Search Results

You are looking at 1 - 9 of 9 items for

  • Author or Editor: Edwin F. Harrison x
  • Refine by Access: All Content x
Clear All Modify Search
Patrick Minnis
and
Edwin F. Harrison

Abstract

A hybrid bispectral threshold method (HBTM) is developed for hourly regional cloud and radiative parameters from geostationary satellite visible and infrared radiance data. The quantities derived with the HBTM include equivalent blackbody temperatures for clear skies, for the total cloud cover and for the cloud cover at three levels in the atmosphere; the total fractional cloud cover and the fractional cloud amounts at three altitudes; and the clear-sky and total cloud reflectance characteristics. Geostationary satellite data taken during November 1978 are analyzed. A minimum reflectance technique is used to determine clear-sky brightness. A visible bidirectional reflectance model is derived for clear ocean areas. Clear-sky radiative temperature is found with a bispectral clear radiance technique during daylight hours. An empirical model is derived to predict clear-sky temperature at night. A combination of previously published infrared threshold and bispectral techniques is used to determine the remaining parameters. Sources of uncertainty are discussed and means to minimize them are proposed. Monthly mean, regional fractional cloudiness determined with this method agrees well with more conventional subjective techniques. On the average, the present results are approximately 0.05 less than corresponding surface observations; this is consistent with previous comparisons of satellite- and surface-based nephanalyses. Comparisons between subjective analyses of satellite photographs and the HBTM yielded average differences in mean regional cloudiness, mean hourly cloudiness and instantaneous cloud amounts of 0.04, 0.05 and 0.11 respectively. Root-mean-square differences in these same quantities derived by two satellite data analysts were 0.03, 0.04 and 0.08 respectively.

Full access
Patrick Minnis
and
Edwin F. Harrison

Abstract

Regional (250 × 250 km2) diurnal cloud variability is examined using mean hourly cloud amounts derived from November 1978 GOES-East visible and infrared data with a hybrid bispectral threshold technique. A wide variety of diurnal variations in cloud cover is presented. A morning maximum in low cloudiness is found over much of the eastern Pacific. Many regions in the western Atlantic have peak low-cloud cover near noon. Low clouds reach a maximum most often near noon over most of South America and in the morning over North America. Midlevel clouds are most frequent in the evening over oceans and in the early morning over land. High-cloud maxima are found mainly in the late afternoon over land and in the midafternoon over the oceans. An early morning minimum in high-cloud-top temperature is observed over marine areas. The amplitude of the semidiurnal component of cloudiness is generally much less than that of the diurnal component.

The largest diurnal cloud variations occur over the southeastern Pacific where low clouds are dominant. On the average, mean cloud fraction varied by about 0.35 in this area with a maximum near sunrise. Over the Amazon Basin, the vertical distribution of cloud cover follows a pronounced diurnal cycle which shows maximum high-cloud cover occurring in the late afternoon. A large-scale diurnally modulated circulation feature between the Amazon and the adjacent oceans is suggested. High clouds occur most frequently over the southern Andes during the afternoon and are most common over the adjacent lowlands during the night, indicating the existence of a diurnally-dependent mountain-plains circulation.

Full access
Patrick Minnis
and
Edwin F. Harrison

Abstract

The diurnal variability of the radiation emitted and reflected from the earth-atmosphere is investigated at the regional scale using November 1978 GOES-East visible and infrared data and GOES-derived cloud information. Narrowband GOES data are converted to broadband radiances using spectral calibration functions determined empirically from colocated Nimbus-7 ERB and GOES-East measurements over ocean, land and cloud surfaces. Shortwave radiances are used to estimate radiant exitances with bidirectional reflectance models derived from GOES and aircraft data for ocean, land and clouds.

Average albedo over clear ocean and land changed by factors of 4.2 and 2.2, respectively, for a solar zenith angle range of 0 to 80°. Average cloud albedo changed by a factor of 1.8 for the same range of solar zenith angles, but varied considerably from region to region. Mean clear-sky longwave radiant exitance varied diurnally from 2 W m−2 over some ocean areas to 100 W m−2 in one high elevation desert area in the Andes. In some regions having regular deep convective diurnal cycles, the mean cloud longwave flux had a diurnal range as high as 50 W m−2. The mean difference in net radiation between cloudy and clear areas was -55 W m−2, indicating that the clouds had a net cooling effect for the GOES-East viewing area during this time period.

Monthly mean Earth radiation budget (ERB) measurements from Sun-synchronous satellites were simulated to estimate the magnitude of the errors which would result from limited local time sampling of the resultant radiation field. It was found that the monthly mean regional longwave flux could be estimated with a precision better than 3 W m−2. The precision in estimated regional albedo ranged from 1.5 to 4.0% for averaging which uses directional reflectance models and from 2.6 to 11.1% for simple averaging which is dependent on equatorial crossing time. For simple averaging, regional net radiation errors ranged from 10 to 40 W m−2 with “global” bias errors as high as 36 W m−2 depending on the satellite equatorial crossing time. Similarly, monthly mean regional net radiation errors ranged from 6 to 14 W m−2 with “global” bias errors of up to 7 W m−2 when directional reflectance models were used.

