Ruiqiang Ding

The Victoria mode in the North Pacific linking extratropical sea level pressure variations to ENSO

The Victoria mode (VM) represents the second dominant mode (empirical orthogonal function, EOF2) of North Pacific variability, independent of the Pacific Decadal Oscillation and is defined as the EOF2 of SST anomalies in the North Pacific poleward of 20°N. The present study indicates that the VM is closely linked to the development of El Nino–Southern Oscillation (ENSO). The VM may effectively act as an ocean bridge (or conduit) through which the extratropical atmospheric variability in the North Pacific influences ENSO. The VM can trigger the onset of ENSO via the following two dominant processes: (1) surface air-sea coupling associated with the VM in the subtropical/tropical Pacific and (2) evolution of subsurface ocean temperature anomalies along the equator associated with the VM. These two processes may force sufficient surface warming to occur in the central eastern equatorial Pacific from spring to summer, which in turn initiates an ENSO event. The VM influence on ENSO relies on a basin-scale air-sea interaction dynamic, as opposed to more local-scale dynamics typically associated with the seasonal footprinting mechanism or Pacific meridional mode. The majority of VM events are followed by ENSO events. These ENSO events triggered by VM include El Nino Modoki (EM) as well as conventional El Nino. There is no evidence that the VM tends to be more conducive to the initialization of EM than conventional El Nino.

Predictability of the Madden–Julian Oscillation Estimated Using Observational Data

Abstract Existing numerical models produce large error in simulating the Madden–Julian oscillation (MJO), thereby underestimating its predictability. In this paper, the predictability limit of the MJO is determined by the nonlinear local Lyapunov exponent approach, which provides an estimate of atmospheric predictability based on the observational data. The results show that the predictability limit of the MJO obtained from the bandpass-filtered (30–80 days) outgoing longwave radiation and wind fields, which serves as an empirical estimate of the theoretical potential predictability of the MJO, can exceed 5 weeks, which is well above the 1-week predictability of background noise caused by bandpass filtering. In contrast, a real-time analysis of MJO predictability using the real-time multivariate MJO (RMM) index, as introduced by Wheeler and Hendon, reveals a predictability limit of about 3 weeks. The findings reported here raise the possibility of obtaining a higher predictability limit in real-time predi...

Estimate of the Predictability of Boreal Summer and Winter Intraseasonal Oscillations from Observations

AbstractTropical intraseasonal variability (TISV) shows two dominant modes: the boreal winter Madden–Julian oscillation (MJO) and the boreal summer intraseasonal oscillation (BSISO). The two modes differ in intensity, frequency, and movement, thereby presumably indicating different predictabilities. This paper investigates differences in the predictability limits of the BSISO and the boreal winter MJO based on observational data. The results show that the potential predictability limit of the BSISO obtained from bandpass-filtered (30–80 days) outgoing longwave radiation (OLR), 850-hPa winds, and 200-hPa velocity potential is close to 5 weeks, comparable to that of the boreal winter MJO. Despite the similarity between the potential predictability limits of the BSISO and MJO, the spatial distribution of the potential predictability limit of the TISV during summer is very different from that during winter. During summer, the limit is relatively low over regions where the TISV is most active, whereas it is re...

Influence of the North Pacific Victoria mode on the Pacific ITCZ summer precipitation

This study demonstrates the close connection between the second dominant mode of spring sea surface temperature anomalies (SSTAs) in the North Pacific poleward of 20°N, referred to as the Victoria mode (VM), and the Pacific Intertropical Convergence Zone (ITCZ) precipitation during the following summer. Our analysis shows that strong positive VM cases are followed by positive precipitation anomalies over the central-eastern Pacific ITCZ region, in association with negative precipitation anomalies over the ITCZ regions of the tropical western Pacific and eastern North Pacific. The hypothesized physical mechanism through which the spring VM induces the Pacific ITCZ summer precipitation is similar to but slightly different from the seasonal footprinting mechanism. During strong positive VM cases, SSTAs in the subtropics associated with the spring VM persist until summer and develop toward the equator, where low-level convergence and divergence caused by SSTA gradients give rise to enhanced precipitation over the central-eastern Pacific ITCZ region and to reduced precipitation over the ITCZ regions of the tropical western Pacific and eastern North Pacific. The thermodynamic ocean-atmosphere coupling between the ITCZ and SSTAs associated with the VM may play a vital role in the initiation of El Nino–Southern Oscillation (ENSO) events. The VM influence on tropical Pacific summer precipitation can be passed on to the next year through its influence on ENSO. A VM-based linear model is established to predict the tropical Pacific summer precipitation, which yields skillful forecasts for summer precipitation across almost the entire tropical Pacific.

