scholarly journals The Effects of Background Zonal and Meridional Winds on ENSO in a Coupled GCM

2020 ◽  
Vol 33 (6) ◽  
pp. 2075-2091 ◽  
Author(s):  
Bowen Zhao ◽  
Alexey Fedorov
Keyword(s):  
Zonal Wind ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Meridional Wind ◽  
Wind Component ◽  
Coupled Models ◽  
Positive Feedbacks ◽  
Zonal Winds ◽  
Meridional Winds

AbstractChanges in background zonal wind in the tropical Pacific are often invoked to explain changes in ENSO properties. However, the sensitivity of ENSO to mean zonal winds has been thoroughly explored only in intermediate coupled models (following Zebiak and Cane), not in coupled GCMs. The role of mean meridional winds has received even less attention. Accordingly, the goal of this study is to examine systematically the effects of both zonal (equatorial) and meridional (cross-equatorial) background winds on ENSO using targeted experiments with a comprehensive climate model (CESM). Changes in the mean winds are generated by imposing heat flux forcing in two confined regions at a sufficient distance north and south of the equator. We find that the strengthening of either wind component reduces ENSO amplitude, especially eastern Pacific SST variability, and inhibits meridional swings of the intertropical convergence zone (ITCZ). The effect of zonal winds is generally stronger than that of meridional winds. A stability analysis reveals that the strengthening of zonal and meridional winds weakens the ENSO key positive feedbacks, specifically the zonal advection and thermocline feedbacks, which explains these changes. Zonal wind enhancement also intensifies mean upwelling and hence dynamical damping, leading to a further weakening of El Niño events. Ultimately, this study argues that the zonal and, to a lesser extent, meridional wind strengthening of the past decades may have contributed to the observed shift of El Niño characteristics after the year 2000.

scholarly journals Analisa Angin Zonal dan Meridional Dalam Menentukan Awal Musim Hujan di Kota Jambi

2020 ◽  
Vol 8 (1) ◽  
pp. 43-50
Author(s):  
Presli Panusunan Simanjuntak ◽  
◽  
Agus Safril ◽  
Keyword(s):  
Wind Speed ◽  
Zonal Wind ◽  
El Niño ◽  
Rainy Season ◽  
Prediction Models ◽  
El Nino ◽  
Meridional Wind ◽  
Wind Component ◽  
Meridional Winds ◽  
The City

In Indonesia, prediction models for the beginning of the rainy season have not developed intensively. Jambi City is the capital of Jambi Province as it has quite extensive rainfed gardens / fields and rice fields and contributes significantly to the economy of Jambi Province. Jambi City really needs an accurate prediction of the start of the rainy season to support the economic continuity through agriculture and plantations. This study aims to analyze the zonal and meridional wind components in the 1000 mb layer in determining the start of the rainy season in the city of Jambi. The prediction of the beginning of the season using zonal and meridional winds will be divided into 2 conditions, namely when the normal conditions of monthly rainfall in 1997-2017 and when the El Nino conditions are strong in 1997/1998 and 2015/2016. Based on data processing for 1997-2017, it shows that the beginning of the rainy season is December when the zonal wind speed is highest. In this study, the zonal wind component is more dominant than the meridional wind component in determining the start of the rainy season. However, when conditions are el nino, the zonal wind component is not good to become

