Feasibility of observations of stratospheric trace gases using the Hubble Space Telescope

The stellar occultation method has been successfully used in the past from orbiting observatories to measure concentrations of certain trace gases in the Earth's mesosphere. The greatly improved spectroscopic capabilities of the Hubble Space Telescope (HST) have prompted recent suggestions for its use to measure stratospheric C10. We examine this possibility along with that for other species relevant to the chemistry of the ozone layer. We conclude that stratospheric (as opposed to mesospheric) observations with HST are not practical, in part because of its orbital and pointing characteristics, but primarily because the high opacity of stratospheric ozone over most of the band-pass of the HST's most suitable spectrometer will obscure observation of other trace species, such as C10, having mixing ratios <10^–3 that of ozone.     

东亚季风转换对西北太平洋近地面O3春季高值的影响

以东亚酸沉降监测网近地面O3资料,结合NCEP/NCAR的全球再分析风场、NOAA总云量及全球降水气候项目降水资料,分析2000～2007年东亚西太平洋地区近地层O3的区域和季节变化,重点分析不同站点O3月均浓度最大值时间差异的原因。结果表明,东亚以及大部分北半球中纬度清洁背景地区,近地层O3春季最高、夏季最低是广泛存在的现象。东亚夏季风的推进过程造成不同地区春季O3月均最大值出现的时间略有不同,Ogasawara和Hedo站O3浓度在3月达最大值,而Rishiri、Happo、Oki和Cheju站在4、5月达最大值。2007年副热带高压西进较晚且推进过程受阻导致Happo站2007年春季O3浓度高于气候平均值,Cheju地区2007年5月O3浓度达最大;2004年东亚夏季风爆发较早导致Hedo站2004年春季O3浓度明显低于平均值。     

Assessment of the dependence of the skill and predictability of seasonal forecasts on boundary conditions of the model

A comparison of estimates of the root-mean-square error (RMSE) and potential predictability index (PPI) is carried out between experiments with observed and “persistent” anomalies of sea surface temperature (SST). The results obtained point to a possible significant bias of seasonal forecasting results in some regions when boundary conditions are introduced by a “persistence” procedure, particularly for summer T ₈₅₀. Indirect evidence of the influence of extratropical SST anomalies points to their possible role in seasonal forecasts, which is more substantial in the summer season. Although the conclusions should rather be regarded as preliminary ones because of a limited size of the sample, it is nonetheless certain that the influence of boundary conditions governing the signal becomes more significant in summer because of a decrease in the instability of the internal atmospheric dynamics.     

Measurement of methane flux over an evergreen coniferous forest canopy using a relaxed eddy accumulation system with tuneable diode laser spectroscopy detection

Very few studies have conducted long-term observations of methane (CH₄) flux over forest canopies. In this study, we continuously measured CH₄ fluxes over an evergreen coniferous (Japanese cypress) forest canopy throughout 1?year, using a micrometeorological relaxed eddy accumulation (REA) system with tuneable diode laser spectroscopy (TDLS) detection. The Japanese cypress forest, which is a common forest type in warm-temperate Asian monsoon regions with a wet summer, switched seasonally between a sink and source of CH₄ probably because of competition by methanogens and methanotrophs, which are both influenced by soil conditions (e.g., soil temperature and soil moisture). At hourly to daily timescales, the CH₄ fluxes were sensitive to rainfall, probably because CH₄ emission increased and/or absorption decreased during and after rainfall. The observed canopy-scale fluxes showed complex behaviours beyond those expected from previous plot-scale measurements and the CH₄ fluxes changed from sink to source and vice versa.     

