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This study investigates the relationship between sea surface temperature (SST) anomalies in the subtropical Atlantic Ocean, as represented by the Southern Atlantic subtropical dipole (SASD), and SST anomalies in the tropical Pacific Ocean, identified by the El Niño‐Southern Oscillation (ENSO). Contrary to the previously held notion of a weak relationship between SASD and ENSO as suggested by earlier literature, our analysis reveals a substantial inverse correlation between the two. This correlation exhibits significant multi‐decadal variability, which has notably intensified over the most recent two decades compared with the preceding two decades. This intensification in the SASD–ENSO inverse correlation may be attributed to the shift in ENSO regime from predominance of eastern Pacific El Niño to central Pacific El Niño events around the turn of the century. This transition triggers wavetrains that propagate along different paths, consequently influencing the South Atlantic subtropical high and inducing alterations in anomalous SST patterns in the subtropical Atlantic Ocean. These findings advance our comprehension of the interactions between South Atlantic and Pacific SST variations, which strongly influence rainfall patterns, particularly in South America and southern Africa. Understanding such teleconnection holds promise for improving sub‐seasonal to seasonal precipitation predictions in these regions. [ABSTRACT FROM AUTHOR]

Near‐surface wind fields in the Prydz Bay and Amery Ice Shelf region of East Antarctica play a crucial role in the formation and variability of Antarctic Bottom Water, a cold, dense water mass that sinks and spreads across the deep ocean basins influencing ocean circulation and modulating earth's climate system. This study investigates the primary modes of variability of these wind fields using the self‐organizing map (SOM) method and data from the latest version of the European Centre for Medium‐Range Weather Forecasts (ECMWF) ReAnalyses (ERA5), spanning four decades from 1979 to 2020. While the wind field climatology, characterized by small seasonal variation, is dominated by katabatic and large‐scale forcing, the spatial patterns of the primary variability modes are mainly influenced by synoptic system activities. The overall trend in annual wind speed anomalies is positive across the study region, with the exception of the southwestern part and central Prydz Bay. However, significant trends are observed in only two out of nine SOM nodes (nodes 4 and 9), which collectively explain less than 30% of the averaged trends over the region. The interannual variability in the seasonal occurrences of certain nodes is linked to several well‐known climate modes, including the El Niño–Southern Oscillation, the Southern Annular Mode and Zonal Wavenumber 3. Our results provide a reference for forecasting the occurrence frequency of specific patterns, which could help mitigate the impact of extreme wind events through improved forecasting. [ABSTRACT FROM AUTHOR]

Based on statistical analyses of gridded data over the past four decades (1979–2020), we examined the teleconnection between the variability of the Antarctic sea ice and the leading modes of subtropical sea surface temperature (SST) variability known as the Indian Ocean subtropical dipole (IOSD), the South Atlantic subtropical dipole (SASD) and the South Pacific subtropical dipole (SPSD). We show that the pattern and strength of the teleconnection differ with the SST modes. For each mode, while the regional distributions of significant Antarctic sea ice anomalies are broadly similar throughout the year, the areal extent and the magnitudes of the anomalies display a strong seasonality. Larger areas and magnitudes of significant sea ice anomalies occur in austral winter for the SASD, autumn and spring for the SPSD and non‐summer seasons for the IOSD. We demonstrate that the spatial and seasonal variations of the sea ice anomalies associated with each of the three subtropical SST variability modes are largely consistent with the patterns of the anomalous temperature advection and sea ice transport by the anomalous atmospheric circulations induced by planetary wavetrains that are triggered by anomalous convective activities over different regions of subtropical oceans. These relationships between subtropical SST modes and Antarctic sea ice may serve as a valuable reference for predicting seasonal to interannual scale variations of Antarctic sea ice concentrations across each austral season. [ABSTRACT FROM AUTHOR]

