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Diurnal precipitation variability over the Gulf Stream and the Kuroshio Shoshiro Minobe and Shogo Takabeyashi (Hokkaido University, Sapporo, Japan) Outline Introduction Global View Gulf Stream region Kuroshio region Summary, schematics & discussion

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Introduction 1/3 A challenge of air-sea interaction studies is to understand how high-frequency variability (weather) interact with low-frequency phenomena (climate). A number of studies are conducted for synoptic disturbances. Today, I would like to show that another interesting high-frequency phenomenon, diurnal variability, plays important role in air-sea interaction over WBCs as implicitly mentioned by Minobe et al. (2008). 1

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Introduction 2/3 They showed 2 Minobe et al. (2008 Nature) Occurrence frequency of daytime satellite- derived OLR levels lower than 160 W m -2 (colour). This implies that the Gulf Stream influence is not clear in nighttime. So, diurnal variability should occur.

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Introduction 3/3 3 Kikuchi and Wang (2007) Actually, diurnal variability of precipitations are seen in previous studies, but they focus their attentions on tropics and did not mention about mid-latitude air-sea interaction nor WBCs. So, we explorer how diurnal cycles are related to WBCs.

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Data Satellite precipitation products GSMaP MVK v. 5 as the main precipitation data 0.1x0.1, hourly, March 2000 to December 2010 Microwave + IR satellite (movement vector & brightness) with Kalman filter TRMM 3B42 v7 for check 0.25x0.25, 3 hourly, analysis period is 2000-2010 Microwave (at available points) + IR (otherwise) temporal & spatial heterogeneity OLR for high clouds NASA/GEWEX Surface Radiation Budget (SRB) project ver. 3.1, 1x1, 3 hourly analysis period is 2000-2007 (data end at 2007 Dec.) Occurrence rate of OLR

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Methods Harmonic analysis of diurnal climatology in each month and each season. 5 We also define relative amplitude (RA) RA amp/mean For a sinusoidal diurnal climatology, 0