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 Aerosol meteorology of the Maritime Continent for the 2012 7SEAS southwest monsoon intensive study – Part 1: regional-scale phenomena

2016 ◽  
Vol 16 (22) ◽  
pp. 14041-14056 ◽  
Author(s):  
Jeffrey S. Reid ◽  
Peng Xian ◽  
Brent N. Holben ◽  
Edward J. Hyer ◽  
Elizabeth A. Reid ◽  
...  
Keyword(s):  
Biomass Burning ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Regional Scale ◽  
Intraseasonal Oscillation ◽  
Southwest Monsoon ◽  
Boreal Summer ◽  
Maritime Continent ◽  
Fire Activity

Abstract. The largest 7 Southeast Asian Studies (7SEAS) operation period within the Maritime Continent (MC) occurred in the August–September 2012 biomass burning season. Included was an enhanced deployment of Aerosol Robotic Network (AERONET) sun photometers, multiple lidars, and field measurements to observe transported smoke and pollution as it left the MC and entered the southwest monsoon trough. Here we describe the nature of the overall 2012 southwest monsoon (SWM) and biomass burning season to give context to the 2012 deployment. The MC in 2012 was in a slightly warm El Niño/Southern Oscillation (ENSO) phase and with spatially typical burning activity. However, overall fire counts for 2012 were 10 % lower than the Reid et al. (2012) baseline, with regions of significant departures from this norm, ranging from southern Sumatra (+30 %) to southern Kalimantan (−42 %). Fire activity and monsoonal flows for the dominant burning regions were modulated by a series of intraseasonal oscillation events (e.g., Madden–Julian Oscillation, or MJO, and boreal summer intraseasonal oscillation, or BSISO). As is typical, fire activity systematically progressed eastward over time, starting with central Sumatran fire activity in June related to a moderately strong MJO event which brought drier air from the Indian Ocean aloft and enhanced monsoonal flow. Further burning in Sumatra and Kalimantan Borneo occurred in a series of significant events from early August to a peak in the first week of October, ending when the monsoon started to migrate back to its wintertime northeastern flow conditions in mid-October. Significant monsoonal enhancements and flow reversals collinear with tropical cyclone (TC) activity and easterly waves were also observed. Islands of the eastern MC, including Sulawesi, Java, and Timor, showed less sensitivity to monsoonal variation, with slowly increasing fire activity that also peaked in early October but lingered into November. Interestingly, even though fire counts were middling, resultant AERONET 500 nm aerosol optical thickness (AOT) from fire activity was high, with maximums of 3.6 and 5.6 in the Sumatra and Kalimantan source regions at the end of the burning season and an average of ∼ 1. AOTs could also be high at receptor sites, with a mean and maximum of 0.57 and 1.24 in Singapore and 0.61 and 0.8 in Kuching Sarawak. Ultimately, outside of the extreme 2015 El Niño event, average AERONET AOT values were higher than any other time since sites were established. Thus, while satellite fire data, models, and AERONET all qualitatively agree on the nature of smoke production and transport, the MC's complex environment resulted in clear differences in quantitative interpretation of these datasets.

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.

scholarly journals Atmospheric Rivers over the Northwestern Pacific: Climatology and Interannual Variability

2017 ◽  
Vol 30 (15) ◽  
pp. 5605-5619 ◽  
Author(s):  
Youichi Kamae ◽  
Wei Mei ◽  
Shang-Ping Xie ◽  
Moeka Naoi ◽  
Hiroaki Ueda
Keyword(s):  
Water Vapor ◽  
Interannual Variability ◽  
El Niño ◽  
El Nino ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Boreal Summer ◽  
Northwestern Pacific ◽  
Atmospheric Rivers ◽  
Low Level