A connection from Arctic stratospheric ozone to El Niño-Southern oscillation

Antarctic stratospheric ozone depletion is thought to influence the Southern Hemisphere tropospheric climate. Recently, Arctic stratospheric ozone (ASO) variations have been found to affect the middle-high latitude tropospheric climate in the Northern Hemisphere. This paper demonstrates that the impact of ASO can extend to the tropics, with the ASO variations leading El Nino-Southern Oscillation (ENSO) events by about 20 months. Using observations, analysis, and simulations, the connection between ASO and ENSO is established by combining the high-latitude stratosphere to troposphere pathway with the extratropical to tropical climate teleconnection. This shows that the ASO radiative anomalies influence the North Pacific Oscillation (NPO), and the anomalous NPO and induced Victoria Mode anomalies link to the North Pacific circulation that then influences ENSO. Our results imply that incorporating realistic and time-varying ASO into climate system models may help to improve ENSO predictions.

The Application of Nonlinear Local Lyapunov Vectors to Ensemble Predictions in Lorenz Systems

Nonlinear local Lyapunov vectors (NLLVs) are developed to indicate orthogonal directions in phase space with different perturbation growth rates. In particular, the first few NLLVs are considered to be an appropriate orthogonal basis for the fast-growing subspace. In this paper, the NLLV method is used to generate initial perturbations and implement ensemble forecasts in simple nonlinear models (the Lorenz63 and Lorenz96 models) to explore the validity of the NLLV method. The performance of the NLLV method is compared comprehensively and systematically with other methods such as the bred vector (BV) and the random perturbation (Monte Carlo) methods. In experiments using the Lorenz63 model, the leading NLLV (LNLLV) captured a more precise direction, and with a faster growthrate, than any individualbred vector. It may be the larger projectionon fastest-growing analysiserrors that causes the improved performance of the new method. Regarding the Lorenz96 model, two practical measures—namely the spread‐skill relationship and the Brier score—were used to assess the reliability and resolution of these ensemble schemes. Overall, the ensemble spread of NLLVs is more consistent with the errors of the ensemble mean,which indicatesthe better performanceof NLLVs in simulating the evolution of analysiserrors.Inaddition,theNLLVsperformsignificantlybetterthantheBVsintermsofreliabilityandthe random perturbations in resolution.

Decadal and seasonal dependence of North Pacific sea surface temperature persistence

[1] Decadal and seasonal dependence of the persistence characteristics of area-averaged sea surface temperature (SST) anomalies in the North Pacific (150E140W, 20N60N) are investigated using two different SST data sets for the period 1948–2005. It is found that a persistence barrier exists around July–September (especially in September). This July–September persistence barrier is accompanied by a summer decline in the wind stress. The results confirm the existence of the July–September persistence barrier in the North Pacific SST discovered by Namias and Born (1970). Besides the seasonal change, North Pacific SST persistence also exhibits a pronounced decadal change. Taking all calendar months into account, North Pacific SST persistence is relatively strong from the mid-1950s to the mid-1960s but then weak from the mid-1960s to the mid-1980s, and becomes stronger again from the mid-1980s until the mid-1990s, after which it tends to become weak again. The recurrence of SST anomalies from one winter to the next is obvious from the mid-1950s to mid-1960s, but no obvious recurrence occurs after the mid-1960s. Decadal changes of the PacificNorth America (PNA) pattern, the SST-clouds feedback, and the Southern Oscillation Index (SOI) are found to be related to those of North Pacific SST persistence. The PNA index shows a significant upward trend after the 1980s. Besides, the PNA pattern also exhibits a high persistence in winter from the mid-1980s to the mid-1990s. These changes of PNA pattern are favorable to the occurrence of strong SST persistence in winter from the mid-1980s to the mid-1990s. In summer, the positive feedback between the marine boundary clouds and SST enhances the SST persistence in the North Pacific. It is found that the positive feedback between the SST and clouds in the North Pacific during summer becomes stronger from the mid-1980s to the mid-1990s, which would contribute to the longer SST persistence in summer from the mid-1980s to the mid-1990s. The SOI shows negative correlation with the North Pacific SST persistence and the PNA index, indicating the remote forcing of ENSO on the North Pacific climate change. In addition, the high north Pacific SST persistence from the mid-1980s to the mid-1990s coincides with the warm phase of the Pacific Decadal Oscillation (PDO). We concluded that the changes in the tropical SST or the PDO phase might explain the origin of decadal changes of North Pacific SST persistence.