Rainfall variability and kinetic energy in Southern Nigeria

A decreasing trend of rainfall has been observed in West Africa, where rainfall erosivity is also considered to be high. Therefore, this study was carried out to evaluate the variability of rainfall and its erosivity in two contrasting zones in southern Nigeria between 1977 and 1999 to understand the implications of climate variability on rainfall erosivity. The study sites were Ibadan, a sub-humid zone, and Port-Harcourt, a humid zone. Time of occurrence of rainfall, rainfall amount (A), intensity (I ₁₅ and I ₃₀), kinetic energy (E) and rainfall erosivity factor (R), were evaluated. Kinetic energy was estimated with Brown–Foster (BF) equation, making the rainfall erosivity (product of kinetic energy and intensity) to be designated as EI ₃₀-BF and EI ₁₅-BF. The frequency of rainfall during daylight (06:00–18:00 h) was 48% for Ibadan and 69% for Port-Harcourt. There were time-specific differences in daily rainfall occurrence between the zones, suggesting a strong influence of local effects on rainfall generation, such as, relief in Ibadan and proximity to the sea in Port-Harcourt. Annual E was 213 MJ ha⁻¹for Ibadan and 361 MJ ha⁻¹ for Port-Harcourt. Ibadan had a significantly higher daily E than Port-Harcourt because of higher intensity while Port-Harcourt had significantly higher annual E than Ibadan because of higher annual rainfall amount. Annual erosivity at Ibadan using the EI ₃₀-BF was 9,742 MJ mm ha⁻¹ h⁻¹ whereas it was 15,752 MJ mm ha⁻¹ h⁻¹ at Port-Harcourt. Using the EI ₁₅-BF, Ibadan had an annual value of 14,806 MJ mm ha⁻¹ h⁻¹ while Port-Harcourt had 20,583 MJ mm ha⁻¹ h⁻¹. Thus, annual rainfall erosivity was significantly higher in the humid than the sub-humid zone because of higher amount of rainfall but the reverse was the case with daily erosivity because of higher intensities in the sub-humid zone. Rainfall intensity was, therefore, a key measure of erosivity. There was a strong positive relationship between rainfall erosivity and rainfall amount. Between 1977 and 1988, 50–88% of the 12 years had rainfall erosivity which exceeded the long-term average but rainfall erosivity was less than the long-term average between 1989 and 1999. This suggested a decreasing trend in erosivity due to the decreasing trend in rainfall amount in West Africa. However, the trend did not imply lesser soil erosion and environmental degradation risks.     

On the use of compliant fairings on conventional moorings

Abstract

Compliant fairing made of plastic ribbons or flexible rubber filaments can be attached to the cables of taut‐line moorings to reduce the drag force of the currents. The efficiency of such fairing depends upon its orientation in the flow and the Reynolds number of the cable. Results of using filament fairing manufactured by ENDECO Inc. on a 337‐m long mooring in the mouth of Hudson Strait are discussed. The fairing was found to be detrimental in this application because of twisting of the wire rope, producing a “bottle‐brush” configuration, and because the normal drag coefficient Cd ? 2.5 ± 0.45 was found to exceed that of a bare cable by 65 per cent on average. The Reynolds number range for this drag coefficient was 2.6 × 10³ to 4.2 × 10³ and was determined by force measurements in a flume. It is concluded that the problems of correctly orienting the fairing in the flow, and the true drag coefficient for Reynolds numbers less than about 5 × 10⁴ must be carefully addressed in the design of conventional taut‐line moorings. Drag coefficients found in this study imply that compliant fairings would not be warranted for Reynolds numbers below about 5 × 10⁴ unless strumming was expected for bare cables.     

Consequences of Uncertainties in CO<Subscript>2</Subscript> Density for Estimating Net Ecosystem CO<Subscript>2</Subscript> Exchange by Open-path Eddy Covariance

Errors in the estimation of CO₂ surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol Soc 106:85–100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65–85, (2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements of absolute CO₂ density (ρ _c ). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to reliably report ρ _c and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ρ _c in a semi-arid climate with large sensible heat fluxes (H _s ) and (wet) mineral deposition. When ρ_c is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO₂ uptake.     

