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1.
Spatial reconstructions of drought for central High Asia based on a tree-ring network are presented. Drought patterns for central High Asia are classified into western and eastern modes of variability. Tree-ring based reconstructions of the Palmer drought severity index (PDSI) are presented for both the western central High Asia drought mode (1587–2005), and for the eastern central High Asia mode (1660–2005). Both reconstructions, generated using a principal component regression method, show an increased variability in recent decades. The wettest epoch for both reconstructions occurred from the 1940s to the 1950s. The most extreme reconstructed drought for western central High Asia was from the 1640s to the 1650s, coinciding with the collapse of the Chinese Ming Dynasty. The eastern central High Asia reconstruction has shown a distinct tendency towards drier conditions since the 1980s. Our spatial reconstructions agree well with previous reconstructions that fall within each mode, while there is no significant correlation between the two spatial reconstructions.  相似文献   

2.
The association between the lunar phases and the atmospheric electric field has been investigated from the superposed epoch analysis of the lone series of continuous data of the vertical electric field for Colaba, Bombay (18o53’N, 73o48’E 11 mASL) for the period 1947-1966. Also the periodicities in the atmospheric electric field have been studied from the spectral analysis of the data. The study has indicated that when the full moon is within 4o of the ecliptic plane i. e., Bf 4o, the electric field peaks on the day of the full moon followed by a steep fall in the field val-ues up to 4 days following the full moon day and there after it showed a steep increase. Also, the electric field has exhibited 5-9 day periodicity and its multiples are nearly always present. The periodicity in the electric field corresponds with the average time interval between the successive magnetic sector boundary (MSB) crossings i.e., 7 days. On most of the occasions, the MSB crossing day is associated with a maximum of one or more of the wavelengths derived from the spectral analysis of the atmospheric electric field.  相似文献   

3.
 The horizontal and vertical structure of the 3–5-day and 6–9-day easterly waves over West Africa and tropical Atlantic are investigated. NCEP/NCAR reanalyses are used for the period 1979–1995 to produce a 17-year climatology of both 3–5-day and 6–9-day easterly waves. Composite patterns of convection, wind, temperature and vertical velocity are analysed with respect to the following: the modulation by 3–5-day and 6–9-day wave regimes; the contrasts between the ITCZ (5°N–10°N) and the Sahelo-Saharan band (15°N–20°N); the difference between land and ocean, and seasonal variations. Similarities and differences in the characteristics of the two wave regimes are identified. Received: 18 August 1999 / Accepted: 14 March 2001  相似文献   

4.
In this short communication we highlight the NATO Advanced Research Workshop (ARW) “Atmospheric Boundary Layers: Modelling and Applications for Environmental Security”, to be held in Dubrovnik, Croatia, 18–22 April 2006 (http:// pbl-nato-arw.dmi.dk) and the “Summer School on Air-Sea Interaction” to be held in Helsinki, Finland, 28 August–1 September 2006 (http://www.scasi.fi). These two events are connected to the ongoing Ev Marie Curie Chair Project “Planetary boundary layers – Theory, modelling and role in earth systems” (PBL – TMRES, Contract MEXC-CT-2003-509742, www.atm.helsinki.fi/PBL/).  相似文献   