Full access
Patrick Minnis
,
David F. Young
, and
Edwin F. Harrison

Abstract

The relationship between narrowband and broadband thermal radiances is explored to determine the accuracy of outgoing longwave radiation derived from narrowband data. Infrared window (10.2–12.2 μm) data from the Geostationary Operational Environmental Satellite (GOES) are correlates with longwave (5.0–50.0 μm) data from the Earth Radiation Budget Experiment (ERBE)- A simple quadratic fit between the narrowband and longwave fluxes results in standard errors of 4.4%–5.3% for data that are matched closely in time and space. The use of matched regional flux data with temporal differences up to 59 minutes yields standard errors of 4.1%–5.4%. About 30% of the error may be attributed to limb darkening and spatial and temporal differences in the matched fluxes. The relationship shows a statistically significant dependence on the relative humidity of the atmosphere above the radiating surface. Although this dependency accounts for only about 1% of the standard error, it reduces the monthly mean regional errors by more than 10%. Data taken over land produced a relationship slightly different from data taken over water. The differences appear to be primarily due to daytime heating of the land surface. Cloud amount and cloud-top height also influence the narrowband-broadband relationship. Inclusion of these statistically relevant parameters does not affect the standard errors, but it reduces the monthly mean regional errors by 9%. Better humidity and temperature data and knowledge of cloud microphysics may be required to further improve the relationship. Using the best global fits, it is concluded that the monthly mean outgoing flux may be determined with an rms uncertainty of 1.7% using a single infrared window channel with coincident cloud and humidity data. The atmospheric structure that dictates the infrared-longwave relationship does not vary randomly; it changes with climate regimes. Thus, the errors resulting from using the global fits tend to be biases concentrated in certain geographical areas. This arms biasing dampens the utility of the narrowband data for monitoring the climatic-scale changes in the longwave flux. Regressions performed on a region-by-region basis eliminate most of the monthly mean regional bias errors. Thus, the regional regressions may be useful for short-term studies requiring high temporal sampling. Because of varying atmospheric conditions, regional regressions require continual calibration with broadband instruments, thereby limiting their utility for longer-term climate applications.

Full access
Patrick Minnis
,
Edwin F. Harrison
, and
Patrick W. Heck

Abstract

A methodology for estimating cirrus cloud amounts and altitudes using visible and infrared satellite data was developed and tested using FIRE Cirrus Intensive Field Observation (IFO) coincident lidar and satellite data with a theoretical cloud albedo model. On average, cloud center heights could be determined to within ±0.9 km of the lidar-derived values using the satellite data alone. Satellite-derived, total cloud tops are generally 0.5 ± 0.9 km lower than the lidar cloud tops. If only high clouds are considered, the avenge cloud top is 0.1 ± 0.6 km higher than the lidar cloud top. The accuracies of the lidar cloud-center and cloud-top heights are estimated to be within ±0.7 km of the actual values. Satellite-derived average cloud emittance and visible optical depths can be determined to within ±0.05 and ±0.13, respectively, of the reference cloud emittance. Cirrus cloud thickness was also derived. The satellite retrieval yields cloud depths that are 0.3±1.0 km thinner than the lidar-derived cloud thicknesses. The accuracy of the lidar-derived cloud depths is estimated to be 0.7 km. It was concluded that compared to a method which analyzes each pixel individually, a bispectral approach, which averages some of the pixel values before analysis, yields lower rms and bias errors in some of the derived parameter values.

The technique was applied to GOES and AVHRR data taken during the daylight hours of the FIRE Cirrus IFO case study on a 0.5° grid covering most of Wisconsin. Broadband radiation fields from the ERBE corresponding to the AVHRR results were also analyzed. During the afternoon of 27 October 1996, a cirrus field was tracked with the GOES data as it developed over northern Wisconsin. The satellite analyses revealed average cloud-top heights ranged between 9 and 11 km. Decreases in the outgoing longwave fluxes caused by the cloud appeared to be balanced by increases in the cloud albedo resulting in a negligible change in energy balance at the top of the atmosphere due to the cloud. During 28 October, the cloud fields were highly variable with both cirrus and midlevel clouds. An organized cirrus “wedge” developed and passed though the region during the middle of the day with cloud-top heights greater than 11 km. In addition to other cirrus clouds, an apparent cirrus convective complex passed through central Wisconsin during the afternoon with cloud tops between 10.0 km and the tropopause at ∼11.3 km. A north–south line of clearing with scattered altocumulus separated the morning and afternoon cloud fields. This paper provides a comprehensive, quantified description of the case study clouds and should be useful for verifying ISCCP results and for improving the understanding of cirrus processes when combined with other IFO measurements.

