scholarly journals Increasing precipitation variability on daily-to-multiyear time scales in a warmer world

2021 ◽  
Vol 7 (31) ◽  
Author(s):  
Wenxia Zhang ◽  
Kalli Furtado ◽  
Peili Wu ◽  
Tianjun Zhou ◽  
Robin Chadwick ◽  
...  
Keyword(s):  
Time Scales ◽  
Precipitation Variability ◽  
Increasing Precipitation

Divergent responses of primary production to increasing precipitation variability in global drylands

2021 ◽  
Author(s):  
Enqing Hou ◽  
Marcy E. Litvak ◽  
Jennifer A. Rudgers ◽  
Lifen Jiang ◽  
Scott L. Collins ◽  
...  
Keyword(s):  
Primary Production ◽  
Precipitation Variability ◽  
Increasing Precipitation

scholarly journals Responses of groundwater to precipitation variability and ENSO in the Vietnamese Mekong Delta

2021 ◽  
Author(s):  
Phong V. V. Le ◽  
Hai V. Pham ◽  
Luyen K. Bui ◽  
Anh N. Tran ◽  
Chien V. Pham ◽  
...  
Keyword(s):  
Water Resources ◽  
Climate Variability ◽  
Time Scales ◽  
Groundwater Level ◽  
Southern Oscillation ◽  
Mekong Delta ◽  
Precipitation Variability ◽  
Annual Precipitation ◽  
Aquifer Recharge ◽  
Deep Aquifers

Abstract Groundwater is a critical component of water resources and has become the primary water supply for agricultural and domestic uses in the Vietnamese Mekong Delta (VMD). Widespread groundwater level declines have occurred in the VMD over recent decades, reflecting that extraction rates exceed aquifer recharge in the region. However, the impacts of climate variability on groundwater system dynamics in the VMD remain poorly understood. Here, we explore recent changes in groundwater levels in shallow and deep aquifers from observed wells in the VMD and investigate their relations to the annual precipitation variability and El Niño–Southern Oscillation (ENSO). We show that groundwater level responds to changes in annual precipitation at time scales of approximately 1 year. Moreover, shallow (deep) groundwater in the VMD appears to correlate with the ENSO over intra-annual (inter-annual) time scales. Our findings reveal a critical linkage between groundwater level changes and climate variability, suggesting the need to develop an understanding of the impacts of climate variability across time scales on water resources in the VMD.

Atmospheric and Oceanic Origins of Tropical Precipitation Variability

2017 ◽  
Vol 30 (9) ◽  
pp. 3197-3217 ◽  
Author(s):  
Jie He ◽  
Clara Deser ◽  
Brian J. Soden
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Noise Spectrum ◽  
Precipitation Variability ◽  
Ocean Dynamics ◽  
Atmospheric Variability ◽  
Tropical Precipitation ◽  
Summer Hemisphere

The intrinsic atmospheric and ocean-induced tropical precipitation variability is studied using millennial control simulations with various degrees of ocean coupling. A comparison between the coupled simulation and the atmosphere-only simulation with climatological sea surface temperatures (SSTs) shows that a substantial amount of tropical precipitation variability is generated without oceanic influence. This intrinsic atmospheric variability features a red noise spectrum from daily to monthly time scales and a white noise spectrum beyond the monthly time scale. The oceanic impact is inappreciable for submonthly time scales but important at interannual and longer time scales. For time scales longer than a year, it enhances precipitation variability throughout much of the tropical oceans and suppresses it in some subtropical areas, preferentially in the summer hemisphere. The sign of the ocean-induced precipitation variability can be inferred from the local precipitation–SST relationship, which largely reflects the local feedbacks between the two, although nonlocal forcing associated with El Niño–Southern Oscillation also plays a role. The thermodynamic and dynamic nature of the ocean-induced precipitation variability is studied by comparing the fully coupled and slab ocean simulations. For time scales longer than a year, equatorial precipitation variability is almost entirely driven by ocean circulation, except in the Atlantic Ocean. In the rest of the tropics, ocean-induced precipitation variability is dominated by mixed layer thermodynamics. Additional analyses indicate that both dynamic and thermodynamic oceanic processes are important for establishing the leading modes of large-scale tropical precipitation variability. On the other hand, ocean dynamics likely dampens tropical Pacific variability at multidecadal time scales and beyond.

scholarly journals A Hybrid Precipitation Index Inspired by the SPI, PDSI, and MCDI. Part II: Application to Investigate Precipitation Variability along the West Coast of North America

