scholarly journals Wintertime Nonbrightband Rain in California and Oregon during CALJET and PACJET: Geographic, Interannual, and Synoptic Variability

2005 ◽  
Vol 133 (5) ◽  
pp. 1199-1223 ◽  
Author(s):  
Paul J. Neiman ◽  
Gary A. Wick ◽  
F. Martin Ralph ◽  
Brooks E. Martner ◽  
Allen B. White ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Winter Season ◽  
Radar Data ◽  
Operational Environment ◽  
Low Level ◽  
Synoptic Variability ◽  
Synoptic Conditions ◽  
Cloud Tops

Abstract An objective algorithm presented in White et al. was applied to vertically pointing S-band (S-PROF) radar data recorded at four sites in northern California and western Oregon during four winters to assess the geographic, interannual, and synoptic variability of stratiform nonbrightband (NBB) rain in landfalling winter storms. NBB rain typically fell in a shallow layer residing beneath the melting level (<∼3.5 km MSL), whereas rainfall possessing a brightband (BB) was usually associated with deeper echoes (>∼6 km MSL). The shallow NBB echo tops often resided beneath the coverage of the operational Weather Surveillance Radar-1988 Doppler (WSR-88D) scanning radars yet were still capable of producing flooding rains. NBB rain contributed significantly to the total winter-season rainfall at each of the four geographically distinct sites (i.e., 18%–35% of the winter-season rain totals). In addition, the rainfall observed at the coastal mountain site near Cazadero, California (CZD), during each of four winters was composed of a significant percentage of NBB rain (18%–50%); substantial NBB rainfall occurred regardless of the phase of the El Niño–Southern Oscillation (which ranged from strong El Niño to moderate La Niña conditions). Clearly, NBB rain occurs more widely and commonly in California and Oregon than can be inferred from the single-winter, single-site study of White et al. Composite NCEP–NCAR reanalysis maps and Geostationary Operational Environment Satellite (GOES) cloud-top temperature data were examined to evaluate the synoptic conditions that characterize periods of NBB precipitation observed at CZD and how they differ from periods with bright bands. The composites indicate that both rain types were tied generally to landfalling polar-cold-frontal systems. However, synoptic conditions favoring BB rain exhibited notable distinctions from those characterizing NBB periods. This included key differences in the position of the composite 300-mb jet stream and underlying cold front with respect to CZD, as well as notable differences in the intensity of the 500-mb shortwave trough offshore of CZD. The suite of BB composites exhibited dynamically consistent synoptic-scale characteristics that yielded stronger and deeper ascent over CZD than for the typically shallower NBB rain, consistent with the GOES satellite composites that showed 20-K warmer (2.3-km shallower) cloud tops for NBB rain. Composite soundings for both rain types possessed low-level potential instability, but the NBB sounding was warmer and moister with stronger low-level upslope flow, thus implying that orographically forced rainfall is enhanced during NBB conditions.

The Influence of the El Niño–Southern Oscillation on Cloud-to-Ground Lightning Activity along the Gulf Coast. Part I: Lightning Climatology

2008 ◽  
Vol 136 (7) ◽  
pp. 2523-2542 ◽  
Author(s):  
Mark LaJoie ◽  
Arlene Laing
Keyword(s):  
El Niño ◽  
Gulf Coast ◽  
El Nino ◽  
Southern Oscillation ◽  
Winter Season ◽  
Lightning Activity ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Enso Cycle ◽  
Lightning Flash

