Changes In Regional Circulation Research Articles

Hydroclimate Variability in the Equatorial Western Indian Ocean for the Last 250,000 Years

AbstractIndian Ocean sea surface temperatures impact precipitation across the basin through coupled ocean‐atmosphere responses to changes in climate. To understand the hydroclimate response over the western Indian Ocean and equatorial east Africa to different forcing mechanisms, we present four new proxy reconstructions from core VM19‐193 (2.98°N, 51.47°E) that span the last 250 ky. Sub‐surface water temperatures (Sub‐T; TEX86) show strong precessional (23 ky) variability that is primarily influenced by maximum incoming solar radiation (insolation) during the Northern Hemisphere spring season, likely indicating that local insolation dominates the upper water column at this tropical location over time. Leaf waxes, on the other hand, reflect two different precipitation signals: δ13Cwax (in phase with boreal fall insolation) is likely reflecting vegetation changes in response to local rainfall over east Africa, whereas δDprecip (primarily driven by boreal summer insolation) represents changes in regional circulation associated with the summer monsoon. Glacial‐interglacial changes in ocean temperatures support glacial shelf exposure over the Maritime Continent in the eastern Indian Ocean and the subsequent weakening of the Indian Walker Circulation as a mechanism driving 100 ky climate variability across the tropical Indo‐Pacific. Additionally, the 100 ky spectral power in δDprecip supports a basin‐wide weakening of summer monsoon circulation in response to glacial climates. Overall, the proxy records from VM19‐193 indicate that both precession and glacial‐interglacial cycles exert control over hydroclimate at this tropical location.

Evaluation and projections of the East Asian summer monsoon in a perturbed parameter ensemble

The East Asian summer monsoon (EASM) is a dominant driver of East Asian climate, with variations in its strength potentially impacting the livelihoods of millions of people. Understanding, predicting, and assessing uncertainties in these variations are therefore important area of research. Here, we present a study of the projected twenty-first century changes in the EASM using a ‘perturbed parameter ensemble’ (PPE) of HadGEM3-GC3.05 coupled climate models, which samples uncertainties arising from differences in model parameter values. We show that the performance of PPE members for leading order EASM metrics is comparable to CMIP5 and CMIP6 models in many respects. But the PPE also exposes model biases which exist for almost all parameter combinations. These ‘structural’ biases are found mainly to affect metrics for the low-level circulation. We also show that future changes in regional circulation and precipitation are projected consistently across the PPE members. A more detailed moisture budget analysis of the precipitation changes in a region covering the Yangtze River valley shows that the spread of these changes is mainly due to spread in dynamic responses. We also perform parameter sensitivity analyses and find that a parameter controlling the amplitude of deep-level entrainment is the main driver of spread in the PPE’s representation of the EASM circulation. Finally, we discuss how the information provided by the PPE may be used in practice, considering the plausibility of the models, and giving examples of ways to sub-select ensemble members to capture the diversity in the moisture budget changes.

Determination of Long-Term (1993–2019) Sea Level Rise Trends Around the Korean Peninsula Using Ocean Tide-Corrected, Multi-Mission Satellite Altimetry Data

