[1] The size distribution of sea ice floes was observed by coordinated Landsat imagery and video monitoring conducted from an icebreaker and a helicopter for an area 38 km  26 km in seasonal sea ice in the southern Sea of Okhotsk in February 2003. The combination of imagery on several scales allowed measurements of ice floes over three orders of magnitude, from 1 m to 1.5 km. Two different regimes were observed: floes larger than about 40 m have a power-law number density with an exponent of À1.87, in the lower range of earlier results. Below 40 m, the power law exponent is À1.15. The cause of these two different regimes is hypothesized to lie in the effects of swell on floes of different sizes and thicknesses. The importance of the floe size distribution for lateral melting is elucidated.Citation: Toyota, T., S. Takatsuji, and M. Nakayama (2006), Characteristics of sea ice floe size distribution in the seasonal ice zone, Geophys. Res. Lett., 33, L02616,

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ABSTRACT. Characteristic features of the growth of sea-ice extent in the Sea of Okhotsk are discussed statistically in relation to the surface wind and air temperature over the Okhotsk basin. It is shown that cold-air advection from the continent is not the only factor for the growth of ice extent: air-mass transformation with fetch (downwind distance from the coast) is another important factor. Using weekly growth rates of ice extent and objectively analyzed meteorological data, it is shown that the ice cover extends when cold northerly/northwesterly winds blow, whereas the ice cover retreats when warm northeasterly/easterly winds blow. It is concluded that the advance/retreat of the Sea of Okhotsk ice cover is largely determined by the atmospheric circulation, which is in turn controlled by the position and intensity of the Aleutian low. Occasional out-of-phase fluctuations between the Sea of Okhotsk and Bering Sea ice covers are found to occur when an intensified Aleutian low is located in the mid-western part of the Bering Sea and induces cold northwesterly winds to the Okhotsk basin and warm southeasterly winds to the Bering Sea, or when a weakened Aleutian low is displaced eastward and induces cold northeasterly winds to the Bering Sea and warm northeasterly winds to the Okhotsk basin.

Seasonal variations of carbon dioxide (CO 2 ), methane (CH 4 ), carbon monoxide (CO), and nitrous oxide (N 2 O), in the mid-troposphere over the western North Pacific, are investigated using air samples collected onboard a C-130H aircraft. These samples were obtained between Atsugi Base (35.45°N, 139.45°E) and Minamitorishima (MNM; 24.28°N, 153.98°E), once a month, from September 2010 to September 2012. Increasing trends of CO 2 and N 2 O and large variability of CH 4 and CO (at approximately 6 km) have been found. During summer, concentrations of CH 4 and CO were found to increase with height over MNM. High concentrations of CH 4 were persistently observed in the mid-troposphere throughout the observation period. The average enhancement ratios of CH 4 to CO above background levels (∆CH 4 /∆CO) were 0.47 and 1.2 ppb/ppb for winter-spring and summerfall, respectively. The results suggested that the high CH 4 concentrations originated primarily from fossil fuel combustions in winter-spring, while there could be an additional contribution from increased biogenic sources during summer-fall. Because a surface station in MNM rarely observed the summer-fall high CH 4 concentration values in the mid-troposphere, the aircraft measurements could provide a powerful constraint on the CH 4 emission estimates for Asia, in addition to that provided by the surface measurements. This aircraft measurement program is regularly conducted for the long-term monitoring of the greenhouse gases in the mid-troposphere, and it has a significant role for filling the data gap of the existing measurement network.

We examined the standard gas scales and the stability of methane (CH 4 ) standard gases that have been used for atmospheric measurements at the Japan Meteorological Agency (JMA) since 2000. Calibration of the JMA standards at the National Oceanic and Atmospheric Administration (NOAA) using the NOAA04 gravimetric scale, which is the