2020 ◽  
Vol 21 (9) ◽  
pp. 1977-2002 ◽  
Author(s):  
Dudley B. Chelton ◽  
Craig M. Risien
Keyword(s):  
British Columbia ◽  
North America ◽  
Time Scales ◽  
West Coast ◽  
Time Scale ◽  
Opposite Sign ◽  
Precipitation Variability ◽  
The West ◽  
Southeast Alaska ◽  
Precipitation Anomalies

AbstractThe hybrid precipitation index developed in Part I of this study is applied to investigate precipitation variability along the west coast of North America during the wet season November–March on monthly-to-interannual time scales. The variability in each of six regions considered in this study is negatively correlated with nearby 500-hPa geopotential height anomalies. Except in Southeast Alaska, these correlation patterns indicate that precipitation variability in each region is predominantly influenced by local atmospheric forcing analogous to the ridging of the westerly flow that has been studied extensively with regard to California drought variability. The first empirical orthogonal function (EOF) accounts for nearly all of the Southeast Alaska precipitation variability, which is controlled by the strength of the onshore flow rather than ridging. In association with this mode of variability, precipitation anomalies of opposite sign account for about 40% of the precipitation variance in Northern California and Oregon on all time scales. On short time scales, the second and third EOFs account primarily for precipitation variability in British Columbia/Washington and California, respectively. With increasing time scale, the third EOF diminishes in importance and the second EOF evolves into a pattern of synchronous precipitation anomalies of the same sign from British Columbia to Northern California. Precipitation variability in Southern California is only modestly related to precipitation elsewhere. With increasing time scale, Southern California precipitation variability becomes increasingly related to precipitation anomalies of opposite sign in Washington.

scholarly journals Mechanisms for Precipitation Variability of the Eastern Brazil/SACZ Convective Margin

2011 ◽  
Vol 24 (13) ◽  
pp. 3445-3456 ◽  
Author(s):  
H.-Y. Ma ◽  
X. Ji ◽  
J. D. Neelin ◽  
C. R. Mechoso
Keyword(s):  
Los Angeles ◽  
Atlantic Ocean ◽  
Time Scales ◽  
General Circulation ◽  
Austral Summer ◽  
Circulation Model ◽  
Precipitation Variability ◽  
Western Atlantic ◽  
Low Level ◽  
Eastern Brazil

Abstract The present study examines the mechanisms for the connection between the precipitation variability in eastern Brazil and the South Atlantic convergence zone (SACZ) convective margin (eastern Brazil/SACZ convective margin) and the variability of low-level inflow on interannual time scales during austral summer. The authors' methodology is based on the analysis of observational datasets and simulations by the University of California, Los Angeles (UCLA) atmospheric general circulation model (AGCM) coupled to the Simplified Simple Biosphere Model. It is demonstrated that the inflow variability is associated with the leading mode of wind variability over subtropical South America, and the connection is established through the mechanism of an analytic prototype for convective margin shifts proposed in previous studies. Over the eastern Brazil/SACZ convective margin, the weaker (stronger) convection tends to occur together with stronger (weaker) low-level inflows in reference to the mean easterly trades. By changing the “ventilation” effect, stronger (weaker) inflows with low moist static energy from the Atlantic Ocean suppress (promote) convection. The causal relationship is verified by AGCM mechanism-testing experiments performed in perpetual-February mode, in which low-level, nondivergent wind perturbations are imposed in a region overlapping eastern Brazil and the western Atlantic Ocean. With solely the imposed-wind perturbations acting on the moisture advection in the model equation, the AGCM can reproduce the precipitation variability in the eastern Brazil/SACZ convective margin. The capability of the AGCM in capturing such precipitation sensitivity to the low-level inflow variability also suggests that the mechanism can be applied to other regions of convective margins or to other time scales.

Feedbacks of Vegetation on Summertime Climate Variability over the North American Grasslands. Part II: A Coupled Stochastic Model

2006 ◽  
Vol 10 (16) ◽  
pp. 1-30 ◽  
Author(s):  
Weile Wang ◽  
Bruce T. Anderson ◽  
Dara Entekhabi ◽  
Dong Huang ◽  
Robert K. Kaufmann ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Time Scales ◽  
North American ◽  
Power Spectra ◽  
Region Of Interest ◽  
Precipitation Variability ◽  
The North ◽  
Monte Carlo Experiments ◽  
Local Soil

Abstract A coupled linear model is derived to describe interactions between anomalous precipitation and vegetation over the North American Grasslands. The model is based on biohydrological characteristics in the semiarid environment and has components to describe the water-related vegetation variability, the long-term balance of soil moisture, and the local soil–moisture–precipitation feedbacks. Analyses show that the model captures the observed vegetation dynamics and characteristics of precipitation variability during summer over the region of interest. It demonstrates that vegetation has a preferred frequency response to precipitation forcing and has intrinsic oscillatory variability at time scales of about 8 months. When coupled to the atmospheric fields, such vegetation signals tend to enhance the magnitudes of precipitation variability at interannual or longer time scales but damp them at time scales shorter than 4 months; the oscillatory variability of precipitation at the growing season time scale (i.e., the 8-month period) is also enhanced. Similar resonance and oscillation characteristics are identified in the power spectra of observed precipitation datasets. The model results are also verified using Monte Carlo experiments.