tamh tm iedor sphere -1 el 9a8 ti 0vse , lyc li s m im a p te le models. Much more detailed than in the Australian region (Simpson and Downey 1975; run. Rather they are models than simp allysofomuuscehdm ro ourte in eelxypesn in si cvee th to e V ha osicbe ee anndfoH rc uendt 198 recasting El Nino behav­ tures for the p w er iitohd4o ). bsT1eh rv e BMRC climate model iour (e.g., sea surface temperatures in the east simulated by the model ha 9s49e -d 9 1 se , aasnud rf ac th eet em ra p in efraal ­ lfeoqrueactaosrti al r Pacific), they could, in theory, be used to ob been compared with the coupling o ai fnftahleloacnedantetmoptehrea tu artemoosvpehre re la nidn . th Tehseew te asse rv ru end ra fiinvfea ll t i ( m Fr eesd , er w ik istehne th teal. s1a9m9e5 ). seTahesm ur o fa dceelmmo od deellss , ( hPoowweevrere , tis less than perfect. Improved ocean ph m er p ic e ra ctoun re d s it io bnust . s T li h ghtly different starting atmos­ these coupled mode alls . . 1995) are being developed for ialg lu rseterm ate esnttw he it h ‘ noobisseer ’ veind iffe ed rtahier ence betw nfa m ll, o w de e l . neTeoenge th t e ed to av mru uns O era cghep se aarsto ne pro onfalthperebd le ic m ti own it ihstthheeduisfef ic oufltcy oupled models in all five runs as an ‘ens coupled models has in sitmhue la attim ng osrp ai hnefrailclA of u st p ra rleicainpp it raetc io ip n i tat sihoon, w em abtls le’. eoam st e The en o ve srkin ll sem o rt ihne bl sei ave rn Amuusl rag t a ra ti lnegsgoennte he ia. (Ni ra l sp su a c ti caelsssca in le ssiimmuploartt in an gtaftomrousspeh rs e , ridcesvpairtieab th il e it iyr Fur T th h e es resoau tm th o , stphheem ri odels are less successful. sea cshuo rf l a ls ce1t9e9m6p ) e . ra M tu ordeealneoxmpaelriiemsehnatvsewailtohngspheicsitfo ie ry djtohb er e o fo f re si m pr uolbaa ti bnlgyc th cemSoOdIel ( eFx ig pe urrieme3n .3 ts ) . do ThaegSoO od I an be predicted without the need

Droughts ◽  
2016 ◽  
pp. 77-77
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Coupled Models ◽  
Coupled Mode ◽  
Australian Region ◽  
Surface Temperatures

scholarly journals Observed Changes in the Lifetime and Amplitude of the Madden–Julian Oscillation Associated with Interannual ENSO Sea Surface Temperature Anomalies

2007 ◽  
Vol 20 (11) ◽  
pp. 2659-2674 ◽  
Author(s):  
Benjamin Pohl ◽  
Adrian J. Matthews
Keyword(s):  
Zonal Wind ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Average Lifetime ◽  
Wind Component ◽  
Madden Julian Oscillation ◽  
La Nina ◽  
Equatorial Wave

Abstract The Madden–Julian oscillation (MJO) is analyzed using the reanalysis zonal wind– and satellite outgoing longwave radiation–based indices of Wheeler and Hendon for the 1974–2005 period. The average lifetime of the MJO events varies with season (36 days for events whose central date occurs in December, and 48 days for events in September). The lifetime of the MJO in the equinoctial seasons (March–May and October–December) is also dependent on the state of El Niño–Southern Oscillation (ENSO). During October–December it is only 32 days under El Niño conditions, increasing to 48 days under La Niña conditions, with similar values in northern spring. This difference is due to faster eastward propagation of the MJO convective anomalies through the Maritime Continent and western Pacific during El Niño, consistent with theoretical arguments concerning equatorial wave speeds. The analysis is extended back to 1950 by using an alternative definition of the MJO based on just the zonal wind component of the Wheeler and Hendon indices. A rupture in the amplitude of the MJO is found in 1975, which is at the same time as the well-known rupture in the ENSO time series that has been associated with the Pacific decadal oscillation. The mean amplitude of the MJO is 16% larger in the postrupture (1976–2005) compared to the prerupture (1950–75) period. Before the 1975 rupture, the amplitude of the MJO is maximum (minimum) under El Niño (La Niña) conditions during northern winter, and minimum (maximum) under El Niño (La Niña) conditions during northern summer. After the rupture, this relationship disappears. When the MJO–ENSO relationship is analyzed using all-year-round data, or a shorter dataset (as in some previous studies), no relationship is found.