Atmospheric rivers (ARs), conduits of intense water vapor transport in the midlatitudes, are critically important for water resources and heavy rainfall events over the west coast of North America, Europe, and Africa. ARs are also frequently observed over the northwestern Pacific (NWP) during boreal summer but have not been studied comprehensively. Here the climatology, seasonal variation, interannual variability, and predictability of NWP ARs (NWPARs) are examined by using a large ensemble, high-resolution atmospheric general circulation model (AGCM) simulation and a global atmospheric reanalysis. The AGCM captures general characteristics of climatology and variability compared to the reanalysis, suggesting a strong sea surface temperature (SST) effect on NWPARs. The summertime NWPAR occurrences are tightly related to El Niño–Southern Oscillation (ENSO) in the preceding winter through Indo–western Pacific Ocean capacitor (IPOC) effects. An enhanced East Asian summer monsoon and a low-level anticyclonic anomaly over the tropical western North Pacific in the post–El Niño summer reinforce low-level water vapor transport from the tropics with increased occurrence of NWPARs. The strong coupling with ENSO and IPOC indicates a high predictability of anomalous summertime NWPAR activity.

scholarly journals Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10123-10139 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Ocean Atmosphere ◽  
Sst Anomalies

El Niño–Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean–atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean–Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post–El Niño spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean–atmosphere coupling.

The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms

2019 ◽  
Vol 32 (22) ◽  
pp. 7643-7661 ◽  
Author(s):  
Dillon J. Amaya ◽  
Yu Kosaka ◽  
Wenyu Zhou ◽  
Yu Zhang ◽  
Shang-Ping Xie ◽  
...  
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Deep Convection ◽  
Boreal Summer ◽  
Enso Events ◽  
The North ◽  
The North Pacific

Abstract Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales.

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.

Highly Variable El Niño–Southern Oscillation Throughout the Holocene

Science ◽  
2013 ◽  
Vol 339 (6115) ◽  
pp. 67-70 ◽  
Author(s):  
Kim M. Cobb ◽  
Niko Westphal ◽  
Hussein R. Sayani ◽  
Jordan T. Watson ◽  
Emanuele Di Lorenzo ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Climate ◽  
Internal Variability ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Line Islands ◽  
Insolation Forcing ◽  
Fossil Coral

The El Niño–Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some models that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.

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 A New Perspective on the Excitation of Low-Tropospheric Mixed Rossby–Gravity Waves in Association with Energy Dispersion

2012 ◽  
Vol 69 (4) ◽  
pp. 1397-1403 ◽  
Author(s):  
Guanghua Chen ◽  
Chi-Yung Tam
Keyword(s):  
El Niño ◽  
El Nino ◽  
Wave Train ◽  
La Niña ◽  
Boreal Summer ◽  
Mean Flow ◽  
Energy Dispersion ◽  
Low Level ◽  
La Nina ◽  
Equatorial Wave

Abstract This study investigates the synoptic-scale equatorial response to Rossby wave energy dispersion associated with off-equatorial wave activity sources and proposes a new mechanism for triggering low-level mixed Rossby–gravity (MRG) waves. A case study based on observations in boreal summer 2002 reveals that a vortex related to tropical cyclogenesis generated a coherent wave train through southeastward energy dispersion. The southeastward-propagating energy packet gave rise to the equatorial atmospheric response with a temporal scale similar to the wave train and with a structure consistent with the equatorially trapped MRG wave. A baroclinic multilevel anomaly model is employed to verify the excitation of MRG associated with the energy dispersion originating outside of the equatorial region and to explore the discrepancy in the equatorial responses under the different background flows corresponding to El Niño and La Niña. The results show that the prevalence of the low-level westerly flow, the associated zonal wind convergence, and the easterly vertical wind shear can be more favorable for the enhancement of southeastward-propagating energy dispersion and equatorial MRG response in the low troposphere during El Niño than those during La Niña. In addition, the strength of the mean flow can strongly affect the extent of equatorial wave response and modulate its phase and group velocity due to the Doppler shift effect.

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