Estimate of the steric contribution to global sea level rise from a comparison of the WOCE one‐time survey with 2006–2008 Argo observations

Abstract

It is well known from observations by altimetric satellites (predominantly TOPEX/Poseidon and Jason‐1) that global sea level is rising. What is less well known is exactly how the observed sea level rise is partitioned between a steric contribution (sea level rising because of changes in ambient temperature and salinity) and a contribution arising from the addition of new water mass to the oceans. Strictly speaking, such a separation is not possible because of the non‐linearity in the equation of state for sea water, but in practice the non‐linearities are sufficiently small to allow this separation as a very good first approximation.

A careful comparison of the World Ocean Circulation Experiment (WOCE) one‐time survey with recent observations by the Argo array indicate a steric component to sea level rise of 2.2 mm y^–1 between the early 1990s and 2006 to 2008. This is a significantly larger rise rate than previously estimated and, along with recent estimates of melt rate from ice sheets, is in much closer agreement with the total rise rate as reported by altimetric satellites, 3.2 ± 0.4 mm y^–1 over this period.     

Climatic Indices Influencing the Long-Term Variability of Mediterranean Heat and Water Fluxes: The North Atlantic and Mediterranean Oscillations

Interannual to interdecadal precipitation (P), evaporation (E), water deficit (E-P), and total heat flux have been correlated with North Atlantic Oscillation (NAO) and Mediterranean Oscillation (MO) indices to explore the influence of large-scale atmospheric forcing on the variability of the Mediterranean water and heat budgets. Basin-averaged precipitation decrease from the mid-1960s to the late 1980s clearly corresponds to a switch from a low to a high state of both indices. The variability of E-P is not so well correlated with the atmospheric indices because of the different sensitivity of E and P that leads to correlations of opposite sign in the eastern and western sub-basins. The effectiveness of the NAO and MO indices is quite similar for P and E-P but the regional MO index has turned out to be a more successful indicator of interdecadal evaporation and net heat flux because, from the mid-1970s to the early 1990s, correlation with the NAO index decreases considerably. Because the MO centre remains relatively steady, it influences most of the Mediterranean Sea year round, so it is more suitable for monitoring long-term water and especially heat budget variability.     

Globalisation of water resources: international virtual water flows in relation to crop trade

The water that is used in the production process of a commodity is called the ‘virtual water’ contained in the commodity. International trade of commodities brings along international flows of virtual water. The objective of this paper is to quantify the volumes of virtual water flows between nations in the period 1995–1999 insofar related to international crop trade and to analyse national virtual water balances in relation to national water needs and water availability. The basic approach is to multiply international crop trade flows (ton/yr) by their associated virtual water content (m³ ton⁻¹). The calculations show that the global volume of crop-related international virtual water flows between nations was 695 Gm³ yr⁻¹ in average over the period 1995–1999. For comparison: the total water use by crops in the world has been estimated at 5400 Gm³ yr⁻¹. This means that 13% of the water used for crop production in the world is not used for domestic consumption but for export (in virtual form). This is a conservative estimate because only a limited number of crops––although the most important ones––have been taken into account and because crop products (such as cotton clothes) have been excluded from the study. The countries with the largest net virtual water export are United States, Canada, Thailand, Argentina and India. The largest net import appears to be in Japan, the Netherlands, the Republic of Korea, China and Indonesia.     