In contrast to the declining sea ice extent across most of the Arctic in the past several decades, sea ice extent in the Antarctic has experienced opposite regional trends with regions of sea ice expansion exceeding those of contraction. Various mechanisms have been put forward to explain the Antarctic sea ice trends, but few have been successful at explaining a large portion of the observed trends. Dividing the Southern Ocean into the Pacific, Atlantic, and Indian Ocean sectors and examining the trends over 1979–2018 separately for each sector and for each season of the year, we are able to identify modes of variability that statistically explain more than 42% of the trends in all three sectors and all four seasons. In certain sector and season, up to 94% of the trends can be explained. The leading modes of variability that explain a substantial portion of the trends appear to be related to several known climate variability modes including the Southern Annular Mode (SAM), the Pacific South American (PSA) 1 and 2, and the Zonal Wavenumber 2–6 patterns. In the Atlantic and Indian Ocean sectors, the changes in the occurrences of the main contributing modes to sea ice trends are dominated by local sea‐surface temperature (SST) variations, while in the Pacific sector, they are related to changes in global SST. [ABSTRACT FROM AUTHOR]

The spatial distribution of trends in temperature extremes over Antarctica remains largely unknown. Here we investigate the seasonal and spatial characteristics of extreme warm occurrence across Antarctica. The Antarctic inland areas show significant positive trends in the number of extreme warm days in austral spring and summer. The trends in the seasonal mean of daily maximum temperature show strong coherence with the trends in extreme warm occurrences. In addition, the long‐term longwave radiation, water vapor flux and regional atmospheric circulation changes are closely connected to the trends of extreme warm days in all seasons outside of summer; the summer longwave radiation and interior wind trends show little coherence with warm extreme trends, indicating other processes at play driving extreme warm days in summer. Plain Language Summary: Antarctica interacting with the global ocean and atmosphere is a key area in studying climate change. The extreme high temperatures in Antarctica have profound impacts on surface melt and local ecosystems. We find that the trends of extreme warm days in the Antarctic continent vary by region and season, showing significant positive trends over the inland areas in austral spring and summer. The background warming of daily maximum temperature is closely connected to the extreme warm occurrences. The trends of surface downward longwave radiation, integrated water vapor flux and the 10 m wind are to a large extent associated with the trend of extreme warm days, especially in spring. Key Points: The extreme warm days in Antarctic inland areas increase significantly in austral spring and summerThe long‐term trends in extreme warm days show strong coherence with the trends in averaged daily maximum temperatureThe temperature trends are closely connected to changes in the surface longwave radiation in all seasons except summer [ABSTRACT FROM AUTHOR]

This study presents different characteristics of precipitation and synoptic‐scale circulation associated with extreme precipitation events in inland and coastal Antarctica. The focus is on two stations, inland Vostok and coastal Casey. We use observed daily precipitation data from years 2004–2017 to investigate and compare the statistics on precipitation at both stations. The key areas for synoptic features favouring extreme precipitation are identified on the basis of air‐mass backward trajectories, computed applying the Lagrangian HYSPLIT model. The air moisture accounting for high‐precipitation events originates from the ocean but in many (some) cases the trajectories cover long distances over the ice sheet before reaching Vostok (Casey). Multiple statistical methods including composite analysis, empirical orthogonal functions (EOF), and self‐organizing maps (SOMs) are used to examine the full view of synoptic patterns. At Vostok in the inland high plateau, ERA‐Interim reanalysis shows that the synoptic patterns governing the extreme precipitation events are relatively complicated. Amplified planetary waves allow water vapour to reach the Vostok Station from different source regions, including the Weddell Sea, Ross Sea, and the Indian Ocean off the Amery Ice Shelf. A dipole structure of negative height anomalies to the west and positive ones to the east of the station is identified as the cause of southward water vapour transport and resulting precipitation at Casey in coastal Antarctica. [ABSTRACT FROM AUTHOR]

