Anomalous summer climate in China influenced by the tropical Indo-Pacific Oceans

Possible influences of three coupled ocean–atmosphere phenomena in the Indo-Pacific Oceans, El Niño, El Niño Modoki and the Indian Ocean Dipole (IOD), on summer climate in China are studied based on data analysis for the summers of 1951–2007. Partial correlation/regression analysis is used to find the influence paths through the related anomalous mid- and low-level tropospheric circulations over the oceanic region and East Eurasia, including the western North Pacific summer monsoon (WNPSM). Among the three phenomena, El Niño Modoki has the strongest relationship with the WNPSM. When two or three phenomena coexist with either positive or negative phase, the influences exerted by one phenomenon on summer climate in different regions of China may be enhanced or weakened by other phenomena. In 1994 when both El Niño Modoki and IOD are prominent without El Niño, a strong WNPSM is associated with severe flooding in southern China and severe drought in the Yangtze River Valley (YRV). The 500 hPa high systems over China are responsible for heat waves in most parts of China. In 1983 when a strong negative phase of El Niño Modoki is accompanied by moderate El Niño and IOD, a weak WNPSM is associated with severe flooding in the YRV and severe drought in southern China. The 500 hPa low systems over China are responsible for the cold summer in the YRV and northeastern China. For rainfall, the influence path seems largely through the low-level tropospheric circulations including the WNPSM. For temperature, the influence path seems largely through the mid-level tropospheric circulations over East Eurasia/western North Pacific Ocean.     

The interannual precipitation variability in the southern part of Iran as linked to large-scale climate modes

The interannual variation of precipitation in the southern part of Iran and its link with the large-scale climate modes are examined using monthly data from 183 meteorological stations during 1974–2005. The majority of precipitation occurs during the rainy season from October to May. The interannual variation in fall and early winter during the first part of the rainy season shows apparently a significant positive correlation with the Indian Ocean Dipole (IOD) and El Ni?o-Southern Oscillation (ENSO). However, a partial correlation analysis used to extract the respective influence of IOD and ENSO shows a significant positive correlation only with the IOD and not with ENSO. The southeasterly moisture flux anomaly over the Arabian Sea turns anti-cyclonically and transport more moisture to the southern part of Iran from the Arabian Sea, the Red Sea, and the Persian Gulf during the positive IOD. On the other hand, the moisture flux has northerly anomaly over Iran during the negative IOD, which results in reduced moisture supply from the south. During the latter part of the rainy season in late winter and spring, the interannual variation of precipitation is more strongly influenced by modes of variability over the Mediterranean Sea. The induced large-scale atmospheric circulation anomaly controls moisture supply from the Red Sea and the Persian Gulf.     

一个基于模拟退火法的陆面数据同化算法

陆面数据同化系统是近年来兴起的新领域。我们发展了一个实验型的陆面数据同化方案,它使用一种启发式优化算法——模拟退火法极小化目标泛函。与变分法和Kalman滤波方法比较,这一算法具有独立于目标泛函的优点,可处理模型和观测算子的非线性和不连续性。使用GAME—Tibet实验中的土壤水分观测值进行单点数值实验,成功地将土壤水分观测同化到陆面过程模型SiB2中。结果表明,与不进行同化相比,土壤水分的估计值有较大改善。     

Oxygen isotopic distribution in an amoeboid olivine aggregate from the Allende CV chondrite: Primary and secondary processes