scholarly journals The Effect of the Galápagos Islands on ENSO in Forced Ocean and Hybrid Coupled Models

2008 ◽  
Vol 38 (11) ◽  
pp. 2519-2534 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Raghu Murtugudde ◽  
Antonio J. Busalacchi
Keyword(s):  
Wind Stress ◽  
Zonal Wind ◽  
El Niño ◽  
Time Scale ◽  
El Nino ◽  
Galapagos Islands ◽  
Galápagos Islands ◽  
Coupled Models ◽  
Zonal Wind Stress ◽  
Sst Anomaly

Abstract An ocean general circulation model (OGCM) of the tropical Pacific Ocean is used to examine the effects of the Galápagos Islands on the El Niño–Southern Oscillation (ENSO). First, a series of experiments is conducted using the OGCM in a forced context, whereby an idealized El Niño event may be examined in cases with and without the Galápagos Islands. In this setup, the sensitivity of the sea surface temperature (SST) anomaly response to the presence of the Galápagos Islands is examined. Second, with the OGCM coupled to the atmosphere via zonal wind stress, experiments are conducted with and without the Galápagos Islands to determine how the Galápagos Islands influence the time scale of ENSO. In the forced setup, the Galápagos Islands lead to a damped SST anomaly given an identical zonal wind stress perturbation. Mixed layer heat budget calculations implicate the entrainment mixing term, which confirms that the difference is due to the Galápagos Islands changing the background mean state, that is, the equatorial thermocline as diagnosed in a previous paper. In the hybrid coupled experiments, there is a clear shift in the power spectrum of SST anomalies in the eastern equatorial Pacific. Specifically, the Galápagos Islands lead to a shift in the ENSO time scale from a biennial to a quasi-quadrennial period. Mechanisms for the shift in ENSO time scale due to the Galápagos Islands are discussed in the context of well-known paradigms for the oscillatory nature of ENSO.

scholarly journals Generation of westerly wind bursts by forcing outside the tropics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Arnold Sullivan ◽  
Wenxiu Zhong ◽  
Gian Luca Eusebi Borzelli ◽  
Tao Geng ◽  
Chloe Mackallah ◽  
...  
Keyword(s):  
Time Scales ◽  
El Niño ◽  
East Asian Monsoon ◽  
El Nino ◽  
Coupled Model ◽  
Western Pacific ◽  
Wind Component ◽  
Westerly Wind ◽  
Coupled Models ◽  
The Western Pacific

AbstractThe westerly wind burst (WWB) is an important triggering mechanism of El Niño and typically occurs in the western Pacific Ocean. The Fourier spectrum of the wind field over the western tropical Pacific is characterised by a large variety of peaks distributed from intra-seasonal to decadal time scales, suggesting that WWBs could be a result of nonlinear interactions on these time scales. Using a combination of observations and simulations with 15 coupled models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we demonstrate that the main drivers initiating WWBs are quantifiable physical processes rather than atmospheric stochastic signals. In this study, ensemble empirical mode decomposition (EEMD) from the Holo-Hilbert spectral analysis (HHSA) is used to decompose daily zonal winds over the western equatorial Pacific into seasonal, interannual and decadal components. The seasonal element, with prominent spectral peaks of less than 12 months, is not ENSO related, and we find it to be strongly associated with the East Asian monsoon (EAM) and cross-equatorial flow (CEF) over the Australian monsoon region. The CEF is directly related to the intensity of the Australian subtropical ridge (STR-I). Both the EAM and CEF are essential sources of these high-frequency winds over the western Pacific. In contrast, the interannual wind component is closely related to El Niño occurrences and usually peaks approximately two months prior to a typical El Niño event. Finally, the decadal element merely represents a long-term trend and thus has little to no relation to El Niño. We identified EAM- and CEF-induced westerly wind anomalies in December–January–February (DJF) and September–October–November (SON). However, these anomalies fade in March–April–May (MAM), potentially undermining the usual absence of WWBs in the boreal spring. Similar results are found in CMIP6 historical scenario data.

