Seasonal dependence of stratospheric temperature variations

Stratospheric temperatures show distinct trends, not necessarily monotonically upward or downward. At the North Pole, trends were large only during winter and spring and were different for different months; downward for November, December, mixed for January and upward for February, March and April. For the 10°-90°N belt, the trends were variable, viz., downward during 1971-1975, upward during 1975–1978 and downward again from 1978 onwards up to date, opposite to the upward trend of ground temperature in the Northern hemisphere in recent years. Twelve-monthly running averages revealed strong QBO (quasi-biennial oscillation). For the North Pole, the QBO showed colder (lower) temperatures during 50-mb wind QBO westerly phase maxima. For the 10°-90°N belt, the QBO was similar for 30 mb and 50 mb but the QBO phases did not match well with 50-mb wind QBO phases.     

Quasi-Biennial and Quasi-Triennial Oscillations in some atmospheric parameters

A spectral analysis of the 12-month running averages of several atmospheric parameters for 40 years (1951–1990) indicated prominent QBO (Quasi-Biennial Oscillations) and QTO (Quasi-Triennial Oscillations). The 50 mb tropical wind has a very prominent QBO peak atT=2.33 years, which was well reflected in N. Pole 30 mb temperature but not in average surface air temperatures of Northern and Southern Hemispheres. The 50 mb wind had no prominent QTO; but sea-surface temperatures showed prominent QTO at 3.6 years as well as peaks at 4.8 years (also shown by N. Pole 30 mb temperature) which matched very well with similar peaks in the Pacific SST and SO (Southern Oscillation) index. Specific humidity in the lower troposphere (1000 and 700 mb) and temperature at 300 mb obtained by radiosondes in the western Pacific for 15 years (1974–1988) showed mainly a biennial oscillation.     

Quasi-biennial oscillation in ozone and temperature over tropics

Spatiotemporal variations of the quasi-biennial oscillation (QBO) in temperature and ozone over the tropical–subtropical belts (40°N–40°S) have been studied using Microwave Limb Sounder data for the period 1992–1999. Wavelet analysis has been performed to study inter-annual variations in amplitude and phases of the QBO. Latitude-height cross-sections of the amplitudes of temperature and ozone QBO exhibit a double-peak structure near the equator. Phase structure reveals that the temperature QBO descended faster than the ozone QBO. Cross-wavelet analysis shows an anti-phase relation between the amplitudes of the temperature and ozone QBO in the upper stratospheric region, whereas in-phase relation exists in the middle stratospheric region.     

Observational evidence of deep convection over Indonesian sector in relation with major stratospheric warming events of 2003–04 and 2005–06

The major sudden stratospheric warming (SSW) events of 2003–04 and 2005–06 are considered to investigate changes in equatorial convection due to circulation changes associated with the SSW events. It is observed that the SSW events are accompanied by a considerable decrease in Outgoing Longwave Radiation (OLR), a proxy for tropical convection, over equatorial latitudes (15°N–15°S) in the Indonesian sector (90°E–150°E). However, unlike noted by earlier observations, the zonal mean OLR does not show any notable relationship with the SSW events. It can be explained from the latitude–longitude map of potential vorticity (PV) at 100 hPa, which shows a tongue of high PV emanating from high latitudes towards equator and converges in the longitude band of 90°E–150°E on the day of peak warming at 1 hPa in the case of 2003–04 and 10 hPa in the case of 2005–06. The latitude-height map of Eliassen–Palm (EP) vector and its divergence show convergence of EP flux in the upper troposphere at latitudes even lower than 20°N on these days. Further, vertical winds computed from the convergence of momentum flux are upward indicating convective activity at low-latitudes and downward at mid-latitudes.     

