scholarly journals Modelling Hydrometeorological Extremes Associated to the Moisture Transport Driven by the Great Plains Low-Level Jet

2021 ◽  
Author(s):  
Luis Gimeno-Sotelo ◽  
Patricia de Zea Bermudez ◽  
Iago Algarra ◽  
Luis Gimeno
Keyword(s):  
Great Plains ◽  
North Atlantic ◽  
Source Region ◽  
Lower Troposphere ◽  
Dynamical Instability ◽  
Low Level ◽  
Extremal Dependence ◽  
The North ◽  
Low Level Jet ◽  
The North Atlantic

Abstract The Great Plains Low-Level Jet system consists of very strong winds in the lower troposphere that transport a huge amount of moisture from the Gulf of Mexico to the American Great Plains. This paper aims to study the extremes of the Transported Moisture (TM) from the GPLLJ source region to the jet domain; and, for low and high TM, to analyze the extremal dependence between the upper tail of the precipitation in the GPLLJ sink region and the lower tail of the tropospheric stability in that region (omega). The declustered extremes of TM were analyzed using Peaks Over Threshold (POT). A non-stationary Exponential model was fitted to the cluster maxima. Estimated return levels show that the extremes of TM are expected to decrease in the future. This is meteorologically congruent with the known displacement of the western edge of the North Atlantic Subtropical High, which controls atmospheric circulation in the North Atlantic, and to a higher scale with the change of phase from negative to positive of the Atlantic Multidecadal Oscillation. Bilogistic and Logistic models were fitted to the extremes of (-omega, precipitation) for low and high TM, respectively. The extremal dependence between "-omega" and precipitation proves to be stronger in the case of high TM. This confirms that dynamical instability represented by “-omega” is the most important parameter for achieving high values of precipitation once there is a mechanism that allows the continuous supply of large amounts of moisture, such as the derived from a low-level jet system.

scholarly journals WRF Forecasts of Great Plains Nocturnal Low-Level Jet-Driven MCSs. Part II: Differences between Strongly and Weakly Forced Low-Level Jet Environments

2016 ◽  
Vol 31 (5) ◽  
pp. 1491-1510 ◽  
Author(s):  
Brian J. Squitieri ◽  
William A. Gallus
Keyword(s):  
Great Plains ◽  
Convective Available Potential Energy ◽  
Initiation Time ◽  
Mixing Ratio ◽  
Atmospheric Water ◽  
Low Level ◽  
The North ◽  
Low Level Jet ◽  
Convective Inhibition ◽  
Water Vapor Mixing Ratio

Abstract The classic Great Plains southerly low-level jet (LLJ) is a primary factor in sustaining nocturnal convection. This study compares convection-allowing WRF forecasts of LLJ events associated with MCSs in strongly and weakly forced synoptic environments. The depth of the LLJs and magnitude, altitude, and times of the LLJ peak wind were evaluated in observations and WRF forecasts for 31 cases as well as for case subsets of strongly and weakly forced synoptic regimes. LLJs in strongly forced regimes were stronger, deeper, and peaked at higher altitudes and at earlier times compared to weakly forced cases. Mean error MCS-centered composites of WRF forecasts versus RUC analyses were derived at MCS initiation time for the LLJ atmospheric water vapor mixing ratio, LLJ total wind magnitude, convergence, most unstable convective available potential energy (MUCAPE), and most unstable convective inhibition (MUCIN). In most configurations, simulated MCSs in strongly and weakly forced regimes initiated to the north and east of observations, generally in a region where LLJ moisture, MUCAPE, and MUCIN fields were forecast well, with larger errors outside this region. However, WSM6 simulations for strongly forced cases showed a southward displacement in MCS initiation, where a combination of ambient environmental factors and microphysics impacts may simultaneously play a role in the location of forecast MCS initiation. Strongly forced observed and simulated MCSs initiated west of the LLJ axis and moved eastward into the LLJ, while observed and simulated MCSs in weakly forced environments traversed the termini of the LLJ. A northward bias existed for simulated MCS initiation and LLJ termini for weakly forced regimes.

Natural Versus Anthropogenic Factors Affecting Low-Level Cloud Albedo over the North Atlantic

Science ◽  
1992 ◽  
Vol 256 (5061) ◽  
pp. 1311-1313 ◽  
Author(s):  
P. G. Falkowski ◽  
Y. Kim ◽  
Z. Kolber ◽  
C. Wilson ◽  
C. Wirick ◽  
...  
Keyword(s):  
North Atlantic ◽  
Anthropogenic Factors ◽  
Factors Affecting ◽  
Low Level ◽  
Cloud Albedo ◽  
The North ◽  
The North Atlantic

