Tropical intraseasonal oscillations in CFSv2 during Boreal summer and winter

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.

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Kernel Analog Forecasting of Tropical Intraseasonal Oscillations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0147.1 ◽

2017 ◽

Vol 74 (4) ◽

pp. 1321-1342 ◽

Cited By ~ 8

Author(s):

Romeo Alexander ◽

Zhizhen Zhao ◽

Eniko Székely ◽

Dimitrios Giannakis

Keyword(s):

Intraseasonal Oscillation ◽

Empirical Method ◽

Temperature Data ◽

Training Data ◽

Weighted Averaging ◽

Boreal Summer ◽

Madden Julian Oscillation ◽

Pattern Correlation ◽

Intraseasonal Oscillations ◽

Tropical Intraseasonal Oscillations

Abstract This paper presents the results of forecasting the Madden–Julian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO) through the use of satellite-obtained global brightness temperature data with a recently developed nonparametric empirical method. This new method, referred to as kernel analog forecasting, adopts specific indices extracted using the technique of nonlinear Laplacian spectral analysis as baseline definitions of the intraseasonal oscillations of interest, which are then extended into forecasts through an iterated weighted averaging scheme that exploits the predictability inherent to those indices. The pattern correlation of the forecasts produced in this manner remains above 0.6 for 50 days for both the MJO and BSISO when 23 yr of training data are used and 37 days for the MJO when 9 yr of data are used.

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Modulation of Tropical Intraseasonal Oscillations by Ocean–Atmosphere Coupling

Journal of Climate ◽

10.1175/jcli3638.1 ◽

2006 ◽

Vol 19 (3) ◽

pp. 366-391 ◽

Cited By ~ 61

Author(s):

K. Rajendran ◽

A. Kitoh

Keyword(s):

General Circulation Model ◽

General Circulation ◽

Circulation Model ◽

Boreal Summer ◽

Coupled Modes ◽

Structure Amplitude ◽

Ocean Atmosphere ◽

Intraseasonal Oscillations ◽

The Impact ◽

Tropical Intraseasonal Oscillations

Abstract The impact of ocean–atmosphere coupling on the structure and propagation characteristics of 30–60-day tropical intraseasonal oscillations (TISOs) is investigated by analyzing long-term simulations of the Meteorological Research Institute coupled general circulation model (CGCM) and its stand-alone atmospheric general circulation model (AGCM) version forced with SSTs derived from the CGCM and comparing them with recent observation datasets [Global Precipitation Climatology Project (GPCP) precipitation, 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), and Reynolds SST]. Composite events of (i) eastward propagating Madden–Julian oscillations (MJOs) during boreal winter and (ii) northward propagating intraseasonal oscillations (NPISOs) during boreal summer, constructed based on objective criteria, show that the three-dimensional structure, amplitude, and speed of propagation, and the phase relationship among surface fluxes, SST, and convection, are markedly improved in the CGCM simulation. Consistent with the frictional wave conditional instability of the second kind mechanism, successive development of low-level convergence to the east (north) of deep convection was found to be important for eastward (northward) propagation of MJO (NPISO). Complex interaction between large-scale dynamics and convection reveals the importance of atmospheric dynamics and suggests that they are intrinsic modes in the atmosphere where coupling is not essential for their existence. However, as in observations, realistic coupling in the CGCM is found to result in the evolution of TISOs as coupled modes through a coherent coupled feedback process. This acts as an amplifying mechanism for the existing propagating convective anomalies and plays an important modifying role toward a more realistic simulation of TISOs. In contrast, the simulated TISOs in its atmosphere-alone component lack many of the important features associated with their amplitude, phase, and life cycle. Thus, a realistic representation of the interaction between sea surface and the atmospheric boundary layer is crucial for a better simulation of TISOs.

