Temporal and spatial variations of global solar radiation over the Qinghai–Tibetan Plateau during the past 40 years

Global solar radiation is of great significance to the balance of ground surface radiation, the energy exchange between the Earth’s surface and atmosphere, and the development of weather and climate systems in various regions. In this study, the monthly global radiation recorded at 23 stations over the Qinghai–Tibetan Plateau (QTP) was utilized to estimate global solar radiation (Q) from sunshine duration and to obtain improved fits to the variation coefficients of the monthly Angström–Prescott model (APM). The modeling results were evaluated by calculating the statistical errors, including mean bias error, mean absolute error, root mean square error, and mean relative error. We demonstrate that the monthly Q values can be predicted accurately by APM over the QTP. We also assess the variations of Q values at 116 meteorological stations by APM over the QTP during 1961–2000. The analysis shows that the annual mean sunshine duration amounted to more than 3,000 h over the whole plateau, implying promising prospects for economic applications of solar energy. During the past 40 years, the mean global solar radiation has been relatively high in the western QTP, extending northward to the Inner Mongolian Plateau. Although its decadal variations in the QTP and surrounding regions were inconsistent, the anomaly values of global solar radiation were generally positive during the 1960s and 1970s, indicating that the QTP’s global solar radiation has increased during those periods. The anomaly values were negative during the 1980s and 1990s, showing that the plateau’s global solar radiation has decreased during those periods. Global solar radiation over the QTP is negatively proportional to latitude but positively proportional to altitude and relative sunshine duration. Three factors, the sunshine duration, latitude, and altitude, exert great influence on global surface radiation, of which sunshine duration is most significant. A high-variation-coefficient zone of global solar radiation occurred in the western part of the QTP but, on average, the variation coefficient of the plateau’s global solar radiation was only 0.031, suggesting that the variation in global radiation was relatively stable over the whole QTP.     

Precipitation variability during the past 400?years in the Xiaolong Mountain (central China) inferred from tree rings

We developed the first tree-ring chronology, based on 73 cores from 29 Pinus tabulaeformis trees, for the Xiaolong Mountain area of central China, a region at the boundary of the Asian summer monsoon. This chronology exhibits significant (at 0.01 level) positive correlations with precipitation in May and June, and negative correlations with temperature in May, June and July. Highest linear correlation is observed between tree growth and the seasonalized (April–July) precipitation, suggesting that tree rings tend to integrate the monthly precipitation signals. Accordingly, the April–July total precipitation was reconstructed back to 1629 using these tree rings, explaining 44.7?% of the instrumental variance. A severe drought occurred in the area during the 1630s–1640s, which may be related to the weakened Asian summer monsoon caused by a low land-sea thermal gradient. The dry epoch during the 1920s–1930s and since the late 1970s may be explained by the strengthened Hadley circulation in a warmer climate. The dry (wet) epochs of the 1920s–1930s (the 1750s and 1950s) occurred during the warm (cold) phases of the El Ni?o-Southern Oscillation and the Pacific Decadal Oscillation that are often associated with weakened (strengthened) East Asian summer monsoon. These relationships indicate significant teleconnections operating over the past centuries in central China related to large-scale synoptic features.     

Quantifying the effects of climate trends in the past 43 years (1961–2003) on crop growth and water demand in the North China Plain

This paper explores changes in climatic variables, including solar radiation, rainfall, fraction of diffuse radiation (FDR) and temperature, during wheat season (October to May) and maize season (June to September) from 1961 to 2003 at four sites in the North China Plain (NCP), and then evaluates the effects of these changes on crop growth processes, productivity and water demand by using the Agricultural Production Systems Simulator. A significant decline in radiation and rainfall was detected during the 43 years, while both temperature and FDR exhibit an increasing trend in both wheat and maize seasons. The average trend of each climatic variable for each crop season from the four sites is that radiation decreased by 13.2 and 6.2 MJ m^?2 a^?1, precipitation decreased by 0.1 and 1.8 mm a^?1, minimum temperature increased by 0.05 and 0.02°C a^?1, maximum temperature increased by 0.03 and 0.01°C a^?1, FDR increased by 0.21 and 0.38% a^?1 during wheat and maize season, respectively. Simulated crop water demand and potential yield was significantly decreased because of the declining trend in solar radiation. On average, crop water demand was decreased by 2.3 mm a^?1 for wheat and 1.8 mm a^?1 for maize if changes in crop variety were not considered. Simulated potential crop yields under fully irrigated condition declined about 45.3 kg ha^?1 a^?1 for wheat and 51.4 kg ha^?1 a^?1 for maize at the northern sites, Beijing and Tianjin. They had no significant changes in the southern sites, Jinan and Zhengzhou. Irrigation, fertilization development and crop variety improvement are main factors to contribute to the increase in actual crop yield for the wheat–maize double cropping system, contrasted to the decline in the potential crop yield. Further research on how the improvement in crop varieties and management practices can counteract the impact of climatic change may provide insight into the future sustainability of wheat–maize double crop rotations in the NCP.     