5.
 An improved concept of the best analogues method was used to reconstruct the Last Glacial Maximum (LGM) climate from a set of botanical records from the former Soviet Union and Mongolia. Terrestrial pollen and macrofossil taxa were grouped into broad classes – plant functional types (PFTs), defined by the ecological and climatic parameters used in the BIOME1 model. PFT scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from Eurasia and North America. In contrast to individual taxa, which exhibit great variability and may not be present in the palaeoassemblages, even in suitable climates, PFTs are more characteristic of the vegetation types. The modified method thus allows climate reconstruction at time intervals with partial direct analogues of modern vegetation (e.g. the LGM). At 18 kBP, mean temperatures were 20–29 °C colder than today in winter and 5–11 °C colder in summer in European Russia and Ukraine. Sites from western Georgia show negative, but moderate temperature anomalies compared to today: 8–11 °C in January and 5–7 °C in July. LGM winters were 7–15 °C colder and summers were 1–7 °C colder in Siberia and Mongolia. Annual precipitation sums were 50–750 mm lower than today across northern Eurasia, suggesting a weakening of the Atlantic and Pacific influences. Reconstructed drought index shows much drier LGM conditions in northern and mid-latitude Russia, but similar to or slightly wetter than today around the Black Sea and in Mongolia, suggesting compensation of precipitation losses by lower-than-present evaporation. Received: 11 May 1998 / Accepted: 25 September 1998  相似文献   

6.
Summary  Variations of surface temperature are studied at six southern Mediterranean stations: Marakesh (1910–1991), Alger (1823–1991), Tripoli (1944–1991), Alexandria (1942–1991), Amman (1923–1991), and Beirut (1863–1991). The homogeneity of the temperature data is examined for each station by means of the short-cut Bartlet test. Abrupt climatic changes towards warm or cold periods exist at all stations with the exception of Tripoli. Persistence is also found in annual and seasonal temperatures, however, this persistence is not always linear. Annual and seasonal temperature fluctuations are examined and periods important warming begin in 1910 and 1970. Fluctuations in winter temperature are around the mean value, while summer temperatures, during the last three decades, have been distinctly higher than the long term mean values. Received October 3, 1997 Revised April 17, 1998  相似文献   

7.
A nonlinear backpropagation network (BPN) has been trained with high-resolution multiproxy reconstructions of temperature and precipitation (input data) and glacier length variations of the Alpine Lower Grindelwald Glacier, Switzerland (output data). The model was then forced with two regional climate scenarios of temperature and precipitation derived from a probabilistic approach: The first scenario (“no change”) assumes no changes in temperature and precipitation for the 2000–2050 period compared to the 1970–2000 mean. In the second scenario (“combined forcing”) linear warming rates of 0.036–0.054°C per year and changing precipitation rates between −17% and +8% compared to the 1970–2000 mean have been used for the 2000–2050 period. In the first case the Lower Grindelwald Glacier shows a continuous retreat until the 2020s when it reaches an equilibrium followed by a minor advance. For the second scenario a strong and continuous retreat of approximately −30 m/year since the 1990s has been modelled. By processing the used climate parameters with a sensitivity analysis based on neural networks we investigate the relative importance of different climate configurations for the Lower Grindelwald Glacier during four well-documented historical advance (1590–1610, 1690–1720, 1760–1780, 1810–1820) and retreat periods (1640–1665, 1780–1810, 1860–1880, 1945–1970). It is shown that different combinations of seasonal temperature and precipitation have led to glacier variations. In a similar manner, we establish the significance of precipitation and temperature for the well-known early eighteenth century advance and the twentieth century retreat of Nigardsbreen, a glacier in western Norway. We show that the maritime Nigardsbreen Glacier is more influenced by winter and/or spring precipitation than the Lower Grindelwald Glacier.  相似文献   