scholarly journals ANALISIS SPASIAL PENGARUH KEJADIAN EL NINO KUAT TAHUN 2015 DAN LA NINA LEMAH TAHUN 2016 TERHADAP KELEMBAPAN, ANGIN DAN CURAH HUJAN DI INDONESIA

2017 ◽  
Vol 18 (1) ◽  
pp. 33 ◽  
Author(s):  
Ibnu Athoillah ◽  
Rini Mariana Sibarani ◽  
Deassy Eirene Doloksaribu
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Observation Data ◽  
Positive Anomaly ◽  
Wet Season ◽  
Zonal Winds ◽  
La Nina ◽  
Meridional Winds ◽  
The Impact

IntisariKejadian El Nino Kuat tahun 2015 dan La Nina Lemah tahun 2016 sangat berpengaruh terhadap beberapa parameter cuaca di Indonesia seperti kelembapan udara, angin dan curah hujan. Dilihat dari kelembapan udara pada saat El Nino, kelembapan udara memiliki anomali negatif dan pada saat La Nina cenderung anomali positif. Dari pengaruhnya terhadap angin, saat El Nino angin zonal lebih dominan angin timuran, dan angin meridional lebih dominan angin selatan yang menyebabkan berkurangnya suplai uap air di Indonesia. Sedangkan saat La Nina, angin zonal lebih dominan baratan dan angin meridional lebih dominan dari utara. Pengaruh yang jelas terlihat dari adanya fenomena El Nino dan La Nina adalah kejadian hujan di wilayah Indonesia. Pola spasial kejadian hujan di wilayah Indonesia pada tahun 2015 dan tahun 2016 memperlihatkan pengaruh dari fenomena El Nino dan La Nina yang telah terjadi. Data hujan yang digunakan dalam tulisan ini adalah data observasi per 1 jam dari satelit TRMM pada tahun 2015, 2016 dan data historis dari tahun 2001 - 2014. Dari hasil analisis spasial menunjukkan bahwa kejadian El Nino mulai terlihat dampaknya pada musim kering yaitu berupa penurunan curah hujan di bawah normalnya sekitar 50 – 300 mm/bulan terjadi pada bulan Agustus hingga Oktober 2015 terutama di wilayah Indonesia bagian Selatan sedangkan pada musim basah November 2015 – Maret 2016 tidak terlalu signifikan dampaknya. Kejadian La Nina terlihat dampaknya pada bulan September – Desember tahun 2016 dimana terlihat adanya penambahan curah hujan dibandingkan normalnya sekitar 50 – 400 mm/bulan. AbtractThe strong El Nino in 2015 and the weak La Nina in 2016 are very influential on weather in Indonesia. In this case will be seen the influence of them againts relative humidifty, wind, and rainfall. The relative humidity during El Nino tends to be a negative and when La Nina tends to be a positive anomaly. Impact to the wind during El Nino, zonal winds are dominant northern and meridional winds are dominant southern which leads to reduced supply of water vapor in Indonesia. While during La Nina, zonal winds are dominant western and meridional winds are dominant northern. The obvious influence of El Nino and La Nina are the occurrence of rainfall in Indonesia. Spatial pattern of rainfall events in Indonesia can show the effects of the El Nino and La Nina. Rainfall data used in this paper are the observation data from TRMM Satellite hourly from 2001 – 2016. Data were analyzed by monthly and seasonal analysis. From the result of spatial analysis shows the impact of El Nino began on dry season. That is decrease of rainfall below the normal around 50 – 300 mm/month occurs in August to October 2015, especially in southern Indonesia. while in wet season November 2015 – March 2016 the impact is not significant. The impact of La Nina is seen in September – December 2016, where there is an increase of rainfall above the normal around 50 – 400 mm/month. 