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Dependence of Simulation of Boreal Summer Tropical Intraseasonal Oscillations on the Simulation of Seasonal Mean

Journal of the Atmospheric Sciences ◽

10.1175/jas3844.1 ◽

2007 ◽

Vol 64 (2) ◽

pp. 460-478 ◽

Cited By ~ 34

Author(s):

R. S. Ajayamohan ◽

B. N. Goswami

Keyword(s):

Indian Monsoon ◽

Cumulus Parameterization ◽

Boreal Summer ◽

Monsoon Region ◽

Parameterization Schemes ◽

Northern Summer ◽

Intraseasonal Oscillations ◽

Indian Monsoon Region ◽

Cumulus Parameterization Schemes ◽

Tropical Intraseasonal Oscillations

Abstract The link between realism in simulation of the seasonal mean precipitation and summer tropical intraseasonal oscillations and their dependence on cumulus parameterization schemes is investigated using the Florida State University Global Spectral Model (FSUGSM). Forty-member model ensemble simulations of the northern summer season are generated for three different cumulus parameterization schemes [namely, Arakawa–Schubert (Naval Research Laboratory; NRL), Zhang and McFarlane (National Center for Atmospheric Research; NCAR), and Emanuel (Massachusetts Institute of Technology; MIT)]. The MIT scheme simulates the regional pattern of seasonal mean precipitation over the Indian monsoon region well but has large systematic bias in simulating the precipitation over the western Pacific and the Maritime Continent. Although the simulation of details of regional distribution of precipitation over the Indian monsoon region by the NRL and NCAR schemes is not accurate, they simulate the spatial pattern of precipitation over the tropical Indo–Pacific domain closer to observation. The NRL scheme seems to captures the observed northward and eastward propagation of intraseasonal precipitation anomalies realistically. However, the simulations of the NCAR and MIT schemes are dominated by a westward propagating component. The westward propagating mode seen in the model as well as observations is indicated to be an equatorial Rossby wave modified by the northern summer mean flow. An examination of the relationship between simulation of the model climatology and eastward propagating character of monsoon intraseasonal oscillations (ISOs) in a limited sample shows that the scheme that simulates better seasonal mean pattern of rainfall over the tropical Indo–Pacific domain also simulates better intraseasonal variance and more realistic eastward propagation of monsoon ISOs. Among the parameters known to be important for meridional propagation of the summer monsoon ISOs, the meridional gradient of mean humidity in the lower atmosphere seems to be crucial in determining the northward propagation in the equatorial Indian Ocean (between 10°S and 10°N). For better prediction of the seasonal mean Indian monsoon, therefore, the model climatology should have minimum bias not only over the Indian monsoon region but also over the entire Indo–Pacific basin.

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A multiscale model for tropical intraseasonal oscillations

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.0401034101 ◽

2004 ◽

Vol 101 (14) ◽

pp. 4736-4741 ◽

Cited By ~ 133

Author(s):

A. J. Majda ◽

J. A. Biello

Keyword(s):

Multiscale Model ◽

Intraseasonal Oscillations ◽

Tropical Intraseasonal Oscillations

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The skeleton of tropical intraseasonal oscillations

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.0903367106 ◽

2009 ◽

Vol 106 (21) ◽

pp. 8417-8422 ◽

Cited By ~ 181

Author(s):

A. J. Majda ◽

S. N. Stechmann

Keyword(s):

Intraseasonal Oscillations ◽

Tropical Intraseasonal Oscillations

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Relative Roles of Background Moisture and Vertical Shear in Regulating Interannual Variability of Boreal Summer Intraseasonal Oscillations

Journal of Climate ◽

10.1175/jcli-d-15-0498.1 ◽

2016 ◽

Vol 29 (19) ◽

pp. 7009-7025 ◽

Cited By ~ 11

Author(s):

Li Deng ◽

Tim Li

Keyword(s):

Interannual Variability ◽

Intraseasonal Oscillation ◽

Longwave Radiation ◽

Tropical Indian Ocean ◽

Atmospheric Model ◽

Vertical Shear ◽

Boreal Summer ◽

Moisture Condition ◽

Intensity Index ◽

Intraseasonal Oscillations

Abstract The interannual variability of the boreal summer intraseasonal oscillation (BSISO) is investigated using observed outgoing longwave radiation (OLR) and ERA-Interim data for the period of 1980–2012. It is found that the interannual variability of BSISO intensity is much stronger in the tropical western Pacific (TWP) than the tropical Indian Ocean (TIO). A BSISO intensity index is defined based on a multivariate EOF analysis in TWP. It is found that strong BSISO years are associated with El Niño–like sea surface temperature anomalies in the tropical Pacific, anomalous easterly shear, and enhanced background moisture condition in the region. Using a 2.5-layer atmospheric model with a specified idealized background mean state, the authors further examine the relative roles of background moisture and vertical shear fields in modulating the BSISO intensity. Sensitivity numerical experiments indicate that the background moisture change is most important in regulating the BSISO intensity, whereas the background vertical shear change also plays a role.

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