated empirical orthogonal function (REOF) analysis method is used to divide the study area into five parts according to precipitation. The precipitation exhibited greater fluctuations in the last two decades. This finding indicates that extreme precipitation events are increasing. The frequent occurrence of extreme precipitation has made drought and flood disasters more serious. The Mann–Kendall test (M–K test) and moving t test methods are used to analyze the jump and monotonic trends of extreme precipitation indices. It is determined that extreme precipitation indices, including Rx1d, Rx5d, R95p, R99p, CWD and R10 mm, exhibited a weak upward trend during the past 60 years, suggesting that the precipitation amount in the study area decreased slightly, but the maximum daily precipitation amount (Rx1d) and the extremely wet day precipitation (R99p) increased. This finding indicates that precipitation is more concentrated and the extreme precipitation is more serious. The jump for most of the extreme precipitation indices occurred in the 1990s. In terms of spatial scale, extreme precipitation indices, except CDD and CWD, exhibited an increasing trend from the northwest to the southeast. The regions with especially high or low values are easy to identify. Drought risk in northwest Sichuan and the junction of Sichuan and Yunnan is higher. Guangxi Zhuang Autonomous Region and southern part of Yunnan Province have a higher flood risk. The trends of nine extreme precipitation indices also demonstrated the spatial differences. There are more stations exhibiting upward trends than stations showing downward trends for six extreme precipitation indices. The risk of drought/flood may increase in Yunnan and Guangxi, and the storm flood risk in Chongqing exhibited an increasing trend.

Temporal dynamics and spatial patterns of drought and the relation to ENSO: a case study in Northwest China

ABSTRACTAn investigation of temporal dynamics and spatial patterns of dryness/wetness conditions over the eastern part of Northwest China (including Shaanxi, Ningxia, the eastern part of Gansu, and a part of southern Inner Mongolia) during the period 1960–2009 is presented. The analysis of this study is threefold. First, the dryness/wetness conditions over the study area were characterized using the self‐calibrating Palmer Drought Severity Index (PDSI). The spatiotemporal variability of dryness/wetness conditions in the study area was then investigated by the rotated empirical orthogonal function (REOF) and Mann–Kendall trend test. Third, we examined the periodical oscillations of dryness/wetness conditions and the multi‐scale relationships between dryness/wetness conditions and El Niño‐Southern Oscillation (ENSO). The results indicate that most parts of the study area were characterized by a dry trend in both the rainy season (May–September) and winter. Four sub‐regions of dryness/wetness conditions across the study area were identified. Based on the wavelet analysis, the periodical features in the PDSI time series for each sub‐region were explored. Negative relationships between the PDSI in the sub‐region I (representing the central and southern parts of Shaanxi and the southeastern Gansu) and the Niño 3.4 index can be consistently detected on 2–6 year scales during the entire period 1960–2009. This suggests that the strong El Niño events generally lead to very dry conditions in the sub‐region I on multi‐year scales. In addition, we further investigated how the ENSO cycle modulates the strength of the East Asian summer monsoon (EASM) in both developing and decaying phases of El Niño and La Niña events. The results of this study could be beneficial for efficient water resources management and drought assessment in the current study area and also provide a valuable reference for other areas with similar climatic characteristics.

Spatial distribution, seasonal variation and regionalization of PM2.5 concentrations in China

In order to provide scientific support to policy makers in the regulation of PM2.5 pollution in China, it is important to accurately assess the current status, spatiotemporal characteristics and regionalization data for this air pollutant. An analysis of the pollution status of PM2.5 was conducted using daily averaged mass concentration data recorded in 74 cities in 2013 and 161 cities in 2014. The rotated empirical orthogonal function (REOF) method was applied to analyze this data. Results showed that the average annual PM2.5 concentration in urban areas of China is 62.2±21.5 µg/m3, and that the distribution is spatially heterogeneous. The North China Plain, middle and lower Yangtze River Plain, Si Chuan Basin and Guanzhong Plain had relatively high annual PM2.5 concentrations compared with the southeast coastal region, the Tibetan Plateau and the Yungui Plateau. PM2.5 mass concentrations tended to be higher in winter than in summer, however, the data for many cities showed a small peak in concentrations from May to July. An analysis of the spatial correlation of PM2.5 indicated a significant influence of topographic conditions. A lower correlation was observed where terrain features varied greatly. Based on the results of the REOF analysis and topographic characteristics, ten regions were identified in mid-eastern China, which could be considered as basic pollution prevention divisions for PM2.5; these include the North China Plain region, Pearl River Delta region, Jianghuai Plain region, middle Yangtze River Plain region, Northeast Plain region, Jiangnan coastal region, Si chuan Basin region, Qiantao Plain region, Guanzhong-Central Plain region and Yungui Plateau region. Seasonal variations in the regionalization data were observed, especially for the North China Plain and Pearl River Delta regions. Among the ten regions identified in this study, the North China Plain, Guanzhong-Central Plain, middle Yangtze River Plain and Jianghuai Plain had relatively high PM2.5 mass concentrations in comparison with the others. Therefore, these regions should be considered as the key regions to target in developing PM2.5 pollution prevention strategies. This study improves the present understanding of the spatial distribution, seasonal changes and regional status of PM2.5 pollution in China and helps establish possible control strategies for the reduction of this air pollutant.