Decadal variability and trends of oceanic barrier layers in tropical Pacific

Decadal variability and trends of the isothermal layer depth (ILD), mixed layer depth (MLD), and barrier layer thickness (BLT) were analyzed for the tropical Pacific during 1979–2015. The decadal variability of ILD, MLD, and BLT shows a close connection with the Pacific Decadal Oscillation (PDO). At PDO positive phase, the eastward shift of precipitation and weakened trade winds result in thinner BLT in western Pacific and thicker BLT in central and eastern Pacific. The situation is reversed at PDO negative phase. The differences in BLT can be up to 9–15 m. The spatial distributions of decadal trends of ILD and MLD are complex, but a thickening of BLT in the western tropical Pacific is clearly present. The raw trends of ILD, MLD, and BLT averaged in the tropical Pacific (30° N–30° S, 120° E–75° W) from 1979 to 2015 are 1.62, 1.20, and 0.51 m per decade, respectively. PDO can explain about 25% of the increasing trends of BLT, while El Niño-Southern Oscillation (ENSO) only explains about 1.7%. Global warming and/or variability at longer time scales is responsible for the remaining increasing trends. The BLT change is related to the warming and freshening of the western Pacific warm pool in recent decades. The ocean-atmosphere interactions about trade winds, wind-driven ocean circulation, temperature, and precipitation/evaporation are discussed.     

平流层气溶胶的准两年周期特征分析

本文采用HALOE和SAGE Ⅱ资料,分析了平流层气溶胶的准两年周期变化(简称QBO)特征及其与臭氧QBO的关系,结果表明:(1)北半球中高纬上空平流层气溶胶存在明显的QBO特征,其QBO信号自上向下传播,振荡幅度在平流层中下层可以达到20%;而在赤道和南半球上空的平流层气溶胶的QBO特征相对于北半球则不明显;(2)在...     

Interannual variability of United States cloudiness

United States cloudiness data for 1950–1992 show quasi-biennial (QBO) and quasi-triennial (QTO) oscillations which match partly with the QBO and QTO of the Southern Oscillation (SO) index (the Tahiti minus Darwin pressure), but not with the QBO of the 50-mb equatorial zonal wind. Cloudiness also shows significant periodicities near 4.2 and 7.5 years, and probably a sunspot cycle effect (periodicities 11–14 years), with minimum cloudiness at or soon after sunspot minima, though this could also be due to periodicities of 10 and 17 years observed in the SO index. During 1955-1970, cloudiness increased by about 1%. Thereafter, it remained almost steady for the eastern and central parts of the USA, but continued to rise until about 1980 for the western USA.     

Streamflow variability and its relationship with climate indices in western rivers of Argentina

The objective of this study was to examine the streamflow variability of Argentinean Andean basins (22°–52°S). Trends and step changes of seven hydrological variables were analysed. In addition, relationships between the hydrological variables and Pacific Decadal Oscillation (PDO), Niño 3.4, and Southern Annular Mode (SAM) indices were analysed. Most streamflow variables showed upward trends in the northwest and central-western basins, while downward trends were identified in the Patagonia (southwestern) region. Streamflow of the central-western and Patagonian basins was positively correlated with the Niño 3.4 index. Moreover, an inverse relationship with the SAM was found in watersheds south of 37°S. Positive step changes associated with the PDO phases in the north and central-western basins in the mid-1970s were detected, while negative step changes resulted in Patagonia between 1970 and 2000. This research provides new evidence of the influence of major climate modes on streamflow variability in the western rivers of Argentina.     

Monsoon activity and coupling between low-latitude and high-latitude stratospheric activities

From a Fourier analysis of the monthly mean values of the northern hemispheric geopotential heights at 30 and 50 mb levels, for the period 1972–1979, the transports of momentum and of sensible heat, and the energy conversion terms,C(K _E ,K _Z ) andC(A _Z ,A _E ), have been computed along 30°N and 60°N latitutudes. The variation in these dynamical parameters at 60°N, in relation to monsoon activity in low latitudes and the easterly and westerly phases of the QBO over Gan Island, suggest that a coupling may exist between the high-latitude stratospheric changes and low-latitude monsoon activity and that the low-latitude stratospheric activity modulates high-latitude circulation, confirming the results obtained byHolton andTan (1980) and byLabitzke (1983). The study of the low-latitude stratospheric changes in relation to the high-latitude warmings also indicates a linkage between the low- and high-latitude features     