The Antarctic sea ice variability has been linked to tropical sea surface temperature. However, little is known as to whether and how the Indian Ocean Basin Mode (IOBM) influences Antarctic sea ice changes. We revealed the existence of a teleconnection between the IOMB and Antarctic sea ice anomalies, which is much stronger in austral spring and autumn than summer and winter. In particular, under the positive phase of the IOBM, significant positive sea ice anomalies occur in the Bellingshausen and northern Weddell Seas, in contrast to negative anomalies in the Amundsen Sea, the southern Atlantic Ocean, and the coastal seas off Dronning Maud Land. This teleconnection is established by planetary wavetrains excited over the tropical Indian Ocean and the tropical Pacific Ocean and is modulated by El Niño‐Southern Oscillation. The IOBM‐related Antarctic sea ice anomalies are largely consistent with those of the anomalous surface air temperature and wind fields associated with the IOBM. Plain Language Summary: The variability of sea surface temperature in the tropical Indian Ocean is dominated by two modes, the Indian Ocean Dipole (IOD) and the Indian Ocean Basin Mode (IOBM). While previous studies have linked IOD to Antarctic sea ice changes, little is known about whether and how IOBM may affect seasonal Antarctic sea ice. Using 40‐year (1979–2018) observational and reanalysis data, we found that there exists a significant teleconnection between the IOBM and the Antarctic sea ice anomalies in austral autumn and spring, and that this remote connection can be largely explained by anomalous atmospheric circulations. Key Points: A teleconnection exists between the Antarctic sea ice anomalies and the sea‐surface‐temperature anomaly known as the Indian Ocean Basin Mode (IOBM)The IOBM and Antarctic sea ice connection varies spatially and seasonally, is stronger in autumn and spring, and is modulated by El Niño‐Southern Oscillation (ENSO)Removing the ENSO modulation, the extent of sea ice concentration anomalies shrinks a lot, and the source of the wavetrain moves westward [ABSTRACT FROM AUTHOR]

The most recent historic heat wave in Siberia with record‐shattering temperatures is a reflection that, as a manifestation of global warming, the Arctic is experiencing more frequent and severe warm‐temperature extremes that could have global consequences. Here, we apply the self‐organizing map (SOM) clustering method to 6‐hr data from ERA‐Interim from 1979 to 2017 to document the spatial and seasonal variations of the trends in the number of warm‐extreme days over the pan‐Arctic region, and to apportion the trends into a dynamic component representing changes in atmospheric circulation patterns, a thermodynamic component not directly related to circulations, and an interaction component. We show significant upward trends in the occurrence of warm extremes across much of the Arctic Ocean in all seasons except for summer when regions of significant upward trends move from the Arctic Ocean to the Canadian Arctic Archipelago, Greenland, and the northern North Atlantic. The direction and magnitude of the trends in seasonal warm extremes as well as their seasonal and spatial variations are dominated by the thermodynamic component, with the dynamic component and the interaction component at least an order of magnitude smaller. Although negligible to the long‐term, pan‐Arctic averaged trend, the dynamic component may be comparable with, or even larger than, the thermodynamic component at some locations and under certain atmospheric circulation patterns. [ABSTRACT FROM AUTHOR]

