Precipitation Belt Research Articles

Physical and chemical properties of sound-producing and soundless sand particles from booming sand dunes, northern China

This study here is the result of a comparative study of the geomorphic features, grain size distribution, major mineral components, and micro-textures of sound-producing and soundless sands from three geoparks in north China, and discusses the possible causes of this naturally occurring, physical phenomenon. The sound-producing sand dunes we have investigated are situated along a curvilinear belt of deserts and experience variable precipitation–evaporation rates on a yearly basis. “Singing sands” occur mainly on barchan-type dunes and adjacent to lakes or springs, whereas soundless sands are mainly located in desert areas where there is no nearby surface or groundwater sources. We have analyzed samples from nine sound-producing and two soundless sand dunes using grain size, X-ray diffraction and fluorescence, and SEM analyses. All sand types are composed largely of quartz and feldspar, but sound-producing sands also contain secondary minerals such as kaolinite (3–5%), albite (2–6%), microcline (2–5%), and calcite (5%) that are lacking in the soundless sand samples. Sound-producing sands are generally fine-grained whereas soundless sands are coarse-grained, and all sand types are generally sub-rounded to rounded indicating long transport distance from their provenance. Sphericity values of both sand types are nearly identical with predominantly oblate shapes. Surface pitting is not a unique feature of either sand types, and hence can be ruled out as a major cause of the acoustic properties of sound-producing sands. Densely distributed dissolution features such as scale-like upturned plates and silica scales on grain surfaces contribute significantly to the sound emission of singing sands. Thus, the physical–climatic conditions in deserts such as the presence of surface water and groundwater and precipitation–evaporation rates, which collectively control the formation and distribution of dissolution features on sand surfaces, have a first-order control on the production of sound-producing sands.

Evaluation of the COSMO‐CLM high‐resolution climate simulations over West Africa

AbstractThe evaluation of a high‐resolution simulation at 0.11° (12 km) with the COnsortium for Small‐scale MOdelling in CLimate Mode (CCLM) regional climate model, applied over West Africa, is presented. This simulation is nested in a CCLM run at resolution of 0.44°, driven with boundary forcing data from the ERA‐Interim reanalysis, and covers the period from 1981 to 2010. The simulated temperature and precipitation are evaluated using three selected climate indices for temperature and eight indices for precipitation in five different regions against a new, daily precipitation climatology covering West Africa and against other state of the art climatologies. The obtained results indicate that CCLM is able to reproduce the observed major climate characteristics including the West African Monsoon within the range of comparable regional climate modeling evaluations studies, but substantial uncertainties remain, especially in the Sahel zone. The seasonal mean temperature bias for the rainy season from June to September ranges from −0.8°C to −1.1°C. The CCLM simulations also underestimate the observed precipitation with biases in precipitation reaching −10% in the high‐resolution and −20% in the low‐resolution model runs. CCLM extends the monsoon precipitation belt too far north, which results in an overestimation of precipitation in the Sahel zone of up to 60%. In the coastal zone, the precipitation is underestimated by up to −90%. These biases in precipitation amounts are associated with errors in the precipitation seasonality. The added value of the higher resolution of the nested run is reflected in a smaller bias in extreme precipitation statistics with respect to the reference data.

Impacts of Spatiotemporal Anomalies of Tibetan Plateau Snow Cover on Summer Precipitation in Eastern China

Abstract Tibetan Plateau (TP) snow cover undergoes significant temporal and spatial variations during the winter and spring months. This study investigates the relationship between the spatiotemporal distribution of winter–spring snow cover (SC) over the TP and summer precipitation in eastern China (EC) using the singular value decomposition (SVD) method. Four simulation experiments are designed to validate the results of SVD analysis. Both observations and simulations show that heavier snow cover in the southern TP leads to more rainfall in the Yangtze River basin and northeastern China, and less precipitation in southern China, whereas heavier snow cover in the northern TP results in enhanced rainfall in southeastern and northern China and weakened precipitation in the Yangtze River basin. The linkage is attributed to anomalous westerly winds in the upper troposphere at around 200 hPa and to changes of the southern branch of westerlies at 500 hPa on the south side of the TP, which are caused by lasting diabatic heat anomalies over the TP. The shifts in position of the westerly jet at the exit region and negative anomalies of geopotential height at 500 hPa further result in anomalous anticyclone over the East China Sea and the corresponding 850-hPa water vapor convergence and influence the anomalous summer precipitation belt in EC.

