Infrared radiative cooling in the mesosphere and lower thermosphere

This paper discusses the current status of calculating infrared cooling by CO₂ in the mesosphere and lower thermosphere. It is desirable to have fast but accurate procedures for use in dynamic models. The most difficult region is from 70 to 90 km, where cooling rates are strongly influenced or, in the case of the summer mesopause region, dominated by the absorption of radiation emitted by underlying layers, with the hot bands and isotopic bands playing a significant role. A three-energy-level model is derived for the excited population levels of a CO₂ molecule. Vibrational-vibrational coupling between isotopes is also included as significant. Results from model calculations for cooling rates and NLTE source functions are presented. Global average infrared cooling rates appear to be in reasonable balance with solar heating rates, considering the uncertainties in calculating both these terms. Radiative cooling rates by CO₂ above 100 km are strongly dependent on atomic oxygen concentrations and on the rate of energy exchange between atomic oxygen and CO₂. Likewise, NO cooling, which is important above 120 km, is proportional to atomic oxygen concentrations. Since CO₂, NO and O concentrations can all vary with motions, these dependencies suggest interesting feedbacks to atmospheric dynamics.     

The impact of gravity waves on nitric oxide in the lower thermosphere

Observations of nitric oxide (NO) by the Solar Mesosphere Explorer (SME) during equinox indicate a lower-thermosphere equatorial minimum which is at variance with theoretical predictions. To address this discrepancy a zonally averaged model of the thermosphere and upper mesosphere is used to evaluate the influence of a latitude variation in turbulence. Five numerical simulations were performed with different latitude structures of eddy diffusion (K_T), ranging from uniform in latitude, peaks at low, mid-, or high-latitude, to a hemispherically asymmetric distribution. A local increase in eddy diffusion causes the lower thermosphere to cool and induces a latitude pressure gradient that drives horizontal and vertical winds. The circulation, turbulent transport and temperature dependent chemistry act to change the distribution of species. Comparison of the model predictions of NO with SME data, and simulated wind and temperature structure with empirical climatology, indicates a preference for a midlatitude peak in K_T.     

Diurnal tide in the Antarctic and Arctic mesosphere/lower thermosphere regions

The behaviour of the diurnal tide at 95 km over various years between 1965 and 1986 is studied using radar data from Heiss Island (81°N), Mawson (67°S), Molodezhnaya (68°S) and Scott Base (78°S). The observations are also compared with the model results of FORBES and HAGAN [(1988) Planet. Space Sci. 36, 579] for the same latitudes. There are substantial fluctuations in amplitude and phase at all stations, particularly in winter. Phase fluctuations can be as large as a uniform random distribution over the 24-h cycle. In summmer the phases of the meridional components are well defined and suggest the presence of a dominant symmetric mode. The meridional amplitudes are larger in summer whereas the zonal components have a greater variation and show no significant variation with season.     

Monthly simulations of the solar semidiurnal tide in the mesosphere and lower thermosphere

Monthly simulations of the solar semidiurnal tide in the 80–100 km height regime are presented. These calculations benefit from the recent heating rates provided by Groves G. V. (1982a,b) (J. atmos. terr. Phys. 44, 111; 44, 281), the zonally-averaged wind, temperature and pressure fields developed for the new COSPAR international reference atmosphere [Labitzke K., Barnett J. J. and Edwards B. (1985) Handbook for MAP 16, 318], and eddy diffusivities determined from gravity wave saturation climatologies and used by Garcia R. R. and Solomon S. (1985) (J. geophys. Res. 90, 3850) to simulate oxygen photochemistry and transport in the mesosphere and lower thermosphere. Some of the main characteristics of the observed semidiurnal tide at middle and high latitudes are reproduced in our simulations: larger amplitudes in winter months than in summer months, and the bi-modal behavior of the phase with summer-like and winter-like months separated by a quick transition around the two equinoxes. The phase transition is also more rapid in the spring, consistent with observations. The wavelengths are also longer in summer than in winter, at least below 95 km (whereas in July and August the simulations exhibit some discrepancies above this altitude), similar to the observational data. Semidiurnal amplitudes are generally smaller and the phases more seasonally symmetric at middle and low latitudes, as compared with the tidal structures above about 50° latitude. In addition, hemispheric differences in the mean zonal wind result in marked asymmetries in tidal behavior between the Arctic and Antarctic regions, and suggest that a comparative study of tide, gravity wave and mean flow interactions in the Arctic and Antarctic mesosphere and lower thermosphere would be fruitful.     

