Temporal and Spatial Variations of Wet Deposition Flux of Mineral Dust in Japan

Abstract

To ascertain the temporal and spatial distribution of mineral dust deposition by wet processes, weekly deposition samples were obtained at Sapporo, Toyama, Nagoya, Tottori, Fukuoka, and Cape Hedo (Okinawa) during October 2008−January 2010 using automatic wet-dry separating samplers. Mineral dust weights in water-insoluble residue mixed with pollen were estimated from Fe contents measured using an X-ray fluorescence analyzer. Highest and lowest annual dust fluxes were found respectively at Toyama (8.7 g m −2 yr ) in 2009, although their annual levels of precipitation were almost equal (ca. 2300 mm). Wet deposition flux was high in spring and low in summer. Simultaneous wet deposition events were observed five times among the sites, but these events were limited to regional scale. Based on the spatial distribution of dust represented as a mosaic of true color images from MODIS/Terra and vertical distributions of dust concentration from lidar observations, a high wet-dust-deposition event occurring in mid-March at Toyama was attributed to a combination of high dust concentration in the atmosphere during precipitation. Higher wet dust deposition at Toyama and Tottori was ascribed to frequent precipitation during the dusty season. IntroductionAeolian dust particles derived from arid regions are an important component of atmospheric aerosols. Dust particles are reportedly important for the accumulation of deep-sea sediment (Prospero 1981) and for their effects on the earth's radiation budget (Tegen et al. 1996;Tanaka et al. 2007). In Japan, visibilityreducing dust events have been observed frequently during spring (Arao et al. 2003).Processes of dust particle removal from the atmosphere to the earth surface are divisible into wet and dry processes, respectively occurring with and without precipitation. High dust deposition flux with precipitation was reported for the North Pacific region when both rainfall and high atmospheric dust concentrations coincide (Uematsu et al. 1985). The vertical distribution of dust concentration in snow at Mt. Tateyama, central Japan was explained by temporal variation of dust concentrations in the atmosphere (Osada et al. 2004). Results of that study implied the importance of a combination between snowfall and high dust concentration in the atmosphere to form thick dirty-snow layers. Furthermore, sporadic "red snow" events have been observed occasionally in northern Japan, causing remarkably high wet dust deposition of about 15 g m −2 during a two-day event at Shishiku near Kanazawa (Tsunogai et al. 1972), which was more than twice the 10-year average of total dust deposition onto snow at Mt. Tateyama during winter−spring (Osada et al. 2007).Dust input is a critical source of dissolved iron for phytoplankton growth in some ocean regions (Jickells et al. 2005). According to their review, 30−95% of total input of Fe to the ocean is attributable to wet deposition. Recently, the importance of wet dust deposition events was also suggested for initiating early spring blooms in the nort...

Temporal Variation in Iron Flux Deposition onto the Northern North Pacific Reconstructed from an Ice Core Drilled at Mount Wrangell, Alaska

“…Osada et al (2011) reported that the wet deposition of Asian dust in Japan is affected by the frequency of precipitation during dust seasons. Figure 3d shows the temporal variation in the precipitation amount during spring (February to March) observed at the Cordova station from the GHCN-Daily dataset (Manne et al 2012).…”

“…Possible sources of the iron supplied to the surface water of the northern North Pacific are deposition of mineral dust from the atmosphere (e.g., Duce and Tindale 1991) and mesoscale oceanic intrinsic processes, such as vertical winter mixing and horizontal Fe-rich intermediate water transport (Nishioka et al 2011). Several studies of mineral dust deposition using continuous multiyear observations have been conducted, especially in the Asian Continent and in Japan (e.g., Osada et al 2011). However, in remote areas, where the main source of iron to the sea surface is atmospheric dust, only short-term or sporadic monitoring observations had been conducted (e.g., Uematsu et al 1985).…”

An Unreported Asian Dust (Kosa) Event in Hokkaido, Japan: A Case Study of 7 March 2016

“…The Kosa has been often transported to Japan (e.g., Iwasaka et al 1983;Osada et al 2011;Yasunari et al 2016) and to remote regions such as the USA, Canada, Greenland, etc. (e.g., Rahn et al 1977;Biscaye et al 1997;McKendry et al 2001;Yasunari et al 2007;Yasunari and Yamazaki, 2009).…”

“…go.jp/Takikawa/). Because the depolarization ratio is available, the lidar data can provide us the information on non-spherical particles such as dust particles (e.g., Shimizu et al 2004;Osada et al 2011;Yasunari et al 2016). We use the calculated dust and spherical extinction coefficients of the lidar data (Sugimoto et al 2003;Shimizu et al 2004) at Takikawa to confirm Kosa (dust) transports there (also see SI Text).…”

The GOddard SnoW Impurity Module (GOSWIM) for the NASA GEOS-5 Earth System Model: Preliminary Comparisons with Observations in Sapporo, Japan

“…We have discussions on off-line LSM simulations including sensitivities and outputs from a global GEOS-5 simulation at a single location using the developed GOSWIM, including the total dust+BC+OC SDE. For validations, we use the unique observed data available in Sapporo, Japan, which include various Aoki et al 2013), and (4) total dust deposition flux during precipitation (called TDP) by Osada et al (2011). We considered EC as BC (see Section 2; SI).…”