Abstract Cloud-to-ground (CG) lightning flashes from the National Lightning Detection Network are analyzed to determine if the El Niño–Southern Oscillation (ENSO) cycle influences lighting activity along the Gulf Coast region. First, an updated climatology of lightning was developed for the region. Flash density maps are constructed from an 8-yr dataset (1995–2002) and compared with past lightning climatologies. Second, lightning variability is compared with the phases of ENSO. Winter lightning distributions are compared with one published study of ENSO and lightning days in the Southeast. Flash density patterns are, overall, consistent with past U.S. lightning climatology. However, the peak flash density for the annual mean was less than observed in previous climatologies, which could be due to the disproportionately large percentage of cool ENSO periods compared to previous lightning climatologies. The highest annual lightning counts were observed in 1997, which consisted of mostly warm ENSO seasons; the 1997–98 El Niño was one of the strongest on record. The lowest lightning counts were observed in 2000, which had mostly cool or neutral phases of ENSO including the lowest Niño-3.4 anomaly of the study period. Analysis of winter season lightning flash densities substantiated the role of the ENSO cycle in winter season lightning fluctuations. Winter lightning activity increased dramatically during the 1997–98 El Niño. The lowest winter flash densities are associated with cool ENSO phases. Although 8 yr is inadequate to establish a long-term pattern, results indicate that ENSO influences lightning and that further study is warranted. As more years of lightning data are acquired, a more complete climatology can be developed.

scholarly journals The Influence of Large-Scale Climate Variability on Winter Maximum Daily Precipitation over North America

2010 ◽  
Vol 23 (11) ◽  
pp. 2902-2915 ◽  
Author(s):  
Xuebin Zhang ◽  
Jiafeng Wang ◽  
Francis W. Zwiers ◽  
Pavel Ya Groisman
Keyword(s):  
North America ◽  
Climate Variability ◽  
El Niño ◽  
Extreme Precipitation ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Statistical Significance ◽  
Winter Season ◽  
The North

Abstract The generalized extreme value (GEV) distribution is fitted to winter season daily maximum precipitation over North America, with indices representing El Niño–Southern Oscillation (ENSO), the Pacific decadal oscillation (PDO), and the North Atlantic Oscillation (NAO) as predictors. It was found that ENSO and PDO have spatially consistent and statistically significant influences on extreme precipitation, while the influence of NAO is regional and is not field significant. The spatial pattern of extreme precipitation response to large-scale climate variability is similar to that of total precipitation but somewhat weaker in terms of statistical significance. An El Niño condition or high phase of PDO corresponds to a substantially increased likelihood of extreme precipitation over a vast region of southern North America but a decreased likelihood of extreme precipitation in the north, especially in the Great Plains and Canadian prairies and the Great Lakes/Ohio River valley.

MJO propagation over the Indian Ocean and Western Pacific in CMIP5 Models: Roles of Background States

2021 ◽  
pp. 1-46
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Western Pacific ◽  
Occurrence Frequency ◽  
Cmip5 Models ◽  
Low Level ◽  
Budget Analysis ◽  
The Indian Ocean

Abstract This study explored the impacts of background states on the propagation of the Madden-Julian Oscillation (MJO) in 24 CMIP5 models using a precipitation-based MJO tracking method. The ability of the model to reproduce the MJO propagation is reflected in the occurrence frequency of individual MJO events. Moisture budget analysis suggests that the occurrence frequencies of MJO events that propagate across the Indian Ocean (IO-MJO) and western Pacific (WP-MJO) in the models are mainly related to the low-level meridional moisture advection ahead of the MJO convection center. This advection is tightly associated with the background distribution of low-level moisture. Drier biases in background low-level moisture over the entire tropical regions account for underestimated MJO occurrence frequency in the bottom-tier simulations. This study highlights the importance of reproducing the year-to-year background states for the simulations of MJO propagation in the models by further decomposing the background states into the climatology and anomaly components. The background meridional moisture gradient account for the IO-MJO occurrence frequency is closely related to its climatology component, however, the anomaly component regulated by the El Niño–Southern Oscillation (ENSO) is also important for the WP-MJO occurrence frequency. The year-to-year variations of background zonal and meridional gradients associated with ENSO account for the IO-MJO occurrence frequency tend to be offset with each other. As a result, the ENSO shows no significant impact on the IO-MJO occurrence frequency. However, the MJO events tend to more likely propagate across the western Pacific during El Niño years.

scholarly journals Atmospheric torques and Earth's rotation: what drove the millisecond-level length-of-day response to the 2015–2016 El Niño?

