Milan Kresl

Air‐ground temperature coupling and subsurface propagation of annual temperature signals

[1] Borehole-based reconstructions of ground surface temperature (GST) have been widely used as indicators of paleoclimate. These reconstructions assume that heat transport within the subsurface is conductive. Climatic interpretations of GST reconstructions also assume that GST is strongly coupled to surface air temperature (SAT) on timescales of decades and longer. We examine these two assumptions using records of SAT and subsurface temperature time series from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. The characteristics of downward propagating annual temperature signals at each site clearly indicate that heat transport can be described as one-dimensional conduction in a homogeneous medium. Extrapolations of subsurface observations to the ground surface yield estimates of annual GST signals and allow comparisons to annual SAT signals. All annual GST signals are modestly attenuated and negligibly phase shifted relative to SAT. The four sites collectively demonstrate that differences between annual GST and SAT signals arise in both summer and winter seasons, in amounts dependent on the climatic setting of each site. INDEX TERMS: 1645 Global Change: Solid Earth; 1875 Hydrology: Unsaturated zone; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 3367 Meteorology and Atmospheric Dynamics: Theoretical modeling; KEYWORDS: heat transport, air-ground termperature coupling, paleoclimate

Daily, seasonal, and annual relationships between air and subsurface temperatures

[1] Inversions of borehole temperature profiles that reconstruct past ground surface temperature (GST) changes have been used to estimate historical changes in surface air temperature (SAT). Paleoclimatic interpretations of GST reconstructions are based on the assumption that GST and SAT changes are closely coupled over decades, centuries, and longer. This assumption has been the subject of some debate because of known differences between GST and SAT at timescales of hours, days, seasons, and years. We investigate GST and SAT relationships on daily, seasonal, and annual timescales to identify and characterize the principal meteorological changes that lead to short-term differences between GST and SAT and consider the effects of those differences on coupling between the two temperatures over much longer time periods. We use observational SAT and subsurface data from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. These records comprise intradaily observations that span parts of one or two decades. We compare subsurface temperature observations to calculations from a conductive subsurface model driven with daily SAT as the surface boundary condition and show that daily differences exist between observed and modeled subsurface temperatures. We also analyze year-to-year spectral decompositions of daily SAT and subsurface temperature time series and show that dissimilarities between mean annual GST and SAT are attributable to differences in annual amplitudes of the two temperature signals. The seasonal partitioning of these amplitude differences varies from year to year and from site to site, responding to variable evapotranspiration and cryogenic effects. Variable year-to-year differences between mean annual GST and SAT are closely estimated using results from a multivariate regression model that associates the partial influences of seasonal meteorological conditions with the attenuation of annual GST amplitudes.

Recent climate warming: Surface air temperature series and geothermal evidence

Long-term (1961 – 1996) meteorological air temperature series together with the reconstructed ground surface temperature histories, obtained by inverting borehole temperature-depth profiles, were used to project regional patterns of the recent (climate) warming rate on the territory of the Czech Republic. The characteristic magnitude of the warming rate of 0.02 –0.03 K/yr was confirmed by the results of several years of monitoring the temperature in two experimental boreholes. The monitoring of shallow temperatures at depths of about 30 –40 m, i.e. below the reach of the seasonal surface temperature variations, can serve as an alternative tool of direct quantitative assessment of the present warming rate. The data also seem to sustain a potential man-made component contributing to the more pronounced recent warming rate observed in the areas of large agglomeration.

Heat Flow, Regional Geophysics and Lithosphere Structure in Czechoslovakia and Adjacent Part of Central Europe

This chapter summarizes 208 values of heat flow that have been collected in Czechoslovakia to date. The mean heat flow and its standard deviation for the region is 71.0 ± 22.8 mW m −2. To interpret the regional geothermal activity, the results of heat flow measurements in the adjacent part of Central Europe were incorporated into the general picture, and the pattern of the heat flow density is presented in the form of a heat flow map, which shows a good correlation with the major geological features. This map was completed with the results of the deep seismic sounding and the crustal thickness pattern; characteristic temperature-depth profiles were also constructed. Heat flow was correlated with crustal thickness and with near-surface heat production. After the crustal seismic velocities had been converted into heat production, the crustal contribution to the surface heat flow was evaluated and the regional Moho heat flow distribution assessed. Heat flow data were also used to speculate on the depth of the lithosphere-asthenosphere boundary within the region under study.