8.
 Monthly sea surface temperature anomalies (SSTA) at near-global scale (60 °N–40 °S) and May to October rainfall amounts in West Africa (16 °N–5 °N; 16 °W–16 °E) are first used to investigate the seasonal and interannual evolutions of their relationship. It is shown that West African rainfall variability is associated with two types of oceanic changes: (1) a large-scale evolution involving the two largest SSTA leading eigenmodes (16% of the total variance with stronger loadings in the equatorial and southern oceans) related to the long-term (multiannual) component of rainfall variability mainly expressed in the Sudan–Sahel region; and (2) a regional and seasonally coupled evolution of the meridional thermal gradient in the tropical Atlantic due to the linear combination of the two largest SSTA modes in the Atlantic (11% with strong inverse loadings over the northern and southern tropics) which is associated with the interannual and quasi-decadal components of regional rainfall in West Africa. Linear regression and discriminant analyses provide evidence that the main July–September rainfall anomalies in Sudan–Sahel can be detected with rather good skills using the leading (April–June) or synchronous (July–September) values of the four main oceanic modes. In particular, the driest conditions over Sahel, more marked since the beginning of the 1970s, are specifically linked to the warm phases of the two global modes and to cold/warm anomalies in the northern/southern tropical Atlantic. Idealized but realistic SSTA patterns, obtained from some basic linear combinations of the four main oceanic modes appear sufficient to generate quickly (from mid-July to the end of August) significant West African rainfall anomalies in model experiments, consistent with the statistical results. The recent negative impact on West African rainfall exerted by the global oceanic forcing is primarily due to the generation of subsidence anomalies in the mid-troposphere over West Africa. When an idealized north to south SSTA gradient is added in the tropical Atlantic, strong north to south height gradients in the middle levels appear. These limit the northward excursion of the rainbelt in West Africa: the Sahelian area experiences drier conditions due to the additive effect (subsidence anomalies+latitudinal blocking) while over the Guinea regions wet conditions do not significantly increase, since the subsidence anomalies and the blocking effect act here in opposite ways. Received: 26 June 1997 / Accepted: 3 October 1997  相似文献   

9.
Summary The problem of the reconstruction of mean summer temperatures from proxy data on a rigorous statistical basis is addressed: Cross spectral analysis is used for evaluating the suitability of linear transfer models between proxy data and temperature, the linear model is estimated from the data of a calibration period and it is verified using the data of a different period. Strict statistical tests are applied at every step of the analysis. Three examples using the proposed method are given: the reconstruction of mean April–July temperatures at Basel from grape harvest data in NE France (1484–1768), mean April–September temperatures at Basel from late wood density of trees from the Swiss Prealps (1270‐1768), and mean April–September temperatures at Great St. Bernhard from the late wood proxy too (1270–1850). The grape harvest data give a very good reconstruction, the resulting temperatures from 1500–1768 are documented. The late wood data fails to give a good reconstruction.
Die Rekonstruktion von Temperaturreihen aus Proxydaten in Mitteleuropa
Zusammenfassung Es wird das Problem der Rekonstruktion von mittleren Sommertemperaturen aus sogenannten Proxydaten untersucht. Sehr viel Wert wird auf die statistische Signifikanz der Rekonstruktion gelegt. Kreuzspektralanalyse wird benutzt, um die Verwendungsf?higkeit eines linearen Modells als Transfermodell zwischen Temperatur und Proxydaten zu ermitteln. Die Parameter des linearen Transfermodells werden aus den Daten der sogenannten Eichperiode abgesch?tzt und die damit für eine unabh?ngige Periode rekonstruierten Temperaturen werden mit gemessenen verglichen. In jedem Schritt der Analyse werden strikte statistische Tests durchgeführt, um die Ergebnisse zu untermauern. Die Methode wird an drei Beispielen erprobt: die mittlere April–Juli Temperatur in Basel wird mit Hilfe von Weinlesedaten von NE-Frankreich für die Zeit (1484–1768) rekonstruiert, die mittlere April–September Temperatur in Basel und am Gro?en Bernhard wird mit Sp?tholzdichtewerten der Schweizer Voralpen verglichen. Die Weinlesedaten ergeben eine sehr gute Rekonstruktion und die Temperaturreihe für den Zeitraum 1500–1768 wird dokumentiert. Die Sp?tholzdichten liefern keine gute Temperaturrrekonstruktion.