It is vital to improve estimations of long-term trends in global and regional sea level rise to help mitigate and adapt to climate change. Satellite altimetry data have been widely used for this purpose; however, data collected in regions with strong tidalmotions often suffer from significant aliasing effects unless they are sufficiently corrected using accurate ocean tide models.Long-term trends estimated from altimetry data are often also considerably affected by regional circulation changes, and by artificial effects arising from inconsistencies between different satellite missions. Here, we focused on two regions with high (>5 mm⋅yr–1) rates of long-term linear trend in sea level rise (LTSLR) around the Korean Peninsula (KP). We addressed the impacts of tidal correction and mission inconsistency in satellite altimetry data, and discussed the potential impacts of circulation changes on LTSLR. Because the LTSLR estimation is affected by the aliasing effects of altimetry data when the tidal motions are not corrected sufficiently, yet the correction depends on the performance of ocean tide models, we employed eight ocean tide models to correct altimetry data for comparison and validated the results against observations from 13 tide gauge (TG) stations around the KP. We also estimated LTSLR from 1993 to 2019 using annual mean sea level anomalies (SLAs) from two satellite (two-sat) and all 21 satellite (all-sat) missions, with corrections for ocean tides. The TPXO9 model showed the most reasonable spatial LTSLR rate pattern (∼3 mm⋅yr–1), with the smallest difference from TG observations. It performed best near the west coast where the tidal range was the largest and when using two-sat data, because of inconsistencies in all-sat altimetry data. In contrast, off the east coast, where the impact of tidal correction is negligible, the high (∼7 mm⋅yr–1) LTSLR rates were robust regardless of ocean tide models and altimetry missions, potentially driven by long-term changes in regional circulation. Our results highlight the importance of tidal correction and mission inconsistency for improving LTSLR estimations around the KP. They also have significant implications for determining regional sea level rise under changing circulation patterns, within and beyond the region.

ЗМІНИ ТИПІВ АТМОСФЕРНОЇ ЦИРКУЛЯЦІЇ НАД ЗАХІДНОЮ УКРАЇНОЮ У ХХ–ХХІ СТ

Changes in regional atmospheric circulation can reflect or cause climate change over several decades and centuries. These changes are linked to both the anthropogenic factor and the cyclical fluctuations of the atmospheric circulation centers in the North Atlantic, which are distinctively manifested in different parts of the European continent. The study aims to identify changes in the atmospheric circulation types in the years 1881-2017 at different time spans in Western Ukraine, where the manifestation of regional atmospheric circulation is like the circulating patterns over Central Europe. For statistical analysis of regional circulation changes, a calendar of types of atmospheric circulation according to the Niedzwiedz T. classification, which identified 21 types of atmospheric circulation, was applied. The peculiarities are detected at the three-time spans (1881-1940, 1940-1970, 1970-2017) and compared to the course of air temperatures and precipitation in the seasonal and annual context. Between 1881 and 2017, there was no clear trend in changes in anticyclonic or cyclonic types, although anticyclonic types are predominant in the year (over 75 % of all the years). At shorter intervals, changes in the ratio of anticyclonic and anticyclonic types correspond to some long-term changes in air temperatures and precipitation amounts (periods of 1881-1940, 1970-2017). Some periods with several years of deviation, such as the years 1940-1970 and 1971-2017, are consistent with certain types of fluctuations in the North Atlantic Oscillation. The most evidenced is the increase in anticyclonic types of atmospheric circulation at the turn of the XX-XXI centuries corresponding to warming. More features in the temporal distribution of types of atmospheric circulation are observed in the seasonal context. In April – November, in 78 % of annual cases, the prevalence of anticyclonic weather was detected, but the predominance is much smaller (up to 16 %) than in terms of years. The anticyclonic type of wedge or high-pressure ridge (Ka) and the cyclonic type of the low-pressure trough (Bc) are invariably frequent in April – November. However, since the 1970s, an increase in anticyclonic types of the western sector (SWa, Wa, NWa) has been observed. In December – March, the number of anticyclonic types from the western sector has also increased. Instead, a decrease in the number of days typical for the region cyclonic situations from the west and northwest has been detected. In terms of months, since the 1970s, the biggest changes were observed in December and January. In December, the number of anticyclonic types increased, and in January the number of days with the western cyclonic type decreased. The multidecadal course of air temperatures and precipitation is associated with the changes in the ratio between the cyclonic and anticyclonic circulation types and NAO phases in three periods between 1881-2017. The changes and the peculiarities detected imply that the types of atmospheric circulation are appropriate to detect decadal climate changes in terms of seasons and months.

