scholarly journals Northward Propagation, Initiation, and Termination of Boreal Summer Intraseasonal Oscillations in a Zonally Symmetric Model

2019 ◽  
Vol 76 (2) ◽  
pp. 639-668 ◽  
Author(s):  
Qiu Yang ◽  
Boualem Khouider ◽  
Andrew J. Majda ◽  
Michèle De La Chevrotière
Keyword(s):  
Warm Pool ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Symmetric Model ◽  
The North ◽  
Beta Effect ◽  
Northward Propagation ◽  
Meridional Winds ◽  
Intraseasonal Oscillations ◽  
Precipitation Anomalies

AbstractA simple multilayer zonally symmetric model, using a multicloud convective parameterization and coupled to a dynamical bulk atmospheric boundary layer, is used here to simulate boreal summer intraseasonal oscillations (BSISO) in the summer monsoon trough and elucidate the underlying main physical mechanisms responsible for their initiation, propagation, and termination. Northward-moving precipitating events initiated near the equator propagate northward at roughly 1° day−1 and terminate near 20°N. Unlike earlier findings, the northward propagation of precipitation anomalies in this model is due to the propagation of positive moisture anomalies in the northward direction, resulting from an asymmetry in the meridional velocity induced by the beta effect. From a moisture-budget perspective, advection constitutes a biased intrusion of dry air into the convection center, forcing new convection events to form north of the wave disturbance, while moisture convergence supplies the precipitation sink. The BSISO events are initiated near the equator when the competing effects between first-baroclinic divergence and second-baroclinic convergence, induced by the descending branch of the Hadley cell and in situ congestus heating, respectively, become favorable to convective intensification. The termination often near 20°N and halfway stalling of these precipitating events occur when the asymmetry in the first-baroclinic meridional winds weakens and when the negative moisture gradient to the north of the convection center becomes too strong as the anomaly exits the imposed warm pool domain.

Subseasonal SST Variability in the Tropical Eastern North Pacific during Boreal Summer

2008 ◽  
Vol 21 (17) ◽  
pp. 4149-4167 ◽  
Author(s):  
Eric D. Maloney ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen
Keyword(s):  
Costa Rica ◽  
Warm Pool ◽  
Boreal Summer ◽  
Sst Variability ◽  
East Pacific ◽  
Pacific Warm Pool ◽  
Northern Edge ◽  
Precipitation Anomalies ◽  
Sst Anomalies ◽  
Costa Rica Dome

Abstract Boreal summer intraseasonal (30–90-day time scale) sea surface temperature (SST) variability in the east Pacific warm pool is examined using Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) sea surface temperatures during 1998–2005. Intraseasonal SST variance maximizes at two locations in the warm pool: in the vicinity of 9°N, 92°W near the Costa Rica Dome and near the northern edge of the warm pool in the vicinity of 19°N, 108°W. Both locations exhibit a significant spectral peak at 50–60-day periods, time scales characteristic of the Madden–Julian oscillation (MJO). Complex empirical orthogonal function (CEOF) and spectra coherence analyses are used to show that boreal summer intraseasonal SST anomalies are coherent with precipitation anomalies across the east Pacific warm pool. Spatial variations of phase are modest across the warm pool, although evidence exists for the northward progression of intraseasonal SST and precipitation anomalies. Intraseasonal SSTs at the north edge of the warm pool lag those in the vicinity of the Costa Rica Dome by about 1 week. The MJO explains 30%–40% of the variance of intraseasonal SST anomalies in the east Pacific warm pool during boreal summer. Peak-to-peak SST variations of 0.8°–1.0°C occur during MJO events. SST is approximately in quadrature with MJO precipitation, with suppressed (enhanced) MJO precipitation anomalies leading positive (negative) SST anomalies by 7–10 days. Consistent with the CEOF and coherence analyses, MJO-related SST and precipitation anomalies near the Costa Rica Dome lead those at the northern edge of the warm pool by about 1 week.

scholarly journals A Precipitation-Based Index for Tropical Intraseasonal Oscillations

2020 ◽  
Vol 33 (3) ◽  
pp. 805-823 ◽  
Author(s):  
Shuguang Wang
Keyword(s):  
Real Time ◽  
Decadal Variability ◽  
Intraseasonal Oscillation ◽  
Longwave Radiation ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Eof Analysis ◽  
Intraseasonal Oscillations ◽  
Precipitation Anomalies ◽  
Tropical Intraseasonal Oscillations