Respiration of Recently-Fixed Plant Carbon Dominates Mid-Winter Ecosystem CO2 Production in Sub-Arctic Heath Tundra

Arctic ecosystems could provide a substantial positive feedback to global climate change if warming stimulates below-ground CO₂ release by enhancing decomposition of bulk soil organic matter reserves.Ecosystem respiration during winter is important in this context because CO₂ release from snow-covered tundra soils is a substantial component of annual net carbon (C) balance, and because global climate models predict that the most rapid rises in regional air temperature will occur in the Arctic during winter. In this manipulative field study, the relative contributions of plant and bulk soil organic matter C pools to ecosystem CO₂ production in mid-winter were investigated. We measured CO₂ efflux rates in Swedish sub-arctic heath tundra from control plots and from plots that had been clipped in the previous growing season to disrupt plant activity. Respiration derived from recently-fixed plant C (i.e., plant respiration, and respiration associated with rhizosphere exudates and decomposition of fresh litter) was the principal source of CO₂ efflux, while respiration associated with decomposition of bulk soil organic matter was low, and appeared relatively insensitive to temperature. These results suggest that warmer mid-winter temperatures in the Arctic may have a much greater impact on the cycling of recently-fixed, plant-associated C pools than on the depletion of tundra bulk soil C reserves, and consequently that there is a low potential for significant initial feedbacks from arctic ecosystems to climate change during mid-winter.     

Lags in vegetation response to greenhouse warming

Fossil pollen in sediments documents vegetation responses to climatic changes in the past. Beech (Fagus grandifolia), with animal-dispersed seeds, moved across Lake Michigan or around its southern margin, becoming established in Wisconsin about 1000 years after populations were established in Michigan. Hemlock (Tsuga canadensis), with wind-dispersed seeds, colonized a 50,000 km² area in northern Michigan between 6000 and 5000 years ago. These tree species extended ranges northward at average rates of 20–25 km per century. To track climatic changes in the future, caused by the greenhouse effect, however, their range limit would need to move northward 100 km per °C warming, or about 300 km per century, an order of magnitude faster than range extension in the past. Yet range extension in the future would be less efficient than in the past, because advance disjunct colonies have been extirpated by human disturbance, and because the seed source is reduced due to reductions in tree populations following logging. Many species of trees may not be able to disperse rapidly enough to track climate, and woodland herbs, which have less efficient seed dispersal mechanisms, may be in danger of extinction.     

A Perspective on the Evolution of Atmospheric Blocking Theories: From Eddy-Mean flow Interaction to Nonlinear Multiscale Interaction

In this paper, we first review the research advancements in blocking dynamics and highlight the merits and drawbacks of the previous theories of atmospheric blocking. Then, the dynamical mechanisms of atmospheric blocking are presented based on a nonlinear multi-scale interaction(NMI) model. Previous studies suggested that the eddy deformation(e.g., eddy straining, wave breaking, and eddy merging) might lead to the formation and maintenance of atmospheric blocking.However, the results were specu...     

Trace ambient levels of particulate mercury and its sources at a rural site near Delhi

Atmospheric particle-bound mercury levels were measured in PM₁₀ aerosols (HgP) at a rural site (Mahasar, Haryana) during winter 2014–15 and summer 2015. The PM₁₀ HgP was determined by using Differential Pulse Anodic Stripping Voltammetry through standard addition methods while the trace metals were determined by using an Atomic Absorption Spectroscopy. The mass concentrations of HgP varied from 591 to 1533 pg/m³ with an average of 1009?±?306 pg/m³ during the winter, while the mass concentrations of HgP varied from 43 to 826 pg/m³ with an average of 320?±?228 pg/m³ during the summer. However, it is difficult to assess whether these levels are harmful or not because there is no standard value available as National Ambient Air Quality Standard. The higher concentrations of HgP during winters were possibly due to favourable local meteorological conditions for the stagnation of particulate matter in the lower atmosphere and the increased emissions from existing natural or anthropogenic sources, regional sources and long-range transportation. Relatively low concentrations of HgP during summer might be due to increased mixing heights as well as scavenging effect because some light to heavy rain events were observed during summer time sampling. However, among other metals determined, the concentration of HgP was the lowest during both the seasons. The study may be useful in assessing the health impacts of PM₁₀ HgP and other metals.     