Climate tendencies of changes in multiyear sea ice thickness in the Arctic Basin (1970–2005)

The area integral of the sea ice thickness in the Arctic Basin is estimated from the measurements of sea ice surface fluctuations at drift-ice stations. The 1970–1990 linear trend is indicative of an approximately 10-cm reduction in the average sea ice thickness over the entire Arctic Basin, which makes 3% of the average ice thickness (about 3 m). Seasonal changes made 40 cm. The amplitude of variations of the average ice thickness in that period is 20 cm with a period of changes of approximately 6–8 years. The observations were interrupted during 1991–2003 and then resumed in 2004. During 1990–2005, the old ice thickness over the entire Arctic Basin decreased, on average, by 110 cm.     

Spatio-temporal variations of optical properties of aerosols in East Asia measured by MODIS and relation to the ground-based mass concentrations observed in central Korea during 2001∼2010

Long-term variations and trends of atmospheric aerosols in the East Asian region were analyzed by using aerosol optical depth (AOD or τ), and ångström exponent (AE or α) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) from 2001 to 2010. The increased emission of anthropogenic fine aerosols in east China resulted in the high AOD in this region during summer. The steady increasing emission of anthropogenic fine aerosols caused an increasing trend of AOD in east China, and the large-scale transport of sandstorms and smoke plume caused by forest fires affected intense inter-annual variations of AOD in the East Asian region. While in the central part of South Korea, located in the lee side of the East Asian continent, AE tended to rise to a level higher than in east China, the ground-based mass concentrations continued to decline. A noticeable decrease of PM10 mass concentration in spring and winter in central Korea is most likely attributable to decreases in sandstorms in the source region of East Asia. However, the ratio of PM2.5 mass concentration to PM10 increases overall with a high level in summer. Aerosol types were classified into dust, smoke plume, and sulphate by using satellite data over Cheongwon in central Korea. The columnar AOD, with different aerosol types, was compared with the ground-based mass concentrations at Cheongwon, and the relatively high level of the correlations presented between PM2.5 and AOD produced in sulphate. Growth and increases of fine hygroscopic aerosols generated as gas-to-particle conversion particularly in summer contribute to increases of columnar AOD in the East Asian region.     

Tracing glacier wastage in the Northern Tien Shan (Kyrgyzstan/Central Asia) over the last 40 years

The status and dynamics of glaciers are crucial for agriculture in semiarid parts of Central Asia, since river flow is characterized by major runoff in spring and summer, supplied by glacier- and snowmelt. Ideally, this coincides with the critical period of water demand for irrigation. The present study shows a clear trend in glacier retreat between 1963 and 2000 in the Sokoluk watershed, a catchment of the Northern Tien Shan mountain range in Kyrgyzstan. The overall area loss of 28% observed for the period 1963–2000, and a clear acceleration of wastage since the 1980s, correlate with the results of previous studies in other regions of the Tien Shan as well as the Alps. In particular, glaciers smaller than 0.5 km² have exhibited this phenomenon most starkly. While they registered a medium decrease of only 9.1% for 1963–1986, they lost 41.5% of their surface area between 1986 and 2000. Furthermore, a general increase in the minimum glacier elevation of 78 m has been observed over the last three decades. This corresponds to about one-third of the entire retreat of the minimum glacier elevation in the Northern Tien Shan since the Little Ice Age maximum.     

