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- Author or Editor: THOMAS H. VONDER HAAR x
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Abstract
Abstract
Abstract
A number of large tropical cumulus clouds which developed and decayed over a one-day period were monitored by both ship-based radar and the reflected solar radiance experiment on the geosynchronous satellite ATS-3. A comparison of the radar height of these clouds to their reflected solar radiance has shown a strong correlation (0.88) such that cumulus cloud height and growth may apparently be inferred from a geostationary satellite platform without the use of ground-based radar.
Abstract
A number of large tropical cumulus clouds which developed and decayed over a one-day period were monitored by both ship-based radar and the reflected solar radiance experiment on the geosynchronous satellite ATS-3. A comparison of the radar height of these clouds to their reflected solar radiance has shown a strong correlation (0.88) such that cumulus cloud height and growth may apparently be inferred from a geostationary satellite platform without the use of ground-based radar.
Abstract
Recent measurements of the earth's radiation budget from satellites, together with extensive atmospheric energy transport summaries based on rawinsonde data, allow a new estimate of the required poleward energy transport by Northern Hemisphere oceans for the mean annual case. In the region of maximum net northward energy transport (30–35N), the oceans transport 47% of the required energy (1.7×1022 cal year−1). At 20N, the peak ocean transport accounts for 74% at that latitude; for the region 0–70N the ocean contribution averages 40%.
Abstract
Recent measurements of the earth's radiation budget from satellites, together with extensive atmospheric energy transport summaries based on rawinsonde data, allow a new estimate of the required poleward energy transport by Northern Hemisphere oceans for the mean annual case. In the region of maximum net northward energy transport (30–35N), the oceans transport 47% of the required energy (1.7×1022 cal year−1). At 20N, the peak ocean transport accounts for 74% at that latitude; for the region 0–70N the ocean contribution averages 40%.
Abstract
Based on the best presently available satellite radiation, atmospheric and oceanic data sets the long-term mean heat balance of the earth and its normal seasonal variation are investigated over the Northern Hemisphere. Quantitative estimates for the various flux and storage terms in the atmospheric and terrestrial branches of the heat balance are given for 10° wide latitude belts and for each calendar month. The results are presented in both graphical and tabular form. As was known before, the storage of heat in the oceans is found to dominate the energy storage in the combined atmosphere-ocean-land-cryosphere system. In the tropics, large changes in oceanic heat storage are found in the 10°N–20°N belt with a maximum in spring and a minimum in late summer. The main new finding of this study is that the inferred oceanic heat transports appear to undergo very large seasonal variations especially in the tropics. Between 10°N and 20°N, maximum northward oceanic transports of 4 to 5 × 1015 W were competed in spring and late fall, which are as large as or larger than the corresponding mid-latitude atmospheric transports. Near the equator the oceanic fluxes were found to reverse seasonally and be directed generally toward the winter hemisphere with an absolute maximum of −8 × 1015 W in August.
Abstract
Based on the best presently available satellite radiation, atmospheric and oceanic data sets the long-term mean heat balance of the earth and its normal seasonal variation are investigated over the Northern Hemisphere. Quantitative estimates for the various flux and storage terms in the atmospheric and terrestrial branches of the heat balance are given for 10° wide latitude belts and for each calendar month. The results are presented in both graphical and tabular form. As was known before, the storage of heat in the oceans is found to dominate the energy storage in the combined atmosphere-ocean-land-cryosphere system. In the tropics, large changes in oceanic heat storage are found in the 10°N–20°N belt with a maximum in spring and a minimum in late summer. The main new finding of this study is that the inferred oceanic heat transports appear to undergo very large seasonal variations especially in the tropics. Between 10°N and 20°N, maximum northward oceanic transports of 4 to 5 × 1015 W were competed in spring and late fall, which are as large as or larger than the corresponding mid-latitude atmospheric transports. Near the equator the oceanic fluxes were found to reverse seasonally and be directed generally toward the winter hemisphere with an absolute maximum of −8 × 1015 W in August.
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Abstract
A technique is presented for determining cloud heights and amounts through the use of simultaneous. infrared and visible satellite radiance data. A set of simultaneous equations are developed which solve for cloud-top temperature (T cld) and cloud amount (A cld) within the geometric field of view of the sensor. The cloud height is determined by comparing T cld to upper air soundings, An error analysis is also presented showing the accuracy that can he obtained in T cld and A cld when uncertainties exist in the measured visible and infrared radiances and in the assumptions required.
Actual satellite measurements taken from the NOAA Scanning Radiometer (SR) are input into the technique and run for three specific geographical locations during several seasons where ground-based cloud observations are available. Results show an rms error in cloud amount of 0.2 and in cloud height of 0.5 km for a 75 km×75 km area for all cloud types except cirrus. For this case we have developed alternate solutions which account for the optical depth and emissivity problems associated with cirrus. The modified method was successfully tested on a few cirrus cases showing a reduction in the rms error in cloud height by 1.5 km to an rms error of 1.1 km.