We present an explanation for the sea ice concentration trends in the Pacific sector of the Southern Ocean (PSSO) in austral autumn (April‐June) during 1979–2018. Sea ice has decreased in the Bellingshausen Sea and increased in the Ross Sea, concurrently with a negative trend in the South Pacific Oscillation (SPO). SPO statistically explains 43% of the sea ice concentration trend averaged over PSSO. Convective activities over East Africa and the southwestern Indian Ocean, the Interdecadal Pacific Oscillation (IPO), and extratropical processes excite a wavetrain that propagates from the Indian Ocean to the Southern Ocean and South America. The wavetrain contributes to the decrease of the autumn SPO index, which influences sea ice changes over PSSO. During the negative phase of SPO, an anomalous surface anticyclonic wind field over high‐latitude South Pacific Ocean generates anomalous sea ice concentrations via heat advection and wind forcing on ice drift. Plain Language Summary: Antarctic sea ice cover has experienced regionally different trends. In austral autumn, sea ice has decreased in the Bellingshausen Sea and increased in the Ross Sea, but reasons for these trends are not well understood. We present an explanation for the observed sea ice concentration trends in the Pacific sector of the Southern Ocean (PSSO) in austral autumn (April‐June) during 1979–2018. During this period, a large‐scale atmospheric circulation pattern, the South Pacific Oscillation (SPO), has had a trend towards its negative phase. This SPO trend statistically explains 43% of the sea ice concentration trend averaged over PSSO. The physical mechanisms are related to atmospheric teleconnections. Convective activities over East Africa and the southwestern Indian Ocean, the Interdecadal Pacific Oscillation (IPO), and extratropical processes excite a planetary wavetrain that propagates from the Indian Ocean to the Southern Ocean and South America. The wavetrain contributes to the decrease of the autumn SPO index, which influences sea ice changes over PSSO. During the negative phase of SPO, an anomalous surface anticyclonic wind field over high‐latitude South Pacific Ocean generates anomalous sea ice concentrations via heat advection and wind forcing on ice drift. Key Points: The autumn South Pacific Oscillation (SPO) index shows a decreasing trend for the 1979–2018 periodThe negative trend in autumn SPO index explains 43% of the total sea ice trend averaged across the Pacific sector of the Southern OceanAn anomalous wavetrain from over the Indian Ocean to the Southern Ocean contributes to the decrease of the autumn SPO index [ABSTRACT FROM AUTHOR]

The relationship of the tropical Indo‐Pacific upper ocean heat content (HC) and the South China Sea (SCS) summer monsoon (SCSSM) onset during 1980–2020 was investigated. It was found that when HC anomalies in the preceding winter–spring are positive (negative) in the eastern Indian–western Pacific Ocean or negative (positive) in the southwestern Indian Ocean and eastern Pacific Ocean, SCSSM onset is usually early (late). Empirical orthogonal function (EOF) analysis suggested that the primary EOF modes of HC anomaly in both tropical Pacific and Indian Oceans are associated with El Niño–Southern Oscillation (ENSO). It is through modulating the westerly over the north Indian Ocean–SCS and the western north Pacific subtropical high (WNPSH) via the Walker circulation over the Indo‐Pacific basin, monsoon circulation in the Indian Ocean that the ENSO related Indo‐Pacific HC variation connects with the SCSSM onset. Both the second EOF modes for the tropical Pacific and Indian Ocean also show significant correlations with the SCSSM onset. The former related vertical motion over the SCS–far northwestern Pacific can influence the WNPSH and convection, thus occurrence of the SCSSM. The latter represents the intrinsic Indian Ocean HC variability; the air temperature variation associated with it can modulate the atmospheric circulation in the Indian Ocean–SCS through thermal wind balance, and thus the SCSSM onset by acting on the westerly over the SCS and the WNPSH. A western Pacific index and an Indian Ocean dipole index were defined to represent the leading HC modes in the tropical Pacific and Indian Ocean, respectively. A binary linear regression model was constructed using these two indices to improve SCSSM onset prediction. [ABSTRACT FROM AUTHOR]

The relative importance of the factors contributing to Arctic spring sea ice decline remains an open question. Here we suggest a new major factor. In spring the North Pacific Gyre Oscillation (NPGO) shows a significantly increasing trend during 1998–2016, in contrast to the insignificant trend of the Pacific Decadal Oscillation (PDO) index. Nearly 40% of Arctic springtime sea ice concentration trend is statistically related to the increase of the NPGO index but only 4% to the PDO trend. Through the destructive linear interference with climatological Aleutian low, the increasing NPGO index tends to weaken the upward propagation of planetary waves, which enhances the strength of the stratospheric Arctic vortex and the Arctic Oscillation (AO). The positive AO anomalies influence the surface wind field and temperature pattern anomalies, contributing to negative sea ice anomalies in the Arctic. Key Points: An increase in the NPGO index for the 1998–2016 period statistically explains nearly 40% of Arctic springtime sea ice lossThe increasing NPGO index produces an anomalous high, weakening climatological Aleutian low and the upward propagation of planetary wavesThe weakened upward propagated waves strengthen the stratospheric vortex and the Arctic Oscillation, which lead to reduced Arctic sea ice [ABSTRACT FROM AUTHOR]