Simulation of East Asian Summer Monsoon (EASM) in SP‐CCSM4: Part I—Seasonal mean state and intraseasonal variability

AbstractThe mean state and intraseasonal variability of the East Asian Summer Monsoon (EASM) simulated by the Super‐Parameterized Community Climate System Model version 4 (SP‐CCSM4) and the conventionally parameterized CCSM4 are evaluated against observations. The SP‐CCSM4 model has a better simulation of the May‐June‐July‐August seasonal mean state of EASM than CCSM4, although it produces a dry bias over the EASM area compared to observations. The dry bias in SP‐CCSM4 is associated with the erroneous northward displacement of the western North Pacific subtropical high. The SP‐CCSM4 model simulates the reasonable monsoon onset and northward propagation of the monsoonal precipitation, yet the rainband marches faster and reaches to a higher latitude than in observations. The mechanisms associated with the northward propagation of the intraseasonal oscillation (ISO) of EASM are also captured by SP‐CCSM4. The cyclonic vorticity and the moisture convergence lead the convective activity, favoring the northward propagation of convection. The easterly wind shear and air‐sea interaction mechanisms in the model are realistic and show contributions to the northward propagation of the ISO of the model. The SP‐CCSM4 model captures many facets of the stepwise northward propagation of the precipitation belt in the EASM region, including the Mei‐yu season. However, compared to the observations, in the model the onset of the Mei‐yu season takes place 5 days earlier and the duration of the Mei‐yu's rainy episode is shorter. The CCSM4 model has large deficiencies in simulating the intraseasonal variability of EASM.

Recent Winter Precipitation Increase in the Middle–Lower Yangtze River Valley since the Late 1970s: A Response to Warming in the Tropical Indian Ocean

Abstract The middle–lower valley of the Yangtze River (MLY), located in the middle of eastern China, has been one of the largest economic centers of China since ancient times. Winter precipitation variability over the MLY is important for China because of its significant influence on the local economy. However, few studies have focused on the long-term variability of winter precipitation over the MLY. This study reports a significant wetting trend over the MLY in winter during the three decades since the late 1970s, forming a “mid-east-China winter wetting” pattern, which has become an important feature of precipitation change under the weakening East Asian winter monsoon. This wetting trend in the MLY also implies the poleward extension of the precipitation belts of southern China. Further investigation reveals that the increasing sea surface temperature (SST) in the tropical Indian Ocean (TIO) is the dominant factor responsible for recent increases in precipitation over the MLY. The thermal forcing driven by warming of the TIO SST gives rise to an anomalous cyclonic circulation along the coast of eastern China. This transports more water vapor onto the Chinese mainland, shifts and causes anomalous convergence over the MLY, and generates the increase in precipitation there. As such, the increasing SST in the TIO induces over 80% of the observed wetting trend over the MLY. This mechanism was verified by results obtained from two sets of sensitivity experiments using a numerical spectral atmospheric general circulation model. Thus, increasing SST in the TIO has made a dominant contribution to the recent winter precipitation increase over the MLY.

The relationship between soil, climate and forest development in the mid-mountain zone of the Sangong River watershed in the northern Tianshan Mountains, China

