Association between upper level diffluence in the Tropical Easterly Jet and the formation of the strongest Atlantic hurricanes in recent years

AbstractPrevious studies found a tight connection between the tropical easterly jet (TEJ) and Indian summer monsoon rainfall (ISMR). Here we show that the TEJ-ISMR relationship is nonstationary and breaks down from 1994–2003 (epoch P2), in contrast to the significant positive correlation during the epoch P1 (1979–1993) and P3 (2004–2016). The breakdown of the TEJ-ISMR relationship concurs with the increased rainfall variability over the tropical eastern Indian Ocean (TEIO). The enhanced TEIO rainfall anomalies excite a significant lower-level cyclonic circulation that reduces the ISMR, meanwhile, strengthens the upper-level divergence and excites a pair of upper-level anticyclone to the west of the TEIO as Rossby wave responses, both accelerating the TEJ. Thus, the TEIO rainfall plays a more important role than the ISMR in the TEJ variability during P2, causing the breakdown of the TEJ-ISMR relationship. In contrast, a relatively weak amplitude of the TEIO rainfall during P1 and P3 was unable to change the positive TEJ-ISMR relationship. The changes in the TEIO rainfall variability is mainly attributed to the increased SST variability over the tropical southeastern Indian Ocean, but the cause of it remains elusive.

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Sahel Rainfall–Tropical Easterly Jet Relationship on Synoptic to Intraseasonal Time Scales

Monthly Weather Review ◽

10.1175/mwr-d-18-0254.1 ◽

2019 ◽

Vol 147 (5) ◽

pp. 1733-1752 ◽

Cited By ~ 3

Author(s):

Alexander Lemburg ◽

Jürgen Bader ◽

Martin Claussen

Keyword(s):

West Africa ◽

Time Scales ◽

West African Monsoon ◽

Reanalysis Data ◽

Limiting Factor ◽

Convective Activity ◽

Affect Intensity ◽

Tropical Easterly Jet ◽

Sahel Rainfall ◽

Upper Level

Abstract The tropical easterly jet (TEJ) is a characteristic upper-level feature of the West African monsoon (WAM) circulation. Moreover, the TEJ over West Africa is significantly correlated with summer Sahel rainfall on interannual and decadal time scales. In contrast, the relationship between Sahel rainfall and the regional TEJ on synoptic to intraseasonal time scales is unclear. Therefore, this relationship is investigated by means of multiple statistical analyses using temporally highly resolved measurement and reanalysis data. It is shown that average correlations between convective activity and regional TEJ intensity remain below 0.3 for all synoptic to intraseasonal time scales. Especially on the synoptic time scale, the TEJ significantly lags anomalies in convective activity by one or two days, which indicates that convection anomalies are more likely to drive changes in the regional TEJ than vice versa. To further shed light on the role of the TEJ for rainfall over West Africa, a previously proposed effect of TEJ-induced upper-level divergence on the development of mesoscale convective systems (MCSs) is examined more closely. An analysis of nearly 300 Sahelian MCSs shows that their initiation is generally not associated with significant TEJ anomalies or jet-induced upper-level divergence. Furthermore, no statistically significant evidence is found that preexisting TEJ-related upper-level divergence anomalies affect intensity, size, and lifetime of MCSs. A limiting factor of this study is the focus on TEJ-induced upper-level divergence. Therefore, a possible effect of the TEJ on Sahel rainfall via other mechanisms cannot be ruled out and should be subject to future studies.

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Performance of Forecasts of Hurricanes with and without Upper-Level Troughs over the Mid-Latitudes

Atmosphere ◽

10.3390/atmos11070702 ◽

2020 ◽

Vol 11 (7) ◽

pp. 702

Author(s):

Kazutoshi Sato ◽

Jun Inoue ◽

Akira Yamazaki

Keyword(s):

Initial Time ◽

Central Position ◽

Observation Data ◽

Strong Wind ◽

Ensemble Forecasts ◽

Position Errors ◽

Operational Forecasts ◽

Radiosonde Observation ◽

Upper Level ◽

Atlantic Hurricanes

We investigated the accuracy of operational medium-range ensemble forecasts for 29 Atlantic hurricanes between 2007 and 2019. Upper-level troughs with strong wind promoted northward movement of hurricanes over the mid-latitudes. For hurricanes with upper-level troughs, relatively large errors in the prediction of troughs result in large ensemble spreads, which result in failure to forecast hurricane track. In contrast, for hurricanes without upper-level troughs, mean central position errors are relatively small in all operational forecasts because of the absence of upper-level strong wind around troughs over the mid-latitudes. Hurricane Irma in September 2017 was accompanied by upper-level strong wind around a trough; errors and ensemble spreads for the predicted upper-level trough are small, contributing to smaller errors and small ensemble spreads in the predicted tracks of Irma. Our observing system experiment reveals that inclusion of additional Arctic radiosonde observation data obtained from research vessel Mirai in 2017 improves error and ensemble spread in upper-level trough with strong wind at initial time for forecast, increasing the accuracy of the forecast of the track of Irma in 2017.

