Perturbations in tropical middle atmosphere during winter, 1984–1985

Summary Using high altitude rocketsonde data for Thumba (8.5 N, 76.9E) and Balasore (21.5 N, 86.9E) and the stratalert messages for high latitudes for the winter (December–March) 1984–1985, an examination has been made to study the perturbations in the temperature and winds in the tropical middle atmosphere and their linkage with the dynamical events occurring over the high-latitude middle atmosphere during that winter.The results of analysis indicated occurrence of strong cooling in the mesosphere over a period of seven days (5–12 December 1984) and the depth of the cooling layer was 15 km. This incident was followed by a strong warming over a period of seven days (12–19 December 1984) and the depth of the warming layer was 13 km. The major warming event, which occurred over high latitudes during the later part of December and the first week of January, was followed by the cooling in the mesosphere and warming in the stratosphere at Thumba. Also the zonal winds were strong easterly and the meridional winds were northerly in the upper stratosphere and the lower mesosphere over tropics during the same period. Weaker zonal winds/stronger easterly winds were generally noticed to be associated with coolings/warmings over tropics.With 7 Figures     

Nitric oxide profiles measured in situ during the Globus '85 campaign

Nitric oxide profiles obtained from three flights of chemiluminescent instruments during the Globus '85 campaign held in France in the autumn of 1985 are reported. When the profile obtained in the early morning of 20 September is compared with the flight made the previous afternoon, an average morning to midday NO ratio of 0.7 for the region between 26 and 33 km is obtained. This value is in good agreement with theoretical studies involving the photolysis of N₂O₅ and the establishment of the NO₂–NO equilibrium.     

Oxygen isotopic variations of snowfall from winter storms in the central Sierra Nevada; Relation to ice growth microphysics and mesoscale structure

Observations have been made of the ice-crystal morphology of snow which fell at two sampling sites during a warm front followed by a cold front in the Sierra Nevada of the western United States. The snow sampling and ice crystal observations were conducted at Kingvale (KV) and Hobart Mills (HM), California, which are located at almost identical elevations on the upwind and down wind sides of the Sierra Nevada crest, respectively.These observations and several mesoscale features of one of the storms, have been used to study the substantial changes which occurred in the stable oxygen isotopic composition (δ¹⁸O) of the precipitation at the two sites.At the beginning of the period of observation, a low level warm front lay across the region and its elevation lowered with time from 2.5 km to 1.7 km. This decrease of the frontal surface height was accompanied by a steady increase in the δ¹⁸O values.In the pre-cold frontal passage time periods, the δ¹⁸O values at the upwind site signified warmer origin ice crystal morphology than the downwind site. This is explained by orographic effects and the production of supercooled liquid water at low elevations on the upslope side of the Sierra Nevada.During the passage of the surface cold front, the differences in δ¹⁸O at the two sites were quite small probably because the orography plays a less significant role in the precipitation production process during such events.The δ¹⁸O peaked around −13% which translates to an “equivalent temperature” of −10.7°C for ice phase water capture at the upwind site KV. At site HM downwind of the Sierra crest, and 25 km east of KV, the weighted mean ice phase water capture occurred at elevations some 5 to 6°C colder than at KV, because of subsidence and loss of supercooled liquid water in the lower elevations on the lee side.     

The sensitivity of topoclimatic models to fine-scale microclimatic variability and the relevance for ecological studies

Microclimatic loggers are increasingly used to collect data from various habitats and interpolate ecologically meaningful landscape-scale topoclimatic grids. However, it is unknown how sensitive these grids are to finer-scale variations in microclimate. We performed a sensitivity analysis using three microclimatic loggers at 27 sites for 5 months in a semi-arid region of Western Australia. We partitioned the within- and between-site variance in temperature and produced 100 different topoclimatic models using a random sensor from each site. For the coldest temperatures, we found within-site variance was negligible (3 %), and models were strong (r ²?=?0.74) and the coefficients consistent. However, for the hottest temperatures, there was substantial within-site variance (39 %), and models were weaker (r ²?=?0.27) and more sensitive. We concluded that careful site design is needed to maximise the reliability of topoclimatic grids, including using large sample sizes, ensuring there is low predictor collinearity and sampling full environmental gradients.     