Increasing large wildfires over the western United States linked to diminishing sea ice in the Arctic

The compound nature of large wildfires in combination with complex physical and biophysical processes affecting variations in hydroclimate and fuel conditions makes it difficult to directly connect wildfire changes over fire-prone regions like the western United States (U.S.) with anthropogenic climate change. Here we show that increasing large wildfires during autumn over the western U.S. are fueled by more fire-favorable weather associated with declines in Arctic sea ice during preceding months on both interannual and interdecadal time scales. Our analysis (based on observations, climate model sensitivity experiments, and a multi-model ensemble of climate simulations) demonstrates and explains the Arctic-driven teleconnection through regional circulation changes with the poleward-shifted polar jet stream and enhanced fire-favorable surface weather conditions. The fire weather changes driven by declining Arctic sea ice during the past four decades are of similar magnitude to other leading modes of climate variability such as the El Niño-Southern Oscillation that also influence fire weather in the western U.S.

The influence of stagnant and transport types weather on heavy pollution in the Yangtze-Huaihe valley, China

The ambient atmospheric PM2.5 concentrations in Anhui Province, China, which links the Yangtze River Delta region, China's fastest growing economy area, with the Beijing-Tianjin-Hebei (BTH) region, China's most polluted region, are influenced not only by local emissions, but also by changes in regional circulation. During the period 2013–2017, when China adopted a series of pollution abatement measures, there were still occasional pollution episodes with significant increases in PM2.5 concentrations. PM2.5 rise instead during the period 2013–2017 in Anhui (the Center of the Yangtze-Huaihe, YH), when pollution emissions continued to decrease? What is the controlling mechanism behind these? By analyzing elements such as ground-based PM2.5 concentration and the planetary boundary layer (PBL) structure affecting it as well as larger scale circulation, combined with the analysis of a parameterized index, one can find that aerosol pollution in the YH region can usually be classified into three types. (1) There is a short-term transport stage (TS) in the initial stage of pollution, then as the pollutant concentrations increase, the PBL height decreases, the temperature inversion is gradually formed or strengthened, the wind speed decreases and the relative humidity of the lower layer increases, forming a two-way feedback mechanism in the cumulative stage (CS). (2) Pollutant concentrations will not drop rapidly in the later stage of CS, while a short-term TS will occur again. (3) The explosive rise (ER) events are mainly affected by transportation in the YH. The first of these types tends to be accompanied by the emergence and maintenance of heavy pollution periods (HPEs), and some phases is accompanied by explosive rises (ERs) in PM2.5 that at least double in a short period of time. To sum up, deterioration of meteorological conditions explaining approximately 68% to the increase in PM2.5 in the ER.

Why Is the Mediterranean a Climate Change Hot Spot?

AbstractHigher precipitation is expected over most of the world’s continents under climate change, except for a few specific regions where models project robust declines. Among these, the Mediterranean stands out as a result of the magnitude and significance of its winter precipitation decline. Locally, up to 40% of winter precipitation could be lost, setting strong limits on water resources that will constrain the ability of the region to develop and grow food, affecting millions of already water-stressed people and threatening the stability of this tense and complex area. To this day, however, a theory explaining the special nature of this region as a climate change hot spot is still lacking. Regional circulation changes, dominated by the development of a strong anomalous ridge, are thought to drive the winter precipitation decline, but their origins and potential contributions to regional hydroclimate change remain elusive. Here, we show how wintertime Mediterranean circulation trends can be seen as the combined response to two independent forcings: robust changes in large-scale, upper-tropospheric flow and the reduction in the regional land–sea temperature gradient that is characteristic of this region. In addition, we discuss how the circulation change can account for the magnitude and spatial structure of the drying. Our findings pave the way for better understanding and improved modeling of the future Mediterranean hydroclimate.

Sahelian Precipitation Change Induced by SST Increase: The Contrasting Roles of Regional and Larger‐Scale Drivers

AbstractRepresenting the West African Monsoon is a major challenge in climate modeling because of complex mechanisms of interaction across scales. We study the monsoon precipitation response to a 4K increase in sea surface temperatures using an idealized meridional‐vertical (2D) model, which allows separating regional‐ and larger‐scale influences. The 2D simulations reproduce key features of Atmospheric Model Intercomparison Project simulations and indicate that, in response to sea surface temperature increase, large‐scale changes induce a decrease of Sahel precipitation, while regional‐scale mechanisms generate a southward shift of the rainband. Large‐scale changes moisten and warm the free troposphere, while regional circulation changes increase low‐level moisture. Precipitation in the control simulations accounts for much of the variance in precipitation change for both Atmospheric Model Intercomparison Project and 2D simulations. This response is strongly connected to the large‐scale drivers of temperature and moisture, with an additional spread associated with the formulation of the convective parameterization.