Applications of the bispectral method include determining cloud parameters for vertical temperature sounders, solo energy studies, aircraft operations and global earth energy budgets.
Abstract
A technique is presented for determining cloud heights and amounts through the use of simultaneous. infrared and visible satellite radiance data. A set of simultaneous equations are developed which solve for cloud-top temperature (T cld) and cloud amount (A cld) within the geometric field of view of the sensor. The cloud height is determined by comparing T cld to upper air soundings, An error analysis is also presented showing the accuracy that can he obtained in T cld and A cld when uncertainties exist in the measured visible and infrared radiances and in the assumptions required.
Actual satellite measurements taken from the NOAA Scanning Radiometer (SR) are input into the technique and run for three specific geographical locations during several seasons where ground-based cloud observations are available. Results show an rms error in cloud amount of 0.2 and in cloud height of 0.5 km for a 75 km×75 km area for all cloud types except cirrus. For this case we have developed alternate solutions which account for the optical depth and emissivity problems associated with cirrus. The modified method was successfully tested on a few cirrus cases showing a reduction in the rms error in cloud height by 1.5 km to an rms error of 1.1 km.
Applications of the bispectral method include determining cloud parameters for vertical temperature sounders, solo energy studies, aircraft operations and global earth energy budgets.
Abstract
This paper summarizes an extended time series of measurements of the earth's radiation budget from the first and second generation United States meteorological satellites. Values of planetary albedo, infrared radiant emittance, and the resulting net radiation budget are now available for 39 months during the period 1962–66. These measurements show a mean global albedo of 30%, and net radiation balance within measurement accuracy. The discussion treats global and zonally averaged values for the “mean annual” case, for “mean seasons,” and includes a comparison of measurements during the same seasons in different years. The role of these radiation budget measurements in the total global energy balance is noted.
Abstract
This paper summarizes an extended time series of measurements of the earth's radiation budget from the first and second generation United States meteorological satellites. Values of planetary albedo, infrared radiant emittance, and the resulting net radiation budget are now available for 39 months during the period 1962–66. These measurements show a mean global albedo of 30%, and net radiation balance within measurement accuracy. The discussion treats global and zonally averaged values for the “mean annual” case, for “mean seasons,” and includes a comparison of measurements during the same seasons in different years. The role of these radiation budget measurements in the total global energy balance is noted.
Abstract
The GOES-8/Imager has provided scientifically valuable imagery since its launch in April of 1994. However, without an onboard calibration source most research applications involving its data have been limited to qualitative analysis of the imagery. Presented herein is a review of previous quantitative work, including the prelaunch calibration information, and results of a new calibration effort that compares GOES-8/Imager raw counts of clear ocean scenes to theoretical satellite-detected radiance values from a radiative transfer model. Monthly averages of the calibration coefficient are presented at 6-month intervals from August 1995 through August 1999. Although the technique differs from previous calibration efforts, which compare Geostationary Operational Environmental Satellite observations to some reference instrument, the new calibration results agree well with previous results. The calibration suggests a one-time decrease of 7.6% shortly after launch, and an ongoing annual degradation of 5.6% thereafter.
Abstract
The GOES-8/Imager has provided scientifically valuable imagery since its launch in April of 1994. However, without an onboard calibration source most research applications involving its data have been limited to qualitative analysis of the imagery. Presented herein is a review of previous quantitative work, including the prelaunch calibration information, and results of a new calibration effort that compares GOES-8/Imager raw counts of clear ocean scenes to theoretical satellite-detected radiance values from a radiative transfer model. Monthly averages of the calibration coefficient are presented at 6-month intervals from August 1995 through August 1999. Although the technique differs from previous calibration efforts, which compare Geostationary Operational Environmental Satellite observations to some reference instrument, the new calibration results agree well with previous results. The calibration suggests a one-time decrease of 7.6% shortly after launch, and an ongoing annual degradation of 5.6% thereafter.
Abstract
Time and space sampling is an increasingly critical aspect of Earth observation satellites. The highly eccentric orbit used by Soviet Molniya satellites functions much like a high-latitude geostationary orbit. Meteorological instruments placed on a satellite in a Molniya orbit would improve the temporal frequency of observation of high-latitude phenomena such as polar lows. Consideration of this new sampling strategy is suggested for future systems such as the “Earth Probe” satellites in the Mission to Planet Earth program as well as for operational meteorological satellite programs.
Abstract
Time and space sampling is an increasingly critical aspect of Earth observation satellites. The highly eccentric orbit used by Soviet Molniya satellites functions much like a high-latitude geostationary orbit. Meteorological instruments placed on a satellite in a Molniya orbit would improve the temporal frequency of observation of high-latitude phenomena such as polar lows. Consideration of this new sampling strategy is suggested for future systems such as the “Earth Probe” satellites in the Mission to Planet Earth program as well as for operational meteorological satellite programs.
