The subtropical anticyclone over the southeast Pacific drives low-level southerly flow along the west coast of South America. In turn, the alongshore flow induces coastal upwelling that supports a wealth of fishery resources. Within this region, satellite data, marine reports, and coastal observations indicate the existence of a southerly coastal jet (i.e., a maximum of wind speed) off central Chile (26°–36°S). The mean features and variability of this southerly jet is documented in this work using 4 yr of satellite-derived sea surface winds, complemented by satellite-derived cloud amount fields and atmospheric reanalysis. Furthermore, analysis of in situ data and model results of a well-defined jet event during October 2000 allows a preliminary description of the jet’s three-dimensional structure and a comparison with the northerly jet off the coast of California. Southerly jet events off central Chile occur year-round, but they are more frequent during spring–summer (over 60% of the time). The jet is characterized by an elongated maximum of surface wind speed (∼10 m s−1) with its axis at about 150 km off the coast and a cross-shore scale of about 500 km. The two Quick Scatterometer (QuikSCAT) fields per day (a.m. and p.m. passes) allow a rough estimate of the amplitude of the diurnal cycle of the surface winds, which appears to be remarkably small in the region of the jet. The jet events are associated with the passage of a midlatitude ridge over the southeast Pacific strengthening the subtropical anticyclone. Upstream and over the jet region the coastal deck of stratocumulus clouds tends to dissipate in contrast to an increase in cloudiness downstream of the jet. In the case study the jet core resides at the top of the marine boundary layer (MBL)/inversion layer. Weak offshore flow prevails above the jet axis, and even weaker onshore flow prevails in the MBL. Consistent with its subtropical location the jet is embedded in a region of large-scale subsidence; nevertheless a mesoscale area of mean upward motion is simulated just downstream of the jet core.

The extensive and persistent deck of stratocumulus (Sc) over the subtropical southeast Pacific (SSEP) plays an important role in the regional and global climate. As in other subtropical regions, the Sc form at the top of a marine boundary layer (MBL), capped by the subsidence inversion. A distinctive feature of this subtropical deck is its pronounced dawn-to-afternoon decrease in cloud amount and liquid water path, partially associated with a regular and marked descent of the inversion base and the warming of the lower troposphere. Furthermore, coastal observations in this area reveal a diurnal cycle in air temperature encompassing up to 5 km MSL. In this work, 15-day regional numerical simulations using the fifth-generation PSU–NCAR Mesoscale Model (MM5) in November (austral spring), May (late fall), and January (summer) 2001 were used to document the mean diurnal cycle in circulation and low-level cloudiness over the SSEP. The simulated amplitude, depth, and phase of the diurnal cycle in air te... Abstract The extensive and persistent deck of stratocumulus (Sc) over the subtropical southeast Pacific (SSEP) plays an important role in the regional and global climate. As in other subtropical regions, the Sc form at the top of a marine boundary layer (MBL), capped by the subsidence inversion. A distinctive feature of this subtropical deck is its pronounced dawn-to-afternoon decrease in cloud amount and liquid water path, partially associated with a regular and marked descent of the inversion base and the warming of the lower troposphere. Furthermore, coastal observations in this area reveal a diurnal cycle in air temperature encompassing up to 5 km MSL. In this work, 15-day regional numerical simulations using the fifth-generation PSU–NCAR Mesoscale Model (MM5) in November (austral spring), May (late fall), and January (summer) 2001 were used to document the mean diurnal cycle in circulation and low-level cloudiness over the SSEP. The simulated amplitude, depth, and phase of the diurnal cycle in air te...

Two years of high-resolution backscatter profiles obtained with a commercial lidar ceilometer in Santiago Basin (33.5°S, 70.6°W) are analyzed. The generally large aerosol load in the Santiago atmospheric boundary layer (ABL) facilitates the use of these backscatter profiles for the retrieval of the daytime mixed layer height (MH), especially around midday. In winter mornings, however, MH retrievals are frequently confused by upper residual aerosol layers, while in summer afternoons very low aerosol concentrations often preclude them. Based on a database formed with successful MH retrievals over Santiago, the hourly, synoptic, and seasonal variability of clear-day MHs are documented. Daytime growth rates of MH show typical values of 50 m h−1 in winter and 100 m h−1 in summer. MHs at 1200 LT (UTC − 4 h) present a fourfold change between the cold months (MH ∼200 m) and the warm months (MH ∼800 m). Interquartile ranges of the monthly distributions of MH are about 200 m, with little change along the seasons. This statistical description of MH data is supplemented with analysis of temperature, solar radiation, and wind data at selected stations located at the basin’s floor, at the basin’s entrance, and at an elevated location representative of a level about 400 m above the basin’s floor. Seasonal MH variability appears highly controlled by the surface energy budget, with about 30% of the top-of-the-atmosphere radiative energy being used in the warming and growth of the daytime MH. Advection of cool air from the marine boundary layer to the west of the basin also appears to be important in the basin’s ABL energy budget in some cases. Stability of the early morning temperature profile in the basin’s air mass is also a factor in the mixed layer growth. Under conditions of large bulk stability of the basin’s air mass, there exist cases of very shallow daytime mixed layers that appear to develop after nights in which the stability is highly enhanced near the surface. Results herein are a first step toward a better understanding of the dynamics of this complex terrain ABL.

The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) was a major field experiment conducted in spring of 2008 off southern Peru and northern Chile, aimed at better understanding the coupled climate systems of the southeast Pacific. Because of logistical constrains, the coastal area around 30° S was not sampled during VOCALS-REx. This area not only marks the poleward edge of the subtropical stratocumulus cloud regime (thus acting as a source of transient disturbances) but is also one of the most active upwelling centers and source of surface ocean kinetic energy along the Chilean coast. To fill such an observational gap, a small, brief, but highly focused field experiment was conducted in late spring 2009 in the near-shore region around 30° S. The Chilean Upwelling Experiment (CUpEx) was endorsed by VOCALS as a regional component. CUpEx included long-term monitoring, an intensive two-week field campaign and off-shore research flights. Our goal was to obtain an atmospheric/oceanic dataset with enough temporal and spatial coverage to be able to document (a) the mean diurnal cycles of the lower-troposphere and upper-ocean in a region of complex topography and coastline geometry, and (b) the ocean-atmosphere response to the rapid changes in coastal winds from strong, upwelling-favorable equatorward flow (southerly winds) to downwelling-favorable poleward flow (northerly winds). In this paper we describe the measurement platforms and sampling strategy, and provide an observational overview, highlighting some key mean-state and transient features.

Over the past 15 years, Chile’s energy agencies have undertaken a series of projects aimed at evaluating the wind energy potential of the northern part of the country (western South America between 18° and 32°S), including the Atacama Desert. These projects have produced an unprecedented database of wind observations and ancillary meteorological data over an especially interesting climatic region, including more than 30 sites with 20-m meteorological masts and six high towers (60–80 m) with multilevel wind and temperature measurements. Measuring periods vary between 1 and 10 years, with about half the stations having 5 or more years of data. Site selection was guided by the results of a mesoscale numerical model, so the program provides a good example of modeling–observation interaction, as well as being a demonstration of a successful collaboration between government, university, and international assistance programs. This paper describes the publically available database of meteorological measurements, provides examples of regional climatological features revealed by the observations, compares observations with model results, and describes how the information provided by the program has contributed to the development of wind energy projects in the region.