The mountainous forests in arid regions, being sensitive to climate change, are one of the key research topics related to the mechanism of interaction between climate and the terrestrial ecosystem. In this study, the spatial distribution of a mid-mountain forest and its environmental factors were investigated by using a combination of remote sensing technology, field survey, climate indices and soil nutrient analysis in the Sangong River watershed of the northern Tianshan Mountains. The forest (Picea schrenkiana) was distributed between 1,510 and 2,720 m asl. Tree height and diameter at breast height (DBH) exhibited a bi-modal pattern with increasing elevation, and rested at 2,450 and 2,250 m asl, respectively. The two maxima of DBH appeared at 2,000 and 2,550 m asl, and the taller trees were observed at 2,100 and 2,600 m asl. For the annual mean temperature, the difference was approximately 5.8°C between the lowest and the highest limits of the forest, and the average decreasing rates per hundred meters were 0.49°C and 0.55°C with increasing altitude between 1,500 and 2,000 m asl and above 2,000 m asl, respectively. The annual precipitation in the forest zone first increased and then decreased with the increase of altitude, and the maximum value was at 2,000 m asl. For per hundred meters, the annual precipitation increased with the rate of 31 mm between 1,500 and 2,000 m asl and decreased by 7.8 mm above 2,000 m asl. The SOM, TN and TP were high between 2,000 and 2,700 m asl and low at the lower and upper forest limits. The minimum CaCO3 concentration, pH value and EC coincided with the maximum precipitation belt at 2,000 m asl. The SOM, TN and TP were high in the topsoil (0–10 cm) and differed significantly from the values observed in the deep soil layers (>10 cm). The soil nutrients exhibited spatial heterogeneity and higher aggregation in the topsoil. In conclusion, soil and climate are closely related to each other, working synergistically to determine the development and spatial distribution of the mid-mountain forest in the study area. The order of the importance of environmental factors to forest development in this study is as follows: soil nutrients>precipitation>elevation>temperature.

Evaluation of TRMM 3B42 product using a new gauge-based analysis of daily precipitation over China

In this study, a new gauge-based analysis of 0.25° daily precipitation data from 756 Chinese stations was constructed using a state-of-the-art gauge data analysis system to evaluate the Tropical Precipitation Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis (TMPA) 3B42 Version 6 product over China during the period of 1998–2010. Tests by withdrawing a fraction of the gauge records from the analysis shows that the gauge data analysis system used in this study has a good performance in constructing daily high-resolution gridded analysis data over China. Analyses reveal that the 3B42-V6 product is capable of describing the observed spatial patterns and seasonal variations for most areas of China during the wet season, as well as the evolution of the summer precipitation belt in the Yangtze River valley. The differences between the satellite product and the gauge analysis of daily precipitation are within ∼10% over most of east China, but the satellite product underestimates the observed precipitation by 20% ∼ 50% for most of western China, especially the western Tibetan Plateau where the underestimates are over 50%. For daily variations of precipitation, the satellite product captures the observed precipitation signals but fails to show the correct magnitude or the timing of precipitation on synoptic or sub-synoptic scales. In addition, this satellite product overestimates the heavy and extreme daily precipitation for some areas of southeastern China but underestimates the light and moderate precipitation over most of northwestern China. Thus, the TRMM 3B42-V6 product should be used cautiously for monitoring droughts and heavy and extreme precipitation for some regions of China. An empirical orthogonal function (EOF) analysis shows that the TRMM product can well depict the spatiotemporal evolution of the observed daily precipitation for most China during the warm season.

Decadal Change in the Correlation Pattern between the Tibetan Plateau Winter Snow and the East Asian Summer Precipitation during 1979–2011

AbstractObservational evidence indicates that the correlation between Tibetan Plateau (TP) winter snow and East Asian (EA) summer precipitation changed in the late 1990s. During the period 1979–99, the positive correlation between the TP winter snow and the summer precipitation along the Yangtze River valley (YRV) and southern Japan was disrupted by the decadal climate shift. In contrast, the summer precipitation over the Huaihe River valley (HRV) and the Korean Peninsula showed a strong positive correlation with the preceding winter snow over the TP during the period 2000–11.The radiosonde temperature measurements over the TP show a pronounced warming since the late 1990s. This warming is associated with the significant increase in surface sensible heat flux and longwave radiation into atmosphere. The latter is closely related to the decrease of surface albedo and the soil hydrological effect of melting snow due to the decadal decrease in the preceding winter and spring snow over the TP. The TP warming induced by the decrease in winter snow, together with the cooling of the sea surface temperature in the tropical central and eastern Pacific, intensifies the land–sea thermal contrast in the subsequent spring and summer over EA, thus causing a northward advance of the EA summer monsoon. Accompanying the northward migration of the summer monsoon, the summer precipitation belt over EA shifts northward. Consequently, the high summer precipitation region over EA correlating with the preceding winter snow over the TP has shifted northward from the YRV and southern Japan to the HRV and the Korean Peninsula since the late 1990s.

