scholarly journals Diagnosis of the MJO Modulation of Tropical Cyclogenesis Using an Empirical Index

2009 ◽  
Vol 66 (10) ◽  
pp. 3061-3074 ◽  
Author(s):  
Suzana J. Camargo ◽  
Matthew C. Wheeler ◽  
Adam H. Sobel
Keyword(s):  
Vertical Wind Shear ◽  
Tropical Cyclogenesis ◽  
Madden Julian Oscillation ◽  
Cyclone Activity ◽  
Absolute Vorticity ◽  
Potential Index ◽  
Frequency Changes ◽  
Analogous Calculation ◽  
Gp Index ◽  
Genesis Frequency

Abstract The modulation of tropical cyclone activity by the Madden–Julian oscillation (MJO) is explored using an empirical genesis potential (GP) index. Composite anomalies of the genesis index associated with the different MJO phases are consistent with the composite anomalies in TC genesis frequency that occur in the same phases, indicating that the index captures the changes in the environment that are at least in part responsible for the genesis frequency changes. Of the four environmental variables that enter the genesis potential index, the midlevel relative humidity makes the largest contribution to the MJO composite GP anomalies. The second largest contribution comes from the low-level absolute vorticity, and only very minor contributions come from the vertical wind shear and potential intensity. When basin-integrated MJO composite anomalies of the GP index are regressed against basin-integrated composite anomalies of TC genesis frequency, the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities. The GP index captures the MJO modulation of TC genesis to a lesser degree than the climatological annual cycle of genesis (to which it was originally tuned). This may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances, not well captured in the GP index computed from weekly data, to the intraseasonal TC genesis frequency fluctuations.

scholarly journals Impact of the Madden–Julian Oscillation on Western North Pacific Tropical Cyclogenesis Associated with Large-Scale Patterns

2015 ◽  
Vol 54 (7) ◽  
pp. 1413-1429 ◽  
Author(s):  
Haikun Zhao ◽  
Ryuji Yoshida ◽  
G. B. Raga
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Active Phase ◽  
Relative Vorticity ◽  
Tropical Cyclogenesis ◽  
Unexpected Result ◽  
Positive Anomaly ◽  
Madden Julian Oscillation

AbstractThe intraseasonal variability of tropical cyclogenesis in the western North Pacific (WNP) basin is explored in this study. The relation of cyclogenesis in each of the five large-scale patterns identified in recent work by Yoshida and Ishikawa is associated with the Madden–Julian oscillation (MJO). Confirming previous results, more events of cyclogenesis are found during the active MJO phase in the WNP. Furthermore, results indicate that most of the tropical cyclogenesis is associated with the monsoon shear line large-scale pattern during the active phase. The genesis potential index (GPI) and its individual components are used to evaluate the environmental factors that most contribute toward cyclogenesis under the different phases of the MJO. GPI exhibits a large positive anomaly during the active phase of the MJO, and such an anomaly is spatially correlated with the events of cyclogenesis. The analysis of each factor indicates that low-level relative vorticity and midlevel relative humidity are the two dominant contributors to the MJO-composited GPI anomalies. The positive GPI anomalies during the active phase are partially offset by the negative contributions from vertical wind shear and potential intensity. This is valid for all five large-scale patterns. It is noteworthy that the easterly wave (EW) large-scale pattern, while exhibiting the same influence of relative vorticity and midlevel humidity contributing toward positive GPI anomalies, presents slightly more cyclogenesis events under the inactive phase of the MJO. This unexpected result suggests that other factors not included in the definition of the GPI and/or changes in environmental flows on other time scales contribute to the tropical cyclogenesis associated with the EW large-scale pattern.

scholarly journals Predictive Skill and Predictability of North Atlantic Tropical Cyclogenesis in Different Synoptic Flow Regimes