Abstract
Infrared (IR) and visible satellite data from the Japanese Geostationary Meteorological Satellite (GMS-4) with 5-km spatial and 1-h temporal resolution were used to examine the diurnal cycle of deep convection over a sector of the tropical west Pacific warm pool bounded by 0°–20°N, 140°E–180°. Data were analyzed for 45 days of summer from 22 June to 5 August 1994 and for 65 days of winter between 28 November 1994 and 31 January 1995.
Deep convective clouds were identified in IR imagery using brightness temperature (T BB) threshold techniques. Based on previous studies, a −65°C cloud-top T BB threshold was chosen to isolate pixels containing active, deep convection. Spectral analysis of time series constructed from hourly cold cloud (⩽−65°C) pixel counts revealed a powerful diurnal cycle of deep convection significant at the 95% confidence level during summer and winter. Composited hourly statistics of fractional areal cloud cover documented a 0500–0600 local standard time (LST) maximum with a 1500–1900 LST minimum of convection for both seasons.
Objective analysis techniques were developed to analyze the phase and amplitude of the diurnal cycle of deep convection and its relation to the satellite-observed daily spatial and temporal variation of tropical mesoscale convective systems (MCSs). Results showed that the diurnal cycle of convective rainfall with an early morning maximum was disproportionately dominated by the largest ∼10% of MCSs for each time period. While the number of large MCSs increased only slightly throughout nocturnal hours, the area of cold cloud associated with these systems expanded dramatically. An algorithm called “threshold initiation” showed that all scales of organized, intensifying deep convection existed at all times of day and night. In addition, the early morning peak was largely composed of building convection. Conditional recurrence probabilities of deep convection associated with MCSs were computed at 24- and 48-h intervals. Results for summer and December 1994 revealed that when early morning convection associated with a large MCS occurred at any location, the same region contained convection the next morning nearly half the time. Convection was less likely at the 48-h point. These results are not consistent with diurnal theories based on sea surface heating, afternoon initiation of convection, and nocturnal evolution of mesoscale convective systems.
Findings indicate that the diurnal cycle of deep convective cloud is driven by the internal variation of large clusters. MCSs embedded in cloud clusters that exist into or form during the night grow spatially larger and more intense. Some results support direct radiative forcing of clouds and large-scale clear-region radiative destabilization as possible contributors to diurnal convective variability. However, all findings are consistent with the work of Gray and colleagues that emphasizes the role of day–night variations in net tropospheric cooling in clear and longwave cooling in cloudy versus clear regions as an explanation of the observed daily variation of tropical convective rainfall and its significant relationship to organized mesoscale convection.
Abstract
Infrared (IR) and visible satellite data from the Japanese Geostationary Meteorological Satellite (GMS-4) with 5-km spatial and 1-h temporal resolution were used to examine the diurnal cycle of deep convection over a sector of the tropical west Pacific warm pool bounded by 0°–20°N, 140°E–180°. Data were analyzed for 45 days of summer from 22 June to 5 August 1994 and for 65 days of winter between 28 November 1994 and 31 January 1995.
Deep convective clouds were identified in IR imagery using brightness temperature (T BB) threshold techniques. Based on previous studies, a −65°C cloud-top T BB threshold was chosen to isolate pixels containing active, deep convection. Spectral analysis of time series constructed from hourly cold cloud (⩽−65°C) pixel counts revealed a powerful diurnal cycle of deep convection significant at the 95% confidence level during summer and winter. Composited hourly statistics of fractional areal cloud cover documented a 0500–0600 local standard time (LST) maximum with a 1500–1900 LST minimum of convection for both seasons.
Objective analysis techniques were developed to analyze the phase and amplitude of the diurnal cycle of deep convection and its relation to the satellite-observed daily spatial and temporal variation of tropical mesoscale convective systems (MCSs). Results showed that the diurnal cycle of convective rainfall with an early morning maximum was disproportionately dominated by the largest ∼10% of MCSs for each time period. While the number of large MCSs increased only slightly throughout nocturnal hours, the area of cold cloud associated with these systems expanded dramatically. An algorithm called “threshold initiation” showed that all scales of organized, intensifying deep convection existed at all times of day and night. In addition, the early morning peak was largely composed of building convection. Conditional recurrence probabilities of deep convection associated with MCSs were computed at 24- and 48-h intervals. Results for summer and December 1994 revealed that when early morning convection associated with a large MCS occurred at any location, the same region contained convection the next morning nearly half the time. Convection was less likely at the 48-h point. These results are not consistent with diurnal theories based on sea surface heating, afternoon initiation of convection, and nocturnal evolution of mesoscale convective systems.
Findings indicate that the diurnal cycle of deep convective cloud is driven by the internal variation of large clusters. MCSs embedded in cloud clusters that exist into or form during the night grow spatially larger and more intense. Some results support direct radiative forcing of clouds and large-scale clear-region radiative destabilization as possible contributors to diurnal convective variability. However, all findings are consistent with the work of Gray and colleagues that emphasizes the role of day–night variations in net tropospheric cooling in clear and longwave cooling in cloudy versus clear regions as an explanation of the observed daily variation of tropical convective rainfall and its significant relationship to organized mesoscale convection.