Holocene Dune Mobility and Forcing Mechanisms at the Northern Margin of the East Asian Monsoon

Abstract:Dune fields at the northern margin of the East Asian monsoon (EAM), are mosaics of mobile and vegetation‐stabilized aeolian dunes. These sand dunes are highly sensitive to environmental change, thus the distribution and the timing of their development may provide important clues to past environmental dynamics. Due to the strong wind erosion and dune migration, long and continuous stratigraphic records are seldom preserved. Synthesizing a large body of events, ultimately producing a relatively complete and high‐resolution record, may be a proper method to investigate the dune development history and climate change. In this study, we synthesized a large body of luminescence ages for aeolian deposits from the Mu Us, Otindag, Horqin dune fields at the northern margin of the EAM. The results show that these dune fields, as a whole experienced a most extensive mobility during the early Holocene, followed by a widespread shift toward limited mobility and soil development in the mid‐Holocene, and widespread reactivation occurred during late Holocene. The dune developments are directly linked to the effective moisture change controlled by the EAM changes, which respond to the low latitude summer insolation variation. The increased subsidence at the margin contrary to the core EAM, the delay from the feedback of the soil‐vegetation‐air coupled system, the increased evaporation due to the high temperature all play partial role in the lag of the margin EAM effective moisture change to the low latitude summer insolation. The asynchronous end of the wetter mid‐Holocene mainly responds to the southeastwardly shift of the precipitation belt, while the regional sensitivity, response speed and internal feedback also contributed. The correspondence between dune records and North Atlantic drift‐ice records of the rapid climate changes implies a close relationship between North Atlantic climate and the frequent dune activity at the northern margin of EAM.

A Holocene pollen record from the northwestern Himalayan lake Tso Moriri: Implications for palaeoclimatic and archaeological research

This paper presents a new fossil pollen record from Tso Moriri (32°54′N, 78°19′E, 4512 m a.s.l.) and seeks to reconstruct changes in mean annual precipitation (MAP) during the last 12,000 years. This high-alpine lake occupies an area of 140 km2 in a glacial-tectonic valley in the northwestern Himalaya. The region has a cold climate, with a MAP <300 mm, and open vegetation. The hydrology is controlled by the Indian Summer Monsoon (ISM), but winter westerly-associated precipitation also affects the regional water balance. Results indicate that precipitation levels varied significantly during the Holocene. After a rapid increase in MAP, a phase of maximum humidity was reached between ca. 11 and 9.6 cal ka BP, followed by a gradual decline in MAP. This trend parallels the reduction in the Northern Hemisphere summer insolation. Comparison of different palaeoclimate proxy records reveal evidence for a stronger Holocene decrease in precipitation in the northern versus the southern parts of the ISM domain. The long-term trend of ISM weakening is overlaid with several short periods of greater dryness, which are broadly synchronous with the North Atlantic cold spells, suggesting reduced amounts of westerly-associated winter precipitation. Compared to the mid and late Holocene, it appears that westerlies had a greater influence on the western parts of the ISM domain during the early Holocene. During this period, the westerly-associated summer precipitation belt was positioned at Mediterranean latitudes and amplified the ISM-derived precipitation. The Tso Moriri pollen record and moisture reconstructions also suggest that changes in climatic conditions affected the ancient Harappan Civilisation, which flourished in the greater Indus Valley from approximately 5.2 to 3 cal ka BP. The prolonged Holocene trend towards aridity, punctuated by an interval of increased dryness (between ca. 4.5 and 4.3 cal ka BP), may have pushed the Mature Harappan urban settlements (between ca. 4.5 and 3.9 cal ka BP) to develop more efficient agricultural practices to deal with the increasingly acute water shortages. The amplified aridity associated with North Atlantic cooling between ca. 4 and 3.6 and around 3.2 cal ka BP further hindered local agriculture, possibly causing the deurbanisation that occurred from ca. 3.9 cal ka BP and eventual collapse of the Harappan Civilisation between ca. 3.5 and 3 cal ka BP.