AbstractCharacteristic patterns of precipitation-associated tropical intraseasonal oscillations, including the Madden–Julian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO), are identified using local empirical orthogonal function (EOF) analysis of the Tropical Rainfall Measuring Mission (TRMM) precipitation data as a function of the day of the year. The explained variances of the EOF analysis show two peaks across the year: one in the middle of the boreal winter corresponding to the MJO and the other in the middle of summer corresponding to the BSISO. Comparing the fractional variance indicates that the BSISO is more coherent than the MJO during the TRMM period. Similar EOF analyses with the outgoing longwave radiation (OLR) confirm this result and indicate that the BSISO is less coherent before the TRMM era (1979–98). In contrast, the MJO exhibits much less decadal variability. A precipitation-based index for tropical intraseasonal oscillation (PII) is derived by projecting bandpass-filtered precipitation anomalies to the two leading EOFs as a function of day of the year. A real-time version that approximates the PII is further developed using precipitation anomalies without any bandpass filtering. It is further shown that this real-time PII index may be used to diagnose precipitation in the subseasonal forecasts.

Interactions between Boreal Summer Intraseasonal Oscillations and Synoptic-Scale Disturbances over the Western North Pacific. Part II: Apparent Heat and Moisture Sources and Eddy Momentum Transport*

2011 ◽  
Vol 24 (3) ◽  
pp. 942-961 ◽  
Author(s):  
Pang-Chi Hsu ◽  
Tim Li
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Wave Train ◽  
Intraseasonal Oscillation ◽  
Momentum Transport ◽  
Boreal Summer ◽  
Synoptic Scale ◽  
Mean Flow ◽  
The North ◽  
Intraseasonal Oscillations

Abstract The interactions between the boreal summer intraseasonal oscillation (ISO) and synoptic-scale variability (SSV) are investigated by diagnosing the atmospheric apparent heat source (Q1), apparent moisture sink (Q2), and eddy momentum transport. It is found that the synoptic Q1 and Q2 heating (cooling) anomalies are in phase with cyclonic (anticyclonic) vorticity disturbances, aligned in a southeast–northwest-oriented wave train pattern over the western North Pacific (WNP). The wave train is well organized and strengthened (loosely organized and weakened) during the ISO active (suppressed) phase. The nonlinearly rectified Q1 and Q2 fields due to the eddy–mean flow interaction account for 10%–30% of the total intraseasonal Q1 and Q2 variabilities over the WNP. During the ISO active (suppressed) phase, the nonlinearly rectified intraseasonal Q1 and Q2 heating (cooling) appear to the northwest of the ISO enhanced (suppressed) convection center, favoring the northwestward propagation of the ISO. A diagnosis of the zonal momentum budget shows that the eddy momentum flux convergence forces an intraseasonal westerly (easterly) tendency to the north of the ISO westerly (easterly) center during the ISO active (suppressed) phase. As a result, the eddy momentum transport may contribute to the northward propagation of the boreal summer ISO over the WNP.

A possible new mechanism for northward propagation of boreal summer intraseasonal oscillations based on TRMM and MERRA reanalysis

2012 ◽  
Vol 40 (7-8) ◽  
pp. 1611-1624 ◽  
Author(s):  
S. Abhik ◽  
M. Halder ◽  
P. Mukhopadhyay ◽  
X. Jiang ◽  
B. N. Goswami
Keyword(s):  
Boreal Summer ◽  
Northward Propagation ◽  
Intraseasonal Oscillations

scholarly journals On the Weakening of Northward Propagation of Intraseasonal Oscillations During Positive Indian Ocean Dipole Events.

2021 ◽  
Author(s):  
Aditya Kottapalli ◽  
Vinayachandran P N
Keyword(s):  
Indian Ocean ◽  
Zonal Wind ◽  
Indian Ocean Dipole ◽  
Monsoon Rainfall ◽  
Equatorial Indian Ocean ◽  
Summer Monsoon Rainfall ◽  
Boreal Summer ◽  
Positive Indian Ocean Dipole ◽  
Northward Propagation ◽  
Intraseasonal Oscillations