Projected future changes in mean precipitation over Thailand based on multi‐model regional climate simulations of CORDEX Southeast Asia

AbstractThis paper highlights detailed projected changes in rainfall over Thailand for the early (2011–2040), middle (2041–2070) and late (2071–2099) periods of the 21st century under the representative concentration pathways (RCP) 4.5 and RCP 8.5 using the high‐resolution multi‐model simulations of the Coordinated Regional Climate Downscaling Experiment (CORDEX) Southeast Asia. The ensemble mean is calculated based on seven members consisting of six general circulation models (GCMs) and three regional climate models (RCMs). Generally, the ensemble mean precipitation agrees reasonably well with observations, best represented by the Global Precipitation Climatology Center (GPCC) data, over Thailand during the historical period (1976–2005). However, inter‐model variations can be large among ensemble members especially during dry months (December to March) for northern‐central‐eastern parts, and throughout the year for the southern parts of Thailand. Similarly for future projection periods, inter‐model variations in the sign and magnitude of changes exist. The ensemble means of projected changes in rainfall for both RCPs during dry months show distinct contrast between the northern‐central‐eastern parts and the southern parts of Thailand with generally wetter and drier conditions, respectively. The magnitude of change can be as high as 15% of the historical period, which varies depending on the sub‐region, season, projection period, and RCP scenario. In contrast, generally drier conditions are projected during the wet season (June to September) throughout the country for both RCPs where the rainfall reduction can be as high as 10% in some areas. However, the magnitude of projected rainfall changes of some individual models can be much larger than the ensemble means, exceeding 40% in some cases. These projected changes are related to the changes in regional circulations associated with the winter and summer monsoons, which are projected to weaken. The drier (wetter) condition is associated with the enhanced subsidence (rising motion).

Understand the Direct Effect of CO2 Increase on Tropical Circulation and TC Activity: Land Surface Warming Versus Direct Radiative Forcing

AbstractThe direct effect of increased CO2 involves contributions from both land warming and direct radiative forcing. Here, their relative impacts on tropical circulation and tropical cyclones (TCs) are quantified by increasing CO2 over land and ocean separately in a high‐resolution atmosphere‐only model. It is found that land warming induces substantial vertical velocity changes over nearby oceans and such local changes are compensated by opposite motions within tropical ascending regions. The cloud mask effect leads to smaller CO2‐induced radiative heating over ascending regions. Such inhomogeneity in radiative forcing dominates compensated changes in surface fluxes and gross moist stability, leading to the slowdown of the tropical overturning circulation. TC activity is tightly linked with the large‐scale ascent because of the influence on the atmospheric humidity. Regional circulation changes caused by land warming strongly suppresses TC activity over the northwest Pacific, while weakened ascent from direct radiative forcing causes an overall TC reduction.

Separating the Influences of Land Warming, the Direct CO2 Effect, the Plant Physiological Effect, and SST Warming on Regional Precipitation Changes

AbstractRegional precipitation responses to land warming are separated from other aspects of CO2 forcing using idealized atmosphere‐only climate model experiments. Land warming is crucial in determining the regional responses to direct CO2 forcing and the plant physiological effect and partially mitigates the response to sea surface temperature (SST) warming. The plant physiological effect causes large reductions in transpiration over forest regions but also produces significant land warming which increases moisture convergence in tropical forest regions, opposing transpiration‐related reductions in precipitation. The balance between these two large terms differs by region and explains why some regions actually experience increased precipitation in response to reduced transpiration. Regional circulation changes driven by increased CO2 atmospheric radiative heating appear to be mainly related to land‐sea differences in water cycle adjustments rather than spatial variations in radiative heating. This drives increased rainfall in several monsoon regions, particularly over West Africa. SST warming generally leads to reduced precipitation over land and increases over the oceans, while the associated land warming enhances moisture convergence and precipitation over land. However, the combination of SST and land warming effects is highly nonlinear in the tropics, which is likely to be because of strong coupling between precipitation change and land warming.