The oxygen isotopic distribution in an amoeboid olivine aggregate (AOA), TTA1-02, from the Allende CV3 chondrite has been determined by secondary ion mass spectrometry. The irregular shaped TTA1- 02 (5×3mm) consists mostly of olivine grains of ca. 5μm in diameter. Olivine grains of Mg-rich (Fo₉₅) and Fe-rich (Fo₆₀) composition are in direct contact with each other, with a sharp compositional boundary. Oxygen isotopic compositions of Fe-rich olivine grains are ¹⁶O-poor (Δ¹⁷O ≅ −5‰), whereas Mg-rich olivine is ¹⁶O-rich (Δ¹⁷O ≅ −25‰). Several Al-rich inclusions (<ca. 500 μm in diameter) are enclosed by olivine grains in the AOA. Oxygen isotopic compositions of spinel and fassaite in Al-rich inclusions are ¹⁶O-rich (Δ¹⁷O ≅ −20‰), whereas those of anorthite, nepheline and phyllosilicate are ¹⁶O-poor (Δ¹⁷O ≅ −5‰). We propose the following sequence of events during the formation of AOAs in the Allende meteorite: 1) Formation of Al-rich inclusions with ¹⁶O-rich oxygen isotopic composition; 2) Accretion of Mg-rich olivine grains with ¹⁶O-rich oxygen isotopic composition around Al-rich inclusions; 3) Accretion into parent body; and 4) Aqueous alteration in the parent body, which led to crystallization of ¹⁶O-poor minerals, Fe-rich olivine, anorthite, nepheline, and phyllosilicate. This is reflecting reactions among primary ¹⁶O-rich AOA minerals and aqueous fluid having ¹⁶O-poor oxygen isotopic composition. Fe-rich olivine grains precipitated from aqueous fluids, which partially dissolved pre-existing Mg-rich olivine grains. Sintering and Mg-Fe diffusion occurred during thermal metamorphism. Anorthite, nepheline and phyllosilicate in Al-rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage.     

On the Ningaloo Niño/Niña

Using both observational and reanalysis data, evolution processes of a regional climate phenomenon off Western Australia named recently “Ningaloo Niño (Niña)” are studied in detail. It is also shown that the Ningaloo Niño (Niña) has significant impacts on the precipitation over Australia. The Ningaloo Niño (Niña), which is associated with positive (negative) sea surface temperature (SST) anomalies and atmospheric anomalies off the western coast of Australia, peaks during austral summer and is classified into two types based on the difference in the evolution process. The first type called a locally amplified mode develops through an intrinsic unstable air–sea interaction off the western coast of Australia; an anomalous cyclone (anticyclone) generated by positive (negative) SST anomalies forces northerly (southerly) alongshore wind anomalies, which induce coastal downwelling (upwelling) anomalies, and enhance the positive (negative) SST anomalies further. The second type called a non-locally amplified mode is associated with coastally trapped waves originating in either the western tropical Pacific, mostly related to El Niño/Southern Oscillation, or the northern coast of Australia. Positive (negative) SST anomalies in both modes are associated with an anomalous low (high) off the western coast of Australia. The sea level pressure (SLP) anomalies in the locally amplified mode are regionally confined with a cell-like pattern and produce a sharp offshore pressure gradient along the western coast of Australia, whereas those in the non-locally amplified mode tend to show a zonally elongated pattern. The difference is found to be related to conditions of the continental SLP modulated by the Australian summer monsoon and/or the Southern Annular Mode.     

Four Decadal Ocean-Atmosphere Modes in the North Pacific Revealed by Various Analysis Methods

Various statistical methods (empirical orthogonal function (EOF), rotated EOF, singular value decomposition (SVD), principal oscillation pattern (POP), complex EOF (CEOF) and joint CEOF) were applied to low-pass filtered (>7 years) sea surface temperature (SST), subsurface temperature and 500 hPa geopotential height in order to reveal standing and propagating features of decadal variations in the North Pacific. Four decadal ocean-atmosphere covariant modes were found in this study. The first mode is the well-known ENSO-like mode associated with the “Pacific-North American” atmospheric pattern, showing SST variations reversed between the tropics and the extratropics. In the western tropical Pacific, subsurface temperature variations were found to be out of phase with the SST variations. The other three modes are related to the oceanic general circulation composed of the subtropical gyre, the Alaskan gyre and the subpolar gyre, respectively. The 1988/89 event in the northern North Pacific was found to be closely associated with the subtropical gyre mode, and the atmospheric pattern associated with this mode is the Arctic Oscillation. An upper ocean heat budget analysis suggests that the surface net heat flux and mean gyre advection are important to the Alaskan gyre mode. For the subpolar gyre mode, the mean gyre advection, local Ekman pumping and surface net heat flux play important roles. Possible air-sea interactions in the North Pacific are also discussed. The oceanic signals for these decadal modes occupy a thick layer in the North Pacific, so that accumulated heat content may in turn support long-term climate variations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mid-latitude horizontal electric fields in the stratosphere during magnetically disturbed periods

