Climate Dynamics Research Papers - Academia.edu (original) (raw)

Land surface and atmosphere are interlocked by the hydrological and energy cycles and the effects of soil water-air coupling can modulate near-surface temperatures. In this work, three paired experiments were designed to evaluate impacts... more

Land surface and atmosphere are interlocked by the hydrological and energy cycles and the effects of soil water-air coupling can modulate near-surface temperatures. In this work, three paired experiments were designed to evaluate impacts of different soil moisture initial and boundary conditions on summer temperatures in the Mediterranean transitional climate regime region. In this area, evapotranspiration is not limited by solar radiation, rather by soil moisture, which therefore controls the boundary layer variability. Extremely dry, extremely wet and averagely humid ground conditions are imposed to two global climate models at the beginning of the warm and dry season. Then, sensitivity experiments, where atmosphere is alternatively interactive with and forced by land surface, are launched. The initial soil state largely affects summer near-surface temperatures: dry soils contribute to warm the lower atmosphere and exacerbate heat extremes, while wet terrains suppress thermal peak...

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere... more

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper troposphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feed-backs in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Niño versus La Nina events but whether climate change associated with “global warming” is a factor is an open question.

The link between the Pacific/North American pattern (PNA) and the North Atlantic Oscillation (NAO) is investigated in reanalysis data (NCEP, ERA40) and multi-century CGCM runs for present day climate using three versions of the ECHAM... more

The link between the Pacific/North American pattern (PNA) and the North Atlantic Oscillation (NAO) is investigated in reanalysis data (NCEP, ERA40) and multi-century CGCM runs for present day climate using three versions of the ECHAM model. PNA and NAO patterns and indices are determined via rotated principal component analysis on monthly mean 500 hPa geopotential height fields using the varimax criteria.

We describe an improved tree-ring reconstruction of mean warm-season (November-April) temperatures for Tasmania from Huon pine. This record extends back to 1600 BC and is based on a tree-ring chronology that was processed to retain as... more

We describe an improved tree-ring reconstruction of mean warm-season (November-April) temperatures for Tasmania from Huon pine. This record extends back to 1600 BC and is based on a tree-ring chronology that was processed to retain as much low-frequency variance as possible. The resulting reconstruction explains 46.6% of the variance and verifies significantly when compared to withheld instrumental data. Cross-spectral analysis of actual and estimated temperatures over the 1886-1991 common period indicates that most of the unexplained variance is at periods < 12 years in length. At periods > 12 years, the squared coherency ranges between 0.6-0.8, and the cross-spectral gain indicates that the amplitude of the reconstruction is a nearly unbiased estimate of the true temperature amplitude. Therefore, this reconstruction should be especially useful for studying multi-decadal temperature variability in the Tasmanian sector of the Southern Hemisphere over the past 3592 years. To this end, we examined the time evolution of low-frequency temperature amplitude fluctuations and found evidence for a 35% amplitude reduction after AD 100 that persisted until about AD 1900. Since that time, the low-frequency temperature amplitude has systematically increased. We also show how this reconstruction is related to large-scale sea surface temperatures (SST) in the Indian Ocean and eastward to the dateline. Pointwise correlations between the Tasmanian record and SSTs reveal a relationship that extends across the southern Indian Ocean and towards the Arabian Sea. This pattern is largely determined by inter-decadal temperature variability, with correlations in this > 10-year bandwidth commonly exceeding 0.6 over most of the southern Indian and southwestern Pacific sectors. A rotated empirical orthogonal function analysis reveals that the pattern of pointwise correlations found between the temperature reconstruction and SSTs is largely explained by the linear combination of three orthogonal modes of SST variability.

The prediction of Indian summer monsoon rainfall (ISMR) on a seasonal time scales has been attempted by various research groups using different techniques including artificial neural networks. The prediction of ISMR on monthly and... more

The prediction of Indian summer monsoon rainfall (ISMR) on a seasonal time scales has been attempted by various research groups using different techniques including artificial neural networks. The prediction of ISMR on monthly and seasonal time scales is not only scientifically challenging but is also important for planning and devising agricultural strategies. This article describes the artificial neural network (ANN) technique with error- back-propagation algorithm to provide prediction (hindcast) of ISMR on monthly and seasonal time scales. The ANN technique is applied to the five time series of June, July, August, September monthly means and seasonal mean (June +July+ August+September) rainfall from 1871 to 1994 based on Parthasarathy data set. The previous five years values from all the five time-series were used to train the ANN to predict for the next year. The details of the models used are discussed. Various statistics are calculated to examine the performance of the models and it is found that the models could be used as a forecasting tool on seasonal and monthly time scales. It is observed by various researchers that with the passage of time the relationships between various predictors and Indian monsoon are changing, leading to changes in monsoon predictability. This issue is discussed and it is found that the monsoon system inherently has a decadal scale variation in predictability.