The semidiurnal tides at the midlatitude lower thermosphere over East Siberia

Results from the study of semidiurnal tides in the horizontal wind field at 85–95 km over East Siberia are presented. The seasonal variation of tidal amplitudes and the effects of stratospheric warmings are discussed.     

A comparison of three methods of measuring tidal oscillations in the lower thermosphere using EISCAT common programmes

The EISCAT Common Programme can be used in three ways to monitor tidal oscillations in the lower thermosphere. In Common Programme One (CPI) tristatic observations provide measurements of the ion-velocity vector at several heights in the E-region and one height in the F-region. In Common Programme Two (CP2) monostatic measurements give profiles of ion velocity in the E-region while tristatic measurements give continuous measurements of ion velocity in the F-region. From the ion velocities and the ion-neutral collision frequency, the vector of the E-region neutral wind can be determined and both east-west and north-south components of the diurnal, semi-diurnal and ter-diurnal oscillations can be identified. CP1 and CP2 also provide profiles of the field-aligned ion velocity, and these can be used to calculate the north-south component of the neutral wind without knowing the ion-neutral collision frequency, but the result is affected by any vertical component of neutral velocity. The three methods are compared and the advantages of CP2 demonstrated.     

Vertical winds in the midlatitude thermosphere from Fabry-Perot interferometer measurements

Monostatic and bistatic measurements of thermospheric winds have been made with Fabry-Perot Interferometers at the Millstone Hill and Laurel Ridge Observatories. Synchronized observing sequences have been chosen to enable the determination of vertical winds from the measurements. The vertical winds are found to be significant on some nights with velocities of tens of m/s. For geomagnetically quiet nights, the averaged values for eight samples in the July–October 1992 period show little variation during the night, averaging ∼10 m/s downward. The average for three geomagnetically disturbed nights oscillates from a downward maximum of ∼50 m/s at ∼02 UT to an upward maximum of ∼20 m/s at ∼07 UT. Temporal variations in the vertical motions suggest oscillatory behavior with periods of ∼0.7, ∼1.8 and ∼3.4 h, respectively, on three quiet nights, possibly associated with gravity wave or tidal-harmonic effects.     

Evidence for a Neolithic Age fire-irrigation paddy cultivation system in the lower Yangtze River Delta,China

Establishing stable cropping systems was vital in antiquity, assuring certain yields and enabling ancient people to settle, thus possibly causing various modern food habits and culture to form around the world, especially in cereal-cultivation-dominated countries. China, one of the most famous ancient agricultural countries, has a long history of rice planting, and the fire-irrigation paddy cultivation system is prevalent in the lower Yangtze region, which is considered a rice domestication center. However, its origin and cultivation pattern remain unclear. We studied a famous agricultural vestige, the Chuodun site, involved in rice planting in the lower Yangtze River Delta in eastern China, during the Neolithic Age. Clear evidence from archaeology, paleobiology, pedology and biogeochemistry suggest both that the rice fire-irrigation cultivation system formed during the Neolithic Age and that ancient peoples lived there steadily. Under this extensive cultivation system, soil structures and properties changed significantly; in particular, it left more black carbon in the soil and increased the organic carbon soil stability, which can be used to reconstruct prehistoric environments. Meanwhile, the prevalent fire-irrigation paddy cultivation system used by farmers in this area, though for a different purpose than ancient people, may be inherited from the Neolithic Age.     

Secular variations in seawater chemistry as a control on the chemistry of basinal brines: test of the hypothesis

The hypothesis that basinal brines inherited their major ion chemistries and elevated salinities from evaporated paleoseawaters is tested by comparing the compositions of basinal brines in Silurian (Michigan basin, Illinois basin, Appalachian basin in eastern Ohio) and Jurassic/Cretaceous (Central Mississippi Salt Dome basin, Arkansas shelf, and south‐central Texas) host rocks, when the world oceans were ‘CaCl₂ seas’, with those from Permian and Pennsylvanian rocks (Palo Duro basin, Central Basin Platform, and Delaware basin, Texas and New Mexico) when the world oceans were ‘MgSO₄ seas’. Basinal brines examined are assumed to have originally formed from evaporation of the same seawaters that produced major evaporites. Sulfate, Mg and K levels in basinal brines are below the concentrations expected from evaporation of seawater of any type, which emphasizes the importance of diagenetic mineral–brine interactions in controlling basinal brine chemistry. There are no major differences in SO₄, Mg and K concentrations between basinal brines hosted by rocks originally formed during ages when the world oceans were MgSO₄ seas versus CaCl₂ seas. Basinal brines in Pennsylvanian–Permian rocks are compositionally distinct (relatively high Na and low Ca) from basinal brines in Silurian, Jurassic and Cretaceous host rocks, which may reflect original differences in seawater chemistry. Basinal brines enriched in Ca and depleted in Na relative to evaporated seawater of any type have traditionally been interpreted to form by albitization of plagioclase feldspar. A new explanation for Ca enrichment and Na depletion of basinal brines is the mixing of evaporated CaCl₂‐type seawater with more dilute water. Some basinal brines are similar in major ion composition to evaporated seawater of a particular age, for example basinal brines in the Cretaceous Edwards Group carbonates, Texas, where dolomitization is the only reaction required to convert evaporated Mesozoic CaCl₂ seawater into Edwards Group brine.     