2018 ◽  
Vol 75 (1) ◽  
pp. 361-378 ◽  
Author(s):  
Zhuo Wang ◽  
Weiwei Li ◽  
Melinda S. Peng ◽  
Xianan Jiang ◽  
Ron McTaggart-Cowan ◽  
...  
Keyword(s):  
North Atlantic ◽  
Vertical Wind Shear ◽  
Flow Regimes ◽  
Tropical Cyclogenesis ◽  
Low Level ◽  
The North ◽  
Predictive Skill ◽  
Potential Index ◽  
Forecast Lead Time ◽  
Upper Level

Practical predictability of tropical cyclogenesis over the North Atlantic is evaluated in different synoptic flow regimes using the NCEP Global Ensemble Forecast System (GEFS) reforecasts with forecast lead time up to two weeks. Synoptic flow regimes are represented by tropical cyclogenesis pathways defined in a previous study based on the low-level baroclinicity and upper-level forcing of the genesis environmental state, including nonbaroclinic, low-level baroclinic, trough-induced, weak tropical transition (TT), and strong TT pathways. It is found that the strong TT and weak TT pathways have lower predictability than the other pathways, linked to the lower predictability of vertical wind shear and midlevel humidity in the genesis vicinity of a developing TT storm. Further analysis suggests that stronger extratropical influences contribute to lower genesis predictability. It is also shown that the regional and seasonal variations of the genesis predictive skill in the GEFS can be largely explained by the relative frequency of occurrence of each pathway and the predictability differences among pathways. Predictability of tropical cyclogenesis is further discussed using the concept of the genesis potential index.

scholarly journals A numerical study of the early stages of a tropical cyclogenesis in relation to the MJO

2015 ◽  
Vol 3 (8) ◽  
pp. 4919-4935
Author(s):  
J. Guerbette ◽  
M. Plu ◽  
C. Barthe ◽  
J.-F. Mahfouf
Keyword(s):  
Numerical Study ◽  
Active Phase ◽  
Atmospheric Model ◽  
Tropical Cyclogenesis ◽  
Limited Area ◽  
Madden Julian Oscillation ◽  
Low Level ◽  
Convective Systems ◽  
South West Indian Ocean ◽  
Low Level Jet

Abstract. The role of an active phase of the Madden–Julian Oscillation (MJO) on the evolution of a mesoscale convective systems (MCS) leading to a tropical depression is investigated in the South-West Indian Ocean during the Dynamics of the Madden–Julian Oscillation (DYNAMO) field experiment, with a numerical limited-area atmospheric model. A mesoscale vortex is followed in the low-troposphere from the initiation of the active MJO phase. It is shown that the interaction of the vortex with the Equatorial jet associated with the MJO plays an important role on the vortex development. As the vortex encounters the southern part of the low-level jet, it undergoes intensification that is explained by the barotropic conversion of kinetic energy from the low-level jet to the vortex.

scholarly journals An intercomparison of tropical cyclone best-track products for the southwest Pacific

2016 ◽  
Vol 16 (6) ◽  
pp. 1431-1447 ◽  
Author(s):  
Andrew D. Magee ◽  
Danielle C. Verdon-Kidd ◽  
Anthony S. Kiem
Keyword(s):  
Tropical Cyclone ◽  
Vertical Wind Shear ◽  
Geostationary Satellite ◽  
Vertical Shear ◽  
Tropical Cyclogenesis ◽  
Southwest Pacific ◽  
Zonal Winds ◽  
Spatio Temporal ◽  
Joint Typhoon Warning Center

