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71.
Hironori Iwai Yasuhiro Murayama Shoken Ishii Kohei Mizutani Yuichi Ohno Taichiro Hashiguchi 《Boundary-Layer Meteorology》2011,141(1):117-142
To study the wind field within the atmospheric boundary layer over the Tokyo metropolitan area, Doppler lidar observations
were made 45 km north of Sagami Bay and 30 km west of Tokyo Bay, from 14 May to 15 June 2008. Doppler lidar on 27 May 2008
observed the vertical and horizontal wind structure of a well-developed sea-breeze front (SBF) penetrating from Sagami Bay.
At the SBF, a strong updraft (maximum w approximately equal to 5 m s−1) was formed with a horizontal scale of about 500 m and vertical scale of 2 km. The spatial relationship between the strong
updraft over the nose of the SBF and prefrontal thermal suggests that the strong updraft was triggered by interaction between
the SBF and the thermal. After the updraft commenced, a collocated ceilometer observed an intense aerosol backscatter up to
2 km above ground level. The observational results suggest that the near-surface denser aerosols trapped in the head region
of the SBF escaped from the nose of the SBF and were then vertically transported up to the mixing height by the strong updraft
at the SBF. This implies that these phenomena occurred not continuously but intermittently. The interaction situations between
the SBF and prefrontal thermal can affect the wind structure at the SBF and the regional air quality. 相似文献
72.
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74.
Jung-Yoon Kang Taichu Y. Tanaka Masao Mikami Soon-Chang Yoon 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(1):57-65
There are few dust simulation studies for East Asian dust events that took place in the wintertime, when the surface conditions of the dust source region differ from those of the springtime. The soil water turns into ice when the temperature falls below freezing, and the ice might prohibit wind erosion by increasing the binding strength between soil particles. However, the contribution of frozen soil to reducing dust outbreaks remains unclear. This study investigates the effect of frozen soil on dust emission through a case study of a severe wintertime East Asian dust event that originated on 23 and 24 December 2009 in Southern Mongolia and Inner Mongolia and reached Korea on 25 and 26 December 2009 using WRF/Chem with a new dust emission scheme. Model simulations with and without the effect of frozen soil were conducted. A temperature below 0°C and relative soil saturation exceeding 40% were used for frozen soil criteria, and the frozen soil was prohibited from emitting dust. The dust concentrations derived from the simulation without the effect of frozen soil were about three times higher than the observed PM10 concentrations, while the results from the simulation with the frozen-soil effect were quite similar to those of the observation data. The simulation of the wintertime East Asian dust event with the frozen-soil effect improved the model representation. The sensitivity tests for frozen soil indicate that the criteria of frozen soil used in this study are appropriate for this case study. 相似文献
75.
Lara M. Kueppers Mark A. Snyder Lisa C. Sloan Dan Cayan Jiming Jin Hideki Kanamaru Masao Kanamitsu Norman L. Miller Mary Tyree Hui Du Bryan Weare 《Global and Planetary Change》2008,60(3-4):250-264
In the western United States, more than 79 000 km2 has been converted to irrigated agriculture and urban areas. These changes have the potential to alter surface temperature by modifying the energy budget at the land–atmosphere interface. This study reports the seasonally varying temperature responses of four regional climate models (RCMs) – RSM, RegCM3, MM5-CLM3, and DRCM – to conversion of potential natural vegetation to modern land-cover and land-use over a 1-year period. Three of the RCMs supplemented soil moisture, producing large decreases in the August mean (− 1.4 to − 3.1 °C) and maximum (− 2.9 to − 6.1 °C) 2-m air temperatures where natural vegetation was converted to irrigated agriculture. Conversion to irrigated agriculture also resulted in large increases in relative humidity (9% to 36% absolute change). Modeled changes in the August minimum 2-m air temperature were not as pronounced or consistent across the models. Converting natural vegetation to urban land-cover produced less pronounced temperature effects in all models, with the magnitude of the effect dependent upon the preexisting vegetation type and urban parameterizations. Overall, the RCM results indicate that the temperature impacts of land-use change are most pronounced during the summer months, when surface heating is strongest and differences in surface soil moisture between irrigated land and natural vegetation are largest. 相似文献
76.
