Search Results

You are looking at 1 - 10 of 24 items for

  • Author or Editor: Donald Wylie x
  • Refine by Access: All Content x
Clear All Modify Search
Donald Wylie

Abstract

Diurnal cycles of clouds were investigated using the NOAA series of polar-orbiting satellites. These satellites provided four observations per day for a continuous 11-yr period from 1986 to 1997. The High Resolution Infrared Radiation Sounder (HIRS) multispectral infrared data were used from the time trend analysis of Wylie et al. The previous study restricted its discussion to only the polar orbiters making observations at 0200 and 1400 LT because gaps in coverage occurred in the 0800 and 2000 LT coverage. This study shows diurnal cycles in cloud cover over 10% in amplitude in many regions, which is very similar to other studies that used geostationary satellite data. The use of only one of the polar-orbiting satellites by Wylie et al. caused biases up to 5% in small regions but in general they were small (e.g., ≤2% for most of the earth). The only consistently large bias was in high cloud cover over land in North America, Europe, and Asia north of 35°N latitude in the summer season where the 0200 and 1400 LT average high cloud frequency was 2%–5% more than the daily average. This occurred only in the summer season, not in the winter.

Full access
Donald P. Wylie

Abstract

The use of geostationary satellite data for estimating precipitation in non-tropical areas was explored with data taken in Montreal, Canada. The previous studies using geostationary images for rain estimation have concentrated primarily on tropical clouds (Griffith et al., 1978; Stout, et al., 1979). The intent of this study was to evaluate the applicability of using these data and techniques in other geographical areas. The Montreal area provided a wide range of weather situations common to midlatitudes for which the techniques could be tested. Because of the many variables in this area (different cloud types, moisture availability, temperature vertical structure and others) the rain rates of the cloud areas varied. Large differences in rain rates between the days studies in Montreal were found. The Montreal data also had rain rates that were considerably smaller than found in the tropical studies.

To explain these differences the environments of the clouds were investigated using sounding data. By applying a cumulus model (Simpson and Wiggert, 1969) to the soundings most of the daily differences in rain rates were explained. The large differences between the tropical studies and Montreal also were described by the model. It is proposed that future rain estimation schemes combine satellite image with sounding data through a cloud model to form a technique applicable to a wide variety of weather situations and geographical areas.

Full access
Donald P. Wylie and Denise Laitsch

Abstract

Rain estimates for the Great Plains States were made for a one-month period, August 1979, using different combinations of satellite and other data. The data tested were as follows: 1) two satellite images per day without any other data, 2) four satellite images per day, 3) 24 images per day, 4) 24 images per day with hourly surface observations and two per day radiosonde soundings (excluding the 6 h raingage reports), 5) two images per day with the Service A 6 h raingage reports, 6) 24 images per day with the Service A raingage reports, and 7) an automatic rain estimate made from infrared temperatures without human intervention.

Each method was applied to the same geographic area by the same meteorologists. Estimates produced from the seven data combinations were compared to a withheld data set of 538 hourly recording raingages.

The rain estimates from all methods tested were very similar in their ability to locate rainfall and estimate the monthly patterns. The first two methods tested, using only satellite imagery at low-frequency sampling rates, gave slightly poorer skill scores than the more data-rich methods. Best scores were found for methods using the Service A raingage reports (Methods 5 and 6). The frequency of satellite imagery did not change the quality ofthe estimates when the raingages were included.

The rain estimates made without the judgment of a meteorologist (Method 7) scored surprisingly close to the other methods tested. The additional effort of a meteorologist improved the rain estimates in all cases, but the level of improvement was small beyond that produced by a simple automated scheme.

Full access
Robert A. Mack and Donald P. Wylie

Abstract

A technique was developed for estimating the condensation rates of convective storms using satellite measurements of cirrus anvil expansion rates and radiosonde measurements of environmental water vapor. Three cases of severe conviction in Oklahoma were studied and a diagnostic model was developed for integrating radiosonde data with satellite data.

Two methods were used to measure the anvil expansion rates–the expansion of isotherm contours on infrared image, and the divergent motions of small brightness anomalies tracked on the visible images. The differences between the two methods were large as the storms developed, but these differences became small in the latter stage of all three storms.

A comparison between the three storms indicated that the available moisture in the lowest levels greatly affected the rain rates of the storms. This was evident from both the measured rain rates of the storms and the condensation rates estimated by the model. The possibility of using this diagnostic model for estimating the intensities of convective storms also is discussed.