Response of the Atlantic meridional overturning circulation to a reversal of greenhouse gas increases

The reversibility of the Atlantic meridional overturning circulation (AMOC) is investigated in multi-model experiments using global climate models (GCMs) where CO₂ concentrations are increased by 1 or 2 % per annum to 2× or 4× preindustrial conditions. After a period of stabilisation the CO₂ is decreased back to preindustrial conditions. In most experiments when the CO₂ decreases, the AMOC recovers before becoming anomalously strong. This "overshoot" is up to an extra 18.2Sv or 104 % of its preindustrial strength, and the period with an anomalously strong AMOC can last for several hundred years. The magnitude of this overshoot is shown to be related to the build up of salinity in the subtropical Atlantic during the previous period of high CO₂ levels. The magnitude of this build up is partly related to anthropogenic changes in the hydrological cycle. The mechanisms linking the subtropical salinity increase to the subsequent overshoot are analysed, supporting the relationship found. This understanding is used to explain differences seen in some models and scenarios. In one experiment there is no overshoot because there is little salinity build up, partly as a result of model differences in the hydrological cycle response to increased CO₂ levels and partly because of a less aggressive scenario. Another experiment has a delayed overshoot, possibly as a result of a very weak AMOC in that GCM when CO₂ is high. This study identifies aspects of overshoot behaviour that are robust across a multi-model and multi-scenario ensemble, and those that differ between experiments. These results could inform an assessment of the real-world AMOC response to decreasing CO₂.     

High-resolution simulations of global climate, part 2: effects of increased greenhouse cases

We report results from the highest-resolution simulations of global warming yet performed with an atmospheric general circulation model. We compare the climatic response to increased greenhouse gases of the National Center for Atmospheric Research (NCAR) climate model, CCM3, at T42 and T170 resolutions (horizontal grid spacing of 300 and 75 km respectively). All simulations use prescribed sea surface temperatures (SST). Simulations of the climate of 2100 ad use SSTs based on those from NCAR coupled model, Climate System Model (CSM). We find that the global climate sensitivity and large-scale patterns of climate change are similar at T42 and T170. However, there are important regional scale differences that arise due to better representation of topography and other factors at high resolution. Caution should be exercised in interpreting specific features in our results both because we have performed climate simulations using a single atmospheric general circulation model and because we used with prescribed sea surface temperatures rather than interactive ocean and sea-ice models.     

The effect of vertical transports of heat and moisture by cumulus convection in typhoon

By utilizing the denser upper-air observations from the Okinawa region and Japanese islands during August 17－23, 1975, the vertical transports of heat and moisture by cumulus convection in the typhoon No. 7507 have been calculated. It is found that there exist a large apparent heat source (Q1) and a mois-ture sink (Q2) in the southern part of the typhoon at the disturbance, growing and mature stages. The magnitudes of the apparent heat source and moisture sink ace rather small, or turn into the apparent heat sink in the northern sector of the typhoon. In the southern part of the typhoon, the total cloud mass flux (Mc) is positive, whereas in the northern part of the typhoon Mc is negative. The above-mentioned distributions of Q1, Q2 and Mc agree well with the major cloud patterns.In the southern part of the typhoon, Q2 is positive because the drying effect is always larger than the evaporative cooling, whereas in the northern part of the typhoon, the opposite case is true because both the drying and evaporating effects of liquid water make a negative contribution to Q2.     

The diurnal cycle of surface air temperature in simulated present and doubled CO2 climates