2017 ◽  
Vol 8 (4) ◽  
pp. 1009-1017 ◽  
Author(s):  
Sébastien B. Lambert ◽  
Steven L. Marcus ◽  
Olivier de Viron
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Winter Season ◽  
Eastern Pacific ◽  
Earth’S Rotation ◽  
Length Of Day ◽  
Central Pacific ◽  
Earth's Rotation ◽  
Enso Events

Abstract. El Niño–Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east–west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–1983 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015–2016 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that (i) as a mixed eastern–central Pacific event, the 2015–2016 mountain torque was smaller than for the 1982–1983 and 1997–1998 events, which were pure eastern Pacific events, and (ii) the smaller mountain torque was compensated for by positive friction torques arising from an enhanced Hadley-type circulation in the eastern Pacific, leading to similar AAM–LOD signatures for all three extreme ENSO events. The 2015–2016 event thus contradicts the existing paradigm that mountain torques cause the Earth rotation response for extreme El Niño events.

scholarly journals Interannual Variability of Air Temperature over Myanmar: The Influence of ENSO and IOD

Climate ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 35
Author(s):  
Zin Mie Mie Sein ◽  
Irfan Ullah ◽  
Sidra Syed ◽  
Xiefei Zhi ◽  
Kamran Azam ◽  
...  
Keyword(s):  
Air Temperature ◽  
El Niño ◽  
Water Resource Management ◽  
El Nino ◽  
Southern Oscillation ◽  
Rapid Change ◽  
Winter Season ◽  
Positive Trend ◽  
Study Region ◽  
Target Region

Myanmar is located in a tropical region where temperature rises very fast and hence is highly vulnerable to climate change. The high variability of the air temperature poses potential risks to the local community. Thus, the current study uses 42 synoptic meteorological stations to assess the spatiotemporal changes in air temperature over Myanmar during 1971–2013. The nonparametric sequential Mann-Kendall (SqMK), linear regression, empirical orthogonal function (EOF), Principal Component Analysis (PCA), and composite analysis were used to assess the long-term trends in maximum (Tmax) and minimum (Tmin) temperature series and their possible mechanism over the study region. The results indicate that the trend of Tmax has significantly increased at the rates of 90% in summer season, while the Tmin revealed a substantial positive trend in winter season time series with the magnitude of 30%, respectively. Moreover, during a rapid change of climate (1995–2013) we observed an air temperature increase of 0.7 °C. The spatial distributions of EOF revealed relatively warmer temperatures over the whole region except the south in the summer; however, a similar pattern can be seen for the rainy season and winter, implying warming in the central part and cooling in the northern and southern parts. Furthermore, the Indian Ocean Dipole (IOD) influence on air temperature over Myanmar is more prevalent than that of the El Niño Southern Oscillation (ENSO). The result implies that the positive phase of the IOD and negative phase of the Southern Oscillation Index (SOI; El Niño) events led to the higher temperature, resulting in intense climatic extremes (i.e., droughts and heatwaves) over the target region. Therefore, this study’s findings can help policymakers and decision-makers improve economic growth, agricultural production, ecology, water resource management, and preserving the natural habitat in the target region.

scholarly journals Flood hydrometeorological situations associated with monsoon floods on the Par River in Western India

MAUSAM ◽  
2021 ◽  
Vol 71 (4) ◽  
pp. 687-698
Author(s):  
PATIL ARCHANA D. ◽  
HIRE PRAMODKUMAR S.
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Annual Rainfall ◽  
Western India ◽  
Interannual Rainfall Variability ◽  
Synoptic Conditions ◽  
The Government ◽  
Large Floods