The multivariate adaptive regression splines (MARS) model was used to capture the observed relationships between sea level pressure (SLP) anomalies over the Euro-Atlantic sector and the winter time (December–February) monthly rainfall at... more

The multivariate adaptive regression splines (MARS) model was used to capture the observed relationships between sea level pressure (SLP) anomalies over the Euro-Atlantic sector and the winter time (December–February) monthly rainfall at eight sites in Portugal; possible anthropogenic changes of the rainfall in a perturbed future climate were then estimated by using both the observed SLP-rainfall relationships, described by MARS models, and the GCM simulated SLP, taken from the output of the Hadley Centre Transient Climate Change Experiment (UKTR). Also, principal component analysis was carried out to reduce the dimensionality of the SLP data, and to assess the ability of the GCM in simulating the large-scale circulation; the first six principal components were retained as predictors in the MARS model. The MARS model were built up by using the data for 1946–1991 as the training set and that for 1901–1943 as the testing set, showing satisfactory prediction skills. It is concluded that the UKTR control simulation successfully reproduced main features of the large-scale circulation, but the observed relationship between SLP and the regional rainfall was not well preserved. With respect to the 54-year experiment of perturbed run, the MARS estimation of rainfall and the relevant direct GCM rainfall output possess similar multi-annual variations; however, there are substantial differences regarding details; the change in the area mean of winter time mean monthly rainfall in Portugal estimated by MARS (indirect GCM output) is about −12.7 mm per 54-year, and the relevant direct GCM output is −16.9 mm/54-year. This reduction tendency is consistent with previously reported findings respecting rainfall in the Iberian Peninsula, which were based on the MPI (Max-Planck Institute for Meteorology) transient simulations.

• Deterministic TSI periods • TSI variability control by large planets • Next Dalton TSI minimum a b s t r a c t Total solar irradiance (TSI) is the primary quantity of energy that is provided to the Earth. The properties of the TSI... more

• Deterministic TSI periods • TSI variability control by large planets • Next Dalton TSI minimum a b s t r a c t Total solar irradiance (TSI) is the primary quantity of energy that is provided to the Earth. The properties of the TSI variability are critical for understanding the cause of the irradiation variability and its expected influence on climate variations. A deterministic property of TSI variability can provide information about future irradiation variability and expected long-term climate variation, whereas a non-deterministic variability can only explain the past. This study of solar variability is based on an analysis of two TSI data series, one since 1700 A.D. and one since 10 0 0 A.D.; a sunspot data series since 1610 A.D.; and a solar orbit data series from 10 0 0 A.D. The study is based on a wavelet spectrum analysis. First, the TSI data series are transformed into a wavelet spectrum. Then, the wavelet spectrum is transformed into an autocorrelation spectrum to identify stationary , subharmonic and coincidence periods in the TSI variability. The results indicate that the TSI and sunspot data series have periodic cycles that are correlated with the oscillations of the solar position relative to the barycenter of the solar system, which is controlled by gravity force variations from the large planets Jupiter, Saturn, Uranus and Neptune. A possible explanation for solar activity variations is forced oscillations between the large planets and the solar dynamo. We find that a stationary component of the solar variability is controlled by the 12-year Jupiter period and the 84-year Uranus period with subharmonics. For TSI and sunspot variations, we find stationary periods related to the 84-year Uranus period. Deterministic models based on the stationary periods confirm the results through a close relation to known long solar minima since 10 0 0 A.D. and suggest a modern maximum period from 1940 to 2015. The model computes a new Dalton-type sunspot minimum from approximately 2025 to 2050 and a new Dalton-type period TSI minimum from approximately 2040 to 2065.