Impact of city belt in Yangtze River Delta in China on a precipitation process in summer: A case study

The Weather Research and Forecasting (WRF) model was used to investigate the influence of city belt in the Yangtze River Delta (YRD) in China on a summertime rainstorm process. The comparisons for simulations with and without the presence of the urban areas show that the increase in precipitation mainly occurs downwind of the city belt, while the increases and decreases in precipitation represent as adjacent belts in the main precipitation belt. It was found that the downstream propagation of the urban heat island (UHI) signal alters the general circulation pattern, thermal distribution and moisture transportation at local and regional scale. The variation in accumulated rainfall is in excellent correspondence with the changes in the atmospheric dynamic and thermodynamic property associated with the downstream propagation of the UHI signal, suggesting that the variations in precipitation resulting from the effect of scattered urban clusters can be strongly related to this downstream propagation of the UHI signal. The “chain flow”, generated by the combination of the sea-breeze–heat-island circulations over the coastal urban areas and the heat-island circulation over the inland urban areas, should also make a contribution.

Climatic controls on facies in Palaeogene Mediterranean subtropical carbonate platforms

Cenozoic carbonate platforms in the central Mediterranean region show distinct vertical changes in carbonate skeletal assemblages and porosity characteristics that reflect shifts in environmental conditions affecting the western Tethys. The Photozoan Association produced by carbonate ecosystems adapted to low nutrient environments and the Heterozoan Association favoured by mesotrophic conditions alternate through time over the Malta Platform and nearby carbonate platforms, although not in phase with trans-Mediterranean Oligocene carbonates. This anomaly reflects the transitional nature of Cenozoic climate as well as continental convergence of the Tethyan margins. Restricted conditions amplified the effect of nutrient flux from North African fluvial systems, which was controlled by meridional shifts in the inter-tropical convergence zone (ITCZ) precipitation belt. We model the climate–carbonate interaction by comparing the global oxygen isotope proxy to ice volume and meridional position of the ITCZ to changes in trophic level of carbonate ecosystems. The results show that the development of Palaeogene Mediterranean photozoan assemblages coincides with periods when the ITCZ had shifted away from North Africa (as is the case presently), whereas the heterozoan assemblages thrived during increased nutrient flux when the precipitation belt was located over the Sahara. The climatic controls resulted in facies characteristics that exert a fundamental influence on porosity in carbonate reservoirs.

Climatology of precipitation extremes in Estonia using the method of moving precipitation totals

A method of moving precipitation totals is described and applied for the analysis of precipitation extremes in Estonia. Numbers of extremely wet and extremely dry days and other indices of precipitation extremes were calculated using the daily precipitation data measured at 51 stations over Estonia during 1957–2009. Mean regularities of spatial and seasonal distribution were determined. Long-term changes were detected using Sen's method and Mann–Kendall test. The highest risk of heavy precipitation is in the regions of higher mean precipitation on the uplands and on the belt of higher precipitation in the western part of continental Estonia. Wet spells have their sharp maxima in July and August. The highest risk of droughts is observed in the coastal regions of West Estonia. In the coastal area, droughts appear mostly in the first half of summer, while in the eastern Estonia, they are usually observed during the second half of summer. Extreme precipitation events have become more frequent and intense. Statistically significant increasing trends were, first of all, found in the time series of winter extreme precipitation indices. In summer and autumn, trends existed in some indices, but in spring, there were no trends at all. There were no trends in time series of dryness indices in Estonia in 1957–2009.

Twenty-First-Century Multimodel Subtropical Precipitation Declines Are Mostly Midlatitude Shifts

Abstract Declines in subtropical precipitation are a robust response to modeled twenty-first-century global warming. Two suggested mechanisms are the “dry-get-drier” intensification of existing subtropical dry zones due to the thermodynamic increase in vapor transport and the poleward expansion of these same dry zones due to poleward shifts in the modeled general circulation. Here, subtropical drying in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report multimodel archive is compared to each of these two mechanisms. Each model’s particular, biased, and seasonally and zonally varying mean state is considered relative to the location of that model’s predicted changes, and these relationships are recorded in a common framework that can be compared across models. The models have a strong tendency to reduce precipitation along the subtropical flanks of their existing midlatitude cyclonic precipitation belts. This broad result agrees with the poleward expansion mechanism and with a poleward storm-track shift in particular. In contrast, the models have no clear tendency to reduce precipitation in the central nor equatorward portions of their subtropical dry zones, implying that the thermodynamic mechanism is broadly unimportant for the precipitation reductions. This is unlike the response of precipitation minus evaporation, which robustly declines in large portions of these regions, especially over the oceans. The models also tend to increase precipitation in their wet deep tropical areas, but this is not as robust as the above reduction in the subtropical midlatitudes. High-latitude precipitation increases are the most robust precipitation changes of all in this framework.