Dust transport and palaeoclimate during the Oldest Dryas in Central Europe — implications from varves (Lake Constance)

This paper evaluates evidence for seasonal loess deposits in peri-Alpine Lake Constance at the end of the last Glacial (Oldest Dryas chronozone). The usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed. The sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves (i.e. annual rhythmites) comprising alternations of loess and glacial silt and clay. The laminae are mostly less than 1 mm thick and include from bottom to top: (1) a matrix of well-sorted, non-graded fine yellow silt with sand-size intraclasts, (2) coarsening-upward grey silt with a cap of fining-upward silt to clay. The latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits (silt and clay, respectively). We propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits. Volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake, indicating an easterly palaeowind direction. Deposition of loess in the lake occurred regularly at the beginning of each annual cycle, suggesting that the palaeowinds were associated with winter and/or spring conditions. Two transport scenarios are suggested to explain the sand grains scattered in this deep-water lacustrine record. 1. The grains may have been transported as bedload over the annual winter ice-cover of the lake under moderate wind strengths, frozen into the ice, and released for deposition during spring melt. 2. The sand grains were blown directly out onto the lake water by very strong winds during spring. The first scenario is contrary to the general view that loess was transported during summer, and that loess deposits thus reflect summer conditions only. Loess input to the lake shows a transitional decrease after ca. 14.3 kyr BP and cessation at ca. 14 kyr BP, probably as a result of a change of wind behaviour, increased humidity and/or vegetational changes during the Oldest Dryas in central Europe.This paper was presented at Clima Locarno 90, the International Conference on Past and Present Climate Dynamics: Reconstruction of Rates of Change, held in Locarno, Switzerland, September 24 to 28, 1991, supported by a grant from the Swiss Academy of Sciences. It was convened jointly by the Swiss National Climate Program - ProClim, the Swiss Committee for the IGBP, the Swiss COL, the Swiss SCOPE Committee, and the Swiss CCA. Guest editor for the papers published following the conference is Dr. K. Kelts (see also Climate Dynamics 6:3/4, Jan. 1992)     

Impact of the winter North Atlantic Oscillation (NAO) on the Western Pacific (WP) pattern in the following winter through Arctic sea ice and ENSO: part I—observational evidence

Climate Dynamics - On the basis of a 51-year statistical analysis of reanalysis data, we propose for the first time that the positive phase of the Western Pacific (WP) pattern in the winter is...     

Analysis of measurement data on carbon dioxide concentration in the near-ice surface atmosphere at North Pole-35 drifting ice station (2007–2008)

Significant CO₂ concentration disturbances with an amplitude of 150 ppm are observed in October–November in the region of North Pole-35 drifting ice station over the continental slope of the Arctic Ocean. A local maximum of the CO₂ concentration disturbances is observed in April; it is connected with a change in the regime of the sea ice deformation at that time of the year in the western Arctic basin. Changes in the CO₂ concentration have oscillations at the frequency of oceanic tides. Several episodes of the initial phase of CO₂ release into the near-ice surface atmosphere in October 2007 are recorded. The CO₂ amount released into the atmosphere as a result of ice formation in the Arctic Ocean is a significant quantity in the total balance of the CO₂ release on the global scale and accounts for approximately 30% of the anthropogenic release of CO₂ per year.     

Is the storminess in the Twentieth Century Reanalysis really inconsistent with observations? A reply to the comment by Krueger et al. (2013b)

In a recent study of trends and low frequency variability of extra-tropical cyclone activity in the ensemble of Twentieth Century Reanalyses, we concluded that “For the North Atlantic-European region and southeast Australia, the 20CR cyclone trends are in agreement with trends in geostrophic wind extremes derived from in-situ surface pressure observations”. This conclusion has been challenged by Krueger et al. (Clim Dyn, submitted, 2013b), because a recent study (doi:10.1175/JCLI-D-12-00309.1, by the same lead author) comparing annual 95th percentiles (P95) of geostrophic wind speed (geo-wind) derived from surface pressure observations and from the 20CR found that “20CR-geostrophic storminess deviates to a large extent from the observation-based curve” in the period prior to 1950. In this reply, we show that our conclusion is valid; and we clarify that several factors contribute to the reported inconsistencies between the 20CR and observation-based geo-wind extremes. These include the choice of index that is used to represent the temporal variation of extremes (e.g., annual vs. seasonal percentiles), the use of different sampling intervals (6-hourly vs. 3-hourly), and the presence of very large errors in the observations that were not identified, corrected, or excluded in any of the previous studies of observation-based geo-wind extremes. We show that the time series of consecutive seasonal P95 geo-winds derived from the observations and from 20CR are in good agreement back to about 1893, with some deviation earlier when the observations (especially digitized data) remain limited and are more uncertain. We find that the correlation between the 20CR and observation-based geo-wind extremes (P95) time series for the full 134-year record is highly significant statistically, with and without the correction or exclusion of the newly identified erroneous SLP values. The agreement between 20CR and observations is further improved after the correction or exclusion of these erroneous values.     