Recurrent Supersynoptic Evolution of the Great Plains Low-Level Jet

2011 ◽  
Vol 24 (2) ◽  
pp. 575-582 ◽  
Author(s):  
Scott J. Weaver ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Analysis Strategy ◽  
Precipitation Anomalies ◽  
North American Regional Reanalysis ◽  
Low Level Jet ◽  
Regional Reanalysis

Abstract The evolution of supersynoptic (i.e., pentad) Great Plains low-level jet (GPLLJ) variability, its precipitation impacts, and large-scale circulation context are analyzed in the North American Regional Reanalysis (NARR)—a high-resolution precipitation-assimilating dataset—and the NCEP–NCAR reanalysis. The analysis strategy leans on the extended EOF technique, which targets both spatial and temporal recurrence of a variability episode. Pentad GPLLJ variability structures are found to be spatially similar to those in the monthly analysis. The temporal evolution of the supersynoptic GPLLJ-induced precipitation anomalies reveal interesting lead and lag relationships highlighted by GPLLJ variability-leading precipitation anomalies. Interestingly, similar temporal phasing of the GPLLJ and precipitation anomalies were operative during the 1993 (1988) floods (drought) over the Great Plains, indicating the importance of these submonthly GPLLJ variability modes in the instigation of extreme hydroclimatic episodes. The northward-shifted (dry) GPLLJ variability mode is linked to large-scale circulation variations emanating from remote regions that are modified by interaction with the Rocky Mountains, suggesting that the supersynoptic GPLLJ fluctuations may have their origin in orographic modulation of baroclinic development.

scholarly journals Influence of the North Atlantic SST Variability on the Atmospheric Circulation during the Twentieth Century

2015 ◽  
Vol 28 (4) ◽  
pp. 1396-1416 ◽  
Author(s):  
Guillaume Gastineau ◽  
Claude Frankignoul
Keyword(s):  
Twentieth Century ◽  
North Atlantic ◽  
Lower Troposphere ◽  
Atlantic Multidecadal Oscillation ◽  
Early Winter ◽  
Tropical Forcing ◽  
The North ◽  
Sst Variability ◽  
Sst Anomaly ◽  
The North Atlantic

Abstract The ocean–atmosphere coupling in the North Atlantic is investigated during the twentieth century using maximum covariance analysis of sea surface temperature (SST) and 500-hPa geopotential height analyses and performing regressions on dynamical diagnostics such as Eady growth rate, wave activity flux, and velocity potential. The North Atlantic Oscillation (NAO) generates the so-called SST anomaly tripole. A rather similar SST anomaly tripole, with the subpolar anomaly displaced to the east and a more contracted subtropical anomaly, which is referred to as the North Atlantic horseshoe pattern, in turn influences the atmosphere. In the fall and early winter, the response is NAO like and primarily results from subpolar forcing centered over the Labrador Sea and off Newfoundland. In summer, the largest atmospheric response to SST resembles the east Atlantic pattern and results from a combination of subpolar and tropical forcing. To emphasize the interannual to multidecadal variability, the same analysis is repeated after low-pass filtering. The SST influence is dominated by the Atlantic multidecadal oscillation (AMO), which also has a horseshoe shape, but with larger amplitude in the subpolar basin. A warm AMO phase leads to an atmospheric warming limited to the lower troposphere in summer, while it leads to a negative phase of the NAO in winter. The winter influence of the AMO is suggested to be primarily forced by the Atlantic SSTs in the northern subtropics. Such influence of the AMO is found in winter instead of early winter because the winter SST anomalies have a larger persistence, presumably because of SST reemergence.

Summer Rainfall Seesaw between Hetao and the Middle and Lower Reaches of the Yangtze River and Its Relationship with the North Atlantic Oscillation

2017 ◽  
Vol 30 (17) ◽  
pp. 6629-6643 ◽  
Author(s):  
Dachao Jin ◽  
Zhaoyong Guan
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Yangtze River ◽  
Lower Troposphere ◽  
Summer Rainfall ◽  
Northern China ◽  
Upper Troposphere ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Using the NCEP–NCAR reanalysis and other observational datasets, the authors have investigated the relationship of summer rainfall variations between the Hetao region of northern China and the middle and lower reaches of Yangtze River (MLRYR). The results have demonstrated that rainfall in Hetao varies out of phase with that in MLRYR on the interannual time scales. This phenomenon is referred to as the Hetao–Yangtze rainfall seesaw (HYRS). An HYRS index is defined to reveal both spatial and temporal features of HYRS. It is found that the North Atlantic Oscillation (NAO) affects the HYRS. In years when the NAO is in its positive phase, anomalous divergences in the lower troposphere and anomalous convergences in the upper troposphere are observed in regions of the Mediterranean and eastern Europe. The anomalous convergences in the upper troposphere occur as the positive Rossby wave source excites a circumglobal teleconnection (CGT) in the midlatitudes, exhibiting the eastward propagation of Rossby wave energy along the Asian jet. Meanwhile, the Eurasian–Pacific (EUP) teleconnection also affects the HYRS. Influenced mainly by the CGT pattern, the circulations over Hetao and MLRYR are consequently perturbed. The atmosphere over Hetao converges anomalously in the lower troposphere and diverges anomalously in the upper troposphere, facilitating more than normal rainfall there. At the same time, the atmosphere over MLRYR diverges anomalously in the lower troposphere and converges anomalously in the upper troposphere, resulting in more than normal summer rainfall in MLRYR. In this way, the north–south rainfall seesaw is formed. This NAO-induced rainfall seesaw is potentially useful for summer rainfall predictions in both MLRYR and the Hetao region of northern China.