Abstract. Recent efforts to understand tropical cyclone (TC) activity in the southwest Pacific (SWP) have led to the development of numerous TC databases. The methods used to compile each database vary and are based on data from different meteorological centres, standalone TC databases and archived synoptic charts. Therefore the aims of this study are to (i) provide a spatio-temporal comparison of three TC best-track (BT) databases and explore any differences between them (and any associated implications) and (ii) investigate whether there are any spatial, temporal or statistical differences between pre-satellite (1945–1969), post-satellite (1970–2011) and post-geostationary satellite (1982–2011) era TC data given the changing observational technologies with time. To achieve this, we compare three best-track TC databases for the SWP region (0–35° S, 135° E–120° W) from 1945 to 2011: the Joint Typhoon Warning Center (JTWC), the International Best Track Archive for Climate Stewardship (IBTrACS) and the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC). The results of this study suggest that SPEArTC is the most complete repository of TCs for the SWP region. In particular, we show that the SPEArTC database includes a number of additional TCs, not included in either the JTWC or IBTrACS database. These SPEArTC events do occur under environmental conditions conducive to tropical cyclogenesis (TC genesis), including anomalously negative 700 hPa vorticity (VORT), anomalously negative vertical shear of zonal winds (VSZW), anomalously negative 700 hPa geopotential height (GPH), cyclonic (absolute) 700 hPa winds and low values of absolute vertical wind shear (EVWS). Further, while changes in observational technologies from 1945 have undoubtedly improved our ability to detect and monitor TCs, we show that the number of TCs detected prior to the satellite era (1945–1969) are not statistically different to those in the post-satellite era (post-1970). Although data from pre-satellite and pre-geostationary satellite periods are currently inadequate for investigating TC intensity, this study suggests that SPEArTC data (from 1945) may be used to investigate long-term variability of TC counts and TC genesis locations.

Modulation of bay of bengal tropical cyclone activity by the madden-julian oscillation

2019 ◽  
Vol 229 ◽  
pp. 23-38 ◽  
Author(s):  
Pankaj Bhardwaj ◽  
Omvir Singh ◽  
D.R. Pattanaik ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclone ◽  
Bay Of Bengal ◽  
Tropical Cyclone Activity ◽  
Madden Julian Oscillation ◽  
Cyclone Activity

Tropical Cyclogenesis Associated with Kelvin Waves and the Madden–Julian Oscillation

2011 ◽  
Vol 139 (9) ◽  
pp. 2723-2734 ◽  
Author(s):  
Carl J. Schreck ◽  
John Molinari
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Western North Pacific ◽  
Diabatic Heating ◽  
Kelvin Waves ◽  
Tropical Cyclogenesis ◽  
Madden Julian Oscillation ◽  
Convective Envelope

The Madden–Julian oscillation (MJO) influences tropical cyclone formation around the globe. Convectively coupled Kelvin waves are often embedded within the MJO, but their role in tropical cyclogenesis remains uncertain. This case study identifies the influences of the MJO and a series of Kelvin waves on the formation of two tropical cyclones. Typhoons Rammasun and Chataan developed in the western North Pacific on 28 June 2002. Two weeks earlier, conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection. The easterlies gave way to equatorial westerlies as the convective envelope of the Madden–Julian oscillation moved into the region. A series of three Kelvin waves modulated the development of the westerlies. Cyclonic potential vorticity (PV) developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward. Rammasun and Chataan emerged from the apparent breakdown of this strip. The cyclonic PV developed in association with diabatic heating from both the MJO and the Kelvin waves. The tropical cyclones also developed during the largest superposition of equatorial westerlies from the MJO and the Kelvin waves. This chain of events suggests that the MJO and the Kelvin waves each played a role in the development of Rammasun and Chataan.

Four Years of Tropical ERA-40 Vorticity Maxima Tracks. Part II: Differences between Developing and Nondeveloping Disturbances

2009 ◽  
Vol 137 (8) ◽  
pp. 2576-2591 ◽  
Author(s):  
Brandon Kerns ◽  
Edward Zipser
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Skill Score ◽  
Relative Vorticity ◽  
Prediction Skill ◽  
Tropical Cyclogenesis ◽  
Linear Discriminant ◽  
Predictive Skill ◽  
Heidke Skill Score

