Kimpei Ichiyanagi

Stable Isotope Variations in Precipitation and Moisture Trajectories on the Western Tibetan Plateau, China

ABSTRACT Observations at the Shiquanhe and Gaize meteorological stations provide data for analysis of δ18O and δD variations in precipitation for the Ngari (Ali) region, western Tibetan Plateau. Temperature controls δ18O in precipitation in this area. δ18O in precipitation positively correlates with air temperature at the Shiquanhe and Gaize stations, especially for precipitation weighted monthly mean δ18O. The δ18O – T correlation gradually strengthens from south to north across the western Tibetan Plateau and adjacent regions, with gradual weakening of southwest monsoon activity. The strongest correlation is found at Hetian. There is a poor correlation between δ18O and air temperature in the south at New Delhi because the moisture derives predominantly from the Indian Ocean in summer. The Ngari region exhibits a close relation between δD and δ18O in precipitation samples, similar to stations in adjacent regions and the global meteoric water line. The summer seasonal averaged deuterium excess (d) values increase gradually from south to north across western Tibetan and adjacent areas, resulting from southwest monsoon activity gradually weakening to the north.

Evaluation of groundwater quality and its suitability for drinking, domestic, and agricultural uses in the Banana Plain (Mbanga, Njombe, Penja) of the Cameroon Volcanic Line

Groundwater quality of the Banana Plain (Mbanga, Njombe, Penja—Cameroon) was assessed for its suitability for drinking, domestic, and agricultural uses. A total of 67 groundwater samples were collected from open wells, springs, and boreholes. Samples were analyzed for physicochemical properties, major ions, and dissolved silica. In 95% of groundwater samples, calcium is the dominant cation, while sodium dominates in 5% of the samples. Eighty percent of the samples have HCO3 as major anion, and in 20%, NO3 is the major anion. Main water types in the study area are CaHCO3, CaMgHCO3, CaNaHCO3, and CaNaNO3ClHCO3. CO2-driven weathering of silicate minerals followed by cation exchange seemingly controls largely the concentrations of major ions in the groundwaters of this area. Nitrate, sulfate, and chloride concentrations strongly express the impact of anthropogenic activities (agriculture and domestic activities) on groundwater quality. Sixty-four percent of the waters have nitrate concentrations higher than the drinking water limit. Also limiting groundwater use for potable and domestic purposes are contents of Ca2+, Mg2+ and HCO3− and total hardness (TH) that exceed World Health Organization (WHO) standards. Irrigational suitability of groundwaters in the study area was also evaluated, and results show that all the samples are fit for irrigation. Groundwater quality in the Banana Plain is impeded by natural geology and anthropogenic activities, and proper groundwater management strategies are necessary to protect sustainably this valuable resource.

Spatial analysis of annual mean stable isotopes in precipitation across Japan based on an intensive observation period throughout 2013

ABSTRACT Spatial distribution of annual mean stable isotopes in precipitation (δ18O, δ2H) was observed at 56 sites across Japan throughout 2013. Annual mean δ18O values showed a strong latitude effect, from −12.4 ‰ in the north to −5.1 ‰ in the south. Annual mean d-excess values ranged from 8 to 21 ‰, and values on the Sea of Japan side in Northern and Eastern Japan were relatively higher than those on the Pacific Ocean side. The local meteoric water line (LMWL) and isotope effects were based on the annual mean values from all sites across Japan as divided into distinct regions: the Sea of Japan side to the Pacific Ocean side and Northeastern to Southwestern Japan. Slopes and intercepts of LMWL ranged from 7.4 to 7.8 and 9.8 to 13.0, respectively. Slopes for latitude, altitude, and temperature effects ranged from −0.27 to −0.48 ‰/°N, −0.0034 to −0.0053 ‰/m, and 0.36 to 0.46 ‰/°C, respectively, with statistically significance at the 99 % level. However, there was no precipitation amount effect. From the result of a multiple regression analysis, the empirical formula of annual mean δ18O in precipitation from latitude and altitude for all sites across Japan was determined to be δ18 O = −0.348 (LAT) − 0.00307 (ALT) + 4.29 (R2 = 0.59). Slopes for latitude and altitude ranged from − 0.28 to − 0.51, and − 0.0019 to − 0.0045, respectively. Even though site distribution was uneven, these equations are the first trial estimation for annual mean stable isotopes in precipitation across Japan. Further research performed on the monthly basis is required to elucidate factors controlling the spatiotemporal variability of stable isotopes in precipitation across Japan.

Large-scale vapor transport of remotely evaporated seawater by a Rossby wave response to typhoon forcing during the Baiu/Meiyu season as revealed by the JRA-55 reanalysis

The modulation of large-scale moisture transport from the tropics into East Asia in response to typhoon-induced heating during the mature stage of the Baiu/Meiyu season is investigated using the Japanese 55-year reanalysis (JRA-55), aided by a Rayleigh-type global isotope circulation model (ICM). We highlighted the typhoons that migrate northward along the western periphery of the North Pacific subtropical high and approach the vicinity of Japan. Anomalous anticyclonic circulations to the northeast and southeast of typhoons and cyclonic circulation to their west become evident as they migrate toward Japan, which could be interpreted as a Rossby wave response to typhoon heating. These resultant anomalous circulation patterns form moisture conveyor belt (MCB) stretching from the South Asian monsoon region to East Asia via the confluence region between the monsoon westerlies and central Pacific easterlies. The ICM results confirm that the well-defined nature of the MCB leads to penetration of the Indian Ocean, South China Sea, Philippine Sea, and Pacific Ocean water vapors into western Japan. The typhoons have the potential to accumulate large amounts of moisture from distant tropical oceans through the interaction of their Rossby wave response with the background flow. In the case of a typical typhoon, the total precipitable water around the typhoon center as it approaches Japan is maintained by the moisture supply from distant oceans rather than from the underlying ocean, which indirectly leads to the occurrence of heavy rainfall over western Japan.