Climate condition of the significant precipitation decrease over the middle-eastern region of Inner Mongolia, China in recent 10 years (2001–2010)

Compared to the 50-year mean climatological value (1961–2010), the precipitation of middle-eastern Inner Mongolia exhibited a significant decrease during the past 10 years (2001–2010). To identify the climatic causes, a comprehensive investigation was conducted by inspecting climatic factors from this 50-year period, which appear to work together in connecting closely to the precipitation. Significant positive correlations with precipitation were found in sea level pressure (SLP) difference between the area of (30° N–20° S; 50–160° E) and the northeastern Pacific Ocean, between the Northern Atlantic and the northeastern Pacific Oceans, and sea surface temperature difference between the northeastern and northwestern Pacific in the previous year, while negative connections were found in the 500-hPa temperature difference between the Antarctic and the belt region around 60° S. During the period of 2001–2010, East Asia was prevailingly controlled by a huge high, which was regarded as one of unfavorable factors for producing rain or snow. Other factors were the enlarged 500 hPa temperature differences between the Antarctic and the zones around 60° S and the Equator, the negative SLP difference between the East Asia, northern Atlantic, and Pacific Oceans. Finally, the unique wind flows and associated moisture transports also played a key role in the precipitation reduction for the first decade of the twenty-first century.     

Influence of climatic factors on the low yields of spring barley and winter wheat in Southern Moravia (Czech Republic) during the 1961–2007 period

The paper aims to study the variability of spring barley and winter wheat yields, the most important crops in the Czech Republic, with respect to the variability of weather and climatic factors. Yields of both crops have been studied for 13 districts in Southern Moravia for the 1961–2007 period. From detrended series of spring barley and winter wheat yields, years with very low (lower than the mean minus a 2.5-multiple of the standard deviation) and extremely low (interval given by the mean minus a 1.5- and 2.5-multiple of the standard deviation) yields were selected. Years in which at least one of the districts had extremely low/very low yields were further analyzed. From 10 such years selected separately for spring barley and winter wheat, six of them agreed for both crops. Extreme years were studied using NUTS4-level yield data with respect to temperature, precipitation, the self-calibrated Palmer Drought Severity Index (scPDSI), snow cover, frost patterns, and the onset and duration of select phenophases. Extremely/very low barley yields in 1993, 2000, and 2007 were related to high April–June (AMJ) temperatures, low AMJ precipitation totals, and negative AMJ scPDSI (indicating drought) with an earlier onset of flowering and full ripeness and shorter intervals from tillering to flowering and from flowering to full ripeness compared to the entire 1961–2007 mean. As for extremely/very low winter wheat yields, in addition to the previously mentioned factors, winter patterns also played an important role, particularly the occurrence of severe frosts with a coinciding lack of snow cover and a long-lasting snow cover (in highlands), indicating that low yields are the result of not only one unfavorable factor but a combination of several of them.     

The Role of In Situ Photochemistry in the Control of Ozone during Spring at the Jungfraujoch (3,580 m asl) – Comparison of Model Results with Measurements