Full access
Bruce A. Wielicki
,
Robert D. Cess
,
Michael D. King
,
David A. Randall
, and
Edwin F. Harrison

The role of clouds in modifying the earth's radiation balance is well recognized as a key uncertainty in predicting any potential future climate change. This statement is true whether the climate change of interest is caused by changing emissions of greenhouse gases and sulfates, deforestation, ozone depletion, volcanic eruptions, or changes in the solar constant. This paper presents an overview of the role of the National Aeronautics and Space Administration's Earth Observing System (EOS) satellite data in understanding the role of clouds in the global climate system. The paper gives a brief summary of the cloud/radiation problem, and discusses the critical observations needed to support further investigations. The planned EOS data products are summarized, including the critical advances over current satellite cloud and radiation budget data. Key advances include simultaneous observation of radiation budget and cloud properties, additional information on cloud particle size and phase, improved detection of thin clouds and multilayer cloud systems, greatly reduced ambiguity in partially cloud-filled satellite fields of view, improved calibration and stability of satellite-observed radiances, and improved estimates of radiative fluxes at the top of the atmosphere, at the surface, and at levels within the atmosphere. Outstanding sampling and remote sensing issues that affect data quality are also discussed. Finally, the EOS data are placed in the context of other satellite observations as well as the critical surface, field experiment, and laboratory data needed to address the role of clouds in the climate system. It is concluded that the EOS data are a necessary but insufficient condition for solution of the scientific cloud/radiation issues. A balanced approach of satellite, field, and laboratory data will be required. These combined data can span the necessary spatial scales of global, regional, cloud cell, and cloud particle physics (i.e., from 108 to 10−7 m).

Full access
Takmeng Wong
,
Edwin F. Harrison
,
Gary G. Gibson
, and
Frederick M. Denn

Abstract

Clouds and the Earth’s Radiant Energy System (CERES) is a NASA spaceborne measurement program for monitoring the radiation environment of the earth–atmosphere system. The first CERES instrument is scheduled to be launched on board the Tropical Rainfall Measuring Mission (TRMM) satellite in late 1997. In addition to gathering traditional cross-track fixed azimuth measurements for calculating monthly mean radiation fields, this single CERES scanner instrument will also be required to collect angular radiance data using a rotating azimuth configuration for developing new angular dependence models (ADMs). Since the TRMM single CERES instrument can only be run in either one of these two configurations at any one time, it will need to be operated in a cyclical pattern between these two scan modes to achieve the intended measurement goals. To minimize the errors in the derived monthly mean radiation field due to missing cross-track scanner measurements during this satellite mission, determination of the optimal scan mode sequence for the TRMM single CERES instrument is carried out. The Earth Radiation Budget Experiment S-4 daily mean cross-track scanner data product for April and July 1985 and January 1986 is used with a simple temporal sampling scheme to produce simulated daily mean cross-track scanner measurements under different TRMM CERES operational scan mode sequences. Error analysis is performed on the monthly mean radiation fields derived from these simulated datasets. It is found that the best monthly mean result occurred when the cross-track scanner is operated on a “2 days on and 1 day off” mode. This scan mode sequence will effectively allow for 2 consecutive days of cross-track scanner data and 1 day of angular radiance measurement for each 3-day period. The root-mean-square errors for the monthly mean all-sky (clear sky) longwave and shortwave radiation field, due to missing cross-track scanner measurements for this particular case, are expected to be less than 2.5 (0.5) and 5.0 (1.5) W m−2, respectively.

Full access
Bruce A. Wielicki
,
Bruce R. Barkstrom
,
Edwin F. Harrison
,
Robert B. Lee III
,
G. Louis Smith
, and
John E. Cooper

Clouds and the Earth's Radiant Energy System (CERES) is an investigation to examine the role of cloud/radiation feedback in the Earth's climate system. The CERES broadband scanning radiometers are an improved version of the Earth Radiation Budget Experiment (ERBE) radiometers. The CERES instruments will fly on several National Aeronautics and Space Administration Earth Observing System (EOS) satellites starting in 1998 and extending over at least 15 years. The CERES science investigations will provide data to extend the ERBE climate record of top-of-atmosphere shortwave (SW) and longwave (LW) radiative fluxes. CERES will also combine simultaneous cloud property data derived using EOS narrowband imagers to provide a consistent set of cloud/radiation data, including SW and LW radiative fluxes at the surface and at several selected levels within the atmosphere. CERES data are expected to provide top-of-atmosphere radiative fluxes with a factor of 2 to 3 less error than the ERBE data. Estimates of radiative fluxes at the surface and especially within the atmosphere will be a much greater challenge but should also show significant improvements over current capabilities.

Full access
Edwin F. Harrison
,
David R. Brooks
,
Patrick Minnis
,
Bruce A. Wielicki
,
W. Frank Staylor
,
Gary G. Gibson
,
David F. Young
,
Frederick M. Denn
, and
the ERBE Science Team

First results for diurnal cycles derived from the Earth Radiation Budget Experiment (ERBE) are presented for the combined Earth Radiation Budget Satellite (ERBS) and NOAA-9 spacecraft for April 1985. Regional scale longwave (LW) radiation data are analyzed to determine diurnal variations for the total scene (including clouds) and for clear-sky conditions. The LW diurnal range was found to be greatest for clear desert regions (up to about 70 W · m−2) and smallest for clear oceans (less than 5 W · m−2). Local time of maximum longwave radiation occurs at a wide range of times throughout the day and night over oceans, but generally occurs from noon to early afternoon over land and desert regions.

Full access