The Eastern Mediterranean is one of the most prominent hot spots of climate change in the world and extreme climatic phenomena in this region such as drought or extreme rainfall events are expected to become more frequent and intense. In... more

The Eastern Mediterranean is one of the most prominent hot spots of climate change in the world and extreme climatic phenomena in this region such as drought or extreme rainfall events are expected to become more frequent and intense. In this study climate extreme indices recommended by the joint World Meteorological Organization Expert Team on Climate Change Detection and Indices are calculated for daily precipitation data in 70 weather stations during 1961-2012. Observed trends and changes in daily precipitation extremes over the EM basin were analysed using the RClimDex package, which was developed by the Climate Research Branch of the Meteorological Service of Canada. Extreme and heavy precipitation events showed globally a statistically significant decrease in the Eastern Mediterranean and, in the southern parts, a significant decrease in total precipitation. The overall analysis of extreme precipitation indices reveals that decreasing trends are generally more frequent than increasing trends. We found statistically significant decreasing trends (reaching 74% of stations for extremely wet days) and increasing trends (reaching 36% of stations for number of very heavy precipitation days). Finally, most of the extreme precipitation indices have a statistically significant positive correlation with annual precipitation, particularly the number of heavy and very heavy precipitation days.

The climate of Labrador is uniquely influenced by Labrador Sea atmosphere-ocean dynamics and related sea surface temperature, sea ice and atmospheric fluctuations in the northwest Atlantic. Here we describe composite ring width and... more

The climate of Labrador is uniquely influenced by Labrador Sea atmosphere-ocean dynamics and related sea surface temperature, sea ice and atmospheric fluctuations in the northwest Atlantic. Here we describe composite ring width and maximum latewood density white spruce records averaged over five (four for density) treeline sites in northern Labrador, spanning the past four centuries. These records correlate significantly with surface air and sea surface temperature records for the northwest Atlantic as well as with the North Atlantic Oscillation (NAO). Temperatures over Labrador appear to have been influenced by climate processes operating on interannual to multidecadal time scales over the length of the tree-ring record. The ring width composite reveals a significant (>99% level) mode of variation centered at around 40-60 years which appears to be robust over the full length of record and may correspond to multidecadal modes identified in model and instrumental studies of North Atlantic climate. The density composite indicates significant peaks at about 21-24, 9 and 2-3 years, which generally correspond to spectral modes identified for the NAO. This density series also shows a significant (>99% level) mode of variation at 3.6 years, which is statistically coherent with the winter (DJF) Southern Oscillation Index. This mode decreases in amplitude in the 1800s period of the Little Ice Age, one of the lowest growth periods in the Labrador tree-ring series as well as other northern temperature proxies. This period was also a time of diminished solar activity and several major volcanic events, including the eruption of Tambora in 1815. The ensuing summer of 1816 was the coldest over the past four centuries as inferred from the Labrador density composite. Hardships suffered by Labrador Inuit resulting from the extreme cold period of 1816-17 are mentioned in Moravian mission records. Archaeological and ethnohistorical data also document shifts in the subsistence practices and settlement patterns of Labrador Inuit throughout the 1800s. Many of the cultural changes have been attributed to the effects of European settlement of the region, but may also be a response to the severe climatic conditions during this time.

FAMOUS is an unfluxadjusted coupled atmosphere-ocean general circulation model (AOGCM) based on the Met Office Hadley Centre AOGCM HadCM3. Its parametrisations of physical and dynamical processes are almost identical to those of HadCM3,... more

FAMOUS is an unfluxadjusted coupled atmosphere-ocean general circulation model (AOGCM) based on the Met Office Hadley Centre AOGCM HadCM3. Its parametrisations of physical and dynamical processes are almost identical to those of HadCM3, but by virtue of reduced horizontal and vertical resolution and increased timestep it runs about ten times faster. The speed of FAMOUS means that parameter sensitivities can be investigated more thoroughly than in slower higher-resolution models, with the result that it can be tuned closer to its target climatology. We demonstrate a simple method for systematic tuning of parameters, resulting in a configuration of FAMOUS whose climatology is significantly more realistic than would be expected for a model of its resolution and speed. FAMOUS has been tuned to reproduce the behaviour of HadCM3 as nearly as possible, in order that experiments with each model are of maximum relevance to the physical interpretation of the other. Analysis of the control climate and climate change simulation of FAMOUS show that it possesses sufficient skill for its intended purposes in Earth system science as a tool for long-timescale integrations and for large ensembles of integrations, when HadCM3 cannot be afforded. Thus, it can help to bridge the gap between models of intermediate complexity and the higher-resolution AOGCMs used for policy-relevant climate prediction.