Olavi Kärner

Some examples of negative feedback in the Earth climate system

Temporal variability of daily time series for total solar irradiance at the top of the atmosphere, the Microwave Sounding Unit (MSU) based global, hemispherical and zonal average temperature for the lower troposphere and stratosphere together with 5 surface air temperature data, measured at various meteorological stations have been studied by means of the structure function. From the growth rate of the structure function in the time interval between 32 and 4096 days it follows that the variability of the series represents an anti-persistent (AP) behavior. This property in turn shows a domination of negative feedback in the physical system generating the lower tropospheric temperature variability. Distribution of the increments over various ranges and correlations between them are calculated in order to determine the quantitative characteristics describing temporal variability.

Time Series Analysis: A New Methodology for Comparing the Temporal Variability of Air Temperature

Temporal variability of three different temperature time series was compared by the use of statistical modeling of time series. The three temperature time series represent the same physical process, but are at different levels of spatial averaging: temperatures from point measurements, from regional Baltan65

Temporal Variability in Local Air Temperature Series Shows Negative Feedback

Long daily surface air temperature series from 24 European and Asian stations are analyzed, among them the Central England temperature dataset (1772 – 2005). The mean seasonal cycle in each series is removed and correlations between the consecutive increments of various increment intervals for the anomaly series are calculated. The sample correlations appear to behave similarly for all series. A positive coefficient between the short-term (daily etc) increments rapidly changes to the negative side while the increment interval increases. The value of the coefficient saturates at the level −0.5 and stays at that level for long range of intervals from 20 to 2000 days. The feature is a testimony to the regulating role of (cumulative) negative feedback in the climate system during the last two centuries.

A method to derive surface insolation from NOAA AVHRR data

Abstract Histogram technique in cloud classification is based on the idea that the histogram of pixel radiances over an area will show clusters of pixels that represent different cloud or surface types. Assuming that radiance reflected (emitted) by a certain cloud level or surface type is normally distributed, the radiance histograms collected over any regular area are mixtures of normal components. A scheme is produced for a two-dimensional case to analyse NOAA AVHRR CH1 and CH4 radiance histograms and separate the components. As a result, mean reflectance and (top) temperature values for each component can be obtained together with the weights of the components that describe cloudy and cloud-free fractions. A simple method to calculate mean (over the histogram area) daily surface insolation is introduced. The necessary coefficients to convert cloud amount and cloud reflectance into atmospheric transmittance have been found by means of ground-truth measurements at seven actinometric stations of Poland.

Local air temperature tolerance: a sensible basis for estimating climate variability

The customary representation of climate using sample moments is generally biased due to the noticeably nonstationary behaviour of many climate series. In this study, we introduce a moment-free climate representation based on a statistical model fitted to a long-term daily air temperature anomaly series. This model allows us to separate the climate and weather scale variability in the series. As a result, the climate scale can be characterized using the mean annual cycle of series and local air temperature tolerance, where the latter is computed using the fitted model. The representation of weather scale variability is specified using the frequency and the range of outliers based on the tolerance. The scheme is illustrated using five long-term air temperature records observed by different European meteorological stations.

Surface insolation from AVHRR data by means of a three-dimensional histogram separation

Abstract An analysis has been carried out to investigate the possibilities of the retrieval of surface insolation in the Baltic Sea region from satellite data. For this purpose, radiation measurements in three channels of AVHRR (CH1, CH2 and CH4) during eight overpasses of NOAA-11 have been used. The method is based on the idea that the outgoing radiation contains sufficient information on the cloud cover. Three-dimensional radiation histograms over target areas of approximately 200×200 km2 were approached by means of mixtures of Gaussian components that can be ascribed to different cloud layers or surface areas. Use of the ratio of CH2/CH1 radiances as the third variable permits to separate clear and cloudy components better. Therefore, an advanced threshold scheme can be built in comparison with a two-dimensional case that uses only CH1 and CH4 data and needs additional information on the temperature profiles. The method enables one to derive surface insolation over large areas. To get better results, ground-based measurements in sparse actinometric stations could be used to tune the retrieval.