Application of Continuous 222Rn Monitor with Dual Loop System in a Small Lake

To estimate the spatial distribution of groundwater discharge from the bottom of a small lake of Kumamoto in Japan, we applied continuous radon measurements with a dual loop system and verified the results obtained using the radon method by visual diving surveys. Time-shifting correction in the dual-loop system is reasonable to obtain the true radon activity in water. Distributions of radon activity and water temperature in the study area reveal the effects on groundwater discharge and mixing situation of lake water. The estimated discharge zone ascertained using the radon method agrees with the groundwater discharge distribution observed through diving surveys. Although the data resolution of the radon method is much greater than the width of observed discharge zones, the general distribution of groundwater discharge is recognizable. The dual loop system of radon measurement is useful for smaller areas.

An estimation of water origins in the vicinity of a tropical cyclone’s center and associated dynamic processes

To clarify the time evolution of water origins in the vicinity of a tropical cyclone (TC)’s center, we have simulated Typhoon Man-yi (July 2007) in our case study, using an isotopic regional spectral model. The model results confirm that the replacement of water origins occurs successively as the TC develops and migrates northward over the western North Pacific. It is confirmed that, in this case, a significant proportion of total precipitable water around the cyclone center comes from external regions rather than the underlying ocean during the mature stage of a TC. Similar features can also be seen in the proportion of each oceanic origin to total condensation. Indian Ocean, South China Sea, and Maritime Continent water vapors begin to increase gradually at the developing stage and reach their peak at the decay stage when the TC approaches southwestern Japan. These remote ocean vapors are transported to the east of the cyclone via the moisture conveyor belt, a zone characterized by distinct low-level moisture flux that stretches from the Indian Ocean to the TC, and are further supplied into the inner region of the TC by inflow within the boundary layer associated with its secondary circulation. Since it takes time to undergo these two dynamic processes, the delayed influence of remote ocean vapors on the TC appears to become evident during the mature stage.

Verification of the isotopic composition of precipitation simulated by a regional isotope circulation model over Japan.

ABSTRACT The isotopic composition (δ18O and δ2H) of precipitation simulated by a regional isotope circulation model with a horizontal resolution of 10, 30 and 50 km was compared with observations at 56 sites over Japan in 2013. All simulations produced reasonable spatio-temporal variations in δ18O in precipitation over Japan, except in January. In January, simulated δ18O values in precipitation were higher than observed values on the Pacific side of Japan, especially during an explosively developing extratropical cyclone event. This caused a parameterisation of precipitation formulation about the large fraction of precipitated water to liquid detrained water in the lower troposphere. As a result, most water vapour that transported from the Sea of Japan precipitated on the Sea of Japan side. The isotopic composition of precipitation was a useful verification tool for the parameterisation of precipitation formulation as well as large-scale moisture transport processes in the regional isotope circulation model.

Meridional march of diurnal rainfall over Jakarta, Indonesia, observed with a C-band Doppler radar: an overview of the HARIMAU2010 campaign

AbstractThis paper presents an overview of the HARIMAU2010 campaign focusing on convective activity with the diurnal rainfall meridional march (DRMM) over Jakarta, which is located on the northern coast of Jawa Island of the Indonesian maritime continent (IMC), based on 1-month intensive observations by a C-band Doppler radar and multi-point atmospheric sounding array conducted during 16 January–14 February 2010. The campaign period corresponded to a phase after large-scale Madden–Julian oscillation (MJO) active convections passed over Jakarta (MJO inactive phase). The cross-equatorial northerly surge (CENS) intruded into the Jawa Sea with a cold tongue (CT) of sea surface temperature (SST) in the beginning of the period (CENS active period: 16–26 January), and then, it started to retreat (transition period: 27 January–05 February); afterward, only a few signs of it were apparent (CENS inactive period: 06–14 February). The observational results showed that (1) rainfall over Jakarta has the nature of DRMM during the MJO inactive phase at least, (2) the DRMM is likely driven primarily by “land-breeze”-like local meridional circulation, and (3) the meridional spatiotemporal variation of rainfall over Jakarta is thus controlled by activities of both the CENS and CT over the Jawa Sea.

Estimation of the Isotopic Composition and Origins of Winter Precipitation Over Japan Using a Regional Isotope Circulation Model

The deuterium excess (d-excess) of precipitation aids in identifying vapor source regions because it reflects humidity conditions in those regions. For Japan, studies have assumed that the Sea of Japan was the dominant source of winter precipitation when the d-excess value in winter is >20‰ or higher than the average value in summer. Because this assumption is based on an interpretation that the high d-excess value is due to an interaction between the continental winter monsoon (WM) and warm Sea of Japan, it may not be appropriate for winter precipitation due to extratropical cyclones (ECs). Here, we clarify local patterns of water isotopic composition and the origins of precipitation in WM and EC types over Japan using a regional isotope circulation model. The results indicate that the Sea of Japan made the highest contribution to precipitation on the Sea of Japan side in the WM type, whereas the Pacific Ocean was the dominant source of precipitation over Japan in the EC type. Because d-excess values were higher in the WM type than the EC type, we can assume that the Sea of Japan is the dominant source of precipitation on the Sea of Japan side when the d-excess value is high. In comparison, we cannot identify the source regions from d-excess values alone for Honshu Island bordering the Pacific Ocean, because the difference in the d-excess value between the WM and EC types is unclear. WM variability can be estimated from observed d-excess values due to their clear positive correlation.