Long‐term streamflow trends in the middle reaches of the Yellow River Basin: detecting drivers of change

The catchments in the Loess Plateau, in China's middle reaches of the Yellow River Basin, experienced unprecedented land use changes in the last 50 years as a result of large‐scale soil conservation measure to control soil erosion. The climate of the region also exhibited some levels of change with decreased precipitation and increased temperature. This study combined the time‐trend analysis method with a sensitivity‐based approach and found that annual streamflow in the Loess Plateau decreased significantly since the 1950s and surface runoff trends appear to dominate the streamflow trends in most of the catchments. Annual baseflow exhibited mostly downward trends, but significant upward trends were also observed in 3 out of 38 gauging stations. Mean annual streamflow during 1979?2010 decreased by up to 65% across the catchments compared with the period of 1957?1978, indicating significant changes in the hydrological regime of the Loess Plateau. It is estimated that 70% of the streamflow reduction can be attributed to land use change, while the remaining 30% is associated with climate variability. Land use change because of the soil conservation measures and reduction in precipitation are the key drivers for the observed streamflow trends. These findings are consistent with results of previous studies for the region and appear to be reasonable given the accelerated level of the soil conservation measures implemented since the late 1970s. Changes in sea surface temperature in the Pacific Ocean, as indicated by variations in El Niño–Southern Oscillation and phase shifts of the Pacific Decadal Oscillation, appear to have also affected the annual streamflow trends. The framework described in this study shows promising results for quantifying the effects of land use change and climate variability on mean annual streamflow of catchments within the Loess Plateau. Copyright © 2015 John Wiley & Sons, Ltd.     

Hadley环流与北太平洋涛动的显著关系

利用NCEP/NCAR月平均再分析资料,分析了冬季（11～4月）Hadley环流与北太平洋涛动（NPO）的变化特征以及它们之间的关系.本文选取0°~30°N区域里最大质量流函数来描述北半球Hadley环流强度随时间的演变,利用(20°N, 180°~160°W) 和 (60°N, 180°~160°W) 区域平均的标准化海平面气压差代表NPO强度.结果表明,冬季北半球Hadley环流与NPO的变化形势非常一致,两者都具有显著的年际和年代际变化（70年代前处于负位相,80年代之后处于正位相）,同时还呈现出明显的增强趋势.Hadley环流变化与NPO异常的关系非常密切,在年际和年代际时间尺度上都具有显著的正相关.这种强相关性在大气环流场上可以得到很好的印证.研究还揭示,太平洋地区10°~30°N下沉支和40°~60°N上升支的异常运动可能是这种关系存在的主要内在原因.     

Interannual variability of mesospheric mean winds observed with the MU radar

In an effort to study the interannual variation of mesospheric (65–90 km altitude) mean winds, 10 years (1986–1995) of wind data collected with the MU radar at Shigaraki, Japan (34.9°N, 136.1°E) have been analysed. The analysis reveals that the mean zonal wind circulation in the mesosphere is dominated by an annual variation. The summer westward flow in the mesosphere shows a smooth variation with a peak value in the range 40–60 m/s in June/July. In contrast to the summer westward winds, the winter eastward winds exhibit much more variability. In some years it is found that the winds exceed even 60 m/s and the peak value may occur in any one of the winter months. Scrutiny of the duration of the summer westward winds reveals a two-year periodicity, which has been compared with the quasi-biennial oscillation (QBO) phases at the equator. The search for a dependence of the mean wind on solar activity does not reveal any indications of it. Ten-year averaged winds are compared with the model atmosphere, CIRA-86, values and certain agreements and disagreements are pointed out.     

