Global 3D-Nephanalysis of Total Cloud Amount: Climatology for 1979

International Journal of Remote Sensing

Henderson‐Sellers

Goodman

1989

Self Cite

There is a need for cloud information with which to conduct validation of the International Satellite Cloud Climatology Project (ISCCP) cloud retrievals. . The U.S. Air Force (USAF) nephanalysis is at present the only operational realtime global cloud analysis and the available archive from this offers a potential database for comparison with ISCCP retrievals. The performance of the USAF 3D (three dimensional) Nephanalysis during the month of July 1983, one of the months designated for validation/intercomparison, is examined here on a regional basis. The cloud field retrieved by the USAF Nephanalysis is examined in relation to features unique to the archive such as the inclusion, where appropriate, of conventional observations. A direct comparison with ground-based observations illustrates the effect of conventional data on the archive over a range of time scales. Examination of the Nephanalysis over difficult areas such as polar and desert regions reveals some of the problems pertinent to most current cloud algorithms. Comparisons between 3D Nephanalysis archives separated by 4 years (1979 and 1983) show interannual and synoptic effects and illustrate the evolution of this retrieval algorithm. The most obvious change is due to modifications to the technique employed for spreading conventional observations (surface and aircraft) into the satellite-based analysis. The more recent method results in input from isolated stations being more obvious in the final archive although the values reported are generally close to those in the surrounding satellite retrieval. Bogussing (the imposition of cloud amounts derived, at the time, by an analyst usually from geostationary satellite data) is another feature unique to the USAF Nephanalyses. These two characteristics mean that unsupervised (i.e. purely computer-based) comparison between real-time (RT) Nephanalysis and, for example, ISCCP would be unwise. On the other hand, the year-to-year consistency of the USAF retrieval algorithm, the clear lack of reference to previously determined climatological fields and the time and space resolution and continuity of the Nephanalysis product suggest that the USAF Nephanalysis offer a valuable data set for comparison with ISCCP provided that comparisons are undertaken with care.

contrasting

confidence: 43%

Regional analysis of 3D (three-dimensional) Nephanalysis total cloud amounts for July 1983

International Journal of Remote Sensing

Henderson‐Sellers

Goodman

1989

Self Cite

“…The automated algorithm is the US Air Force 3D-nephanalysis which has been described by Fye (1978) and more briefly in Hughes and Henderson-Sellers (1985). It categorizes cloud cover fraction and cloud level over the northern hemisphere on a 46 x 46 km grid.…”

Section: Analysis Techniquesmentioning

confidence: 99%

Intercomparison of satellite-derived cloud analyses for the Arctic Ocean in spring and summer

International Journal of Remote Sensing

Barry

Schweiger

et al. 1988

Several methods of deriving Arctic cloud information, primarily from satellite imagery, have been intercompared. The comparisons help in establishing .what cloud information is most readily determined in polar regions from satellite data analysis. The analyses for spring-summer conditions show broad agreement, but subjective errors affecting some geographical areas and cloud types are apparent. The results suggest that visible and thermal infrared data may be . insufficient for adequate cloud mapping over some Arctic surfaces.

“…not research projects such as ERBE in which algorithms may change], the U.S. Air Force's operational cloud analysis (Fye, 1978;Hughes and Henderson-Sellers, 1985), RT (real time) Nephanalysis, integrates conventional cloud information into a predominantly satelliteretrieved database while ISCCP (International Satellite Cloud Climatology Project, Rossow, 1983, 1985) excludes all conventional observations. One reason given for this exclusion is the heterogeneity which would be involved if surface observations were introduced.…”

Section: Introduction: Surface Satellite and 'Earth' Views Of Cloudsmentioning

confidence: 99%

Basis for integration of conventional observations of cloud into global nephanalyses

Henderson‐Sellers

1990

J Atmos Chem

Self Cite

Water vapour is the largest and, radiatively, the most important trace gas in the Earth's atmosphere. Cloud amount and cloud optical depth feedbacks are, as yet, poorly understood and improvements in model parameterization schemes await an adequate observational data base. Satellite retrievals do not, and will not for some time, provide more than 'snapshot' (a few months to a few years) records. Conventional surface-based observations of cloudiness could complement the global coverage offered by satellite retrievals if a sound relationship between the two observational measurements could be found. Observations underline the importance of the vertical dimension of clouds which affects the observational geometries from satellites and the surface. A new basis for the relationship between the (vertical) earthview of cloud amount and the (whole dome) skycover of cloud amount has been sought. Over four and a half thousand all-sky camera photographs, representing a considerable range of seasonal and climatological conditions, have been analyzed to give rise to a database from which predictive relationships for earthview, E, and skycover, S, have been established.Cubic functions are the most soundly based both physically and empirically. We find: S= 0.647 + 2.192E-0.461E 2 + 0.037E 3 and E = -0.001 + 0.082S+ 0.269S 2 -0.019S 3 for the prediction of skycover from earthview and earthview from skycover, respectively. If earthview is required from skycover observations then E = S could be used with little additional error. Hence, conventional surface observations of skycover could be compared directly with satellite-derived earthview values. More importantly, these results do not support the widespread assumption that conventional (surface) observations of cloud amount always exceed the earthview cloud retrieval. Furthermore, climate model predictions of total cloud amount may also be interpreted via these relationships. GCM-predicted layer cloud amounts can be synthesized into 'modelled E' values using the random overlap formula and hence it is possible to construct ~modelled S' values which are directly comparable with conventionally observed cloud climatologies. The 'baseline' observation of skycover by clouds therefore provides a valuable validation tool for both satellite programmes and climate models.