Characteristics of Boreal Winter Total Ozone Distribution in the Northern Hemisphere and Their Relationship with Stratospheric Temperature During Recent 30 Years

AbstractThe characteristics of spatiotemporal distribution of total ozone have a significant impact on the variabilities of climate and environment. As the increase of the high quality and quantity of total ozone datasets, it is necessary to provide a detailed investigation of spatiotemporal distribution characteristics of total ozone and its relationship with climate variability. Based on the ECMWF global monthly mean total ozone and stratopheric temperature data from 1979 to 2013, the spatiotemporal structure of dominant total ozone pattern in the Northern Hemisphere (north of 20°N) during boreal winter is studied using the rotated empirical orthogonal function (REOF) analysis and Morlet wavelet analysis. Besides, the relationship of the dominant total ozone pattern with the temperature anomalies in the upper (2 hPa), middle (30 hPa) and lower (100 hPa) stratosphere is further studied using composite analysis. The results show that the variability of total ozone in the Northern Hemisphere during boreal winter is characterized by five significant dominant patterns during the recent 30 years, which are located in the Arctic region (75°N–90°N, 0°–360°), the subtropics of Northern Hemisphere (20°N–40°N, 0°–360°), the Alaska region (60°N–75°N, 180°E–260°E), the North Atlantic region (45°N–60°N, 310°E–360°E) and the Siberia region (50°N–65°N, 80°E–130°E). The five dominant patterns show significant variabilities on the interannual and interdecadal time scales. The total ozone over these five regions changes from more than normal to less than normal since the late 1980. On the interannual time scale, total ozone over the five regions shows pronounced periodicity. In addition, their periodicities show significant difference. The relationship between the dominant total ozone patterns and the stratospheric temperature indicates that, when the total ozone is increased (reduced), the upper stratosphere will be cooled (warmed), while the middle and lower stratosphere will be warmed (cooled). Furthermore, the middle stratosphere is warmer (cooler) than the lower stratosphere.

Spatial coherence of variations in seasonal extreme precipitation events over Northwest Arid Region, China

ABSTRACTDaily precipitation data covering the period of 1961–2009 from 72 stations in Northwest Arid Region, China, are analysed to investigate coherent subregions of variations in extreme precipitation events. First, four extreme precipitation indices, i.e. number of heavy precipitation days (DPh), precipitation intensity above heavy precipitation (IPh), number of torrential precipitation days (DPt), and precipitation intensity above torrential precipitation (IPt), were defined and analysed seasonally. Then rotated empirical orthogonal function (REOF) technique is used to identify the coherent subregions of these seasonal extreme precipitation indices and related trends. The results indicate that the number of coherent subregions of DPh, IPh, DPt, and IPt is 6, 5, 14, and 10 for spring; 4, 18, 6, and 6 for summer; 15, 8, 10, and 8 for autumn; and 7, 7, 2, and 5 for winter, respectively. Attribute shifts of underlying surfaces should be an important driving factor behind changes of extreme precipitation events. Intensity variations of heavy and torrential precipitation are the main reason behind significant changes of extreme precipitation, especially intensity variations of the heavy precipitation. The highest increasing magnitude of IPh is 584% (10a)−1 which is found in summer in the west parts of the Southern Xinjiang, the middle Tianshan Mountains, and the west parts of the Junggar Basin in the Northern Xinjiang. The findings of this study are potentially relevant for the development of human understanding of hydrological cycle responses in arid regions to regional and global climate changes, particularly in terms of extreme weather extremes.