Abstract The northward propagation of intraseasonal oscillations (ISO) is one of the major modes of variability in the tropics during boreal summer, associated with active and break spells of monsoon rainfall over the Indian region, and modulate the Indian summer monsoon rainfall (ISMR). The northward march starts close to the equator over warm waters of the Indian Ocean and continues till the foothills of the Himalayas. The northward propagations tend to be weaker during positive Indian Ocean Dipole (pIOD) years. We have used the "moisture mode" framework to understand the processes responsible for the weakening of northward propagations during IOD years. Our analyses show that moistening caused by the horizontal advection was the major contributor for the northward propagations during negative IOD (nIOD) years, and its amplitude is much smaller during pIOD years. The reduction in the zonal advection during pIOD is responsible for the weakening of northward propagations. Also, the mean structure of entropy between 925hpa – 500hpa levels remained similar over most of the monsoon region across the contrasting IOD years. The reason for weaker northward propagations can be attributed to the weaker zonal wind perturbations at intraseasonal timescales. The weaker zonal wind perturbations during ISO events in pIOD years owing to cooler sea surface temperatures (SST) in the South-East Equatorial Indian Ocean (SEIO) and warmer West Equatorial Indian Ocean (WEIO) and South-East Arabian Sea (SEAS) is proposed to be the possible reason for the weakening of northward propagations during pIOD years.

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

2011 ◽  
Vol 139 (8) ◽  
pp. 2421-2438 ◽  
Author(s):  
Ruiqiang Ding ◽  
Jianping Li ◽  
Kyong-Hwan Seo
Keyword(s):  
Spatial Distribution ◽  
Intraseasonal Variability ◽  
Intraseasonal Oscillation ◽  
Longwave Radiation ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Potential Predictability ◽  
The North ◽  
Intraseasonal Oscillations ◽  
The North Pacific

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 relatively high over the North Pacific, North Atlantic, southern Africa, and South America. The spatial distribution of the limit during winter is approximately the opposite of that during summer. For strong phases of ISO convection, the initial error of the BSISO shows a more rapid growth than that of the MJO. The error growth is rapid when the BSISO and MJO enter the decaying phase (when ISO signals are weak), whereas it is slow when convection anomalies of the BSISO and MJO are located in upstream regions (when ISO signals are strong).

scholarly journals Mechanism of the Northward-Propagating Intraseasonal Oscillation: Insights from a Zonally Symmetric Model*

2005 ◽  
Vol 18 (7) ◽  
pp. 952-972 ◽  
Author(s):  
Hae-Kyung Lee Drbohlav ◽  
Bin Wang
Keyword(s):  
Boundary Layer ◽  
Wind Shear ◽  
Indian Monsoon ◽  
Intraseasonal Oscillation ◽  
Vertical Wind Shear ◽  
Monsoon Trough ◽  
Symmetric Model ◽  
Free Troposphere ◽  
The North ◽  
Northward Propagation

Abstract The propagation and initiation mechanisms of the boreal summer intraseasonal oscillation (BSISO) in the south Asian summer monsoon are examined with a zonally symmetric atmospheric model. In the axially symmetric model the effects of zonally propagating atmospheric waves are intentionally excluded. The model specifies mean flows and depicts the lowest baroclinic mode and a barotropic mode in the free troposphere. The two vertical modes are coupled by the time-mean vertical wind shear. The model atmosphere produces a 15–20-day oscillation, which is characterized by northward propagation of convection from south of the equator to the Indian monsoon trough region and a reinitiation of convection in the region between 10°S and the equator. The northward propagation in the model is produced by the free troposphere barotropic divergence, which leads convection by about a quarter of a cycle. The vertical advection of summer-mean easterly vertical wind shear by perturbation vertical motion inside the convective region induces barotropic divergence (convergence) to the north (south) of convection. This barotropic divergence triggers the moisture convergence in the boundary layer to the north of convection, causing the northward propagation of precipitation. The development of convection in the Southern Hemisphere near the equator is also produced by the development of the barotropic divergence in the free troposphere. When the BSISO convection is located in the Indian monsoon trough region, it creates Hadley-type anomalous circulation. This Hadley-type circulation interacts with the monsoon flow through the meridional and vertical advections creating anomalous barotropic divergence and boundary layer convergence.

scholarly journals A Regime Shift in the Interhemispheric Teleconnection between the Yellow and East China Seas and The Southeastern Tropical Pacific in The Southern Hemisphere during The Boreal Summer

2021 ◽  
Author(s):  
Yong Sun Kim ◽  
Minho Kwon ◽  
Eui-Seok Chung ◽  
Sang-Wook Yeh ◽  
Jin-Yong Jeong ◽  
...  
Keyword(s):  
Regime Shift ◽  
Tropical Pacific ◽  
Boreal Summer ◽  
The North ◽  
Southeastern Pacific ◽  
Basin Scale ◽  
Precipitation Anomalies ◽  
Statistical Estimations ◽  
The Tropical Pacific