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Opposite Effects of ENSO on the Rainfall over the Northern and Equatorial Great Horn of Africa and Possible Causes

Advances in Meteorology ◽

10.1155/2020/9028523 ◽

2020 ◽

Vol 2020 ◽

pp. 1-16

Author(s):

K. Abebe Kiflie ◽

Li Tao

Keyword(s):

Rainfall Variability ◽

Summer Rainfall ◽

Western Indian Ocean ◽

Annual Rainfall ◽

Horn Of Africa ◽

Tropical Africa ◽

Low Level ◽

Tropical Easterly Jet ◽

Rainfall Anomalies ◽

Upper Level

In this study, we explore the possible mechanism of opposite ENSO effects on summer rainfall in the JJAS region (northern GHA) and autumn rainfall in the OND region (equatorial GHA). The two regions are identified based on the spatial distribution of high seasonal fractions of annual rainfall for the period 1979–2016. The summer rainfall over the JJAS region is negatively correlated with ENSO. It is because the warm Niño3.4 SST triggers zonal wave one pattern in tropics and forces upper-level westerly anomaly and the low-level easterly anomaly over tropical Africa. Thus, the weakened upper-level Tropical Easterly Jet (TEJ) and the low-level westerly over the JJAS region result in deficient rainfall during JJAS over the northern GHA. For the autumn rainfall variability over the equatorial GHA, IOD is a pivotal factor. But, autumn rainfall anomalies are far greater in ENSO and IOD coexisting years than those in IOD alone years. In other words, ENSO has a significant impact on the autumn rainfall over the equatorial GHA by means of IOD. It is because the warming SST, which is fully developed over western Indian Ocean (IO) in autumn of ENSO developing year, causes low-level convergence over the equatorial GHA and enhances upper-level easterly over tropical Africa. Those conditions are favorable for abundant rainfall over the equatorial GHA in autumn.

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Dramatic Weakening of the Tropical Easterly Jet Projected by CMIP6 Models

Journal of Climate ◽

10.1175/jcli-d-19-1002.1 ◽

2020 ◽

Vol 33 (19) ◽

pp. 8439-8455

Author(s):

Sihua Huang ◽

Bin Wang ◽

Zhiping Wen

Keyword(s):

General Circulation ◽

Critical Role ◽

Coupled Model ◽

Tropical Indian Ocean ◽

Monsoon Circulation ◽

Tropical Eastern Pacific ◽

Tropical Easterly Jet ◽

Crucial Component ◽

The Future ◽

Upper Level

AbstractThe upper-level tropical easterly jet (TEJ) is a crucial component of the summer monsoon system and tropical general circulation. The simulation and projection of the TEJ, however, have not been assessed. Here we evaluate models’ fidelity and assess the future change of the TEJ by utilizing 16 models that participated in phase 6 of the Coupled Model Intercomparison Project (CMIP6). Most of the models can reproduce the TEJ reasonably well in terms of climatology, seasonal evolution, and interannual variability. Nevertheless, underestimation of the TEJ’s intensity and extent is identified, with the maximum bias occurring in the jet centers over the tropical Indian Ocean (IO) and the tropical eastern Pacific (EP). Under the shared socioeconomic pathway 5–8.5, the multimodel ensemble projects a remarkable reduction in the central TEJ intensity by about 18% over the IO and 77% over the EP toward the end of the twenty-first century. The mean intensity of TEJ will weaken by about 11%, and the extent will reduce by 6%, suggesting a significantly weakened upper-level monsoon circulation in the future climate. The projected El Niño–like warming pattern over the tropical Pacific may play a critical role in the future weakening of the TEJ via inducing suppressed rainfall over the tropical eastern IO and Central America. The model uncertainties in the projected TEJ changes may arise from the uncertainties in the models’ projected tropical EP warming. The sensitivity of future projections to model selection is also examined. Results show that the selection of models based on different physical considerations does not yield a significantly different projection.

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Behavioral correction in repeated social dilemma exercises: A comparison between an upper-level course and an introductory retention course

PsycEXTRA Dataset ◽

10.1037/e413792005-590 ◽

2000 ◽

Author(s):

Jeffrey S. Bartel ◽

Steven J. Hoekstra

Keyword(s):

Social Dilemma ◽

Upper Level

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State special primary acceleration measurement standard for gravimetry GET 190-2019

Izmeritel`naya Tekhnika ◽

10.32446/0368-1025it.2020-7-3-8 ◽

2020 ◽

pp. 3-8

Author(s):

L.F. Vitushkin ◽

F.F. Karpeshin ◽

E.P. Krivtsov ◽

P.P. Krolitsky ◽

V.V. Nalivaev ◽

...

Keyword(s):

High Precision ◽

Free Fall ◽

Measurement Range ◽

Measurement Standard ◽

Acceleration Measurement ◽

Measurement Systems ◽

Free Fall Acceleration ◽

Investigation Methods ◽

Measurement Results ◽

Upper Level

The State special primary acceleration measurement standard for gravimetry (GET 190-2019), its composition, principle of operation and basic metrological characteristics are presented. This standard is on the upper level of reference for free-fall acceleration measurements. Its accuracy and reliability were improved as a result of optimisation of the adjustment procedures for measurement systems and its integration within the upgraded systems, units and modern hardware components. A special attention was given to adjusting the corrections applied to measurement results with respect to procedural, physical and technical limitations. The used investigation methods made it possibled to confirm the measurement range of GET 190-2019 and to determine the contributions of main sources of errors and the total value of these errors. The measurement characteristics and GET 90-2019 were confirmed by the results obtained from measurements of the absolute value of the free fall acceleration at the gravimetrical site “Lomonosov-1” and by their collation with the data of different dates obtained from measurements by high-precision foreign and domestic gravimeters. Topicality of such measurements ensues from the requirements to handle the applied problems that need data on parameters of the Earth gravitational field, to be adequately faced. Geophysics and navigation are the main fields of application for high-precision measurements in this field.

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