scholarly journals FPI observations of nighttime mesospheric and thermospheric winds in China and their comparisons with HWM07

2013 ◽  
Vol 31 (8) ◽  
pp. 1365-1378 ◽  
Author(s):  
W. Yuan ◽  
X. Liu ◽  
J. Xu ◽  
Q. Zhou ◽  
G. Jiang ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Annual Variation ◽  
Middle Atmosphere ◽  
Geomagnetic Latitude ◽  
Meridional Wind ◽  
Central China ◽  
Horizontal Wind ◽  
Zonal Winds ◽  
Meridional Winds ◽  
First Time

Abstract. We analyzed the nighttime horizontal neutral winds in the middle atmosphere (~ 87 and ~ 98 km) and thermosphere (~ 250 km) derived from a Fabry–Perot interferometer (FPI), which was installed at Xinglong station (40.2° N, 117.4° E) in central China. The wind data covered the period from April 2010 to July 2012. We studied the annual, semiannual and terannual variations of the midnight winds at ~ 87 km, ~ 98 km and ~ 250 km for the first time and compared them with Horizontal Wind Model 2007 (HWM07). Our results show the following: (1) at ~ 87 km, both the observed and model zonal winds have similar phases in the annual and semiannual variations. However, the HWM07 amplitudes are much larger. (2) At ~ 98 km, the model shows strong eastward wind in the summer solstice, resulting in a large annual variation, while the observed strongest component is semiannual. The observation and model midnight meridional winds agree well. Both are equatorward throughout the year and have small amplitudes in the annual and semiannual variations. (3) There are large discrepancies between the observed and HWM07 winds at ~ 250 km. This discrepancy is largely due to the strong semiannual zonal wind in the model and the phase difference in the annual variation of the meridional wind. The FPI annual variation coincides with the results from Arecibo, which has similar geomagnetic latitude as Xinglong station. In General, the consistency of FPI winds with model winds is better at ~ 87 and ~ 98 km than that at ~ 250 km. We also studied the seasonally and monthly averaged nighttime winds. The most salient features include the following: (1) the seasonally averaged zonal winds at ~ 87 and ~ 98 km typically have small variations throughout the night. (2) The model zonal and meridional nighttime wind variations are typically much larger than those of observations at ~ 87 km and ~ 98 km. (3) At ~ 250 km, model zonal wind compares well with the observation in the winter. For spring and autumn, the model wind is more eastward before ~ 03:00 LT but more westward after. The observed nighttime zonal and meridional winds on average are close to zero in the summer and autumn, which indicates a lack of strong stable tides. The consistency of FPI zonal wind with model wind at ~ 250 km is better than the meridional wind.

scholarly journals The role of tropical volcanic eruptions in exacerbating Indian droughts

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Suvarna Fadnavis ◽  
Rolf Müller ◽  
Tanusri Chakraborty ◽  
T. P. Sabin ◽  
Anton Laakso ◽  
...  
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Volcanic Eruptions ◽  
Summer Monsoon Rainfall ◽  
Indian Region ◽  
Volcanic Plume ◽  
Kelvin Wave ◽  
Central Pacific ◽  
Climate Model Simulations

AbstractThe Indian summer monsoon rainfall (ISMR) is vital for the livelihood of millions of people in the Indian region; droughts caused by monsoon failures often resulted in famines. Large volcanic eruptions have been linked with reductions in ISMR, but the responsible mechanisms remain unclear. Here, using 145-year (1871–2016) records of volcanic eruptions and ISMR, we show that ISMR deficits prevail for two years after moderate and large (VEI > 3) tropical volcanic eruptions; this is not the case for extra-tropical eruptions. Moreover, tropical volcanic eruptions strengthen El Niño and weaken La Niña conditions, further enhancing Indian droughts. Using climate-model simulations of the 2011 Nabro volcanic eruption, we show that eruption induced an El Niño like warming in the central Pacific for two consecutive years due to Kelvin wave dissipation triggered by the eruption. This El Niño like warming in the central Pacific led to a precipitation reduction in the Indian region. In addition, solar dimming caused by the volcanic plume in 2011 reduced Indian rainfall.