Study of the North West Cape electron belts observed by DEMETER satellite

We analyzed observation data collected by the Instrument for the Detection of Particles (IDP) on board the DEMETER satellite during a period of 17 months in 2007 and 2008. In the meantime, the VLF transmitter located at North West Cape (NWC) ground station was shut down during 7 months and working for a total of 10 months. By an (on‐off) method, our analysis for the first time revealed in detail the transient properties of the space electron precipitation belt which is induced by the man‐made VLF wave emitted from NWC. We mapped the electron flux distribution and figured out the space regions that the NWC belt covered. The NWC electron spectrograms have been investigated in a wide range of the McIlwain parameter L (1.1–3.0). Furthermore, we obtained the averaged energy spectra of the NWC electrons within the drift loss cone and compared their characteristics during daytime and nighttime. Our results confirm the previous studies of the enhancement of NWC electrons, the wisp structure, and the day/night difference of the electron flux. In addition, more detailed information is provided. We provide not only evidence of a momentary flux enhancement up to 3 orders of magnitude but also a flux reduction at higher L shells with a maximum up to 60% of the original value. For the first time, the energy spectra of NWC electrons covering the entire IDP energy band are presented for both nighttime and daytime and are quantitatively compared. At the end, our results are discussed, and their agreement with the theory of wave‐particle interactions is checked.

Oxygen ion precipitation in the Martian atmosphere and its relation with the crustal magnetic fields

Without a global intrinsic magnetic field, oxygen ions in the Martian atmospheric corona can be picked up by the solar wind directly. The majority of the pickup ions escape, while some can precipitate into the atmosphere, producing sputtering of atmospheric constituents, which may play a significant role in the loss of neutral atmosphere. With its widely distributed crustal magnetic fields, Mars is unique. While it has been shown that Mars's crustal fields can alter the global distribution of escaping ions, little is known about the influence of the crustal fields on the spatial distribution and energy deposition of precipitating pickup ions. In this paper, the global distribution and energy spectrum of the precipitating pickup oxygen ions are calculated using the test particle method in the electric and magnetic fields set up by MHD simulation. Cases of different crustal field conditions are compared to show the influence of the crustal fields on the oxygen ion precipitation. We find, using a test particle code, that the crustal fields likely change the spatial distribution of the precipitation, resulting in irregularly distributed low-energy ion precipitation parches and wide high-energy ion precipitation belts on both the dayside and nightside. The crustal fields increase O(+) ion precipitation substantially, enhancing energy deposition especially on the nightside. Our results imply that atmospheric sputtering, and accompanying neutral escape, might happen globally and may be enhanced by a factor of almost 2 with the presence of the crustal magnetic fields.

Contrasting rainfall patterns over North America during the Holocene and Last Interglacial as recorded by sediments of the northern Gulf of Mexico

The comparison of geochemical and mineralogical characteristics of terrigenous sediments deposited in the northern Gulf of Mexico (GoM) during the Holocene and Last Interglacial (LIG) is used to document the impact of slight differences in insolation and ice-sheet retreat rates on moisture transfer and precipitation patterns over central North America. The records indicate distinct sedimentological signatures over the two time periods, which likely reflect a modification of the main detrital provenance during the LIG compared to the Holocene. Here we postulate that the observed differences in the terrigenous supply during the LIG relative to the Holocene reflect a northeast migration of the main precipitation belt over the Mississippi River watershed likely in response to deglaciation of the Laurentide Ice Sheet prior to the peak in boreal summer insolation and the overall greater increase in boreal summer insolation relative to the Holocene. These combined effects allowed more northward migration of the Jet Stream, Atlantic Warm Pool and Intertropical Convergence Zone than during the Holocene, which may have also forced the Bermuda High farther to the northeast of its present position, thereby pumping more moisture from the GoM and the Caribbean region into both the Upper Mississippi River and northeast Great Lakes area. Citation: Montero-Serrano, J.-C., et al. (2011), Contrasting rainfall patterns over North America during the Holocene and Last Interglacial as recorded by sediments of the northern Gulf of Mexico