Intraseasonal Variability of the West African Monsoon and Atlantic ITCZ

2008 ◽  
Vol 21 (12) ◽  
pp. 2898-2918 ◽  
Author(s):  
Eric D. Maloney ◽  
Jeffrey Shaman
Keyword(s):  
Time Series ◽  
Tropical Cyclone ◽  
Time Scales ◽  
West African Monsoon ◽  
Precipitation Variability ◽  
Tropical Cyclone Activity ◽  
Cyclone Activity ◽  
East Atlantic ◽  
Atlantic Itcz ◽  
Precipitation Events

Abstract Intraseasonal variability of boreal summer rainfall and winds in tropical West Africa and the east Atlantic is examined using daily Tropical Rainfall Measuring Mission (TRMM) precipitation and the NCEP–NCAR reanalysis during 1998–2006. Intraseasonal precipitation variability is dominated by two significant spectral peaks at time scales near 15 and 50 days, accompanied by corresponding peaks in eddy kinetic energy (EKE) and eddy enstrophy. Regional precipitation variability on 30–90-day time scales is significantly correlated (+0.6) with a global Madden–Julian oscillation time series based on equatorial zonal winds, supporting the results of A. J. Matthews. The overall amplitude of the 30–90-day West African monsoon precipitation variability during a given summer, however, does not appear to be strongly regulated by interannual variability in MJO amplitude. Composite analysis and complex empirical orthogonal function analysis shows that 30–90-day precipitation anomalies are generally zonally elongated, grow and decay in place, and have maximum amplitude near the Gulf of Guinea and in the Atlantic ITCZ. Composite 30–90-day enhanced precipitation events are accompanied by a significant suppression of eastern North Atlantic trade winds. Suppressed 30–90-day precipitation events are associated with an enhancement of the Atlantic trade winds. Enhanced (suppressed) EKE occurs just to the north of the east Atlantic ITCZ during positive (negative) 30–90-day precipitation events, with the maximum EKE magnitude lagging precipitation events by about 5 days. East Atlantic tropical cyclone activity is significantly modulated on intraseasonal time scales. The number of tropical cyclones that occur in the Atlantic’s main development region to the east of 60°W is suppressed about 5–10 days before maxima in a regional intraseasonal precipitation time series, and enhanced about 5–10 days after time series maxima. An analysis of east Atlantic tropical cyclone activity based on an equatorial MJO index produces similar results. Consistent with the results of K. C. Mo, variations in vertical shear may help explain this modulation of tropical cyclone activity.

LVSEM: Past Present and Future

1990 ◽  
Vol 48 (1) ◽  
pp. 364-365
Author(s):  
James B. Pawley
Keyword(s):  
Field Emission ◽  
Line Width ◽  
Time Scales ◽  
Silicon Oxide ◽  
Beam Current ◽  
High Brightness ◽  
High Beam ◽  
Fixed Charges ◽  
Beam Voltage ◽  
Deposited Metal

Past: In 1960 Thornley published the first description of SEM studies carried out at low beam voltage (LVSEM, 1-5 kV). The aim was to reduce charging on insulators but increased contrast and difficulties with low beam current and frozen biological specimens were also noted. These disadvantages prevented widespread use of LVSEM except by a few enthusiasts such as Boyde. An exception was its use in connection with studies in which biological specimens were dissected in the SEM as this process destroyed the conducting films and produced charging unless LVSEM was used.In the 1980’s field emission (FE) SEM’s came into more common use. The high brightness and smaller energy spread characteristic of the FE-SEM’s greatly reduced the practical resolution penalty associated with LVSEM and the number of investigators taking advantage of the technique rapidly expanded; led by those studying semiconductors. In semiconductor research, the SEM is used to measure the line-width of the deposited metal conductors and of the features of the photo-resist used to form them. In addition, the SEM is used to measure the surface potentials of operating circuits with sub-micrometer resolution and on pico-second time scales. Because high beam voltages destroy semiconductors by injecting fixed charges into silicon oxide insulators, these studies must be performed using LVSEM where the beam does not penetrate so far.

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