With 11 Figures  相似文献   

10.
Palaeoclimates across Europe for 6000 y BP were estimated from pollen data using the modern pollen analogue technique constrained with lake-level data. The constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration (P–E) is consistent with the regional change in moisture balance as indicated by lakes. An artificial neural network was used for the spatial interpolation of lake-level changes to the pollen sites, and for mapping palaeoclimate anomalies. The climate variables reconstructed were mean temperature of the coldest month (T c ), growing degree days above 5  °C (GDD), moisture availability expressed as the ratio of actual to equilibrium evapotranspiration (α), and P–E. The constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies, especially for P–E. The reconstructions indicate clear spatial and seasonal patterns of Holocene climate change, which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations. Winter temperatures (T c ) were 1–3 K greater than present in the far N and NE of Europe, but 2–4 K less than present in the Mediterranean region. Summer warmth (GDD) was greater than present in NW Europe (by 400–800 K day at the highest elevations) and in the Alps, but >400 K day less than present at lower elevations in S Europe. P–E was 50–250 mm less than present in NW Europe and the Alps, but α was 10–15% greater than present in S Europe and P–E was 50–200 mm greater than present in S and E Europe. Received: 3 January 1996 / Accepted: 15 July 1996  相似文献   

11.
Manzanas  R.  Guti&#;rrez  J. M.  Bhend  J.  Hemri  S.  Doblas-Reyes  F. J.  Penabad  E.  Brookshaw  A. 《Climate Dynamics》2020,54(5):2869-2882
Climate Dynamics - The present paper is a follow-on of the work presented in Manzanas et al. (Clim Dyn 53(3–4):1287–1305, 2019) which provides a comprehensive intercomparison...  相似文献   

12.
 NCEP/NCAR and ECMWF daily reanalyses are used to investigate the synoptic variability of easterly waves over West Africa and tropical Atlantic at 700 hPa in northern summer between 1979–1995 (1979–1993 for ECMWF). Spectral analysis of the meridional wind component at 700 hPa highlighted two main periodicity bands, between 3 and 5 days, and 6 and 9 days. The 3–5-day easterly wave regime has already been widely investigated, but only on shorter datasets. These waves grow both north and south of the African Easterly Jet (AEJ). The two main tracks, noted over West Africa at 5 °N and 15 °N, converge over the Atlantic on latitude 17.5 °N. These waves are more active in August–September than in June–July. Their average wavelength/phase speed varies from about 3000 km/8 m s-1 north of the jet to 5000 km/12 m s-1 south of the jet. Rainfall, convection and monsoon flux are significantly modulated by these waves, convection in the Inter-Tropical Convergence Zone (ITCZ) being enhanced in the trough and ahead of it, with a wide meridional extension. Compared to the 3–5-day waves, the 6–9-day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics. The only main track is located north of the AEJ along 17.5 °N both over West Africa and the Atlantic. The mean wavelength is higher, about 5000 km long, and the average phase speed is about 7 m s-1. Then the wind field perturbation is mostly evident at the AEJ latitude and north of it. The perturbation structure is similar to that of 3–5-days in the north except that the more developed circulation centers, moving more to the north, lead to a large modulation of the jet zonal wind component. South of the AEJ, the wind field perturbation is weaker and quite different. The zonal wind core of the jet appears to be an almost symmetric axis in the 6–9-day wind field pattern, a clockwise circulation north of the AEJ being associated with a counter-clockwise circulation south of the jet, and vice versa. These 6–9-day easterly waves also affect significantly rainfall, convection and monsoon flux but in a different way, inducing large zonal convective bands in the ITCZ, mostly in the trough and behind it. As opposed to the 3–5-day wave regime, these rainfall anomalies are associated with anomalies of opposite sign over the Guinea coast and the Sahelian regions. Over the continent, these waves are more active in June–July, and in August–September over the ocean. GATE phase I gave an example of such an active 6–9-day wave pattern. Considered as a sequence of weak easterly wave activity, this phase was also a sequence of high 6–9-day easterly wave activity. We suggest that the 6–9-day regime results from an interaction between the 3–5-day easterly wave regime (maintained by the barotropic/baroclinic instability of the AEJ), and the development of strong anticyclonic circulations, north of the jet over West Africa, and both north and south of the jet over the Atlantic, significantly affecting the jet zonal wind component. The permanent subtropical anticyclones (Azores, Libya, St Helena) could help initiation and maintenance of such regime over West Africa and tropical Atlantic. Based on an a priori period-band criterion, our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over West Africa and tropical Atlantic. NCEP/NCAR and ECMWF reanalyses are in good agreement, the main difference being a more developed easterly wave activity in the NCEP/NCAR reanalyses, especially for the 3–5-day regime over the Atlantic. Received: 28 May 1998 / Accepted: 2 May 1999  相似文献   