Spatial and temporal variability of drought in the arid region of China and its relationships to teleconnection indices

Summary We studied the drought patterns in the arid region of northwestern China between 1960 and 2010 using the Palmer Drought Severity Index (PDSI). The general evolution of drought was obtained by empirical orthogonal function (EOF), rotated empirical orthogonal function (REOF), the Mann–Kendall test, and the continuous wavelet transform method. Additionally, relationships between rotated principal component time series (RPCs) and seven selected climate indices were analyzed. The results showed that: (1) Four moisture-related spatial patterns (North Xinjiang, western South Xinjiang, Central Xinjiang, and the Hexi Corridor) were objectively defined by REOF analysis. These patterns are related to distinct geographical areas and are associated with distinct temporal variations. (2) The PDSI increased significantly in most regions of Xinjiang, while decreased in the eastern Hexi Corridor. The significant 4–8 year band is the major period band for the annual and seasonal PDSI derived. (3) The seasonal REOFs (RPCs) and EOFs (PCs) have consistent spatial distribution patterns with the annual REOF. The seasonal trends of PDSI are also the same as the annual PDSI trends, indicating space–time consistency between annual PDSI and seasonal PDSI. (4) The drought evolution in this region is affected by the area of northern hemisphere polar vortex, the Arctic Oscillation, and the North Atlantic Oscillation. In addition, the changes of drought in South Xinjiang and the Hexi Corridor may also be associated with the Tibetan Plateau High. Changes in drought pattern are expected to have a strong impact on the economic livelihood of the region, especially for agricultural production.

Changing characteristics and spatial differentiation of spring precipitation in Southwest China during 1961–2012**Project supported by the National Basic Research Program of China (Grant No. 2013CB430200 (2013CB430206)) and the Sixth Program Ten Talented People of the Meteorological Bureau of Gansu Province, China.

In this study, we analyze spring precipitation from 92 meteorological stations spanning between 1961 and 2012 to understand temporal–spatial variability and change of spring precipitation over Southwest China. Various analysis methods are used for different purposes, including empirical orthogonal function (EOF) analysis and rotated EOF (REOF) for analyzing spatial structure change of precipitation anomaly, and the Mann–Kendall testing method to determine whether there were abrupt changes during the analyzed time span. We find that the first spatial mode of the precipitation has a domain uniform structure; the second is dominated by a spatial dipole; and the third contains five variability centers. The 2000s is the decade with the largest amount of precipitation while the 1990s is the decade with the smallest amount of precipitation. The year-to-year difference of that region is large: the amount of the largest precipitation year doubles that of the smallest precipitation year. We also find that spring precipitation in Southwest China experienced a few abrupt changes: a sudden increase at 1966, a sudden decrease at 1979, and a sudden increase at 1995. We speculate that the spring precipitation will increase gradually in the next two decades.

Interdecadal Variability of the South American Precipitation in the Monsoon Season

AbstractInterdecadal variability modes of monsoon precipitation over South America (SA) are provided by a continental-scale rotated empirical orthogonal function analysis, and their connections to well-known climatic indices and SST anomalies are examined. The analysis, carried out for austral spring and summer, uses a comprehensive set of station data assembled and verified for the period 1950–2000. The presented modes are robust, consistent with previous regional-scale studies and with modes obtained from longer time series over smaller domains. Opposite phases of the main modes show differences around 50% in monthly precipitation. There are significant relationships between the interdecadal variability in spring and summer, indicating local and remote influences. The first modes for both seasons are dipole-like, displaying opposite anomalies in central-east and southeast SA. They tend to reverse polarity from spring to summer. Yet the summer second mode and its related spring fourth mode, which affect the core monsoon region in central Brazil and central-northwestern Argentina, show similar factor loadings, indicating persistence of anomalies from one season to the other, contrary to the first modes. The other presented modes describe the variability in different regions with great monsoon precipitation. Significant connections with different combinations of climatic indices and SST anomalies provide physical basis for the presented modes: three show the strongest connections with SST-based indices, and two have the strongest connections with atmospheric indices. However, the main modes show connections with more than one climatic index and more than one oceanic region, stressing the importance of combined influence.