First heat flow density assessments in Cuba

Abstract The first determinations of heat flow density in Cuba are reported. Precise temperature loggings were carried out in 12 holes in the western and central parts of Cuba. Along the northwestern shore, the mean temperature gradient ranges from 14–16 mK/m in the Pinar del Rio province and 18–22 mK/m east of Habana to 30 mK/m in northern Matanzas. In the Central Basin it ranges from 23–24 mK/m west of Ciego de Avila to 28–39 mK/m east of Sancti Spiritus. Rock samples for laboratory determination of thermal conductivity could be collected only from two holes in Pinar del Rio; their mean conductivity amounts to 4.1 W m −1 K −1 . From other holes no core samples were available and characteristic rocks were collected from surface outcrops in the vicinity of each hole. The measured conductivity ranges from 0.8 to 3.0 W m −1 K −1 . Heat flow density assessments revealed very low heat flow near Habana and south of Varadero (30–40 mW m −2 ) and relatively higher but still rather subnormal values in Pinar del Rio (60 mW m −2 ) and in the Central Basin (50–65 mW m −2 ). The generally low heat flow density found in western and central parts of the island thus seems to agree well with the results of marine observations in surrounding areas reported by other authors.

Heat flow in Albania

Abstract As part of a joint geothermal project between Albania and the Czech Republic, a field expedition was organized to Albania in summer 1993 to measure temperature profiles in selected boreholes and to collect rock samples to determine their thermal conductivity. Fourteen localities were visited and nine detailed temperature-versus-depth profiles were obtained. These results were completed with numerous industrial temperature records from other deep holes. The regional patterns of temperatures at 100 m depth and of characteristic near-surface temperature gradients were constructed, and the effect of the topography on the subsurface temperature field was assessed to calculate a total of 49 heat flow density data. A generally low geothermal gradient exists in all of the country, ranging from 7–11 mK/m in the synclinal belt, 11–13 mK/m in southernmost Albania, to a maximum of 18–20 mK/m in the central part of the Pre-Adriatic Depression. These values correspond to a low heat flow zone of 30 to 45–50 mW/m 2 extending from the north and bordering the Adriatic coast. Heat flow generafly increases from west to east, but its distribution in the Inner Albanides is not clear.

Radioactivity and heat production data from several boreholes in the Bohemian Massif

SummaryThe radiogenic heat production of rock samples from boreholes in the Bohemian Massif has been calculated from gamma-radiometric determinations of Th, U and K contents. The results, in general, fit the heat flow distribution on the territory of Czechoslovakia[1]. The values of heat production are in the range from 1.1µW m−3 in the eastern part to 4.4µW m−3 in the north-western part of the Bohemian Massif.

Ground-air temperature tracking and multi-year cycles in the subsurface temperature time series at geothermal climate-change observatory

Long-term observations of air, near-surface (soil) and ground temperatures, collected between 1994 and 2011, monitored in the Geothermal Climate Change Observatory at Spořilov, Prague (GCCO) are analyzed to better understand the relationship between these quantities and to describe the mechanism of heat transport at the land-atmosphere boundary layer. The 17 years long monitoring series provided a surprisingly small mean ground-air temperature offset of only 0.31 K with no clear annual course and with the offset value changing irregularly even on a daily scale. Such value is substantially lower than similar values (1–2 K and more) found elsewhere, but it may be well characteristic for a mild temperate zones, when all so far available information referred rather to more southern locations. As many other observed geophysical data, temperature time series consist of a systematic pattern (usually a set of identifiable components) contaminated by random noise, which makes the identification of the proper pattern difficult. To identify the existing systematic patterns (cycles) of the temperature-time series at several depth levels in the investigated depth interval 0–40 m, the observed data were processed with the help of the Fast Fourier Transform (FFT) and Recurrence Quantification Interval (RQI) analysis. The latter represents recently developed powerful technique to uncover hidden periodicities in a noisy time environment. At low frequency band the RQI may provide far finer resolution than the conventional FFT technique. The results proved considerable similarity for all investigated depth levels. In addition to the annual wave all measured series proved to have a more complex pattern including predominantly 8-year and 11 years long periodicities. The results were compared with similar analysis of the meteorological air temperature series as well as with the results of other similar studies. The potential dynamics explaining the occurrence of the 8-year wave is briefly discussed.

Experimental determination of the coefficient of heat transfer during hole boring and the re-establishment of the temperature field equilibrium

The results of 7 temperature measurements repeated in bore hole MB-5A have been analyzed, and the character of the disturbance of the natural temperature field during hole boring has been studied. The results make it possible to determine the heat transfer coefficient between the circulating drilling fluid and the surrounding tock. The heat flow in the bore hole is 2.14 ± 0.06 μcal/cm 2 sec, which proves the location of a region of high heat flow in the centre part of the Bohemian Cretaceous.

Terrestrial heat flow in Cuba

Abstract The results of two joint expeditions to Cuba to measure terrestrial heat flow in 1983 and 1986 are summarized. Twenty-three new values are presented, which confirm the low heat flow in practically all of the island. The mean and standard deviation (44.7 ± 13.4 mW m −2 ) agree well with previous observations.