Effects of climate change on thermal properties of lakes and reservoirs, and possible implications

Meteorologic-driven processes exert large and diverse impacts on lakes’ internal heating, cooling, and mixing. Thus, continued global warming and climate change will affect lakes’ thermal properties, dynamics, and ecosystem. The impact of climate change on Lake Tahoe (in the states of California and Nevada in the United States) is investigated here, as a case study of climate change effects on the physical processes occurring within a lake. In the Tahoe basin, air temperature data show upward trends and streamflow trends indicate earlier snowmelt. Precipitation in the basin is shifting from snow to rain, and the frequency of intense rainfall events is increasing. In-lake water temperature records of the past 38 years (1970–2007) show that Lake Tahoe is warming at an average rate of 0.013°C/year. The future trends of weather variables, such as air temperature, precipitation, longwave radiation, downward shortwave radiation, and wind speed are estimated from predictions of three General Circulation Models (GCMs) for the period 2001–2100. Future trends of weather variables of each GCM are found to be different to those of the other GCMs. A series of simulation years into the future (2000–2040) is established using streamflows and associated loadings, and meteorologic data sets for the period 1994–2004. Future simulation years and trends of weather variables are selected so that: (1) future simulated warming trend would be consistent with the observed warming trend (0.013°C/year); and (2) future mixing pattern frequency would closely match with the historical mixing pattern frequency. Results of 40-year simulations show that the lake continues to become warmer and more stable, and mixing is reduced. Continued warming in the Tahoe has important implications for efforts towards managing biodiversity and maintaining clarity of the lake.     

Possible role of warming on Indian summer monsoon precipitation over the north-central Indian subcontinent

ABSTRACT

Broad disagreement between modelled and observed trends of Indian summer monsoon (ISM) over the north-central part of the Indian subcontinent (NCI) implies a gap in understanding of the relationship between the forcing factors and monsoonal precipitation. Although the strength of the land–sea thermal gradient (LSG) is believed to dictate monsoon intensity, its state and fate under continuous warming over the Bay of Bengal (BoB) and part of the NCI (23–28°N, 80–95°E) are less explored. Precipitation (1901–2017) and temperature data (1948–2017) at different vertical heights are used to understand the impact of warming in the ISM. In NCI, surface air temperature increased by 0.1–0.2°C decade^?1, comparable to the global warming rate. The ISM precipitation prominently weakened and seasonality reduced after 1950, which is caused by a decrease in the LSG at the depth of the troposphere. Warming-induced increase in local convection over the BoB further reduced ISM precipitation over NCI.     

The effect of the 11-year solar cycle on the temperature in the lower stratosphere

Two temperature datasets are analyzed for quantifying the 11-year solar cycle effect in the lower stratosphere. The analysis is based on a regression linear model that takes into account volcanic, Arctic Oscillation (AO), Quasi-Biennial Oscillation (QBO) and El Nino Southern Oscillation (ENSO) effects. Under solar maximum conditions, temperatures are generally warmer for low- and mid-latitudes than under solar minimum, with the effect being the strongest in northern summer. At high latitudes, the vortex is generally stronger under solar maximum conditions, with the exception of February and to a lesser extent March in the Northern Hemisphere; associated with this positive signal at high latitudes, there is a significant negative signal at the equator. Observations also suggest that contrary to the beginning of the winter, in February–March, the residual circulation in the Northern Hemisphere is enhanced. A better understanding of the mechanisms at work comes from further investigations using the ERA-40 reanalysis dataset. First, a consistent response in terms of temperature and wind is obtained. Moreover, considering Eliassen-Palm (EP) flux divergence and residual circulation stream functions, we found an increased circulation in the Northern Hemisphere in February during solar maxima, which results in more adiabatic warming at high latitudes and more adiabatic cooling at low latitudes, thus demonstrating the dynamical origin of the response of the low stratosphere to the solar cycle.     