Spatial and temporal variations of annual precipitation during 1960–2010 in China

China is situated in the East Asian Monsoon zone, and the heterogeneity of the temporal and spatial characteristics of precipitation might result in serious flood and drought disasters. Based on precipitation data from 1840 stations across China, the empirical orthogonal function (EOF) analysis and the rotated empirical orthogonal function (REOF) analysis were used to analyze the spatiotemporal characteristics of precipitation variations in China in 1960–2010. Results showed that: (1) precipitation in the East China witnessed changes in the late 1970s, from the late 1980s to early 1990s, and in the early 21st Century respectively, featuring the recurrent south-north shifts of the rainbelt in both directions. Precipitation in Northwest China experienced an abrupt change in the mid-1980s, showing that the western part of Northwest China became wet from the previous dry conditions, whereas the eastern part of the region became dry from the previous wet conditions. However, precipitation in Northeast China underwent abrupt changes in early 1980s and late 1990s respectively, when precipitation changed from near normal in the previous period to more than normal in early 1980s and from more to less than normal in late 1990s. Evident phases in changes in precipitation had been detected over Southwest China, showing that the precipitation changes over both western and northeastern parts of this region were almost opposite; (2) decadal changes of precipitation in East China were closely correlated with the East Asian summer monsoon and the atmospheric circulation, while as important external forcing factors, the Pacific SST and snow cover on the Tibetan Plateau also had indirect impacts on the precipitation in the region through their influences on the East Asian summer monsoon and the atmospheric circulation.

Spatiotemporal Variability and Change of the South China Spring Precipitation during 1961–2012

We analyze precipitation data from 47 meteorological stations spanning between 1961 and 2012 and NCEP/NCAR reanalysis to understand spatiotemporal variability and change of spring precipitation of South China and their relations to atmospheric circulations. Empirical orthogonal function (EOF) analysis and rotated EOF (REOF) are used to reveal dominant spatial structures of precipitation anomaly and Mann-Kendall testing method to determine the temporal locations of abrupt changes during the analyzed time span. We find that the first spatial mode of the spring precipitation of the South China has a domain uniform structure; the second is dominated by a spatial dipole; and the third contains six variability centers. 1980s was the decade of the largest amount of precipitation while 1960s the decade of the smallest amount of precipitation. The spring precipitation also appeared to have a decreasing trend since 2000. We also find that spring precipitation of the South China has experienced a few abrupt changes: sudden increment at 1964, sudden decrement at 2002, and sudden increment at 1995. In addition to these abrupt changes, the precipitation could also be characterized by variability of multiple temporal scales, with dominant periodicities of 4 years, 8 years, and 14 years. The South China spring precipitation is also closely tied to the atmospheric circulations: when Aleutian Low strengthens, westerly weakens, and the center of the Western Pacific subtropical high shifts southeastward in the early spring; and the South China precipitation tends to be abundant (positive anomaly). In contrast, when Ural ridge strengthens, the southern branch of the East Asian trough weakens and the Western Pacific subtropical high shifts northwestward in the early spring, the South China precipitation tends to be reduced (negative anomaly).

On the Extratropical Influence of Variations of the Upper-Tropospheric Equatorial Zonal-Mean Zonal Wind during Boreal Winter

Abstract Variations in the global tropospheric zonal-mean zonal wind [U] during boreal winter are investigated using rotated empirical orthogonal functions applied to monthly means. The first two modes correspond to the northern and southern annular mode and modes 3 and 4 represent variability in the tropics. One is related to El Niño–Southern Oscillation and the other has variability that is highly correlated with the time series of [U] at 150 hPa between 5°N and 5°S [U150]E and is related to activity of the Madden–Julian oscillation. The extratropical response to [U150]E is investigated using linear regressions of 500-hPa geopotential height onto the [U150]E time series. Use is made of reanalysis data and of the ensemble mean output from a relaxation experiment using the European Centre for Medium-Range Weather Forecasts model in which the tropical atmosphere is relaxed toward reanalysis data. The regression analysis reveals that a shift of the Aleutian low and a wave train across the North Atlantic are associated with [U150]E. It is found that the subtropical waveguides and the link between the North Pacific and North Atlantic are stronger during the easterly phase of [U150]E. The wave train over the North Atlantic is associated with Rossby wave sources over the subtropical North Pacific and North America. Finally, it is shown that a linear combination of both [U150]E and the quasi-biennial oscillation in the lower stratosphere can explain the circulation anomalies of the anomalously cold European winter of 1962/63 when both were in an extreme easterly phase.