 The diurnal range of surface air temperature (rT _a ) simulated for present and doubled CO₂ climates by the CSIRO9 GCM is analysed. Based on mean diurnal cycles of temperature and surface heat fluxes, a theory for understanding the results is developed. The cycles are described as the response to a diurnal forcing which is represented well by the diurnal mean flux of net shortwave radiation at the surface (SW) minus the evaporative (E) and sensible (H) fluxes. The response is modified by heat absorbed by the ground, and by the cycle in downward longwave (LW) radiation, but these effects are nearly proportional to the range in surface temperature. Thus in seasonal means, rT _a is approximately given by SW–E–H divided by 6 W m^-2/^°C. A multiple regression model for (rT _a ) is developed, based on quantities known to influence SW, E and H, and applied to both spatial variation in seasonal means, and day-to-day variation at a range of locations. In both cases, rT _a is shown to be influenced by cloud cover, snow extent and wind speed. It is influenced by soil moisture, although this effect is closely tied to that of cloud. In seasonal means rT _a is also well correlated with precipitable water, apparently because of the latter’s influence on E+H. The regression model describes well the spatial variation in the doubled CO₂ change in rT _a . The annual mean change in rT _a over land on doubling CO₂ was −0.36 ^°C, partly because of a decrease in the mean diurnal forcing (as defined in the theory), but also apparently because of the effect of nonlinearity in T _s of the upward longwave emission. A diagnostic radiation calculation indicates that the CO₂ and water vapour provide a small increase in rT _a through the downward LW response, which partially counters a decrease due to a reduction of SW by the gases. Received: 8 November 1995 / Accepted: 3 January 1997     

Evaluation of clouds and radiative fluxes in the EC-Earth general circulation model

Observations, mostly from the International Satellite Cloud Climatology (ISCCP), are used to assess clouds and radiative fluxes in the EC-Earth general circulation model, when forced by prescribed observed sea surface temperatures. An ISCCP instrument simulator is employed to consistently compare model outputs with satellite observations. The use of a satellite simulator is shown to be imperative for model evaluation. EC-Earth exhibits the largest cloud biases in the tropics. It generally underestimates the total cloud cover but overestimates the optically thick clouds, with the net result that clouds exert an overly strong cooling effect in the model. Every cloud type has its own source of bias. The magnitude of the cooling due to the shortwave cloud radiative effect ( \(\mid \hbox {SWCRE}\mid\) ) is underestimated for the stratiform low-clouds, because the model simulates too few of them. In contrast, \(\mid \hbox {SWCRE}\mid\) is overestimated for trade wind cumulus clouds, because in the model these are too thick. The clouds in the deep convection regions also lead to overestimate the \(\mid \hbox {SWCRE}\mid\) . These clouds are generally too thick and there are too few mid and high thin clouds. These biases are consistent with the positive precipitation bias and the overly strong mass flux for deep convective plumes. Potential sources for the various cloud biases in the model are discussed.     

Sensitivity of FORGRO to climatic change scenarios: A case study on Betula pubescens, Fagus sylvatica and Quercus robur in The Netherlands

The impacts of the climate change predictions of four general circulation models (GFDL, GISS, OSU and UKMO) on net primary production (NPP) ofBetula pubescens, Fagus sylvatica and Quercus robur in The Netherlands were analysed using the process-based model FORGRO. FORGRO is a model suitable to simulate growth of managed mono-species stands. For the GCMs mentioned, both transient and equilibrium 2 × CO₂ scenarios of temperature and precipitation change were evaluated and compared with responses under current climate. It was found that the NPP increases in the transient scenarios, but remains the same or declines in the 2 × CO₂ scenarios. This is because respiration increases more with rising temperature than photosynthesis. During the transient scenarios this effect gradually increases, while in the 2 × CO₂ scenario this effect is operating over the entire simulation period.If water limitation is taken into account, then the NPP of the reference scenario is reduced. In both the transient and 2 × CO₂ scenarios mis water limitation is annulated, resulting in a stronger response of NPP compared to the situation without water limitation. This enhancement of the response is most pronounced in the transient scenario due to the gradual effect of temperature on respiration.Similar results were obtained with a version of FORGRO in which the photosynthesis module of HYBRID (PGEN) is incorporated, although the response in FORGRO-PGEN is usually higher than that of FORGRO. This is because the response of photosynthesis to CO₂ rises with increasing temperature as defined in the PGEN-model, but not according to FORGRO.