A photochemical box model has been used to model themeasured diurnal ozone cycle in spring at Jungfraujochin the Swiss Alps. The comparison of the modelleddiurnal ozone cycle with the mean measured diurnalozone cycle in spring, over the period 1988–1996,shows a good agreement both with regard to the shapeand amplitude. Ozone concentrations increase duringthe daytime and reach a maximum at about 16:00–17:00(GMT) in both the modelled and the mean observed ozonecycle, indicative of net ozone production during thedaytime at Jungfraujoch in spring. The agreement isbetter when the modelled ozone cycle is compared withthe mean measured diurnal cycle (1988–1996) filteredfor north-westerly winds >5 m/s (representative ofregional background conditions at Jungfraujoch). Inaddition to ozone, the modelled diurnal cycle of[HO₂] + [CH₃O₂] also shows rather goodagreement with the mean diurnal cycle of the peroxyradicals measured during FREETEX '96, a FREETropopsheric Experiment at Jungfraujoch in April/May1996. Furthermore, this mean diurnal cycle of the sumof the peroxy radicals measured during FREETEX '96 isused to calculate, using steady-state expressions, therespective diurnal cycle of the OH radical. Thecomparison of the OH diurnal cycle, calculated fromthe peroxy radical measurements during FREETEX '96,with the modelled one, reveals also good agreement.The net ozone production rate during the day-time is0.27 ppbv h^-1 from the model, and 0.13 ppbvh^-1 from the observations during FREETEX '96. Theobservations and model results both suggest that thediurnal ozone variation in spring at Jungfraujoch isprimarily of photochemical origin. Furthermore, theobserved and modelled positive net ozone productionrates imply that tropospheric in situphotochemistry contributes significantly to theobserved high spring ozone values in the observedbroad spring-summer ozone maximum at Jungfraujoch.     

Net air�Csea surface heat flux during 1984�C2004 over the North Pacific and North Atlantic oceans (10��N�C50��N): annual mean climatology and trend

Using the Objectively Analyzed air?Csea Fluxes dataset (and also the National Oceanography Centre Southampton Flux Dataset v2.0), we examined both the annual mean climatology and trend of net air?Csea surface heat flux (Q _net) for 1984?C2004 over the North Pacific and North Atlantic oceans (10°N?C50°N). The annual mean Q _net climatology shows that oceans obtain the positive Q _net over much of the North Pacific and North Atlantic oceans. Exceptions are the regions of western boundary currents (WBCs) including the Kuroshio and its extension off Japan and the Gulf Stream off the USA and its extension, where oceans release lots of heat into the atmosphere, mainly ascribed to the large surface turbulent heat loss. The statistically significant negative Q _net trends occurred in the WBCs, while the statistically significant positive Q _net trends appeared in the central basins of Northern Subtropical Oceans (CNSOs) including the central basin of Northern Subtropical Pacific and the central basin of Northern Subtropical Atlantic. These indentified Q _net trends, which are independent of both El Ni?o-Southern Oscillation (ENSO) and ENSO Modoki but closely related to global warming forcing, are predominately due to the statistically significant surface latent heat (LH) trends. Over the WBCs, the positive LH trends are mainly induced by the sea surface temperature increasing, indicating the ocean forcing upon overlying atmosphere. In contrast, over the CNSOs, the negative LH trends are mainly caused by the near-surface air specific humidity increasing, indicative of an oceanic response to overlying atmospheric forcing.     

Precipitation chemistry and ozone and sulfate concentrations in the ocean atmosphere observed by multi-year cruising in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September

A comprehensive study on the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere was carried out for the data sets in 1990’s. It is important to study the atmospheric situation over the past years as well as the latest, especially in the East Asian region where emission amount of anthropogenic air pollutants have increased year by year due to rapid economic growth. The survey was conducted for 5 years in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September in 1990’s. The purpose of the survey was to study and understand the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere comprehensively in one project. Rainfall over the ocean was insufficiently neutralized. Gas and aerosol over the ocean were mature, i.e., well-mixed, during the period of the transportation. The characteristic latitudinal dependence was observed in the tropospheric ozone concentration, namely, higher in the southern hemisphere and lower in the northern hemisphere (approximately 25 ppb in the 10–40°S region and 5–15 ppb in the 20–40°N region). On the other hand, high concentrations of tropospheric ozone of over 30 ppb were observed in the northern hemisphere, which was attributable to the long-range transportation. The TSP concentration was approximately under the level of 40 μg m^?3 irrespectively of the latitude; in contrast, the nss-SO₄ ^2- concentration showed a clear latitudinal dependence, i.e., higher in the northern hemisphere and lower in the southern hemisphere. The background levels of the nss-SO₄ ^2- concentration were approximately 0.5 μg m^?3 in the 10–40°S region and 2–3 μg m^?3 and 4–5 μg m^?3 in the 0–20°N and 20–40°N regions, respectively.