The response of actual evaporation to global warming in China based on six reanalysis datasets

ABSTRACTIn this paper, we present the response of actual evaporation to global warming in China based on the National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP/NCAR) reanalysis 1, the NCEP‐Department of Energy (NCEP/DOE) reanalysis 2, 40‐year ECMWF Re‐Analysis (ERA‐40), ECMWF‐Interim Re‐Analysis (ERA‐Interim), Modern‐Era Retrospective Analysis for Research and Applications (MERRA), and Climate Forecast System Reanalysis (CFSR). Rotated empirical orthogonal function (REOF) analysis was applied to reveal the coherent pattern of the change in reanalysis evaporation (RE). According to the first four REOF modes in NCEP/NCAR, we subdivided China into six climatic regions, and found that RE increased significantly in central and southeast of China from 1979 to 2012, especially during the sub‐period of 1985–2004. Various estimates of linear trend are statistically consistent, and most of them are significant at the 95% confidence level. Conversely, RE decreased in northern and northeast although the magnitude of decreasing trends is inconsistently among the reanalysis. Moreover, there is a general tendency of RE to increase in northwest, but mostly RE trends are not significant. In the dry northwest and northern regions, rainfall is an important factor affecting the changing of RE, while RE is less sensitive to the change of temperature. However, RE rates are dominated by temperature in the humid central and southeast regions. These results support the view that the sensitivity of RE to global warming largely depends on the environment. In view of data availability, despite the general similarity, differences exist among the various reanalysis, especially in NCEP/NCAR and CFSR. In summary, it can be concluded that the quality of RE values is higher in central and southeast, while even greater uncertainties lie in the estimates of RE in northwest China and Qinghai‐Tibet Plateau.

Evaluation of observed and simulated teleconnections over the Euro-Atlantic region on the basis of partial least squares regression

An interesting topic in climate research is to determine the variability of teleconnection patterns under warming conditions. The North Atlantic Oscillation (NAO), the East Atlantic, the East Atlantic-West Russian and the Scandinavian (SCAND) patterns are the most important teleconnection patterns affecting Europe. Results associated with traditional methodologies for capturing these patterns, such as conventional and rotated empirical orthogonal function analysis, are difficult to intercompare when using different datasets. Therefore, we employed the method of partial least squares (PLS) regression to find a plausible representation of the teleconnections using the standard set of teleconnection patterns defined by National Oceanic and Atmospheric Administration’s Climate Prediction Center as a reference. The variability and trend of the teleconnection indices and patterns over the twentieth and twenty-first centuries were investigated for 20C3M and SRES A1B experiments from the third phase of the Coupled Model Intercomparison Project (CMIP) and compared with the twentieth-century reanalysis data. The results of this study show a positive trend for the NAO and a negative trend for the SCAND under a future climate scenario. With this study, we were able to extract consistent teleconnection patterns across different models, demonstrating the usefulness of the PLS regression in evaluating models and establishing the basis for future work using the fifth phase of CMIP data to assess atmospheric circulation trends and causes of regional climate change.

Spatiotemporal properties of droughts and related impacts on agriculture in Xinjiang, China

Xinjiang is the largest arid inland region in China and its agricultural development plays an important role in the socio-economy of China. Drought is one of the major natural hazards in this region and has impacts on agriculture. In this study, spatiotemporal patterns of droughts are analysed based on monthly precipitation datasets from 52 meteorological stations covering the period of 1961–2008 using the Rotated Empirical Orthogonal Functions (REOF) technique and also the Mann–Kendall trend test (MK test). Results of the study indicate that: (1) a wetting tendency is observed in recent years, particularly in northern Xinjiang. Seasonally, the wetting tendency is found mainly in winter. The modes of REOF can be divided by the Tianshan mountain and the principal component (PC) of the northern Xinjiang mode in winter has a significant increasing trend. (2) The area of drought-affected regions is decreasing in northwestern Xinjiang and along the northern side of Tianshan mountain. Seasonally, the area of drought-affected regions is significantly decreasing in winter. (3) The wetting tendency of Xinjiang may alleviate the drought influence. However, uneven spatial patterns of precipitation changes may enhance drought impacts. Besides, drought-related impacts can be greatly alleviated where irrigation conditions are favourable.