To get a deep understand of the carbon cycle of Tibetan lakes, the CO2 flux over Ngoring Lake (NL), a large freshwater lake in the source region of the Yellow River, was monitored from 2011 to 2013 using an eddy covariance system. Based on the monthly mean CO2 flux, NL was a significant sink of atmospheric CO2 in 2012, with the greatest negative (downward) CO2 flux of −0.83 (±0.27) g C m−2 d−1 occurring in October. While in 2011 and 2013, NL was in quasi‐equilibrium with atmospheric CO2. The process controlling the daily variation in the CO2 flux was investigated using statistical analysis. The daily mean of the surface wind speed was significantly correlated with the observed daily CO2 flux. Under the assumption that the vertical gradient in the CO2 concentration near the water surface varied slowly, this correlation confirms the rationality of using the surface wind to express the gas transfer velocity. Following this consideration, because the thermal contrast between NL and the surrounding grassland was also significantly correlated with the daily CO2 flux, a new parameterization scheme of k600 is suggested in this study. Potential mechanisms for the coupling process between the surface wind and the thermal contrast of the lake are discussed. Based on the surface energy balance analysis, the heat storage rate of the lake played different roles in the CO2 fluxes during the three years, depending on the CO2 saturation of the lake water. The process controlling the monthly mean CO2 flux was also investigated. Plain Language Summary: There are more than 1,500 lakes on the Tibetan Plateau. Most of these lakes have not been thoroughly investigated, so little is known about the features of their carbon dynamics. To gain a better understand of the CO2 exchange over these lakes, an observation experiment was conducted over Ngoring Lake (a fresh water lake, with an area of 610.7 km2) from 2011 to 2013, and valuable data were obtained. By investigating these observations, we determined that the CO2 flux was negative (downward) during most of 2012, but it was in quasi‐equilibrium in 2011 and 2013. Second, the surface temperature difference between the lake and the surrounding grasslands may have largely controlled the daily variation in the gas transfer velocity near the water's surface. Because the surface temperature around a lake can be conveniently and accurately monitored by satellite, this finding may be useful in the estimation of the surface CO2 flux over other remote lakes worldwide. Key Points: Ngoring Lake significantly sequestrated atmospheric CO2 in 2012, with the smallest CO2 flux of −0.83 g C m−2 d−1 in OctoberIf any atmospheric variable has an effect with k600, its daily mean may be highly correlated with the CO2 fluxThe thermal contrast of a lake can satisfactorily express the daily variation in gas transfer velocity [ABSTRACT FROM AUTHOR]

Season‐dependent interannual variability of surface winds across Antarctica and the Southern Ocean is investigated using European Centre for Medium‐Range Weather Forecasts Interim (ERA‐Interim) reanalysis for 1979–2017 and the empirical orthogonal function (EOF) technique. The first three EOF modes, which account for 18–23%, 11–15%, and 8–10% of the total variances for the four austral seasons, are related to several known modes of Southern Hemisphere large‐scale circulation including the southern annular mode, Pacific South American (PSA), and Zonal Wave 3 (ZW3) and to sea surface temperature anomalies in eastern (Niño 3) and central (Niño 4) tropical Pacific Ocean. Specifically, EOF1 and EOF2 are significantly correlated with southern annular mode in all seasons except for autumn EOF2. Neither EOF1 nor EOF2 are significantly correlated to Niño 3, but Niño 4 is significantly correlated to winter EOF1 and to EOF2 in all seasons but winter. EOF1 is significantly related to ZW3 for all seasons but summer; however, no significant connection is found between EOF2 and ZW3. Significant correlations exist between spring and winter EOF2 and PSA1 and between spring EOF1 and PSA2. EOF3 is significantly correlated with Niño 3, Niño 4, and PSA2 in all seasons but summer. The spatial patterns of all three modes can be largely explained by the anomalous mean sea level pressure fields that strengthen or weaken climatological winds in different regions of the Antarctica and the Southern Ocean, although variations in katabatic forcing also plays a role in the variations of surface winds especially in East Antarctica and during winter season where and when katabatic forcing dominates. Key Points: An analysis of season‐dependent interannual variability of surface winds in Antarctica and the Southern Ocean has been done using ERA‐Interim dataThe leading modes of the variability are related, depending on seasons, to known modes of Southern Hemisphere large‐scale circulationThe spatial patterns of the variability can be largely explained by anomalous surface pressure and wind relative to climatological patterns [ABSTRACT FROM AUTHOR]

