Toru Takatsuka

Solar radiation and ice heat budget during winter 2002–2003 in Lake Pääjärvi, Finland

Lake Pããjãrvi, loeated in southem Finland, has surfaee dimensions o f l O km x Z km, an average depth o f 15 m, and a maximum depth of 87 m. It is ice eovered every winter. On average, it freezes over in the midDeeember, and the iee breaks up in early May (KuuSISTO 1994). An automatie floating iee station was used in Lake Pããjãrvi during winter ZOOZ-Z003 to monitor iee evolution. Meteorologieal and hydrologieal variables and light level within the iee were reeorded.

Ice-edge detection from Japanese C-band radar and high-frequency radar coastal stations

Abstract A C-band sea-ice radar (SIR) network system was operated to monitor the sea-ice conditions off the Okhotsk Sea coast of northern Hokkaido, Japan, from 1969 to 2004. The system was based on three radar stations, which were capable of continuously monitoring the sea surface as far as 60 km offshore along a 250 km long coastal section. In 2004 the SIR system was closed down and a sea surface monitoring programme was commenced using high-frequency (HF) radar; this system provides information on surface currents in open-water conditions, while areas with ‘no signal’ can be identified as sea ice. The present study compares HF radar data with SIR data to evaluate their feasibility for sea-ice remote sensing. The period of overlapping data was 1.5 months. The results show that HF radar information can be utilized for ice-edge mapping although it cannot fully compensate for the loss of the SIR system. In particular, HF radar does not provide ice concentration, ice roughness and geometrical structures or ice kinematics. The probability of ice-edge detection by HF radar was 0.9 and the correlation of the ice-edge distance between the radars was 0.7.

Observation of the Soya warm current using HF ocean radar

Three HF ocean radar stations were installed at the Soya/La Perouse Strait in the Sea of Okhotsk in order to monitor the Soya Warm Current. Frequency of the HF radar is 13.9 MHz, and range and azimuth resolutions are 3 km and 5 deg., respectively. It covers a range of about 70 km from the coast. Surface current velocity observed by the radars is compared with data from drifting buoys and shipboard ADCPs (Acoustic Doppler Current Profilers). The current velocity derived from the HF radars shows good agreement with that observed by the drifting buoys. The rms (root-mean-squared) differences are about 15 cm/s for the zonal and meridional components. The observed current velocity also exhibits a reasonable agreement with the shipboard ADCP data. It is shown that the HF radars clearly capture seasonal and short-term variations of the Soya Warm Current. The velocity of Soya Warm Current reaches its maximum, which is about 1 m/s, in summer, and becomes weak in winter. The current axis is located at a distance from 20 to 30 km from the coast, and the width is about 40 km. The surface transport across the strait shows a significant correlation with the sea level difference along the strait derived from coastal tide gauge records

Winter Water Formation in Coastal Polynyas of the Eastern Chukchi Shelf: Pacific and Atlantic Influences

Water properties and formation processes of Alaskan Coastal Winter Water (ACWW) over the eastern Chukchi shelf along the Alaska coast, the so-called Barrow Canyon pathway, are examined using data from moorings, atmospheric reanalysis, satellite-derived sea-ice production (SIP), and a numerical tracer experiment. Along this pathway, Pacific Winter Water (PWW) can be modified to produce ACWW through SIP accompanied by production of cold, saline polynya water in the coastal polynyas, upwelling of warm Atlantic Water (AW), and mixing processes on the shelf. Three different types of ACWW are formed: (i) a mixture of AW and PWW, (ii) a mixture of AW and polynya water, and (iii) hypersaline polynya water. The northeasterly winds, correlated with the north-south atmospheric pressure gradient between Beaufort High and Aleutian Low, are common triggers of polynya SIP episodes and AW upwelling in the Barrow Coastal Polynya (BCP). Due to the dual impact of northeasterly winds, PWW modification processes in the BCP are more complicated than what occurs elsewhere in the Chukchi Polynya. The impact of AW upwelling on the ACWW formation is most prominent in the BCP, usually centered along the coast. All types of ACWW are thought to be basically transported westward or northwestward with the Chukchi slope current and/or Beaufort Gyre and finally contribute to maintenance of the lower halocline layer especially over the Chukchi Borderland, Northwind Ridge, and southern Canada Basin. Even in the Pacific sector of the Arctic Ocean, ACWW properties are strongly influenced by both Atlantic-origin and Pacific-origin waters.