Abstract Through statistical estimations on reconstructed datasets for the period 1982−2020 after removing a long-term trend, we observed that there was a drastic regime shift in the early summer’s connection between the YECS and the tropical Pacific in the early 2000s. The summer YECS SSTs had seemed to be modulated by local oceanic and atmospheric processes along with their marginal coupling to the tropical Pacific during the pre-2003 period before the regime shift. In contrast, an interhemispheric YECS−tropical southeastern Pacific (SEP) coupling appeared after the regime shift. This teleconnection was at least partially attributed to a reduced El Niño signature in the tropical Pacific, which favors the emergence of the South Pacific meridional mode (SPMM) independently from ENSO signals. Precipitation anomalies in the western tropical Pacific act as an atmospheric bridge to mediate the air-sea interacted variability associated with the SPMM into the North Pacific. The susceptibility of the YECS to atmospheric forcing may highlight the role of SST over the YECS as a potential indicator of basin-scale climate changes.

scholarly journals A Precipitation Seesaw Mode between Northeast Asia and Siberia in Summer Caused by Rossby Waves over the Eurasian Continent

2008 ◽  
Vol 21 (11) ◽  
pp. 2401-2419 ◽  
Author(s):  
Koki Iwao ◽  
Masaaki Takahashi
Keyword(s):  
Rossby Waves ◽  
Northeast Asia ◽  
Low Frequency ◽  
Northern Eurasia ◽  
The North ◽  
Meridional Winds ◽  
Low Pass ◽  
Precipitation Anomalies ◽  
The Difference ◽  
Stretching Effect

Abstract There is a dominant seesaw pattern in summertime precipitation between northeast Asia and Siberia. Examined here is a mechanism of the seesaw mode, focusing on quasi-stationary Rossby waves propagating on two upper-tropospheric waveguides along the Asian jet and over northern Eurasia. Empirical orthogonal function (EOF) analysis to the low-frequency (10-day low-pass filtered) variation during summer reveals wave-propagation patterns on both of the waveguides. The time evolution of the two composite fields, constructed using the obtained EOF modes for each phase of the seesaw mode, was investigated by the wave-activity flux. In both composite fields, eastward-propagating Rossby waves originating from the North Atlantic–European sector branch off around eastern Europe onto the two waveguides, which become out of phase toward the east because of the difference in longitudinal wavelengths along them. This results in opposite phase anomalies of meridional winds over northeast Asia and Siberia. Budget analyses of vorticity, heat, and water vapor on a day with significant wave patterns along the two waveguides revealed the main balances; the zonal advection of vorticity anomalies around the tropopause was partly balanced by an anomalous stretching effect over these two regions, and the adiabatic heating anomalies in the midtroposphere associated with the stretching effect around the tropopause were balanced with diabatic heating anomalies, explained by condensation heating related to the precipitation anomalies. These events occur frequently in July, when the climatological precipitation is the largest, particularly over northeast Asia.

scholarly journals Stochastic Atmospheric Forcing as a Cause of Greenland Climate Transitions

2015 ◽  
Vol 28 (19) ◽  
pp. 7741-7763 ◽  
Author(s):  
Hannah Kleppin ◽  
Markus Jochum ◽  
Bette Otto-Bliesner ◽  
Christine A. Shields ◽  
Stephen Yeager
Keyword(s):  
Sea Ice ◽  
Warm Pool ◽  
Atmospheric Forcing ◽  
Meridional Heat Transport ◽  
Sea Ice Concentration ◽  
Sea Level Pressure ◽  
Climate System Model ◽  
The North ◽  
Ice Concentration ◽  
Precipitation Anomalies

Abstract An unforced simulation of the Community Climate System Model, version 4 (CCSM4), is found to have Greenland warming and cooling events that resemble Dansgaard–Oeschger cycles in pattern and magnitude. With the caveat that only three transitions were available to be analyzed, it is found that the transitions are triggered by stochastic atmospheric forcing. The atmospheric anomalies change the strength of the subpolar gyre, leading to a change in Labrador Sea sea ice concentration and meridional heat transport. The changed climate state is maintained over centuries through the feedback between sea ice and sea level pressure in the North Atlantic. Indications that the initial atmospheric pressure anomalies are preceded by precipitation anomalies in the western Pacific warm pool are discussed. The full evolution of the anomalous climate state depends crucially on the climatic background state.

Sign in / Sign up

Export Citation Format

Share Document