Moored Observations of Currents and Water Mass Properties between Talaud and Halmahera Islands at the Entrance of the Indonesian Seas

The currents and water mass properties at the Pacific entrance of the Indonesian seas are studied using measurements of three subsurface moorings deployed between the Talaud and Halmahera Islands. The moored current meter data show northeastward mean currents toward the Pacific Ocean in the upper 400 m during the nearly 2-yr mooring period, with the maximum velocity in the northern part of the channel. The mean transport between 60- and 300-m depths is estimated to be 10.1–13.2 Sv (1 Sv ≡ 106 m3 s−1) during 2016–17, when all three moorings have measurements. The variability of the along-channel velocity is dominated by low-frequency signals (periods > 150 days), with northeastward variations in boreal winter and southwestward variations in summer in the superposition of the annual and semiannual harmonics. The current variations evidence the seasonal movement of the Mindanao Current retroflection, which is supported by satellite sea level and ocean color data, showing a cyclonic intrusion into the northern Maluku Sea in boreal winter whereas a leaping path occurs north of the Talaud Islands in summer. During Apri–July, the moored CTDs near 200 m show southwestward currents carrying the salty South Pacific Tropical Water into the Maluku Sea.

Hillslope Contribution to the Clark Instantaneous Unit Hydrograph: Application to the Seolmacheon Basin, Korea

In this study, the time–area curve of an ellipse is analytically derived by considering flow velocities within both channel and hillslope. The Clark IUH is also derived analytically by solving the continuity equation with the input of the derived time–area curve to the linear reservoir. The derived Clark IUH is then evaluated by application to the Seolmacheon basin, a small mountainous basin in Korea. The findings in this study are summarized as follows. (1) The time–area curve of a basin can more realistically be derived by considering both the channel and hillslope velocities. The role of the hillslope velocity can also be easily confirmed by analyzing the derived time–area curve. (2) The analytically derived Clark IUH shows the relative roles of the hillslope velocity and the storage coefficient. Under the condition that the channel velocity remains unchanged, the hillslope velocity controls the runoff peak flow and the concentration time. On the other hand, the effect of the storage coefficient can be found in the runoff peak flow and peak time, as well as in the falling limb of the runoff hydrograph. These findings are also confirmed in the analysis of rainfall–runoff events of the Seolmacheon basin. (3) The effect of the hillslope velocity varies considerably depending on the rainfall events, which is also found to be mostly dependent upon the maximum rainfall intensity.

Experimental Investigation of Rotational Effects on Heat Transfer Enhancement Due to Crossflow-Induced Swirl Using Transient Liquid Crystal Thermography

Rotational effects lead to significant nonuniformity in heat transfer (HT) enhancement and this effect is directly proportional to the rotation number (Ro=ΩD/V). Hence, the development of cooling designs, which have less dependence on rotation, is imperative. This paper studied the effect of rotation on crossflow-induced swirl configuration with the goal of demonstrating a new design that has lesser response toward rotational effects. The new design passes coolant from one pass to the second pass through a set of angled holes to induce impingement and swirling flow to generate higher HT coefficients than typical ribbed channels with 180-deg bend between the two passages. Detailed HT coefficients are presented for stationary and rotating conditions using transient liquid crystal (TLC) thermography. The channel Reynolds number based on the channel hydraulic diameter and channel velocity at inlet/outlet ranged from 25,000 to 100,000. The rotation number ranged from 0 to 0.14. Results show that rotation reduced the HT on both sides of the impingement due to the Coriolis force. The maximum local reduction of HT in the present study was about 30%. Rotation significantly enhanced the HT near the closed end because of the centrifugal force and the “pumping” effect, which caused local HT enhancements up to 100%. Compared to U-bend two pass channels, impingement channels had advantages in the upstream channel and the end region, but HT performance was not beneficial on the leading side of the downstream channel.