Abstract Using a subset of the relative vorticity maxima (VM) tracks described in Part I, large-scale environmental fields, cold cloud area, and rainfall area are used to discriminate between developing and nondeveloping tropical disturbances in the eastern North Pacific (EPAC) and Atlantic Oceans. By using a minimum cold cloud coverage requirement, the nondeveloping VM are limited to disturbances with enhanced low-level relative vorticity and widespread deep convection. Linear discriminant analysis is used to determine the overall discrimination and the relative importance of each predictor for each basin separately. It is important to distinguish the two basins because, for many predictors, the differences between the basins are greater than the differences between developing and nondeveloping VM in each basin. Using the parametric forecast method, there is greater discrimination and prediction skill in the EPAC than in the Atlantic. There are also significant differences between the two basins in terms of the degree of discrimination provided by each of the predictors. Surprisingly, the mean vertical wind shear magnitude is greater for EPAC developing VM than for EPAC nondeveloping VM. Incorporating the satellite-derived predictors marginally improves the potential forecast skill in the EPAC but not in the Atlantic. The prediction skill (Heidke skill score) of tropical cyclogenesis in the Atlantic is similar to what has been obtained in previous studies using cloud cluster tracks. There is greater predictive skill in the EPAC.

North-Central Pacific Tropical Cyclones: Impacts of El Niño–Southern Oscillation and the Madden–Julian Oscillation

2013 ◽  
Vol 26 (19) ◽  
pp. 7720-7733 ◽  
Author(s):  
Philip J. Klotzbach ◽  
Eric S. Blake
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Rapid Intensification ◽  
Madden Julian Oscillation ◽  
Cyclone Activity ◽  
Central Pacific ◽  
North Central ◽  
The North

Abstract Both El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO) have been documented in previous research to impact tropical cyclone (TC) activity around the globe. This study examines the relationship of each mode individually along with a combined index on tropical cyclone activity in the north-central Pacific. Approximately twice as many tropical cyclones form in the north-central Pacific in El Niño years compared with La Niña years. These differences are attributed to a variety of factors, including warmer sea surface temperatures, lower sea level pressures, increased midlevel moisture, and anomalous midlevel ascent in El Niño years. When the convectively enhanced phase of the MJO is located over the eastern and central tropical Pacific, the north-central Pacific tends to have more tropical cyclone activity, likely because of reduced vertical wind shear, lower sea level pressures, and increased vertical motion. The convectively enhanced phase of the MJO is also responsible for most of the TCs that undergo rapid intensification in the north-central Pacific. A combined MJO–ENSO index that is primarily associated with anomalous rising motion over the tropical eastern Pacific has an even stronger relationship with north-central Pacific TCs, as well as rapid intensification, than either individually.

Variations of Northern Hemisphere Storm Track and Extratropical Cyclone Activity Associated with the Madden–Julian Oscillation

2017 ◽  
Vol 30 (13) ◽  
pp. 4799-4818 ◽  
Author(s):  
Yanjuan Guo ◽  
Toshiaki Shinoda ◽  
Jialin Lin ◽  
Edmund K. M. Chang
Keyword(s):  
Storm Track ◽  
Meridional Wind ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Mean Flow ◽  
Cyclone Activity ◽  
Intraseasonal Variations ◽  
The Pacific ◽  
Cyclone Frequency

This study investigates the intraseasonal variations of the Northern Hemispheric storm track associated with the Madden–Julian oscillation (MJO) during the extended boreal winter (November–April) using 36 yr (1979–2014) of reanalysis data from ERA-Interim. Two methods have been used to diagnose storm-track variations. In the first method, the storm track is quantified by the temporal-filtered variance of 250-hPa meridional wind (vv250) or mean sea level pressure (pp). The intraseasonal anomalies of vv250 composited for eight MJO phases are characterized by a zonal band of strong positive (or negative) anomalies meandering from the Pacific all the way across North America and the Atlantic into northern Europe, with weaker anomalies of opposite sign at one or both flanks. The results based on pp are consistent with those based on vv250 except for larger zonal variations, which may be induced by surface topography. In the second method, an objective cyclone-tracking scheme has been used to track the extratropical cyclones that compose the storm track. The MJO-composite anomalies of the “accumulated” cyclone activity, a quantity that includes contributions from both the cyclone frequency and cyclone mean intensity, are very similar to those based on pp. Further analysis demonstrates that major contribution comes from variations in the cyclone frequency. Further analysis suggests that the intraseasonal variations of the storm track can be primarily attributed to the variations of the mean flow that responds to the anomalous MJO convections in the tropics, with possible contribution also from the moisture variations.

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