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Thomas H. Vonder Haar

Abstract

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David Reynolds
and
Thomas H. Vonder Haar

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.

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Thomas H. Vonder Haar
and
Abraham H. Oort

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%.

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Abraham H. Oort
and
Thomas H. Vonder Haar

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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Donald W. Hillger
and
Thomas H. Vonder Haar

Abstract

This is a study of environmental conditions prior to convective development on the Great Plains of the United States on four case study days in August 1975. The tool used was the High-resolution Infrared Radiation Sounder (HIRS) on Nimbus 6. A moisture-temperature retrieval scheme was developed to retrieve various lower tropospheric analysis and forecasting parameters from the HIRS radiances. Specifically, dew points and temperatures and other secondary parameters such as total precipitable water and static stability indices were derived and analyzed at a horizontal resolution of up to 30 km on these days. For the moisture parameters the comparisons to time-interpolated NWS rawinsonde values were especially good in spite of time and resolution differences. Comparisons with higher resolution synoptic surface observations of dew point and temperature were also good. The true quality of the mesoscale analyses, however, is only seen by examining the individual case study days. Small features at a scale of ∼100 km, below the resolution of upper air and surface observations, were detected by the high-resolution satellite data. For example, perturbations on the dry line usually seen at this time of the year were apparent in the satellite data, although only the general dry line position was picked up by synoptic surface observations. The time lead also was important. Convective development starting from 2–2.5 h after the satellite pass at local noon did correlate well with the local maxima of moisture and instability seen in the satellite-derived analyses. A statistical structure analysis of the satellite-derived parameters also gave the highest signal-to-noise values for the moisture and stability parameters, whereas the temperature parameters showed much less signal-to-noise content. Results from these case study days, therefore, show the quality of high-resolution satellite-derived parameters and the applicability of this method of retrieving and using satellite soundings at the mesoscale.

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Andrew J. Negri
and
Thomas H. Vonder Haar

Abstract

Five-minute interval 1 km resolution SMS visible channel data were used to derive low-level wind fields by tracking small cumulus clouds on NASA's Atmospheric and Oceanographic Information Processing System (AOIPS). The satellite-derived wind fields were combined with surface mixing ratios to derive horizontal moisture convergence in the pre-storm environment of 24 April 1975. Storms began developing in an area extending from southwest Oklahoma to eastern Tennessee 2 h subsequent to the time of the derived fields. The maximum moisture convergence was computed to be 2.2 × 10−3 g kg−1 s−1 and areas of low-level convergence of moisture were in general indicative of regions of severe storm genesis. The resultant moisture convergence fields derived from two wind acts 20 min apart were spatially consistent and reflected the mesoscale forcing of ensuing storm development. Results are discussed with regard to possible limitations in quantifying the relationship between low-level flow and satellite-derived cumulus motion in an antecedent storm environment.

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Harold M. Gibson
and
Thomas H. Vonder Haar

Abstract

Visible and infrared data from the GOES West satellite were collected at 0700 CST and at each hour from 1000 CST to 1700 CST during summer 1986. Use of relatively high spatial and temporal resolution satellite data allowed study of local area cloud variations over broad regions in many new ways. Cloud frequency charts were computed for the area from Mississippi cast to Georgia and the Gulf of Mexico north to Tennessee for each of the nine hours as well as convection frequency charts of four convection intensifies as defined by the temperature of the cloud top. Strong diurnal cloud variations were observed.

These new data analyses show an average maximum cloud frequency near 45 percent over the land areas at about 1400 local time. The maximum of deep convection, about 8 percent, was one hour later. Cloudiness and deep convection were at a maximum during the nocturnal hours over the Gulf of Mexico. Cloud frequency shows a strong relationship to small terrain features. Small fresh water bodies have cloud minima relative to the surroundings in the afternoon hours. The higher, steep terrain shows cloud maxima and the adjacent lower terrain exhibits afternoon cloud minima due to divergence caused by the valley to mountain breeze.

The sea breeze-induced convergence causes relative cloud maxima over Gulf of Mexico near-shore land areas with the stronger maxima and greater areal coverage over peninsulas. Peninsulas that are of a similar scale or larger as compared to that of the convective cells show a late afternoon maxima of deep convection. Small scale geographical features such as small coastal islands and reservoirs show no relationship to deep convection in the frequency analysis.

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Alan E. Lipton
and
Thomas H. Vonder Haar

Abstract

The development and evaluation of a system for time-continuous mesoscale analysis is presented, with a focus on retrieving water vapor concentrations and ground surface temperatures from VISSR Atmospheric Sounder (VAS) data. The analysis system is distinguished by an intimate coupling of retrieval and numerical modeling processes that avoids some of the problem researchers have encountered when satellite-retrieved parameters have been input to models. The system incorporates virtually all of the temporal, vertical and horizontal structure that can be resolved in VAS soundings while maintaining model-generated gradients. The two primary components of the system are a version of the CSU Regional Atmospheric Modeling System (RAMS) and an algorithm for retrieving meteorological parameters from VAS data.

The analysis system was evaluated by means of simulations, with a domain that consisted of a vertical cross section through a broad mountain slope. The purposes were to determine the accuracy of coupled analysis results under controlled conditions and to compare results of the coupled scheme with those of other analysis schemes. For water vapor analysis, vertical gradients were more accurately resolved with the coupled method than with conventional retrieval from satellite data. The coupled method's incorporation of VAS data from multiple observation times was valuable for making mesoscale horizontal gradients stand out more clearly amid the noise in the water vapor analysis. In addition, the method was relatively robust when confronted with a common problem in analysis of the preconvective atmosphere—contamination of the satellite data by increasing amounts of small convective clouds. Analyses in which surface temperatures were derived from satellite-based retrievals were compared with the alternative of relying on energy balance computations without mesoscale data about soil characteristics. The surface temperatures from the two methods differed by as much as 5 K, giving rise to prominent differences in the induced mesoscale circulations. The energy balance computations were so sensitive to soil characteristics that the satellite retrieval method gave more accurate results even with cloud contamination.

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Alan E. Lipton
and
Thomas H. Vonder Haar

Abstract

Influences on the mesoscale distribution of summertime convective cloud development in the northeastern Colorado region are described using a new system for time-continuous mesoscale analysis. The analysis system is distinctive in that there is an intimate coupling between integration of a numerical model and retrieval of temperature and water vapor concentrations from VISSR Atmospheric Sounder (VAS) data. We present a case study to compare results of the coupled analysis method with those of related methods, focusing on the roles of variations in ground surface temperatures and water vapor concentrations.

The horizontal and time variations represented in satellite-based (coupled) surface temperature analyses closely corresponded to information from conventional shelter temperature observations, but had much greater detail. In contrast, temperature based on energy balance computations tended to increase too quickly during the morning and were lacking in mesoscale feature. In the water vapor analyses, when the first set of satellite data is less reliable than the later sets, some of the contamination lingers throughout the time-continuous coupled analysis results. However, the coupled method generally appears to be the most valuable method considered in this study because it exploits the major strengths of the numerical model and the satellite data while making it relatively easy to recognize and compensate for any impacts of their weaknesses. In addition, the coupled analysis results illustrated that there can be very large mesoscale gradients in temperatures at the ground surface even on relatively flat terrain. These gradients, in combination with terrain height variations, can play an important role in preconvective water vapor kinematics through their influences on vertical and horizontal winds. The analysis system proved to be valuable for forecasting through the close correspondence between derived stability indices and later convective development in the case we studied.

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Davidn W. Reynolds
and
Thomas H. Vonder Haar

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.

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