The horizontal electric field has been measured with balloons over the Pacific Ocean near the Sanriku Coast in Japan. By comparing the electric-field data obtained during magnetically disturbed periods, 16–17 October 1973, 6–7 October 1975 and 3–4 October 1977, with IMF B_z, auroral zone AU and AL, equatorial Dst and $\text{Δ(Dst)}\text{Δt}$, mid-latitude magnetic fields (H, D, Z at Kakioka), and the ionospheric electron density (?₀F2 at Kokubunji), it is found that the observed electric fields of about 9 mVm^?1 made the clockwise rotation during the growth and recovery stages of the magnetospheric substorms. Relations between high and middle latitude ionospheres and between the magnetosphere and the ionosphere are discussed in relation to the origin and propagation of these electric fields.     

Comparison of upper ocean thermal conditions in the western North Pacific between two pentads: 1938–42 and 1978–82

In order to understand long-term changes in the temperature structure of the upper western North Pacific, we compared thermal conditions in two pentads, 1938–42 (P34) and 1978–82 (P78). The 1938–42 data were taken mostly by the Japanese Imperial Navy in a series of hydrographic surveys. The 1978–82 data were mostly XBT data taken as part of the TRANSPAC program. For each pentad, the data were interpolated to a set of standard depths, put through quality control procedures and averaged on a 1^o×1^o grid. A large area of the central subtropical gyre was warmer during P78, while the southern subtropical gyre, in the area of the North Equatorial Current was warmer during P34. This suggests that the transports of the Kuroshio and North Equatorial currents were larger during P78. Properties of North Pacific subtropical mode water (NPSTMW) were compared between pentads. It was found that NPSTMW was thicker, more uniform in temperature and more confined geographically during P34. A greater thickness is shown to result from stronger wintertime cooling during P34. Changes in the geographic extent of NPSTMW probably result from reduced advection by the Kuroshio current system during P34. The reason for the reduced advection maybe the Kuroshio was in a large meander state for a larger fraction of the earlier pentad, which can cut off advection west of the Izu Ridge.     

Effects of clear-cutting,meteorological, and physiological factors on evapotranspiration in the Kamabuchi experimental watershed in northern Japan

This study investigated the effects of clear-cutting and the meteorological and physiological factors on forest evapotranspiration (ET), by using the water-budget method in the Kamabuchi experimental watershed (KMB; 38° 56′ 21″ N, 140° 15′ 58″ E) in northern Japan. Meteorological and discharge data collected during no-snow periods (from June to October) from 1939 were used to compare ET in three sub-watersheds: No. 1, where the forest had been left undisturbed, and No. 2 and No. 3, where Cryptomeria japonica was planted after clear-cutting. Paired watershed experiments revealed that clear-cutting caused ET to decrease by approximately 100 mm yr⁻¹, and this reduction continued for more than 20 years, even after C. japonica was planted. ET fluctuated similarly across all watersheds, regardless of clear-cutting or planting. This fluctuation is mainly caused by solar radiation and temperature. Intrinsic water-use efficiency (iWUE) calculated using δ¹³C of tree-ring cellulose in C. japonica increased due to elevated atmospheric CO₂ concentration. We estimated annual carbon fixation in a single tree as the annual net photosynthesis (A). Subsequently, transpiration (E) was calculated from the relationship between iWUE and A. The results showed that A and E per tree increased as the tree grew older; however, the trees' responses to increasing c_a suppress the increase in ET. Moreover, the fluctuation of ET from the watershed was small compared to the fluctuation of P during the observation periods because the increase and decrease in E and interception loss complemented each other.