The morphology of westerly wind bursts (WWBs) during the 1980s is investigated using 1000-mbar winds analyzed by the European Center for Medium-Range Weather Forecasts (ECMWF). The variety of synoptic situations in which WWBs occur are explored so that the dynamics of WWB generation and maintenance can be studied and so that those interested in short-and long-term forecasts of conditions over the equatorial Pacific will have an increased knowledge of those elements associated with WWBs. WWBs are identified by searching for episodes in which the zonal wind was at least 5 m s -1 over at least 10 ø longitude for two or more days. This definition, based on surface winds rather than elevated winds or wind anomalies, reflects the impact WWBs have on air/sea interaction processes. The spatial and temporal criteria provide a synoptic-scale envelope for such interactions and mitigate against erroneous analyses. According to these criteria, 131 distinct WWBs occurred during the 1980s. A new twodimensional classification scheme has been developed; the nine patterns in it describe the nearsurface flow during 90% of these WWBs. A single cyclone or a series of cyclones in one or both hemispheres and several different types of cross-equatorial flow are the major components of the patterns. Only 8% of the bursts were associated with concurrent cyclones in both the northern and southern hemispheres. Four bursts involving cross-equatorial flow are subjected to further study. The flow is decomposed into barotropic and baroclinic parts and into rotational and divergent baroclinic components. One of the bursts was predominantly barotropic and another predominantly baroclinic; the cross-equatorial flow in all four cases was predominantly divergent in nature. The information from these cases, coupled with the typical vertical structures and small meridional length scales associated with the various synoptic patterns, suggests that simple baroclinic models of circulations driven by near-equatorial heating are not adequate to describe the dynamics during •s. 1988; Kindle and Phoebus, 1995]. Others have used long-16,997 16,998 HARTFEN: SYNOPTIC SETI'INGS OF WESTERLY WIND BURSTS term data records. Keen's [1982] pioneering work made extensive use of tropical cyclone information along with soundings from Kanton Island (1957-1967) and twice-daily tropical analyses (1971-1980). A comprehensive study of the the longitudinal and temporal characteristics of strong nearsurface westerlies was undertaken by HG91 using 25 years of data from the Line Islands. Chu et al. [1991] presented a statistical analysis of wind direction and constancy over the equatorial western Pacific using daily ship data (1958-1987). Recently Kiladis et al. [1994] have done a cross-correlation analysis of outgoing longwave radiation (OLR) anomalies (indicative of enhanced convection) with 850-mbar wind anomalies. The research presented here is part of a larger project examining the three-dimensional synoptic setting and dynamical generation and maintenance mechanisms of WWBs...

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Surface flux, wind profiler, oceanic temperature and salinity, and atmospheric moisture, cloud, and wind observations gathered from the R/V Altair during the North American Monsoon Experiment (NAME) are presented. The vessel was positioned at the mouth of the Gulf of California halfway between La Paz and Mazatlan (ϳ23.5°N, 108°W), from 7 July to 11 August 2004, with a break from 22 to 27 July. Experimentmean findings include a net heat input from the atmosphere into the ocean of 70 W m . Total accumulated rainfall amounted to 42 mm. The oceanic mixed layer had a depth of approximately 20 m and both warmed and freshened during the experiment, despite a dominance of evaporation over local precipitation. The mean atmospheric boundary layer depth was approximately 410 m, deepening with time from an initial value of 350 m. The mean near-surface relative humidity was 66%, increasing to 73% at the top of the boundary layer. The rawinsondes documented an additional moist layer between 2-and 3-km altitude associated with a land-sea breeze, and a broad moist layer at 5-6 km associated with land-based convective outflow. The observational period included a strong gulf surge around 13 July associated with the onset of the summer monsoon in southern Arizona. During this surge, mean 1000-700-hPa winds reached 12 m s Ϫ1, net surface fluxes approached zero, and the atmosphere moistened significantly but little rainfall occurred. The experiment-mean wind diurnal cycle was dominated by mainland Mexico and consisted of a near-surface westerly sea breeze along with two easterly return flows, one at 2-3 km and another at 5-6 km. Each of these altitudes experienced nighttime cloudiness. The corresponding modulation of the radiative cloud forcing diurnal cycle provided a slight positive feedback upon the sea surface temperature. Two findings were notable. One was an advective warming of over 1°C in the oceanic mixed layer temperature associated with the 13 July surge. The second was the high nighttime cloud cover fraction at 5-6 km, dissipating during the day. These clouds appeared to be thin, stratiform, slightly supercooled liquid-phase clouds. The preference for the liquid phase increases the likelihood that the clouds can be advected farther from their source and thereby contribute to a higher-altitude horizontal moisture flux into the United States.