Distinct Influences of Land Cover and Land Management on Seasonal Climate.

Anthropogenic land use and land cover change is primarily represented in climate model simulations through prescribed transitions from natural vegetation to cropland or pasture. However, recent studies have demonstrated that land management practices, especially irrigation, have distinct climate impacts. Here we disentangle the seasonal climate impacts of land cover change and irrigation across areas of high agricultural intensity using climate simulations with three different land surface scenarios: (1) natural vegetation cover/no irrigation, (2) year 2000 crop cover/no irrigation, and (3) year 2000 crop cover and irrigation rates. We find that irrigation substantially amplifies land cover‐induced climate impacts but has opposing effects across certain regions. Irrigation mostly causes surface cooling, which substantially amplifies land cover change‐induced cooling in most regions except over Central, West, and South Asia, where it reverses land cover change‐induced warming. Despite increases in net surface radiation in some regions, this cooling is associated with enhancement of latent relative to sensible heat fluxes by irrigation. Similarly, irrigation substantially enhances the wetting influence of land cover change over several regions including West Asia and the Mediterranean. The most notable contrasting impacts of these forcings on precipitation occur over South Asia, where irrigation offsets the wetting influence of land cover during the monsoon season. Differential changes in regional circulations and moist static energy induced by these forcings contribute to their precipitation impacts and are associated with differential changes in surface and tropospheric temperature gradients and moisture availability. These results emphasize the importance of including irrigation forcing to evaluate the combined impacts of land surface changes for attributing historical climatic changes and managing future impacts.

Variability of regional atmospheric moisture over Northern South America: patterns and underlying phenomena

We evaluate the spatio-temporal variability of atmospheric moisture in northern South America. The spatial structure of moisture is discussed in seasonal and interannual time scales. We combine the principal component analysis of moisture flux divergence and the physical information flow to measure the relative influence of global climate phenomena in the leading modes of regional variability. Our results highlight the inherent complexity of spatial structure in this region due to the interaction of the Tropical Andes, the regional circulation changes related to the annual migration of the ITCZ, the low-level jet structures of regional atmospheric transport and the moisture transport from surrounding marine areas. Modes of variability related to oscillations in the tropical and extratropical Atlantic and Tropical Pacific are the most important sources of variability underlying the regional atmospheric moisture. To emphasize ENSO related variability, we propose a seasonal state classification index that unambiguously classifies the local evolution of precipitation in El Nino and La Nina years, showing the occurrence of marked differences in local moisture content in each of these phases.

A Dipole Pattern of Summertime Rainfall across the Indian Subcontinent and the Tibetan Plateau

The Tibetan Plateau (TP) has long been regarded as a key driver for the formation and variations of the Indian summer monsoon (ISM). Recent studies, however, have indicated that the ISM also exerts a considerable impact on rainfall variations in the TP, suggesting that the ISM and the TP should be considered as an interactive system. From this perspective, the covariability of the July–August mean rainfall across the Indian subcontinent (IS) and the TP is investigated. It is found that the interannual variation of IS and TP rainfall exhibits a dipole pattern in which rainfall in the central and northern IS tends to be out of phase with that in the southeastern TP. This dipole pattern is associated with significant anomalies in rainfall, atmospheric circulation, and water vapor transport over the Asian continent and nearby oceans. Rainfall anomalies and the associated latent heating in the central and northern IS tend to induce changes in regional circulation that suppress rainfall in the southeastern TP and vice versa. Furthermore, the sea surface temperature anomalies in the tropical southeastern Indian Ocean can trigger the dipole rainfall pattern by suppressing convection over the central IS and the northern Bay of Bengal, which further induces anomalous anticyclonic circulation to the south of TP that favors more rainfall in the southeastern TP by transporting more water vapor to the region. The dipole pattern is also linked to the Silk Road wave train via its link to rainfall over the northwestern IS.