Climate change affecting temperature and aridity zones: a case study in Eastern Inner Mongolia, China from 1960–2008

Recent climate change is substantially affecting the spatial pattern of geographical zones, and the temporal and spatial inconsistency of climatic warming and drying patterns contributes to the complexity of the shifting of temperature and aridity zones. Eastern Inner Mongolia, China, located in the interface region of different biomes and ecogeographic zones, has experienced dramatic drying and warming over the past several decades. In this study, the annual accumulated temperature above 10 °C (AAT10) and the aridity index, two key indicators in geographical regionalization, are used to assess warming and drying processes and track the movements of temperature and aridity zones from 1960 to 2008. The results show a significant warming at the regional level from 1960 to 2008 with an AAT10 increase rate of 7.89 °C·d/year (p?<?0.001) in Eastern Inner Mongolia, while the drying trend was not significant during this period. Spatial heterogeneity of warming and drying distributions was also evident. Analysis of warming and drying via piecewise regression revealed two separate, specific trends between the first 31 years (1960–1990) and the subsequent 18 years (1991–2008). Generally, mild warming and very slight wetting occurred prior to 1990, while after 1991 both warming and drying were significant and enhanced. Continuous warming drove a northward shift of temperature zones from the 1960s to 2000s, while aridity zones displayed enhanced temporal and spatial variability. Climate change effects on temperature and aridity zones imply that the patterns of cropping systems, macro-ecosystems, and human land use modes are potentially undergoing migration and modification due to climate change.     

A new strategy for global climate protection

This essay proposes an innovative institutional strategy for global climate protection, quite distinct from but ultimately complementary to the UNFCCC climate treaty negotiations. Our “building block” strategy relies on a variety of smaller-scale transnational cooperative arrangements, involving not only states, but also subnational jurisdictions, firms, and civil society organizations, to undertake activities whose primary goal is not climate mitigation but which will achieve greenhouse gas reductions as a byproduct. This strategy avoids the problems inherent in developing an enforceable, comprehensive treaty regime by mobilizing other incentives—including economic self-interest, energy security, cleaner air, and furtherance of international development— to motivate a range of actors to cooperate on actions that will also produce climate benefits. The strategy uses three specific models of regime formation (club, linkage, and dominant actor models) which emerge from economics, international relations, and organizational behavior, to develop a variety of transnational regimes that are generally self-enforcing and sustainable, avoiding the free rider and compliance problems endemic in collective action to provide public goods. These regimes will contribute to global climate action not only by achieving emissions reductions in the short term, but also by creating global webs of cooperation and trust, and by linking the building block regimes to the UNFCCC system through greenhouse gas monitoring and reporting systems. We argue that the building blocks regimes would thereby help secure eventual agreement on a comprehensive climate treaty.     

A simple gravity wave drag parametrization for use in medium‐range weather forecast models

Abstract

A simple gravity wave drag parametriiation over mountainous terrain is tested for its ability to reduce the systematic errors of medium‐range weather forecasts. Following Boer et al. (1984), this parametrization is a function of the low‐level wind speed and stability, the local Froude number, and the variance of the subgrid‐scale orographie features.

A comparison study of ten 7‐day forecasts obtained with envelope orography, wave drag or standard orography, shows that wave drag is as effective as envelope orography in reducing the systematic errors. A further comparison where the combined effects of the wave drag and that of a complementary enhanced orography (that is one that includes only the subgrid‐scale elements not treated separately by wave drag) are taken into account shows this latter approach to be the most promising in reducing orographically‐related systematic errors.     

Some recent trends in precipitation in Western Canada and their possible link to rising carbon dioxide: Research note

Abstract

Observations of the changes in mean annual and seasonal precipitation with time in British Columbia and western Alberta between the periods 1931–60 and 1951–80 indicate that more stations show an increase than a decrease. Changes tend to be positive on the coast, negative in south‐central British Columbia, positive on the west slopes of the Rockies, and negative to the east. This suggests an orographic influence and increased flow from the southwest at mountain‐top.

The possibility that these changes in precipitation are associated with CO₂ warming is considered.

Both the surface air temperature and sea surface temperature were raised by 2°C for cyclogenesis events over the northeastern Pacific and the consequences were investigated with the aid of a limited‐area, 8‐level primitive equations model. The lows are deepened by as much as 6 mb and precipitation amounts are increased up to 8 mm owing to the increased mixing ratio and the feedback of latent heat energy.     

Subgrid-Scale Dynamics of Water Vapour, Heat, and Momentum over a Lake

We examine the dynamics of turbulence subgrid (or sub-filter) scales over a lake surface and the implications for large-eddy simulations (LES) of the atmospheric boundary layer. The analysis is based on measurements obtained during the Lake-Atmosphere Turbulent EXchange (LATEX) field campaign (August–October, 2006) over Lake Geneva, Switzerland. Wind velocity, temperature and humidity profiles were measured at 20 Hz using a vertical array of four sonic anemometers and open-path gas analyzers. The results indicate that the observed subgrid-scale statistics are very similar to those observed over land surfaces, suggesting that the effect of the lake waves on surface-layer turbulence during LATEX is small. The measurements allowed, for the first time, the study of subgrid-scale turbulent transport of water vapour, which is found to be well correlated with the transport of heat, suggesting that the subgrid-scale modelling of the two scalars may be coupled to save computational resources during LES.