This study investigates the interannual variability of wind energy resources across China and how it changes with season by applying empirical orthogonal function (EOF) analyses to gridded wind data from the Climate Forecast System Reanalysis (CFSR) from January 1979 through December 2011. The first EOF mode (EOF1) represents between 22% variance for winter and 29% for summer. Spatially, the variation is largely consistent across China for summer and autumn and almost opposite between north and south for spring and winter, and the strongest variation in all seasons is found over Inner Mongolia and Tibet. The second EOF mode (EOF2) represents between 13% variance for autumn and 16% for spring, and is largely dominated by a sharp contrast between Inner Mongolia and Tibet for all seasons. The EOF1 appears to be linked statistically to the pacific decadal oscillation for summer and autumn and to the Pacific North American pattern for spring and winter, while the EOF2 seems to be connected to the Arctic Oscillation for spring and winter and to an interdecadal variability for summer and autumn. The anomalous wind fields associated with these large‐scale circulation patterns modify the climatological wind fields in different ways that lead to an increase or a decrease of the 80‐m winds in different regions of China. Understanding the low‐frequency variability of wind speeds, or how and why wind speed and wind power vary from 1 year to another, can be beneficial for seasonal outlook or long‐range forecasting of wind power generation. Using gridded wind data from a third‐generation global reanalysis, we statically identify and characterize the main modes of the interannual variability of wind speeds at the modern wind turbine level across entire China and the dominant climate forcing for these modes.Figure caption: The correlations between the 80‐m wind speed summer season anomalies across China and the Pacific Decadal Oscillation indices for 1979–2011. [ABSTRACT FROM AUTHOR]

We used 35-year (1979-2013) hourly rainfall data from the North American Land Data Assimilation System (NLDAS-2) to examine the relationships of the symmetric and asymmetric components of two types of El Niño-Southern Oscillation (ENSO) (El Niño and El Niño Modoki) episodes with occurrences of extreme precipitation events across the United States. During the cold season, the symmetric impacts of El Niño and El Niño Modoki are more significant than during the warm season. The asymmetric components associated with El Niño during the two seasons are comparable, while the asymmetric components associated with El Niño Modoki during the warm season are more significant than those during the cold season. The connections between the symmetric and asymmetric components of the two types of ENSO and extreme precipitation occurrences are related to atmospheric moisture convergence patterns that tend to occur in response to the anomalous large-scale atmospheric circulations during the ENSO episodes. [ABSTRACT FROM AUTHOR]

