Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: Charles R. Stearns x
  • All content x
Clear All Modify Search
CHARLES R. STEARNS

Abstract

The surface heat budget for the absolutely dry soil of the Pampa de La Joya, Peru, a portion of the Atacama Desert, was determined for three round-the-clock periods in July 1964. The diurnal variations are described by the mean value and the amplitude and phase angle of the first three harmonics. The measurements include global insolation, net radiation, soil heat flux density, sensible heat flux density, surface temperature, and air temperature at 20, 40, 80, 160, and 320 cm. The instruments used are described, and an estimate of the errors in measurement is made for each.

Full access
Hugh Richard Slotten and Charles R. Stearns

Abstract

Row Island, Antarctica with its 3000 m volcanic peaks a prodigious barrier to the predominant southerly airflow of the western Ross Ice Shelf, Antarctica. This study investigates the relationship of Ross Island to the dynamics and kinematics of the atmosphere using surface data from an army of six automatic weather stations on the Ross Ice Shelf just south of Ross Island.

After the actual horizontal pressure gradients had been determined, dynamical relations were obtained which confirmed previous related research. The values of geostrophic departure angle found in this study are in good agreement with the findings of other researchers. Furthermore, a previously determined tendency of the geostrophic departure angle to increase with increasing wind speed over open ice has been confirmed in the region far to the south of the influence of Ross Island. Near the south side of Ross Island, however, this relation does not apply. It is postulated that the forcing of Ross Island on the dynamics of the lowest layers of the atmosphere is causing this difference to occur.

Through an analysis of the individual terms in the equation of motion, further support was found for this hypothesis. On the assumption of a linear decrease of friction with height, the height for zero friction increases towards the south of Ross Island. Finally, tentative evidence of higher pressure immediately to the south of the island has been found, which further supports the theory that the cold stable air advected northward by the predominant southerly flow is piling up on the south side of Ross Island.

Full access
Christopher A. Shuman and Charles R. Stearns

Abstract

Decadal-length, daily average, temperature records have been generated for four inland West Antarctic sites by combining automatic weather station (AWS) and satellite passive microwave brightness temperature records. These records are composites due to the difficulty in maintaining continuously operating AWS in Antarctica for multiyear to multidecade periods. Calibration of 37-GHz, vertical polarization, brightness temperature data during periods of known air temperature by emissivity modeling allows the resulting calibrated brightness temperatures (TC) to be inserted into data gaps with constrained errors. By the same technique, but with reduced constraints, TC data were also developed through periods before AWS unit installation or after removal.

The resulting composite records indicate that temperature change is not consistent in sign or magnitude from location to location across the West Antarctic region. Linear regression analysis shows an approximate 0.9°C increase over 19 yr at AWS Byrd (0.045 yr−1 ±0.135°C), a 0.9°C cooling over 12 yr at AWS Lettau (−0.078 yr−1 ±0.178°C), a 3°C cooling over 10 yr at AWS Lynn (−0.305 yr−1 ±0.314°C), and a 2°C warming over 19 yr at AWS Siple (0.111 yr−1 ±0.079°C). Only the Siple trend is statistically significant at the 95% confidence level however. The temperature increases at Siple and possibly Byrd are suggestive of a broader regional warming documented at sites on the Antarctic Peninsula. The cooling suggested by the shorter records in the vicinity of the Ross Ice Shelf is consistent with results recently reported by Comiso and suggests that significant regional differences exist. Continued data acquisition should enable detection of the magnitude and direction of potential longer-term changes.

Full access
Michael L. Savage, George A. Weidner, and Charles R. Stearns

Abstract

On 20 May 1977 a periodic pressure disturbance over the upper Midwest was detected by synoptic and mesoscale microbarograph arrays. Analysis indicates that a pressure wave with an amplitude of approximately 1.0 mb, a phase speed of approximately 14 m s−1, a period of between 1.5 and 3 h, and a horizontal wavelength of approximately 100 km moved through Illinois, Iowa and Wisconsin from the south within the warm sector of an occluded cyclone. We interpret them pressure data as the signature of an internal atmospheric gravity wave. At several locations convective precipitation occurred coincident with the advancing ridges of the pressure wave, suggesting that the gravity wave influence convection. Openings in the cloud cover correlated with the location of the gravity wave. Simple modeling confirms the destabilization potential of the gravity wave.