scholarly journals Improvement in the decadal prediction skill of the northern hemisphere extra-tropical winter circulation through increased model resolution

2019 ◽  
Author(s):  
Mareike Schuster ◽  
Jens Grieger ◽  
Andy Richling ◽  
Thomas Schartner ◽  
Sebastian Illing ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Climate Models ◽  
Source Region ◽  
Prediction Skill ◽  
Decadal Prediction ◽  
North Atlantic Current ◽  
The North ◽  
The North Atlantic ◽  
Socio Economic Impact

Abstract. In this study the latest version of the MiKlip decadal hindcast system is analyzed and the effect of different horizontal and vertical resolutions on the prediction skill of the northern hemisphere extra-tropical atmospheric circulation is assessed. Four metrics – the stormtrack, blocking frequencies, cyclone frequencies and windstorm frequencies – are analyzed with respect to the anomaly correlation of their winter averages. The model bias and hindcast skill are evaluated in both, a lower resolution version (LR, atm: T63L47, ocean: 1.5° L40) and a higher resolution version (HR, atm: T127L95, ocean: 0.4° L40) of the MPI-ESM system, for the lead years 2–5 using initializations between 1978 and 2012. While the LR version shows common shortcomings of lower resolution climate models, e.g. a too zonal stormtrack and a negative bias of blocking frequencies over the eastern North Atlantic and Europe, the HR version works against these biases. As a result, a functional chain of significantly improved decadal prediction skill between all four metrics is found with the increase of the spatial resolution. While the stormtrack, is significantly improved primarily over the main source region of synoptic activity – the North Atlantic Current, the other extra-tropical measures experience a significant improvement downstream thereof. Thus, the skill of the cyclone frequencies is significantly improved over the central North Atlantic and Northern Europe, the skill of the blocking frequencies is significantly improved over the Mediterranean, Scandinavia and Eastern Europe and the skill of the windstorms is significantly improved over Newfoundland and Central Europe. Not only is the skill improved with the increase in resolution, but the HR system itself exhibits significant skill over large areas of the North Atlantic and European sector for all four circulation metrics. These results are particularly promising regarding the high socio-economic impact of European winter windstorms and blocking situations.

The Extreme Drought Event during Winter–Spring of 2011 in East China: Combined Influences of Teleconnection in Midhigh Latitudes and Thermal Forcing in Maritime Continent Region

2013 ◽  
Vol 26 (20) ◽  
pp. 8210-8222 ◽  
Author(s):  
Dachao Jin ◽  
Zhaoyong Guan ◽  
Weiya Tang
Keyword(s):  
North Atlantic ◽  
Yangtze River ◽  
Lower Troposphere ◽  
The Philippines ◽  
Drought Event ◽  
The Yangtze River ◽  
Maritime Continent ◽  
Thermal Forcing ◽  
The North ◽  
The North Atlantic

Abstract The middle and lower reaches of the Yangtze River (MLRYR) in China experienced an extremely severe and persistent drought event from January to May of 2011. Using both the observational data and NCEP–NCAR reanalysis, features of the drought event and the related circulation anomalies were investigated. It is found that the precipitation during the investigated period of 2011 was deficient mostly along the Yangtze River. The water vapor diverged from MLRYR southward into the Bay of Bengal, South China Sea, and the Philippines. There were two factors facilitating the drought event. One was the quasi-stationary Rossby wave–related teleconnection, which propagated eastward at midhigh latitudes from the North Atlantic to East Asia, reinforcing the Siberian high and the East Asian trough, henceforth resulting in the divergence anomalies in MLRYR in the lower troposphere. This quasi-stationary wave train, though originating from the North Atlantic region, was not essentially related to the North Atlantic Oscillation. Another factor for the drought event was the persistent anomalous thermal forcing over the Maritime Continent, which induced the anomalous divergence in the upper troposphere in this region, building up an anomalous Hadley circulation with its ascent branch over the Maritime Continent and descent branch over MLRYR. This thermal forcing was possibly, but not necessarily, related to the La Niña event. The persistence of the drought event over MLRYR was due to the maintenance of the quasi-stationary waves at midhigh latitudes and the persistent anomalous thermal forcing in the Maritime Continent.

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