This article describes the 1995 and 1996 Flatland boundary layer experiments, known as Flatland95 and Flatland96. A number of scientific and instrumental objectives were organized around the central theme of characterization of the convective boundary layer, especially the boundary layer top and entrainment zone. In this article the authors describe the objectives and physical setting of the experiments, which took place in the area near the

In this paper a five-beam wind profiler and a collocated meteorological tower are used to estimate the accuracy of four-beam and three-beam wind profiler techniques in measuring horizontal components of the wind. In the traditional three-beam technique, the horizontal components of wind are derived from two orthogonal oblique beams and the vertical beam. In the less used four-beam method, the horizontal winds are found from the radial velocities measured with two orthogonal sets of opposing coplanar beams. In this paper the observations derived from the two wind profiler techniques are compared with the tower measurements using data averaged over 30 min. Results show that, while the winds measured using both methods are in overall agreement with the tower measurements, some of the horizontal components of the three-beam-derived winds are clearly spurious when compared with the tower-measured winds or the winds derived from the four oblique beams. These outliers are partially responsible for a larger 30-min, threebeam standard deviation of the profiler/tower wind speed differences (2.2 m s Ϫ1 ), as opposed to that from the four-beam method (1.2 m s Ϫ1 ). It was also found that many of these outliers were associated with periods of transition between clear air and rain, suggesting that the three-beam technique is more sensitive to small-scale variability in the vertical Doppler velocity because of its reliance on the point measurement from the vertical beam, while the four-beam method is surprisingly robust. Even after the removal of the rain data, the standard deviation of the wind speed error from the three-beam method (1.5 m s Ϫ1 ) is still much larger than that from the four-beam method. Taken together, these results suggest that the spatial variability of the vertical airflow in nonrainy periods or hydrometeor fall velocities in rainy periods makes the vertical beam velocities significantly less representative over the area across the three beams, and decreases the precision of the three-beam method. It is concluded that profilers utilizing the four-beam wind profiler technique have better reliability than wind profilers that rely on the three-beam wind profiler technique.

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Abstract.Observations from a wind profiler and a meteorological tower are utilized to study the evolution of a gravity current that passed over the Meteorological Research Institute's (MRI) field site in Tsukuba, Japan. The gravity current was created by katabatic flow originating on the mountainous slopes west of the field site. The passage of the shallow current was marked by a pronounced pressure disturbance and was accompanied by vertical circulations seen in the tower and profiler data. Direct vertical-beam measurements are difficult, especially at low heights during highgradient events like density currents. In this study vertical velocities from the profiler are derived from the four oblique beams by use of the Minimizing the Variance of the Differences (MVD) method. The vertical velocities derived from the MVD method agree well with in situ vertical velocities measured by a sonic anemometer on the tower.The gravity current is analyzed with surface observations, the wind profiler/RASS and tower-mounted instruments. Observations from the profiler/RASS and the tower-mounted instruments illustrate the structure of the gravity current in both wind and temperature fields. The profiler data reveal that there were three regions of waves in the vertical velocity field: lee-type waves, a solitary wave and Kelvin-Helmholtz waves. The lee-type waves in the head region of the gravity current seem to have been generated by the gravity current acting as an obstacle to prefrontal flow. The solitary wave was formed from the elevated head of the gravity current that separated from the feeder flow. Profiler vertical-motion observations resolve this wave and enable us to classify it as a Benjamin-Davis-Ono (BDO) type solitary wave. The ducting mechanism that enabled the solitary wave to propagate is also revealed from the wind profiler/RASS measurements. The combination of high-resolution instruments at the MRI site allow us to develop a uniquely detailed picture of a shallow gravity current structure.

These were largely done in support of the four to eight radiosondes launched each day as the ship travelled from Hawaii to TAO buoy locations along longitudes 140° W and 125° W and then back to port in San Diego, California. The rapid nature of these remote field deployments led to some specific challenges in addition to those common to many surface data collection efforts. This paper documents the two deployments as well as the steps taken to evaluate and process the data. The results are 10 two multi-week surface meteorology data products and one accompanying set of surface fluxes, all collected in the core of the east-central Pacific's extremely warm waters. These data sets, plus metadata, are archived at the NOAA's National Centers for Environmental Information (NCEI) and free for public access: surface meteorology from Kiritimati Island