ABSTRACT The increased extreme warm and decreased extreme cold temperature events across the Arctic strongly influence the natural environment as well as the societal activities. This study investigates temporal and spatial variability of wintertime extreme high and low temperature events defined by the 95 and 5% percentiles across the Arctic and subarctic regions, respectively (north of 60°N) using data from 238 stations in the Global Summary of the Day for the period 1979-2016. Empirical orthogonal function analyses indicate that the first modes (which account for 30-35% of the total variance) are out-of-phase between northern Europe, western and central Russia, and northeastern North America, and that this appears to be related to the Arctic Oscillation ( AO) and the Northern Atlantic Oscillation. The second modes explain about 8% of the total variance. During the positive phase of the first and second modes the anomalous northeasterly and northerly winds decrease Arctic extreme high and increase extreme low temperature occurrences; while the anomalous southerly and southwesterly winds have the opposite effect. Symmetric and asymmetric effects of the AO index on extreme temperature events refer to the difference and sum between the composite of its positive and negative phases. The symmetric components of the spatial patterns are similar to those of the first modes. The asymmetric components occur mainly over western and central Russia for extreme high and low temperatures, respectively. In addition the impacts of six other large-scale climate modes are also explored. [ABSTRACT FROM AUTHOR]

ABSTRACT Valleys can trap cold air to form Valley Cold Pools ( VCPs). Characterized by stable stratification and weak winds, VCPs, especially those that last over multiple days, can produce adverse effects such as poor visibility and severe air pollution. Using the gridded data set of the North American Regional Reanalysis ( NARR) for the period of 1979 through 2012, this study examines the climatology of VCPs in the western United States with a focus on spatial and temporal variability. The results reveal a widespread occurrence of short-lived (1-2 days) VCPs over both the mountainous areas of the West and the Northern Plains. Longer VCP episodes, however, tend to be limited to large basins/valleys in the Northwest and the Intermountain West. The leading mode of variability in the annual number of cold-season multi-day VCP event anomalies appears to be linked to a sea-surface temperature anomaly pattern typically found during the warm phase of Pacific Decadal Oscillation. Corresponding to the positive phase of the leading mode of variability is an anomalous 500- hPa ridge over the western United States induced by a Rossby wave train, which, by blocking cold-air intrusions and producing mid-level subsidence warming, leads to more persistent VCP episodes in the western United States. In addition to large-scale wintertime circulation anomalies, local surface temperature anomalies also contribute to the variability. [ABSTRACT FROM AUTHOR]

ABSTRACT The inter-annual variability of southerly low-level jets ( SLLJs) over North America during the warm (April-September) and cool (October-March) seasons is investigated. SLLJ occurrences over a 31-year period (1979-2009) were identified from the North American Regional Reanalysis ( NARR) vertical wind profiles. The first empirical orthogonal function ( EOF) modes of the SLLJ frequency during the warm and cool seasons account for about 30 and 20% of the total variance, respectively. Both modes can be interpreted as a strengthening or weakening of the core area of SLLJ anomalies. The principal component ( PC) time series display significant positive trends, suggesting an increase in SLLJ activity during both seasons on inter-decadal time scales and are significantly correlated to the summertime Pacific Decadal Oscillation ( PDO) and Atlantic Multidecadal Oscillation ( AMO) for the warm season and the wintertime PDO, AMO and El Niño Modoki for the cool season. The second modes account for about 20 and 15% of the total variance for the warm and cool seasons, respectively, and are interpreted as primarily a subseasonal latitudinal shift in SLLJ activity between the central Great Plains and the western Gulf of Mexico and southern Texas during the warm season and a longitudinal shift between the western Gulf of Mexico and the Caribbean during the cool season. The second mode appears to be significantly correlated to El Niño Modoki for the warm season and to Niño 3.4 for the cool season. [ABSTRACT FROM AUTHOR]