Full access
Mark W. Seefeldt, Gregory J. Tripoli, and Charles R. Stearns

Abstract

A detailed description of the characteristics of the three-dimensional wind flow for the Ross Island region of Antarctica is presented. This region of Antarctica has complex topographic features, and the wind flow is dependent on the topography and the local meteorological conditions. High-resolution nonhydrostatic numerical simulations are conducted over a high-resolution domain in the Ross Island region. Two simulations are performed corresponding to the two dominant wind flow patterns in the Ross Island region. The first simulation is a light wind case with a stable lower atmosphere and the second is a high wind speed event. Froude number calculations, along with a study of the equation of motion, are included for a more complete understanding of the dynamics of the wind flow. The results of the simulations show a favorable correlation to past research results and observations, and provide a more complete understanding of the three-dimensional wind flow in the region. In addition to a more thorough understanding of the wind flow, the results indicate the usefulness and future applicability of nonhydrostatic simulations to understanding the unique meteorological conditions and features in the Antarctic.

Full access
David H. Bromwich, Jorge F. Carrasco, and Charles R. Stearns

Abstract

Five winter months (April–August 1988) of thermal infrared satellite images were examined to investigate the occurrence of dark (warm) signatures across the Ross Ice Shelf in the Antarctic continent. These features are inferred to be generated by katabatic winds that descend from southern Marie Byrd Land and then blow horizontally across the ice shelf. Significant mass is added to this airstream by katabatic winds blowing from the major glaciers that flow through the Transantarctic Mountains from East Antarctica. These negatively buoyant katabatic winds can reach the northwestern edge of the shelf, a horizontal propagation distance of up to 1000 km, 14% of the time. Where the airstream crosses from the ice shelf to the ice-covered Ross Sea, a prominent coastal polynya is formed. Because the downslope buoyancy force is near zero over the Ross Ice Shelf, the northwestward propagation of this katabatic air mass requires pressure gradient support. The study shows that the extended horizontal propagation of this atmospheric density current occurred in conjunction with the passage of synoptic cyclones over the southern Amundsen Sea. These cyclones can strengthen the pressure gradient in the interior of West Antarctica and make the pressure field favorable for northwestward movement of the katabatic winds from West Antarctica across the ice shelf in a geostrophic direction. The glacier winds from East Antarctica are further accelerated by the synoptic pressure gradient, usually undergo abrupt adjustment beyond the exit to the glacier valley, and merge into the mountain-parallel katabatic air mass.

Full access
Matthew A. Lazzara, Linda M. Keller, Charles R. Stearns, Jonathan E. Thom, and George A. Weidner

Abstract

For over 30 years, weather forecasting for the Antarctic continent and adjacent Southern Ocean has relied on weather satellites. Significant advancements in forecasting skill have come via the weather satellite. The advent of the high-resolution picture transmission (HRPT) system in the 1980s and 1990s allowed real-time weather forecasting to become a reality. Small-scale features such as mesocyclones and polar lows could be tracked and larger-scale features such as katabatic winds could be detected using the infrared channel. Currently, HRPT is received at most of the manned Antarctic stations. In the late 1990s the University of Wisconsin composites, which combined all available polar and geostationary satellite imagery, allowed a near-real-time hemispheric view of the Southern Ocean and Antarctic continent. The newest generation of satellites carries improved vertical sounders, special sensors for microwave imaging, and the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor.

In spite of the advances in sensors, shortcomings still impede the forecaster. Gaps in satellite data coverage hinder operations at certain times of the day. The development and implementation of software to derive products and visualize information quickly has lagged. The lack of high-performance communications links at many of the manned stations reduces the amount of information that is available to the forecasters.

Future applications of weather satellite data for Antarctic forecasting include better retrievals of temperature and moisture and more derived products for fog, cloud detection, and cloud drift winds. Upgrades in technology at Antarctic stations would allow regional numerical prediction models to be run on station and use all the current and future satellite data that may be available.

Full access
Christopher A. Shuman, Konrad Steffen, Jason E. Box, and Charles R. Stearns

Abstract

On 4 May 1987, the first automatic weather station (AWS) near the summit of the Greenland Ice Sheet began transmitting data. Air temperature records from this site, AWS Cathy, as well as nearby AWS at the Greenland Ice Sheet Project II (GISP2, now Summit) camp have been combined with Special Sensor Microwave Imager brightness temperature data to create a composite temperature history of the Greenland summit. This decadal-plus-length (4536 days) record covers the period from May 1987 to October 1999 and continues currently. The record is derived primarily from near-surface temperature data from AWS Cathy (May 1987–May 1989), AWS GISP2 (June 1989–November 1996), and AWS Summit (May 1996 and continuing). Despite the 35-km distance between them, the AWS Cathy data have been converted to the equivalent basis of temperatures from the AWS GISP2 and AWS Summit locations. The now completed “Summit” temperature time series represents a unique record that documents a multiyear temperature recovery after the eruption of Mt. Pinatubo in June 1991 and that initiates a baseline needed for climate change detection.

Full access