Changing river temperatures in northern Germany: trends and drivers of change

Climate change is one of the main drivers of river warming worldwide. However, the response of river temperature to climate change differs with the hydrology and landscape properties, making it difficult to generalize the strength and the direction, of river temperature trends across large spatial scales and various river types. Additionally, there is a lack of long‐term and large‐scale trend studies in Europe as well as globally. In this study, we investigated the long‐term (25 years; 132 sites) and the short‐term (10 years; 475 sites) river temperature trends, patterns and underlying drivers within the period 1985–2010 in seven river basins of Germany. The majority of the sites underwent significant river warming during 1985–2010 (mean warming trend: 0.03 °C year^?1, SE = 0.003), with a faster warming observed during individual decades (1985–1995 and 2000–2010) within this period. Seasonal analyses showed that, while rivers warmed in all seasons, the fastest warming had occurred during summer. Among all the considered hydro‐climatological variables, air temperature change, which is a response to climate forcing, was the main driver of river temperature change because it had the strongest correlation with river temperature, irrespective of the period. Hydrological variables, such as average flow and baseflow, had a considerable influence on river temperature variability rather than on the overall trend direction. However, decreasing flow probably assisted in a faster river temperature increase in summer and in rivers in NE basins (such as the Elbe basin). The North Atlantic Oscillation Index had a greater significant influence on the winter river temperature variability than on the overall variability. Landscape and basin variables, such as altitude, ecoregion and catchment area, induced spatially variable river temperature trends via affecting the thermal sensitivity of rivers, with the rivers in large catchments and in lowland areas being most sensitive. Copyright © 2016 John Wiley & Sons, Ltd.     

全球海洋碳循环模式MOM4_L40对碳和营养物自然分布的模拟

本文介绍了国家气候中心发展的一个全球海洋碳循环环流模式,并分析评估了该模式的基本性能.该模式是在美国地球物理流体动力学实验室(GFDL,Geophysical Fluid Dynamics Laboratory)的全球海洋环流模式MOM4(Modular Ocean Model Version 4)基础上发展的一个垂直方向40层、包含生物地球化学过程的全球三维海洋碳循环环流模式,简称为MOM4_L40(Modular Ocean Model Version 4 With 40Levels).该模式在气候场强迫下长期积分1000年,结果分析表明,与观测相比,模式较好地模拟了海洋温度、盐度、总二氧化碳、总碱、总磷酸盐的表面和垂直分布特征.模拟的海洋总二氧化碳分布与观测基本相符,表层为低值区,其下为高值区,高值区域位于10°S—60°N之间,但2000m以上模拟值较观测偏小,2000m以下模拟值较观测偏大.总体来说,MOM4_L40模式是一个可信赖的海洋碳循环过程模拟研究工具.     

Temporal Variability of Lower Stratosphere Temperature

Inter-monthly to inter-decadal global variability of lower stratosphere temperature (LST) is studied in order to improve current knowledge on its variability and trends, as well as natural and anthropogenic influences upon it. Principal Component Analysis (PCA) with S-mode Varimax rotated PCA were used. The first seven components, which explain 70% of variance make it possible to determine homogeneous LST behaviour zones with little overlap between areas, and practically no unclassified areas. Composite time series, referred to as reference series, in the core of the subregions defined by each of the PCs, were calculated in order to obtain the temporal patterns. The equatorial-tropical zone and the subtropical area display warmings caused by the eruptions of El Chichon and Mt. Pinatubo volcanoes as well as the strong influence of the Quasi-Biennial Oscillation (QBO) which leads to equatorial warming (cooling) in the west (east) phase and cooling (warming) in subtropical latitudes. Only low latitudes show some kind of global teleconnection between hemispheres. Significant correlation with several ocean/atmosphere index time-series like ENSO, Antarctic and Arctic Oscillations (AAO, AO), Arctic Circumpolar Vortex was detected over latitudinally separate regions. Antarctic and Arctic ozone hole values were contrasted with warming and cooling features registered in mid and high latitudes in both hemispheres. The LST reference series exhibit a negative trend, commonly attributed to the increase in greenhouse gases that lead to a warming of the troposphere and a cooling of the stratosphere, in all sub regions. The highest cooling rate of − 0.65 °C/ decade is detected in the Gobi desert, and the lowest values of −0.1 °C/ decade over the NE of Canada and Greenland which indicates the great longitudinal variability that the LST trends may present. The difference with other authors is mainly due to the fact that results are based either on latitudinal averages or radiosonde data.     