13.
Summary ?The analysis of ground-based measurements of solar erythemal ultraviolet (UV) irradiance with a Solar Light 501 biometer, and total (300–3000 nm) irradiance with an Eppley B&W pyranometer at the Argentine Antarctic Base “Almirante Brown”, Paradise Bay (64.9° S, 62.9° W, 10 m a.s.l.) is presented. Measurement period extends from February 16 to March 28 2000. A relatively high mean albedo and a very clean atmosphere characterise the place. Sky conditions were of generally high cloud cover percentage. Clear-sky irradiance for each day was estimated with model calculations, and the effect of the cloudiness was studied through the ratio of measured to clear-sky value (r). Two particular cases were analysed: overcast sky without precipitation and overcast sky with rain or slight snowfall, the last one presenting frequently dense fog. Total irradiance was more attenuated than UV by the homogeneous cloudiness, obtaining mean r values of 0.54 for erythemal irradiance and 0.30 for total irradiance in the first case (without precipitation) and 0.27 and 0.17 respectively in the second case (with precipitation). Mean r values for the complete period were 0.58 for erythemal irradiance and 0.43 for total irradiance. Erythemal and total daily insolations reduce quickly at this epoch due to the increase of the noon solar zenith angle and the decrease of daylight time. Additionally, they were strongly modulated by cloudiness. Measured maxima were 2.71 kJ/m2 and 18.42 MJ/m2 respectively. Measurements were compared with satellite data. TOMS-inferred erythemal daily insolation shows the typical underestimation with respect to ground measurements at regions of high mean albedo. Measured mean total daily insolation agrees with climatological satellite data for the months of the campaign. Received August 9, 2002; revised January 4, 2003; accepted January 28, 2003 Published online May 20, 2003  相似文献   

14.
 The relationship between European winter temperature spatial and temporal modes of variability and the North Atlantic Oscillation (NAO) has been studied during the period 1852–1997. Temporal modes of variability of the NAO and temperatures are analysed using wavelet transform. Results show that the NAO presents a strong non-stationary behaviour. The most important feature is the existence of a quasi-periodic oscillation, with a period between 6–10 years and maximum amplitude of eight years, during the periods 1842–1868 and 1964–1994. Between 1875 and 1939 the spectra of the NAO is almost white. The possible relationship between the occurrence of extreme events of the NAO and its spectral behaviour has been analysed. The results indicate that quasi-periodic oscillations in the NAO do not lead to more extreme episodes, but rather that an extreme value of the oscillation is more likely to persist for few years. Particularly energetic modes of coherent variability between temperature and NAO are found between 2–6 years for 1857–1879 and 1978–1984, and between 6–10 years from 1961 to 1991. The relationship between the NAO and temperatures as a function of the state of the oscillation has been studied using composites. Empirical evidence has been found suggesting that winter temperatures, in a great part of the study area, do not vary in a linear manner with respect to phase and intensity of the NAO. Regions in the study area differ in sensitivity to changes in the NAO. The spatial patterns of variability of the temperatures are found to be independent of the NAO spectra. Received: 8 April 1999 / Accepted: 19 September 2000  相似文献   