1,800 Years of abrupt climate change, severe fire, and accelerated erosion, Sierra Nevada, California, USA

This paper provides both a detailed history of environmental change in the Sierra Nevada over the past 1,800 years and evidence for climate teleconnections between the Sierra Nevada and Greenland during the late Holocene. A review of Greenland ice core data suggests that the magnitudes of abrupt changes in temperature and precipitation increased beginning c. 3,700 and 3,000 years ago, respectively. Precipitation increased abruptly 1,300 years ago. Comparing paleotemperature data from Cirque Peak, CA with paleoprecipitation data from Pyramid Lake, NV suggests that hot temperatures occurred at the beginnings of most severe droughts in the Sierra Nevada over the past 1,800 years. Severe fires and erosion also occurred at Coburn Lake, CA at the beginning of all severe droughts in the Sierra Nevada over the past 1,800 years. This suggests that abrupt climate change during the late Holocene caused vegetation and mountain slopes in some areas to be out of equilibrium with abruptly changed climates. Finally, the ending of drought conditions in Greenland coincided with the beginning of drought conditions in the Sierra Nevada over the past 1,800 years, perhaps as a result of the rapidly changed locations of the Earth’s major precipitation belts during abrupt climate change events.

An Experiment of a Statistical Downscaling Forecast Model for Summer Precipitation over China

AbstractA combination of the optimal subset regression (OSR) approach, the coupled general circulation model of the National Climate Center (NCC-CGCM) and precipitation observations from 160 stations over China is used to construct a statistical downscaling forecast model for precipitation in summer. Retroactive forecasts are performed to assess the skill of statistical downscaling during the period from 2003 to 2009. The results show a poor simulation for summer precipitation by the NCC-CGCM for China, and the average spatial anomaly correlation coefficient (ACC) is 0.01 in the forecast period. The forecast skill can be improved by OSR statistical downscaling, and the OSR forecast performs better than the NCC-CGCM in most years except 2003. The spatial ACC is more than 0.2 in the years 2008 and 2009, which proves to be relatively skillful. Moreover, the statistical downscaling forecast performs relatively well for the main rain belt of the summer precipitation in some years, including 2005, 2006, 2008, a...

Changes in precipitation regimes over North America during the Holocene as recorded by mineralogy and geochemistry of Gulf of Mexico sediments

Changes in terrigenous-transfer patterns from North America toward the Gulf of Mexico via the Mississippi River during the Holocene were investigated using mineralogical and geochemical records from the northern Gulf of Mexico (Pigmy Basin). Clay mineralogy (smectite/illite + chlorite) and geochemical signatures (K and Ti intensities) indicate fluctuations in the detrital sedimentation during the Holocene in the Pigmy Basin. They likely reflect alternations between at least two dominant terrigenous sources: the smectite-rich NW Mississippi watershed, and the illite- and chlorite-rich Great Lakes province and NE Mississippi watershed. These recurring and rapid modifications of erosional processes over this period suggest changes in the hydrological regime via rainfall patterns. Such a modification during the Holocene is likely linked with the rapid atmospheric reorganization following the final collapse of the Laurentide Ice Sheet. Indeed, mineralogical and geochemical proxies indicate east-to-west migrations of the main detrital source (from the Great Lakes and northeastern province toward the northwestern province) associated with Mississippi River megaflood episodes. These modifications of the main detrital sources likely record migrations of the precipitation belt, which are constrained by atmospheric configuration (Jet Stream, Bermuda High and Intertropical Convergence Zone position) and subtropical oceanic hydrological properties (meridional extension of the Atlantic Warm Pool). In the frame of previously published rainfall patterns over the Caribbean and North America, our results highlight some marked modifications of moisture transfer throughout the Holocene. These changes are interpreted as resulting from two atmospheric configurations that have driven alternately the precipitation distribution over North America for the last 10 ka with an apparent cyclicity of ~ 2.5 ka. The coherent common cyclicity between the Gulf of Mexico detrital parameters and Greenland atmospheric proxies over the Holocene suggests that the initial external forcing was rapidly transferred latitudinally through atmospheric processes.