Biological continuity between the A- and C-groups in lower Nubia: Evidence from cranial non-metric traits

Data are presented on 45 cranial non-metric traits in skeletal samples of the Lower Nubian A-Group (ca. 3100–2500 BC) and C-Group (ca. 2000–1500 BC) cultural periods. Results, based on the mean measure of divergence statistic, reveal biological continuity, consistent with interpretations of in situ evolution as opposed to models of discontinuity resulting from gene flow. Any differences between the A-and C-Group cultural phases that may be evident in the archaeological record are therefore more likely the result of local cultural evolution, rather than the introduction of new ideas, customs, and materials through the migration of a new population into this area. The problem of small samples necessitates that our results be accepted cautiously.     

Making sense out of cents: compositional variations in European coins as a control model for archaeometallurgy

Archaeometallurgy frequently seeks to correlate between the temporal and spatial distribution of ancient metal objects and their chemical composition. In this study, we examined whether and to what extent local or temporal deviations in the content of modern artifacts can be identified as a proxy for archaeological material that is typically less controlled and therefore more difficult to cluster. For this purpose, Euro coins of 10, 20 and 50 cents from Germany, France, Spain, Italy and Belgium, which are made of copper (Cu) with 5% aluminum (Al), 5% zinc (Zn) and 1% tin (Sn), were analyzed using a simple XRF analyzer. The mass ratios Sn/Cu and Zn/Cu were measured with a relative precision c.a. of 5%. The mean content of the coins from each country was then determined for 20–39 of them. The difference of the mass ratio Sn/Cu observed – from 0.0101 to 0.0111. One coin from Luxemburg shows differences in various areas of its surface of up to a factor of 1.5. Thus, the results of this small pilot research show that even in modern metal artifacts we can detect differences in metal content, which can be correlated to their production and utilization places. Therefore, this study can serve as a model for evaluating compositional variations noted in archaeometallurgical studies where the standard deviations are greater and the differences can be linked more readily to spatial and temporal differences.     

Evidence for the Past

Book reviewed in this article:
The What and the Why of History: Philosophical Essays By Leon J. Goldstein     

A palaeotemperature record for the Finnish Lakeland based on microdensitometric variations in tree rings

X-ray based tree-ring data of maximum latewood densities (MXD) was combined for south-eastern Finland. This data originated from subfossil and modern pine (Pinus sylvestris L.) materials comprising a continuous dendroclimatic record over the past millennium. Calibrating and verifying the MXD chronologies against the instrumental temperature data showed a promising opportunity to reconstruct warm-season (May through September) temperature variability. A new palaeotemperature record correlated statistically significantly with the long instrumental temperature records in the region and adjacent areas since the 1740s. Comparisons with tree-ring based (MXD and tree-ring width) reconstructions from northern Fennoscandia and northern Finland exhibited consistent summer temperature variations through the Medieval Climate Anomaly, Little Ice Age, and the 20^th century warmth. A culmination of the LIA cooling during the early 18^th century appeared consistently with the Maunder Minimum, when the solar activity was drastically reduced. A number of coolest reconstructed events between AD 1407 and 1902 were coeval to years of crop failure and famine as documented in the agro-historical chronicles. Results indicate an encouraging possibility of warm-season temperature reconstructions using middle/south boreal tree-ring archives to detail and enhance the understanding of past interactions between humans, ecosystems and the earth.     

Alternative explanations of the dependence of the density of centers on the density of population

ABSTRACT. The paper is devoted to modeling the relationship between the density of service centers and the density of population (or on the density of demand). Several models lead to an exponential function with the exponent equal to ⅔. For a number of real systems of centers, the power is considerably different from ⅔ (more often it is nearer to 1). I describe a series of models that explain this difference.     