scholarly journals Amplified risk of spatially compounding droughts during co-occurrences of modes of natural ocean variability

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jitendra Singh ◽  
Moetasim Ashfaq ◽  
Christopher B. Skinner ◽  
Weston B. Anderson ◽  
Deepti Singh
Keyword(s):  
El Niño ◽  
Global Economy ◽  
Food System ◽  
Climate Model ◽  
El Nino ◽  
Ocean Variability ◽  
Positive Indian Ocean Dipole ◽  
Precipitation Seasonality ◽  
Multiple Regions ◽  
Climate Model Simulations

AbstractSpatially compounding droughts over multiple regions pose amplifying pressures on the global food system, the reinsurance industry, and the global economy. Using observations and climate model simulations, we analyze the influence of various natural Ocean variability modes on the likelihood, extent, and severity of compound droughts across ten regions that have similar precipitation seasonality and cover important breadbaskets and vulnerable populations. Although a majority of compound droughts are associated with El Niños, a positive Indian Ocean Dipole, and cold phases of the Atlantic Niño and Tropical North Atlantic (TNA) can substantially modulate their characteristics. Cold TNA conditions have the largest amplifying effect on El Niño-related compound droughts. While the probability of compound droughts is ~3 times higher during El Niño conditions relative to neutral conditions, it is ~7 times higher when cold TNA and El Niño conditions co-occur. The probability of widespread and severe compound droughts is also amplified by a factor of ~3 and ~2.5 during these co-occurring modes relative to El Niño conditions alone. Our analysis demonstrates that co-occurrences of these modes result in widespread precipitation deficits across the tropics by inducing anomalous subsidence, and reducing lower-level moisture convergence over the study regions. Our results emphasize the need for considering interactions within the larger climate system in characterizing compound drought risks rather than focusing on teleconnections from individual modes. Understanding the physical drivers and characteristics of compound droughts has important implications for predicting their occurrence and characterizing their impacts on interconnected societal systems.

scholarly journals Characteristics of Stratospheric Winds over Jiuquan (41.1°N, 100.2°E) Using Rocketsonde Data in 1967–2004

2017 ◽  
Vol 34 (3) ◽  
pp. 657-667 ◽  
Author(s):  
Z. Sheng ◽  
J. W. Li ◽  
Y. Jiang ◽  
S. D. Zhou ◽  
W. L. Shi
Keyword(s):  
Zonal Wind ◽  
Middle Atmosphere ◽  
Correlation Coefficients ◽  
Meridional Wind ◽  
Horizontal Wind ◽  
Cycle Period ◽  
Observation Data ◽  
Wind Fields ◽  
Zonal Winds ◽  
Model Research

AbstractStratospheric winds play a significant role in middle atmosphere dynamics, model research, and carrier rocket experiments. For the first time, 65 sets of rocket sounding experiments conducted at Jiuquan (41.1°N, 100.2°E), China, from 1967 to 2004 are presented to study horizontal wind fields in the stratosphere. At a fixed height, wind speed obeys the lognormal distribution. Seasonal mean winds are westerly in winter and easterly in summer. In spring and autumn, zonal wind directions change from the upper to the lower stratosphere. The monthly zonal mean winds have an annual cycle period with large amplitudes at high altitudes. The correlation coefficients for zonal winds between observations and the Horizontal Wind Model (HWM) with all datasets are 0.7. The MERRA reanalysis is in good agreement with rocketsonde data according to the zonal winds comparison with a coefficient of 0.98. The sudden stratospheric warming is an important contribution to biases in the HWM, because it changes the zonal wind direction in the midlatitudes. Both the model and the reanalysis show dramatic meridional wind differences with the observation data.

Sign in / Sign up

Export Citation Format

Share Document