Analysis of precipitation based on ensembles of regional climate model simulations and observational databases over Ethiopia for the period 1989–2008

ABSTRACTThis study examines the performance of multimodel numerical simulations and multiobservational databases focusing on seasonal cycles and spatial variations of precipitation over Ethiopia. Seven regional climate models (RCMs) driven by the European Center for Medium Range Weather Forecasting (ECMWF) Interim reanalysis (ERA‐Interim) and generated in the framework of COordinated Regional climate Downscaling EXperiment (CORDEX) project, and four observational databases computed using different interpolation techniques and blending strategies were evaluated against typical observational database produced by Climate Research Unit (CRU) over Ethiopia on monthly basis. All were produced at 48.8 km grid resolution for the period 1989–2008. The preliminary results showed that ensembles [multimodel ensemble (MME) + multiobservational ensemble (MOE)] were as good as CRU in reproducing the temporal variability and the geographical distribution of precipitation. Comparison of seasonal means and temporal correlation results revealed that there were good agreements between ensembles and CRU at each grid point and in close proximity to each other. Results of rotated principal components (RPCs), rotated empirical orthogonal functions (REOFs), and the associated power spectra showed that every ensemble's element was able to simulate the seasonal cycles and homogeneous precipitation zones of CRU reasonably well. Excessive and deficient rainfall periods, which were seen in every ensemble's RPCs, matched CRU historical records.

Impacts of fire emissions and transport pathways on the interannual variation of CO in the tropical upper troposphere

Abstract. This study investigates the impacts of fire emission, convection, various climate conditions and transport pathways on the interannual variation of carbon monoxide (CO) in the tropical upper troposphere (UT), by evaluating the field correlation between these fields using multi-satellite observations and principle component analysis, and the transport pathway auto-identification method developed in our previous study. The rotated empirical orthogonal function (REOF) and singular value decomposition (SVD) methods are used to identify the dominant modes of CO interannual variation in the tropical UT and to study the coupled relationship between UT CO and its governing factors. Both REOF and SVD results confirm that Indonesia is the most significant land region that affects the interannual variation of CO in the tropical UT, and El Niño–Southern Oscillation (ENSO) is the dominant climate condition that affects the relationships between surface CO emission, convection and UT CO. In addition, our results also show that the impact of El Niño on the anomalous CO pattern in the tropical UT varies strongly, primarily due to different anomalous emission and convection patterns associated with different El Niño events. In contrast, the anomalous CO pattern in the tropical UT during La Niña period appears to be less variable among different events. Transport pathway analysis suggests that the average CO transported by the "local convection" pathway (ΔCOlocal) accounts for the differences of UT CO between different ENSO phases over the tropical continents during biomass burning season. ΔCOlocal is generally higher over Indonesia–Australia and lower over South America during El Niño years than during La Niña years. The other pathway ("advection within the lower troposphere followed by convective vertical transport") occurs more frequently over the west-central Pacific during El Niño years than during La Niña years, which may account for the UT CO differences over this region between different ENSO phases.

Climate mean, variability and dominant patterns of the Northern Hemisphere wintertime mean atmospheric circulation in the NCEP CFSv2

In this study, the climate mean, variability, and dominant patterns of the Northern Hemisphere wintertime mean 200 hPa geopotential height (Z200) in a CMIP and a set of AMIP simulations from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Version 2 (CFSv2) are analyzed and compared with the NCEP/NCAR reanalysis. For the climate mean, it is found that a component of the bias in stationary waves characterized with wave trains emanating from the tropics into both the hemispheres can be attributed to the precipitation deficit over the Maritime continent. The lack of latent heating associated with the precipitation deficit may have served as the forcing of the wave trains. For the variability of the seasonal mean, both the CMIP and AMIP successfully simulated the geographical locations of the major centers of action, but the simulated intensity was generally weaker than that in the reanalysis, particularly for the center over the Davis Strait-southern Greenland area. It is also noted that the simulated action center over Aleutian Islands was southeastward shifted to some extent. The shift was likely caused by the eastward extension of the Pacific jet. Differences also existed between the CMIP and the AMIP simulations, with the center of actions over the Aleutian Islands stronger in the AMIP and the center over the Davis Strait-southern Greenland area stronger in the CMIP simulation. In the mode analysis, the El Nino-Southern Oscillation (ENSO) teleconnection pattern in each dataset was first removed from the data, and a rotated empirical orthogonal function (REOF) analysis was then applied to the residual. The purpose of this separation was to avoid possible mixing between the ENSO mode and those generated by the atmospheric internal dynamics. It was found that the simulated ENSO teleconnection patterns from both model runs well resembled that from the reanalysis, except for a small eastward shift. Based on the REOF modes of the residual data, six dominant modes of the reanalysis data had counterparts in each model simulation, though with different rankings in explained variance and some distortions in spatial structure. By evaluating the temporal coherency of the REOF modes between the reanalysis and the AMIP, it was found that the time series associated with the equatorially displaced North Atlantic Oscillation in the two datasets were significantly correlated, suggesting a potential predictability for this mode.