ABSTRACT The mean climatology, seasonal and interannual variability and trend of wind speeds at the hub height (80 m) of modern wind turbines over China and its surrounding regions are revisited using 33-year (1979-2011) wind data from the Climate Forecast System Reanalysis ( CFSR) that has many improvements including higher spatial resolution over previous global reanalysis products. Mean 80-m wind speeds are consistently higher over China Seas and the ocean areas than over land, and inside China high winds are found in areas of Inner Mongolia and the Tibetan Plateau. There is a considerable seasonal variability that reflects primarily the influence of East and Southeast Asia Monsoon with generally higher speeds in winter followed by summer, and weaker winds in autumn, followed by spring. There is also a strong interannual variability, and regions of larger amplitude of variability coincide with regions of higher mean winds. A decreasing trend, dominated by a sharp decline beginning in 2005, is seen across China and the surrounding seas in summer and autumn, and the summer trends over land and over ocean appear to be related respectively to the Pacific Decadal Oscillation ( PDO) and the East Asian summer monsoon. Trends are not consistent across the region in spring and winter, however, with positive trends over some areas in northeastern and northwestern China, Mongolia and tropical oceans whereas negative trends in other regions. Nearly all areas of China experience mean annual 80-m wind speed less than 6.9 m s−1 (wind power classes of 1-2) except for some areas of Inner Mongolia where mean annual 80-m wind speeds exceed 6.9 m s−1 (Classes 3 or higher, suitable for wind energy development). China Seas and ocean areas generally fall in Class 3 or above, with the Taiwan and Luzon Straights reaching the highest Class 7. [ABSTRACT FROM AUTHOR]

ABSTRACT The frequency and timing of frost events and the length of the growing season are critical limiting factors in many human and natural ecosystems. This study investigates the temporal and spatial variability of the date of last spring frost ( LSF), the date of first fall frost ( FFF), and the length of the frost-free season ( FFS) in the Great Lakes region of the United States using two gridded reanalysis datasets for the period of 1980-2010. Across most of the Great Lakes region, there has been a negative trend for the LSF and a positive trend for the FFF, leading to a lengthening of FFS. The three variables vary spatially across the region and exhibit large interannual variability. Empirical orthogonal function ( EOF) analyses indicate that the first mode for the three variables, which accounts for about 30% of the total variance, is in phase across most of the Great Lakes region and that it appears to be related to Pacific North American ( PNA) pattern in the case of LSF and to Pacific Decadal Oscillation ( PDO) in the case of FFF and FFS. The main reason for these connections is that the 200- hPa geopotential height anomaly over North America induced by a Rossby wave train influences the strength of the trough over North America, which in turn affects surface temperatures over the Great Lakes region. The second mode, explaining about 10% of the total variance, mainly shows the out-of-phase variability between the Great Lakes and the surrounding land and it appears to be related to the circumglobal teleconnection ( CGT) in the case of LSF and again to PDO in the case of FFF and FFS. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigates the influence of the South Indian Ocean subtropical dipole (IOSD) on spring (March-April-May; MAM) rainfall over central-eastern China (CEC) and its dynamic processes by using station observations of China, Met Office Hadley Centre SST data for the period 1951-2012 and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data for the period 1958-2012. It is found that the IOSD event which peaks in the boreal winter can persist to the following spring, with strength slightly weakening. Boreal spring rainfall over CEC, i.e. the middle-lower reaches of Yangtze River, the Yellow River valley as well as regions between them, has a significant correlation with the IOSD event. When the positive (negative) IOSD event occurs in the previous winter, the CEC is dry (wet) in the spring. One of possible mechanisms that the IOSD affects the China spring rainfall is the modulation of the meridional circulation, especially the Hadley cell in the tropic along 100-120°E. In the positive IOSD years, associated with the cold sea surface temperature anomalies (SSTA) and warm SSTA in the southeastern Indian Ocean (SEIO) and southwestern Indian Ocean, there is anomalous ascent over the equatorial Indian Ocean, whereas downward flows over the SEIO and CEC. The Hadley cell over this region intensifies. Anomalous northerly wind at 850 hPa prevails, preventing wet and warm air flow from the low latitudes, which in turn transports less moisture into CEC and favours decreased rainfall. Meanwhile, the CEC is located at the sinking region of the Hadley cell. The atmosphere is fed by low moisture content over this area, also unfavourable for the occurrence of precipitation. This paper suggests that the SSTA in the southern Indian Ocean can be a good predictor for the China spring precipitation and proposes a possible mechanism for the connection of the mid-latitude climate variations of both hemispheres induced by air-sea interaction. [ABSTRACT FROM AUTHOR]