Impact of Amazonian evapotranspiration on moisture transport and convection along the eastern flanks of the tropical Andes

The Weather Research and Forecasting (WRF) model was used to investigate the impact of Amazonian evapotranspiration (ET) on moisture transport and convection along the eastern flanks of the Andes (EADS). To isolate the role of surface ET, quasi‐idealized simulations down to 1.2 km grid spacing were conducted, where over the Amazon lowlands (AMZL) and at every time step the surface sensible‐heat effects are identical to the realistic reference runs while surface latent heat fluxes are prevented from entering the atmosphere. The results show that, without surface ET, daily precipitation within the AMZL decreases by as much as ∼75%, but nearly doubles over the surrounding mountainous regions. This dramatic influence is attributed to a dipole structure of convergence–divergence anomalies over the AMZL, primarily due to the considerable cooling of the troposphere associated with suppressed convection. Further examination of moist static energy evolution indicates that the net decrease in convective available potential energy over the AMZL is due to the removal of surface ET that is only partially compensated by related regional circulation changes. Because of the concave shape of the Andean mountain range, enhanced low‐level divergence promotes air mass accumulation to the east of the central EADS. This perturbation becomes sufficiently strong around nightfall and produces significant eastward low‐level pressure gradient force, rendering stronger winds away from the Andes. Moisture convergence and convection over the EADS vary accordingly, strengthened in the day but attenuated at night. Nocturnal convective motion is, however, more widespread. Analytical solutions of simplified diagnostic equations of convective fraction suggest that reduction of lower troposphere evaporation is the driving mechanism. Additional exploratory experiments with varied surface ET magnitude demonstrate that the connection between the AMZL ET and EADS precipitation is robust.

The use of synoptic climatology with general circulation model output over New Zealand

ABSTRACTA cluster analysis‐based synoptic classification scheme, known as the Kidson types, was applied to reanalyses and Coupled Model Inter‐comparison Project phase 3 (CMIP3) general circulation model (GCM) output over New Zealand to identify the potential for future changes in regional circulation. Results indicate that a number of GCM 20th century control runs reproduce the type frequencies observed in reanalysis data. Application to future scenario runs for the periods 2046–2065 and 2081–2100 displays little variation in the annual frequency of the synoptic types relative to the 20th century, especially when uncertainty associated with the model ensemble is considered. This is surprising in the context of previous work on possible future movements in jet position and subsequent impacts on weather patterns. A sensitivity analysis that mimics the movement of the jet position was performed, revealing that the annual type frequencies are relatively insensitive to change. To determine whether this is a problem with the synoptic typing scheme, a correlation‐based classification technique was also used, but showed similar results. This work highlights issues with applying synoptic classification schemes to GCM output and indicates that if such schemes are to be used they should be designed and tested with this application in mind.

Modern Tasman Sea surface reservoir ages from deep-sea black corals

Marine reservoir ages are a key element in calculating and constraining uncertainty in radiocarbon age estimates and are also essential to better understand regional ocean circulation. In this study, we present a new method to reconstruct long-term, high-resolution sea surface reservoir ages based on analysis of the organic skeleton of deep-sea (560m) black coral (Anthozoa, Antipatharia). Our results confirm that antipatharians are extremely slow growing (typical radial growth rate for a South Pacific specimen around 0.03mm/yr). Coupled uranium series and radiocarbon measurements were made on black coral collected live from the Norfolk Ridge (north Tasman Sea) to provide the first modern reservoir ages for this region. At the Norfolk Ridge, the average reservoir age between 1790 AD and 1900AD was ∼330 years. This was followed by a steep decrease over time of about 70 years to 1950 AD (our most modern value). This indicates an increase in surface ocean ventilation of water masses in this region. These results are consistent with observational studies for the early twentieth century, which suggest significant changes in regional circulation of the southwest pacific.