The objective of present work is to understand flood hydrometeorological situations associated with monsoon floods on the Par River, therefore, the analyses of synoptic conditions connected with large floods was carried out. This encompasses analysis of interannual rainfall variability and associated floods, analysis of storm tracts, investigation of normalized accumulated departure from mean (NADM) and evaluation of the relation between El Niño and monsoon rainfall. In order to accomplish above analyses, the annual rainfall data of the Par Basin have been obtained for 118 years from India Meteorological Department (IMD), Pune and Chennai. The annual maximum series (AMS)/stage data were procured for a gauging site namely Nanivahial for 45 years from Irrigation Department of Gujarat State, Ahmedabad.  The results indicate that the interannual variability was characterized by increased frequency and magnitude of floods on the Par River primarily after 1930s. Majority of the large floods in the basin were connected with low pressure systems. It is observed that most of the floods were associated with positive departure from mean rainfall in the basin. The NADM graph shows epochal behaviour of high and low rainfall of the basin and floods.  The analysis of El Niño and Southern Oscillation indicates that the probability of the occurrence of the floods in the Par Basin is high during the average SST index and majority of the floods in the basin have occurred during above normal conditions of rainfall. The present study can, therefore, prove to be a significant contribution towards the Par-Tapi-Narmada link project of the Government of Gujarat and water divergent projects of the Government of Maharashtra in association with Government of India.

scholarly journals Major Floods and Tropical Cyclones over Bangladesh: Clustering from ENSO Timescales

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 692
Author(s):  
Md Wahiduzzaman
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Flood Events ◽  
Post Monsoon ◽  
La Nina ◽  
Synoptic Conditions ◽  
Major Floods

The present study analyzed major floods and tropical cyclones (TCs) over Bangladesh on El Niño-Southern Oscillation (ENSO) timescales. The geographical location, low and almost flat topography have introduced Bangladesh as one of the most vulnerable countries of the world. Bangladesh is highly vulnerable to the extreme hazard events like floods and cyclones which are impacted by ENSO. ENSO is mainly a tropical event, but its impact is global. El Niño (La Niña) represents the warm (cold) phase of the ENSO cycle. Rainfall and cyclonic disturbances data have been used for the period of 70 years (1948–2017) and compared with the corresponding observations of the Southern Oscillation Index. Result shows that major flood events occurred during the monsoon period, and most of them are during the La Niña condition, consistent with the historical archives of flood events in Bangladesh. Synoptic conditions of these events are well matched during La Niña condition. On the other hand, the major TC cases are in the period of either pre-monsoon or post-monsoon season. The pre-monsoon cases are under neutral (developing La Niña) or El Niño and the post-monsoon cases are under La Niña, consistent with climatology studies that La Niña is favorable to have more intense TCs over the Bay of Bengal.

scholarly journals The Seasonality of the Great Plains Low-Level Jet and ENSO Relationship

2015 ◽  
Vol 28 (11) ◽  
pp. 4525-4544 ◽  
Author(s):  
Lakshmi Krishnamurthy ◽  
Gabriel A. Vecchi ◽  
Rym Msadek ◽  
Andrew Wittenberg ◽  
Thomas L. Delworth ◽  
...  
Keyword(s):  
Great Plains ◽  
El Niño ◽  
Seasonal Changes ◽  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
The United States ◽  
Boreal Summer ◽  
Low Level ◽  
Low Level Jet

Abstract This study investigates the seasonality of the relationship between the Great Plains low-level jet (GPLLJ) and the Pacific Ocean from spring to summer, using observational analysis and coupled model experiments. The observed GPLLJ and El Niño–Southern Oscillation (ENSO) relation undergoes seasonal changes with a stronger GPLLJ associated with La Niña in boreal spring and El Niño in boreal summer. The ability of the GFDL Forecast-Oriented Low Ocean Resolution (FLOR) global coupled climate model, which has the high-resolution atmospheric and land components, to simulate the observed seasonality in the GPLLJ–ENSO relationship is assessed. The importance of simulating the magnitude and phase locking of ENSO accurately in order to better simulate its seasonal teleconnections with the Intra-Americas Sea (IAS) is demonstrated. This study explores the mechanisms for seasonal changes in the GPLLJ–ENSO relation in model and observations. It is hypothesized that ENSO affects the GPLLJ variability through the Caribbean low-level jet (CLLJ) during the summer and spring seasons. These results suggest that climate models with improved ENSO variability would advance our ability to simulate and predict seasonal variations of the GPLLJ and their associated impacts on the United States.

