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Abstract. Striking 20-30-day sea surface temperature waves observed along the equatorial front in the later half of the year are generally believed to be of an oceanic origin. Here we report the detection of atmospheric waves that are unambiguously tied to these oceanic waves, using new satellite measurements of surface winds. A general circulation model simulation reveals that these atmospheric waves have a shallow vertical structure trapped in the planetary boundary layer (PBL), unlike E1 Nino/Southern Oscillation where changes in deep convection are the cause of anomalous winds. Vertical wave motion penetrates well above the PBL and is likely to impact the distribution and transport of climatically important gas species such as ozone and dimethyl sulfide. TlWs start to develop in early June 1993 and a total of six wave packets pass each grid point during the 27-week period (Fig. l a). Visual estimation puts the average phase speed of westward propagation at 0.55 ms -I and the peak-to-trough SST amplitude at 2øC. These SST waves induce significant wind variations as manifested by the clear westward propagation of surface wind divergence (Fig. lb). The phase propagation of wind apparently matches that of SST. TlWs' phase speed and wavelength vary both seasonally and interannually due to changes in equatorial currents. Similar TIW-tied wind disturbances are also observed in late 1996 by NASA scatterometer on Japanese satellite ADEOS, which has a different repeat cycle and higher space-time resolutions than the ERS-1.We obtain the spatial structure of this coupled oceanatmospheric wave (Fig. l c) by cross-correlating wave fields with the SST time series at 120W 3N. The SST perturbations are highly coherent in space, with correlation coefficients exceeding 0.6 found along the mean SST front and south of the equator. In the Northern Hemisphere, the phase of the SST perturbation tilts northeastward, producing a cusp-shaped crest when superimposed on mean SST. SST perturbations vanish at 1 S, the center of the equatorial cold tongue, south of which anomalies change sign as meridional currents advect a reversed gradient of mean SST field. Significant SST correlation is visible down to 6S though the actual dimensional variance is small south of the equator. The cross correlation of wind velocity with SST is highly significant, with the maximum exceeding 0.6. Southeasterly (northwesterly) wind anomalies are found over warm (cold) SST perturbations. The same SST-wind correlation pattern is seen in the Southern Hemisphere, which despite low coefficients, remains statistically significant as it repeats itself over all the four anomaly centers.Our results are consistent with the wind pattern inferred from independent in-situ measurements at 110øW (Hayes et al. (Fig. l c). Divergence correlates with SST better than wind velocity itself because the operation of spatial derivative tends to emphasize TIWinduced disturbances over other large-scale wind variations. A regression map looks similar, with zonal and meridional winds ...

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Cloud patterns are important clues for revealing the atmospheric circulation of Venus. Recently, a planetary-scale streak structure has been discovered in middle- and lower-cloud images of Venus’ night-side taken by IR2, the 2-μm camera, on board the Akatsuki orbiter. However, its formation mechanism has not been investigated. Here we succeed, for the first time, in reproducing the patterns of the observed streak structure, as regions of strong downward flows that develop in high-resolution global simulations of the Venus atmosphere. The streaks are formed in both hemispheres with equatorial symmetry, which is caused by equatorial Rossby-like and Kelvin-like waves with zonal wavenumber one. The low-stability layer that has been suggested by past observations is essential for reproducing the streak structure. The streaks of downward flow result from the interaction of the meridionally tilted phase lines of the Rossby-like waves and the characteristics of baroclinic instability produced around the low-stability layer.

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