Diagnosing eclipse-induced wind changes

Responses in surface winds to solar eclipses have an almost mystical status but are difficult to detect in observations because of their transient nature. High spatial resolution (approx. 1.5 km grid) meteorological models now provide a new technique for their investigation. Measurements from the southern UK meteorological network during the 11 August 1999 total solar eclipse are compared with a high-resolution model ignorant of the lunar shadow's influence. Differences between the model output and measurements at the eclipse time show transient eclipse zone temperature decreases of up to 3 ° C, which also depressed the day's maximum temperature compared with the model prediction. Coherent responses in temperature, and wind speed and direction measurements are detected in the inland cloud-free region (from 51 ° to 52 ° N and −2 ° to 0 ° E). A mean regional wind speed decrease of 0.7 m s −1 during the maximum eclipse hour is apparent with a mean anticlockwise wind direction change of 17 ° ; no such changes occurred in the model output. Such regional circulation changes are consistent with Clayton's 1901 cold-cored eclipse cyclone hypothesis, which may be related to the anecdotal ‘eclipse wind’.

A New Method for Exploring Coupled Land–Atmosphere Dynamics

Abstract This paper proposes a new method for investigating coupled land–atmosphere interactions. The method is to apply an empirical correction technique to distinct components of a model and then examine differences between forecasts of the empirically corrected models. The correction technique is based on adding a time-dependent term to the tendency equations that subtracts the estimated tendency error at every time step. This methodology can be interpreted more generally as a series of data assimilation experiments in which only certain components of a coupled model are assimilated at a time. The correction is applied to a state-of-the-art coupled land–atmosphere model in three different ways, namely, to the atmosphere only, to the land only, and to the land and atmosphere simultaneously. The land–atmosphere interactions are inferred from monthly-mean differences between experiments. The results suggest that the land–atmosphere coupling in midlatitudes can be understood from straightforward water balance considerations, whereas the coupling in the deep tropics involves a more complicated change in regional circulation. Specifically, in midlatitudes, moisture injected into the soil is transferred to the atmosphere directly above, which in turn advects downstream and subsequently moistens the atmosphere in the downwind regions to produce positive precipitation anomalies. In the deep tropics, the regional circulation, including precipitation, is sensitive to perturbations and has no obvious relation to corrections in the atmosphere or land. The similarity of biases among different models suggests that the conclusions and methodology may be relevant to other models.

Sublinguale Mikrozirkulationsstörungen bei Patienten im septischen Schock: Untersuchungen mittels OPS-Imaging-System und PiCCO®-Monitoring

Haemodynamic monitoring of septic patients is impeded by the discrepancy between the macrohaemodynamics and the microcirculation of internal organs. Pulse contour analysis (PiCCO) provides new parameters for an improved assessment of the volume status of critically ill patients. However, changes in regional circulation, in particular those affecting the splanchnic perfusion, have proven to be especially important. The aim of our study was to compare macrohaemodynamic parameters (PiCCO) with microcirculation (OPS imaging) in severely septic patients with multiple organ failure. In seven patients suffering from septic shock and multiple organ failure (APACHE II score > 25) repeated examinations at a twenty-four hour interval were carried out by PiCCO monitoring and OPS imaging. OPS data were recorded for twenty seconds at 6 different buccal and sublingual localisations, adequately reflecting microvascular perfusion of the liver and the small intestine. Data were videotaped for off-line analysis, calculating current velocity in small and large venules (< 25 and > 25 microm), as well as functional capillary density. Significant correlations were found for current velocity in small venules with systemic vascular resistance (r(2) = 0.252, p < 0.05), mean arterial blood pressure (r(2) = 0.259, p < 0.05), and pH value (r(2) = 0.265, p < 0.05). In addition, a significant correlation was found between the oxygen transport index and the density of small vessels (r(2) = 0.355; p < 0.05). According to our findings, data acquired through PiCCO monitoring may be used for a rough estimation of the microcirculation during severe sepsis and multiple organ failure. For an assessment of the local conditions of perfusion, however, there are limits in the use of the parameters that were the object of our research. For the measurement at localisations which are accessible non-invasively and representative of the splanchnic perfusion, OPS is the more accurate method for characterisation of the microcirculation, although a more extensive and time-consuming analysis is needed.