Atmospheric Internal Variability in the Summer Indo–Northwestern Pacific: Role of the Intraseasonal Oscillation

2020 ◽  
Vol 33 (8) ◽  
pp. 3395-3410 ◽  
Author(s):  
Xudong Wang ◽  
Shang-Ping Xie ◽  
Zhaoyong Guan
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Function Analysis ◽  
Intraseasonal Oscillation ◽  
Internal Variability ◽  
Boreal Summer ◽  
Northwestern Pacific ◽  
Residual Variability ◽  
Low Level

AbstractSummer atmospheric interannual variability in the Indo–northwestern Pacific (NWP) is coupled with tropical sea surface temperature (SST) variability. This study investigates the importance and origin of atmospheric internal variability in the Indo-NWP region. Using the reanalysis and the 30-member atmospheric model simulation, two SST-related interannual modes are identified in the Indo-NWP region during boreal summer with the month-reliant empirical orthogonal function analysis. The first mode is related to concurrent El Niño–Southern Oscillation originating from the eastern equatorial Pacific whereas the second mode features an anomalous anticyclone (AAC) in post–El Niño summers over the NWP region, known as the Indo-western Pacific Ocean capacitor. The SST-induced modes show temporal persistence from June to August. The residual variability is the focus of this study. The dominant mode of the residual variability displays an AAC structure over the NWP but little month-to-month persistence, indicative of atmospheric internal dynamics unrelated to SST forcing. Further investigation suggests the monthly internal AAC arises from the summer intraseasonal oscillation (ISO). The broad band of ISO yields nonzero monthly means that project strongly onto the AAC pattern. Finally, the anomalies of rainfall and low-level circulation in summer 2016 are investigated. The reversal of the low-level circulation pattern from an AAC in July to an anomalous cyclone over the NWP in August 2016 is due to the ISO-induced internal variability.

scholarly journals The Gulf of Mexico and ENSO Influence on Subseasonal and Seasonal CONUS Winter Tornado Variability

2018 ◽  
Vol 57 (10) ◽  
pp. 2439-2463 ◽  
Author(s):  
Maria J. Molina ◽  
John T. Allen ◽  
Vittorio A. Gensini
Keyword(s):  
Gulf Of Mexico ◽  
Great Plains ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Winter Season ◽  
La Niña ◽  
Jet Stream ◽  
Southern Great Plains ◽  
La Nina

AbstractEl Niño–Southern Oscillation (ENSO) and the Gulf of Mexico (GoM) influence winter tornado variability and significant tornado (EF2+, where EF is the enhanced Fujita scale) environments. Increases occur in the probability of a significant tornado environment from the southern Great Plains to the Midwest during La Niña, and across the southern contiguous United States (CONUS) during El Niño. Winter significant tornado environments are absent across Florida, Georgia, and the coastal Carolinas during moderate-to-strong La Niña events. Jet stream modulation by ENSO contributes to higher tornado totals during El Niño in December and La Niña in January, especially when simultaneous with a warm GoM. ENSO-neutral phases yield fewer and weaker tornadoes, but proximity to warm GoM climate features can enhance the probability of a significant tornado environment. ENSO intensity matters; stronger ENSO phases generate increases in tornado frequency and the probability of a significant tornado environment, but are characterized by large variance, in which very strong El Niño and La Niña events can produce unfavorable tornado climatological states. This study suggests that it is a feasible undertaking to expand spring seasonal and subseasonal tornado prediction efforts to encompass the winter season, which is of importance given the notable threat posed by winter tornadoes. Significant tornadoes account for 95% of tornado fatalities and winter tornadoes are rated significant more frequently than during other seasons.

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