Inorganic bromine in the lower stratosphere

Inorganic bromine content in the lower stratosphere was determined from a series of three balloon flights conducted in 1981 and 1982 from Holloman AFB, New Mexico (33°N). A Direct Flow Sampler (DFS) sampled large quantities of stratospheric air through a 35 cm diameter filter mounted upstream of a blower. Filters were prepared with an inert organic oil and a strong organic base in order to capture both acidic and particulate species. Following flight, the filters underwent an extraction process. Then, aliquots of the solution were subjected to neutron activation analysis. The methodology involved a radiochemical procedure which was developed and tested to measure, simultaneously, both chlorine and bromine content. High-resolution gamma spectrometry was used and bromine content was determined by counting ⁸⁰Br activity. The resulting values for volume mixing ratios of bromine increased from a low of 2.6 pptv at 15 km to a high of 15.6 pptv for the 25–30 km band. The results are shown to be in agreement with earlier measurements by Sedlacek et al. (1984) and with one-dimensional photochemical model predictions by yung et al. (1980).     

Evidence for early cat taming in Egypt

The remains are described of a young small felid found in a Predynastic burial at Hierakonpolis, Upper Egypt. Osteometric and zoogeographical arguments indicate that the specimen, dated to around 3700 B.C. on the basis of the associated pottery, belongs to Felis silvestris. In the same cemetery several other animal species, both wild and domestic, have been found. The left humerus and right femur of the cat show healed fractures indicating that the animal had been held in captivity for at least 4–6 weeks prior to its burial. We believe that this pathology suggests early cat taming more convincingly than a buried cat recently reported from Neolithic Cyprus (7500 B.C.). Such taming events were probably part of the processes that eventually led to the domestication of Felis silvestris. However, the absence of the cat in Predynastic and Early Dynastic depictions and its rare attestation in the archaeozoological record indicates that domestic status had not yet been attained during those early periods. Other species that were also held in captivity by Ancient Egyptians probably never became domesticated because they had one or more characteristics that prevented it.     

Lithic Evidence for the Peopling of Northern Ethiopia

A comparative study of lithic assemblages from the Gash Delta lowlands of eastern Sudan and from Seglamen in the highlands of northern Ethiopia is used to investigate the origins of the pre-Aksumite people and their anonymous predecessors. Multiple similarities in knapping strategies and in lithic tool types support the hypothesis of a south-eastward movement of agro-pastoralists into the highlands of the Tigray Plateau, probably starting in the fifth millennium BC.     

Evidence for Interaction from Recent Hunter-Gatherer Sites in the Caledon Valley

Evidence for contact between hunter-gatherers and agropastoralists from excavated sites in a well-documented frontier zone in the eastern Free State, South Africa, reveals varied intensities of interaction. These interactions range from clientship to relative autonomy. Comparison between recent (eighteenth- to early twentieth-century) hunter-gatherer occupations of rock shelters in the Caledon Valley also suggests that a variety of social relationships between hunter-gatherers and farmers, known ethnographically, occurred simultaneously.     

Method-dependent variations in stable isotope results for structural carbonate in bone bioapatite

Stable carbon and oxygen isotope values (δ¹³C, δ¹⁸O) were obtained for structural carbonate in the bioapatite of archaeological bones from Guatemala and Sudan using several common analytical methods. For the Sudan samples, the different methods produced δ¹³C values within ±0.1‰ and δ¹⁸O values within ±0.7‰, on average. The isotopic results for the Guatemala samples were similar in reproducibility to the Sudan samples when obtained using methods that employed lower reaction temperatures and reactions in sealed vessels. However, many Guatemala samples had highly variable and extremely low δ¹⁸O values when reacted at higher temperatures in vessels that remained open to cryogenic traps. The latter arrangement caused reaction products to be removed immediately upon their production. The anomalously low δ¹⁸O values are related to the production of a contaminant gas that causes the m/z 46/44 ratio to be lowered, either by adding to the m/z 44 peak or subtracting from the m/z 46 peak. That said, potential contaminant materials were not detectable in “anomalous” bones using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, or inductively-coupled plasma atomic emission spectroscopy. However, subtle structural and chemical differences between “normal” and “anomalous” samples were observed, most notably in the FTIR ν₂ CO₃ domain. We suggest that these changes promote volatilization of an oxyphosphorus compound and oxygen isotope fractionation between PO⁻ derived from this compound and CO₂ derived from bone carbonate. Production of the contaminant gas and the related “anomalous” δ¹⁸O values is reversible if the reaction occurs within a sealed vessel for a sufficient period of time, which allows a “back-reaction” to occur.