Western tropical Pacific multidecadal variability forced by the Atlantic multidecadal oscillation

Observational analysis suggests that the western tropical Pacific (WTP) sea surface temperature (SST) shows predominant variability over multidecadal time scales, which is unlikely to be explained by the Interdecadal Pacific Oscillation. Here we show that this variability is largely explained by the remote Atlantic multidecadal oscillation (AMO). A suite of Atlantic Pacemaker experiments successfully reproduces the WTP multidecadal variability and the AMO–WTP SST connection. The AMO warm SST anomaly generates an atmospheric teleconnection to the North Pacific, which weakens the Aleutian low and subtropical North Pacific westerlies. The wind changes induce a subtropical North Pacific SST warming through wind–evaporation–SST effect, and in response to this warming, the surface winds converge towards the subtropical North Pacific from the tropics, leading to anomalous cyclonic circulation and low pressure over the WTP region. The warm SST anomaly further develops due to the SST–sea level pressure–cloud–longwave radiation positive feedback. Our findings suggest that the Atlantic Ocean acts as a key pacemaker for the western Pacific decadal climate variability.

Strengthening relationship between ENSO and western Russian summer surface temperature

Western Russia (WR) experienced an extremely hot summer in 2010 that caused tremendous social and economic losses. The WR summer surface temperature (WRST) in the observational record is characterized by substantial interannual variability superimposed on the secular warming trend. Analysis of the 130 year observational record reveals that a strong and significant inverse relationship between WRST interannual variability and the tropical El Nino–Southern Oscillation (ENSO) has emerged during the past three decades. The ENSO influence on the summer extratropical atmospheric circulation was weak before 1980 but became strong and significant afterward, showing a structure similar to the East Atlantic/WR teleconnection pattern. This pattern is associated with rising/falling upper level geopotential height over WR, which leads to the warming/cooling of surface and tropospheric air temperatures. Numerical simulations from a theoretical linear baroclinic model and Atmospheric Model Intercomparison Project models further suggest that the enhancement of the ENSO teleconnection to WR may be attributable to a change in the ENSO-related tropical thermal forcing. A tripole-type rainfall anomaly pattern over tropical Pacific and Atlantic is found to be associated with ENSO in the past three decades. The tripole heating pattern can excite a Rossby wave that extends northwestward reachingWR and is necessary for the strong influence of ENSO on WR summer climate.

Linking a sea level pressure anomaly dipole over North America to the central Pacific El Niño

This study demonstrates the close connection between the north–south dipole pattern of sea level pressure anomalies over northeastern North America to the western tropical North Atlantic, referred to as the North American dipole (NAD), and the central Pacific (CP)-type El Niño a year later. In contrast to other ENSO precursors, such as the North Pacific Oscillation (NPO) and Pacific–North America (PNA) pattern, the NAD appears more closely related to the CP-type El Niño than to the eastern Pacific (EP)-type El Niño, indicating that the NAD may serve as a unique precursor for the CP El Niño. The wintertime NAD induces sea surface temperature anomalies in the northern tropical Atlantic (NTA), which subsequently play an important role in developing the CP El Niño-like pattern in the tropical Pacific over the course of the following year. It appears that the NAD influence on CP El Niño involves air–sea interaction over several major basins, including the subtropical/tropical Pacific and the NTA. Additional analysis indicates that the correlation of either the NAD index or the NPO index with the CP El Niño state a year later depends on the status of the other index. When the wintertime NAD index is of the opposite sign to the simultaneous NPO index, the correlation of the NAD or NPO index with the Niño4 index becomes much weaker.