Stratospheric wave activity and the Pacific Decadal Oscillation

Using the monthly mean NCEP/NCAR reanalysis and NOAA Extended Reconstructed sea surface temperature (SST) datasets, strong correlations between the SST anomalies in the North Pacific and calculated three-dimensional Eliassen–Palm vertical fluxes are indicated in December 1958–1976 and 1992–2006. These correlations between the interannual variations of the SST anomalies and the penetration of planetary waves into the stratosphere are much less during the decadal sub-period 1976–1992 in the positive phase of the Pacific Decadal Oscillation (PDO) and the decadal cold SST anomalies in the North Pacific. Interannual variations of the polar jet in the lower stratosphere in January are strongly associated with SST anomalies in the Aleutian Low region in December for the years with positive PDO index. This sub-period corresponds well with that of the violation of the Holton–Tan relationship between the equatorial Quasi-Beinnial Oscillation (QBO) and the stratospheric circulation in the extra-tropics. It is shown that interannual and interdecadal variations of stratospheric dynamics, including stratospheric warming occurrences in January, depend strongly on changes of the upward propagation of planetary waves from the troposphere to the stratosphere over North Eurasia in preceding December. These findings give evidences of a large impact of the decadal SST variations in the North Pacific on wave activity in early winter due to changes of thermal excitation of planetary waves during distinct decadal periods. Possible causes of the decadal violation of the Holton–Tan relationship, its relation to the PDO and an influence of the 11-year solar cycle on the stratosphere are discussed.     

Anisotropic Measurements in the Rhinegraben Area and the French Massif Central: Geodynamic Implications

—As part of an integrated seismic study, polarization of shear waves has been analyzed for teleseismic events recorded at a set of permanent broadband, semi-permanent long- and short-period and temporary short-period seismological stations located in two geodynamically important areas in western Europe, namely the Rhinegraben-Urach area and the French Massif Central volcanic field.¶While for the semi-permanent and the permanent stations there is a good azimuthal coverage of teleseismic earthquakes which allowed us to investigate the azimuthal dependence and the spatial variation over short distances of an anisotropy direction, no even azimuthal distribution of teleseismic recordings with a clear elliptical (or linear) polarization of the S phases could be obtained in the case of the temporary stations.¶While the mean values of the splitting parameters φ and δt are geographically coherent for adjacent stations, our results show a large scatter of the individual splitting parameters for the set of events used. The magnitude of the splitting time suggests that the deformation extends below the lithosphere and that the thickness of the anisotropic structure is at least 100–200 km.¶For some stations located in the Rhinegraben-Urach area (ECH, RG-N, RG-S, RBG), the variations of φ are consistent with a two-layer anisotropic model as suggested by Vinnik et al. (1994) for the South German Triangle. For the stations ECH (Vosges mountains), RG-N and RG-S (Rhinegraben proper), the resulting estimates of fast direction are around N10°E–N30°E and N80°E–N100°E for the upper and lower layers, respectively. For the station RBG (Urach), the results are N60°E–N70°E and N125°E–N135°E, respectively.¶In the Rhinegraben-Urach area, the estimates of the effective fast direction for a one-layer model show a rotation from a graben-related (30°) pattern to an Alpine belt-related pattern in the eastern part (≈ E–W). In the French Massif Central region, the results reveal two distinct fast polarization patterns. While to the west of the Sillon Houiller, φ is parallel to this late-variscan transformlike fault zone and perpendicular to the variscan belt, it is to the east rather perpendicular to the Alpine belt. The results suggest a mixture of both a lithospheric and an asthenospheric component of the seismic anisotropy for the Rhinegraben-Urach as well as for the French Massif Central areas.