15.
We used neural network models to seasonally forecast the tropical Pacific sea surface temperature anomalies (SSTA) in the Ni?o 3.4 region (6 °S–6 °N, 120 °W–170 °W). The inputs to the neural networks (i.e., the predictors) were the first seven wind stress empirical orthogonal function (EOF) modes of the tropical Pacific (20 °S–20 °N, 120 °E–70 °W) for four seasons and the Ni?o 3.4 SSTA itself for the final season. The period of 1952–1981 was used for training the neural network models, and the period 1982–1992 for forecast validation. At 6-month lead time, neural networks attained forecast skills comparable to the other El Ni?o-Southern Oscillation (ENSO) models. Our results suggested that neural network models were viable for ENSO forecasting even at longer lead times of 9 to 12 months. We hypothesized that at these longer leads, the underlying relationship between the wind stress and Ni?o 3.4 SSTA became increasingly nonlinear. The neural network results were interpreted in light of current theories, e.g., the role of the “off-equatorial” Rossby waves in triggering the onset of an ENSO event and the delayed-oscillator theory in the development and termination of an ENSO event. Received: 31 October 1995 / Accepted: 25 July 1996  相似文献   

16.
The peculiarities are studied of variations of average annual and extreme levels in the Russian sector of the Vistula Lagoon situated in the southeastern part of the Baltic Sea. The main regularity of interannual variations of averaged characteristics of the lagoon level is a steady trend towards their increase: the mean level increase is characterized by the linear trend increasing depending on the length of the series, from 1.7–1.9 mm/year (Baltiisk, 1860–2006; Kaliningrad, 1901–2006) to 3.6–3.7 mm/year (Kaliningrad, Baltiisk, Krasnoflotskoe, 1959–2006). On the sea coast (Pionerskii, 1959–2006), this trend in the second half of the 20th century amounted to 2.6 mm/year only. The obtained results illustrate the response of level variations in the Baltic Sea lagoons to the global climate warming and indicate that the long-term evolution of average characteristics of the Vistula Lagoon level cannot be explained only by the increase in the level of the World Ocean and adjacent seas intensified in recent decades but is caused by the changes in the wind load and precipitation in the catchment basin.  相似文献   

17.
Summary The crop growth model CERES-Maize is used to estimate the direct (through enhanced fertilisation effect of ambient CO2) and indirect (through changed climate conditions) effects of increased concentration of atmospheric CO2 on maize yields. The analysis is based on multi-year crop model simulations run with daily weather series obtained alternatively by a direct modification of observed weather series and by a stochastic weather generator. The crop model is run in two settings: stressed yields are simulated in water and nutrient limited conditions, potential yields in water and nutrient unlimited conditions. The climate change scenario was constructed using the output from the ECHAM3/T42 model (temperature), regression relationships between temperature and solar radiation, and an expert judgement (precipitation). Results: (i) After omitting the two most extreme misfits, the standard error between the observed and modelled yields is 11%. (ii) The direct effect of doubled CO2: The stressed yields would increase by 36–41% in the present climate and by 61–66% in the 2 × CO2 climate. The potential yields would increase only by 9–10% as the improved water use efficiency does not apply. (iii) The indirect effect of doubled CO2: The stressed yields would decrease by 27–29% (14–16%) at present (doubled) ambient CO2 concentration. The increased temperature shortens the phenological phases and does not allow for the optimal development of the crop. The simultaneous decrease of precipitation and increase of temperature and solar radiation deepen the water stress, thereby reducing the yields. The reduction of the potential yields is significantly smaller as the effect of the increased water stress does not apply. (iv) If both direct and indirect effects of doubled CO2 are considered, the stressed yields should increase by 17–18%, and the potential yields by 5–14%. (v) The decrease of the stressed yields due to the indirect effect may be reduced by applying earlier planting dates. Received March 9, 2001 Revised September 25, 2001  相似文献   