Full access
David O'C. Starr and Donald P. Wylie

Abstract

Detailed descriptions of the rawinsonde-resolved meteorological conditions (3-hourly soundings) associated with a succession of five distinct mesoscale cirrus cloud regimes, which were observed intensely over a 36-hour period, is given. The synoptic scale systems in which these features were embedded are described and a brief overview of the experiment are given. Regional analyses of the static stability structure and vertical motion are presented and interpreted with respect to the characteristics of the corresponding cloud fields as deduced from satellite and lidar observations. The cloud fields exhibited a high degree of persistent mesoscale organization on scales of 20–500 km reflecting corresponding scales of dynamic and thermodynamic structure/variability as on the synoptic scale. Cloud generation was usually confined to layers less than 1 km deep (typically 0.5 km in depth) and cellular organization was evident in most cases irrespective of the thermal stratification. Multilayered development was prevalent (2–3 layers) and was associated with vertical structure of the temperature and moisture fields resulting primarily from vertical gradients in horizontal advection. One convective generation layer was usually present. Destabilization resulted primarily from advective processes that also led to the formation of a transient stable layer above and/or below the convective layer. Though resembling elevated frontal surfaces, the stable layers were not extensions of surface features. Cloud processes, primarily ice particle fall-out and evaporation, but also including cloud top detrainment, contributed to generating the multilayered structure. Two cases of clouds spawned from an overlying cloud deck were seen where one involved natural seeding of an ice-saturated and conditionally unstable layer in which vigorous convective development was subsequently observed. Subvisual cirrus in the lower stratosphere were found to be associated with prior tropopause features (upwind) where denser cirrus existed. Inferences are drawn with respect to the parameterization of cirrus in large-scale models. In particular, vertical resolution on the order of 0.5 km will probably be required to adequately resolve the forcing required for implementation of a physically-based parameterization. Greater understanding of the nature and causes of the observed mesoscale structure is also needed.

Full access
Donald P. Wylie and Harold M. Woolf

Abstract

An analysis technique for Geostationary Operational Environmental Satellite-VISSR (Visible and Infrared Spin Scan Radiometer) Atmospheric Sounder (GOES-VAS) sounder data was developed to extract cloud and clear radiance information. This technique employed many of the concepts used in the International Satellite Cloud Climatology Project (ISCCP) such as spatial and time comparisons of neighboring satellite pixels. It improved upon the previous studies that used VAS data by using all available VAS data at full time and space resolution. The previous studies utilized <10% of the original data.

The GOES-VAS cloud and clear radiance statistics compared well with rawinsondes and the ISCCP cloud analysis. The best agreement between the ISCCP and this GOES-VAS cloud analysis was for upper-tropospheric clouds (<440 hPa) in both cloud frequency and infrared emissivity. The two cloud datasets agreed to within 2% for both parameters. A comparison of the GOES-VAS clear radiance data to National Weather Service (NWS) rawinsondes showed agreement within 1.7 K (blackbody radiances). The upper-tropospheric VAS channels were warmer than the rawinsondes. The VAS water vapor channels suggested that the NWS rawinsondes have a dry bias in the upper troposphere.

Full access
Donald P. Wylie and Chester F. Ropelewski

A tethered sonde, the Boundary Layer Instrument System (BLIS), was designed for use from shipboard platforms in the GARP Atlantic Tropical Experiment (GATE). This system was able to monitor the thermal and kinematic properties of the boundary layer from approximately 100 m to the level of cloud base (800–1000 m). Five levels were simultaneously sampled for periods up to 24 h in length. More detailed vertical structure measurements were obtained by raising and lowering the tethered balloon. The mechanical details of the system and its accuracy in monitoring boundary layer changes and vertical motions are described.

Full access
Donald P. Wylie and Barry B. Hinton

Abstract

Cloud motions over the Indian Ocean for May–July 1979 were used to obtain spatial auto correlations of the deviations of the wind components from local means. Best correlations were associated with u′, low altitude clouds and alongwind displacements. Worst correlations arose from v′, high clouds and crosswind displacements. The crosswind anisotropy was ∼15%. All correlations were 0.49 or greater at 5° separation or less.

Full access
Donald Wylie, Barry B. Hinton, and Kevin Kloesel

Abstract

We have studied the changes in marine stratocumulus cloud cover observed during the FIRF, Program and how cloud cover related to synoptic conditions. Statistical analyses of the 21 day FIRE period show that marine stratocumulus cloud cover over the eastern Pacific ocean was related to wind direction and temperature advection. Good coorelations were found between the cloud cover fraction observed on satellite imagery and the NMC Global Spectral Model analyses of surface winds and temperature advection. This comparison was made in even locations in the Eastern Pacific. Regional differences were found between the area of FIRE operations several hundred kilometers west of San Diego and the other oceanic areas studied.

Full access
Donald P. Wylie and Barry B. Hinton

Abstract

A detailed analysis of the wind stress patterns over the Indian Ocean was made from 1 May to 31 July 1979. A combination of cloud motion and ship data obtained once per day was used to diagnose the surface-wind patterns to a degree of detail not possible in the past for an individual season. These data show the monsoon development and the fluctuations of the Somali Jet and the Southern Hemispheric tradewinds. Wind stress patterns produced by two traveling tropical storms are discussed. These combined to exert an unusually high westerly wind stress on the equator before the monsoon developed.

Full access