Makoto Naoi Masao Nakatani Shigeki Horiuchi Yasuo Yabe Joachim Philipp Thabang Kgarume Gilbert Morema Sifiso Khambule Thabang Masakale Luiz Ribeiro Koji Miyakawa Atsushi Watanabe Kenshiro Otsuki Hirokazu Moriya Osamu Murakami Hironori Kawakata Nana Yoshimitsu Anthony Ward Ray Durrheim Hiroshi Ogasawara 《Pure and Applied Geophysics》2014,171(10):2665-2684
We investigated frequency-magnitude distribution (FMD) of acoustic emissions (AE) occurring near an active mining front in a South African gold mine, using a catalog developed from an AE network, which is capable of detecting AEs down to M W ?5. When records of blasts were removed, FMDs of AEs obeyed a Gutenberg?Richter law with similar b values, not depending on post-blasting time from the initial 1-min interval through more than 30 h. This result denies a suggestion in a previous study (Richardson and Jordan Bull Seismol Soc Am, 92:1766–1782, 2002) that new fractures generated by blasting disturb the size distribution of background events, which they interpreted as slip events on existing weak planes. Our AE catalog showed that the GR law with b ~ 1.2 was valid between M W ?3.7 and 0 for AEs around the mining front. Further, using the mine’s seismic catalog, which covers a longer time period of the same area, we could extend the validity range of the GR law with the same b value up to M W 1. 相似文献
77.
Tatsuya Hayashi Yoshihiro Tanimura Yoshihiro Kuwahara Masao Ohno Mami Mampuku Rie Fujii Harutaka Sakai Toshiro Yamanaka Takeshi Maki Masao Uchida Wataru Yahagi Hideo Sakai 《Quaternary Research》2009,72(3):377-387
Variations in fossil diatom assemblages and their relationship with global and Indian monsoon climate changes for the last 600,000 yr were investigated using a core of ancient lake (Paleo-Kathmandu Lake) sediments drilled at the Kathmandu Basin, Nepal Himalaya. Chronological scales of the core were constructed by tuning pollen wet and dry index records to the SPECMAP δ18O stack record. Examinations of biogenic silica contents and fossil diatom assemblages revealed that variations in productivity and compositions of diatom assemblages were closely linked with global and Indian monsoon climate changes on glacial and interglacial time scales. When summer monsoonal rainfall increased during interglacials (interstadials), diatom productivity increased because of increased inputs of terrestrial nutrients into the lake. When summer monsoonal rainfall reduced and/or winter monsoonal aridification enhanced during glacials (stadials), productivity of the diatoms decreased and lake-level falling brought about changes in compositions of diatom assemblages. Monospecific assemblages by unique Cyclotella kathmanduensis and Puncticulata versiformis appeared during about 590 to 390 ka. This might be attributed to evolutionary fine-tuning of diatom assemblages to specific lake environmental conditions. Additionally, low-amplitude precessional variations in monsoon climate and less lake-level changes may have also allowed both species to dominate over the long periods. 相似文献
78.
Nobuki Kame Satoshi Fujita Masao Nakatani Tetsuya Kusakabe 《Pure and Applied Geophysics》2015,172(8):2237-2246
Recently Nagata et al. (J Geophys Res 117:B02314, 2012) have proposed a new version of rate- and state-dependent friction law (RSF) that seems to have eventually resolved all the previously known discrepancies in the existing RSFs from laboratory observations. The values of a and b, empirical RSF parameters determined by fitting the same laboratory experiments, have been revised to be five times greater and a newly noticed weakening effect by shear stress with a coefficient c has been introduced. By using this revised RSF, we reinvestigated a problem of 2D quasi-static nucleation on faults. A crack-like nucleation-zone expansion known for the ‘aging’ version of RSF is not sustainable with the ‘Nagata’ law, which is understandable as the Nagata law does not produce a slip-weakening distance proportional to the involved strength reduction, an aging law’s feature that contradicts laboratory observations. The later stage of Nagata-law nucleation shows localization of quasi-static slip within a limited spatial extent, but the localization is much milder than that predicted by the ‘slip’ version of RSF. With an appropriate c parameter of the Nagata law, the nucleation size seems to be reduced only by a factor from that of the aging law. 相似文献
79.
Kazumasa Iwai Masumi Shimojo Shinichiro Asayama Tetsuhiro Minamidani Stephen White Timothy Bastian Masao Saito 《Solar physics》2017,292(1):22
The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is \(7700 \pm 310~\mbox{K}\) at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations. 相似文献
80.