18.
Karachi is the largest city of Pakistan. The temperature change in Karachi is studied in this research by analyzing the time series data of mean maximum temperature (MMxT), mean minimum temperature (MMiT) and mean annual temperature (MAT) from 1947 to 2005 (59 years). Data is analyzed in three parts by running linear regression and by taking anomalies of all time periods: (a) whole period from 1947–2005; (b) phase one 1947–1975 and (c) phase two 1976–2005. During 1947 to 2005 MMxT has increased about 4.6°C, MMiT has no change and MAT has increased 2.25°C. During 1947–1975, MMxT increased 1.9°C, in this period there is − 1.3°C decrease in MMiT and MAT has raised upto 0.3°C. During 1976–2005, the MMxT, MMiT and MAT increased 2.7°C, 1.2°C and 1.95°C, respectively. The analysis shows significantly the role of extreme vulnerability of MMxT in rising the temperature of Karachi than the MMiT.  相似文献   

19.
A model was developed to predict the modification with fetch in offshore flow of mixing ratio, air–water exchange flux, and near-surface vertical gradients in mixing ratio of a scalar due to air–water exchange. The model was developed for planning and interpretation of air–water exchange flux measurements in the coastal zone. The Lagrangian model applies a mass balance over the internal boundary layer (IBL) using the integral depth scale approach, previously applied to development of the nocturnal boundary layer overland. Surface fluxes and vertical profiles in the surface layer were calculated using the NOAA COARE bulk algorithm and gas transfer model (e.g., Blomquist et al. 2006, Geophys Res Lett 33:1–4). IBL height was assumed proportional to the square root of fetch, and estimates of the IBL growth rate coefficient, α, were obtained by three methods: (1) calibration of the model to a large dataset of air temperature and humidity modification over Lake Ontario in 1973, (2) atmospheric soundings from the 2004 New England Air Quality Study and (3) solution of a simplified diffusion equation and an estimate of eddy diffusivity from Monin–Obukhov similarity theory (MOST). Reasonable agreement was obtained between the calibrated and MOST values of α for stable, neutral, and unstable conditions, and estimates of α agreed with previously published parametrizations that were valid for the stable IBL only. The parametrization of α provides estimates of IBL height, and the model estimates modification of scalar mixing ratio, fluxes, and near-surface gradients, under conditions of coastal offshore flow (0–50 km) over a wide range in stability.  相似文献   

20.
Summary ?The LITFASS project (‘Lindenberg Inhomogeneous Terrain – Fluxes between Atmosphere and Surface: a Long-term Study’) of the Deutscher Wetterdienst (DWD, German Meteorological Service) aims to develop and to test a strategy for the determination and parameterisation of the area-averaged turbulent fluxes of heat, momentum, and water vapour over a heterogeneous land surface. These fluxes will be representative for an area of about 10 * 10 km2 (while the typical patch size is between 10−1 to 100 km2) corresponding to the size of a grid cell in the present operational numerical weather prediction model of the DWD. LITFASS consists of three components: – the development of a non-hydrostatic micro-α-scale model (the LITFASS local model – LLM) with a grid-size of about 100 * 100 m2, – experimental investigations of land surface – atmosphere exchange processes and boundary layer structure within a 20 * 20 km2 area around the Meteorological Observatory Lindenberg, – the assimilation of a data base as an interface between measurements and modelling activities. The overall project strategy was tested over a three-week period in June 1998 during the LITFASS-98 field experiment. This paper gives an overview on the LITFASS project, on the design and measurement program of the LITFASS-98 experiment, and on the weather conditions during the period of the experiment. Conclusions are formulated for the operational realisation of the LITFASS measurement concept and for future field experiments aimed at studying the land surface – atmosphere interaction in the Lindenberg area. Selected results from both experimental and modelling activities are presented in a series of companion papers completing this special issue of the journal. Received June 18, 2001; revised March 18, 2002; accepted April 2, 2002  相似文献   

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