Intraseasonal Variations of Nonmigrating Tides Observed Near the Mesopause

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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Role of Sea Surface Salinity Feedback in MJO Predictability: A Study with CFSv2

Journal of Climate ◽

10.1175/jcli-d-18-0755.1 ◽

2019 ◽

Vol 32 (18) ◽

pp. 5745-5759 ◽

Cited By ~ 2

Author(s):

Jieshun Zhu ◽

Arun Kumar

Keyword(s):

Sea Surface Salinity ◽

Initial Attempt ◽

Surface Salinity ◽

Model Framework ◽

Ocean Stratification ◽

Tropical Oceans ◽

Benchmark Experiment ◽

Intraseasonal Variations ◽

Perfect Model

Abstract While previous studies suggested that salinity could feed back onto MJO variability via modulating upper ocean stratification and further on SST, there is no direct evidence yet proving (or disproving) the importance of this feedback in MJO evolution and its predictability. This study is an initial attempt to quantify the role of SSS feedback on MJO predictability, based on a “perfect model” framework with the CFSv2. Specifically, the SSS feedback is isolated by nudging model SSS to climatological states during forecasts. For comparison, two more experiments were done, one as a benchmark experiment by estimating MJO predictability in CFSv2 and another one for estimating the role of SST feedback. Analyses of these experiments indicate that SSS feedback exerts negligible influences on MJO predictability within the constraints of the model, in contrast to significant impacts from SST feedback. Further analysis showed that a lack of SSS influence in MJO predictability can be attributed to marginal changes in SST associated with the SSS nudging. However, there is a caveat to the conclusion about SSS feedback. Because the barrier layer (BL) acts as a “bridge” for possible SSS influences on SST over the tropical Indian and western Pacific oceans, its simulation in CFSv2 is further explored. Analyses indicate that, in spite of realistic simulations of the MJO and intraseasonal SSS variability in CFSv2, significant BL simulation biases are present in the tropical oceans, including too thin a climatological thickness, too small intraseasonal variations, and an unrealistic intraseasonal BL–SST relationship. Thus, our predictability experiments cannot reject the hypothesis that SSS does play a role in MJO predictability; it is possible that biases in CFSv2 influence its ability to capture such signals.

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Contribution of Different Time-Scale Variations to the Tropical Cyclogenesis Environment over the Northern Tropical Atlantic and Comparison with the Western North Pacific

Journal of Climate ◽

10.1175/jcli-d-18-0560.1 ◽

2019 ◽

Vol 32 (19) ◽

pp. 6645-6661 ◽

Cited By ~ 3

Author(s):

Xi Cao ◽

Renguang Wu ◽

Mingyu Bi ◽

Xiaoqing Lan ◽

Yifeng Dai ◽

...

Keyword(s):

Energy Conversion ◽

North Pacific ◽

Western North Pacific ◽

Relative Vorticity ◽

Specific Humidity ◽

Tropical Atlantic ◽

Relative Contribution ◽

Intraseasonal Variations ◽

Barotropic Energy Conversion ◽

Northern Tropical Atlantic

Abstract The present study investigates relative contributions of interannual, intraseasonal, and synoptic variations of environmental factors to tropical cyclone (TC) genesis over the northern tropical Atlantic (NTA) during July–October. Analysis shows that convection, lower-level vorticity, and midlevel specific humidity contribute to TC genesis through intraseasonal and synoptic variations with a larger contribution of the latter. The relative contribution of three components of vertical wind shear depends largely on its magnitude. The contribution of sea surface temperature (SST) to TC genesis is mainly due to the interannual component when total SST is above 27.5°C. The barotropic energy for the development of synoptic-scale disturbances comes mainly from climatological mean flows and intraseasonal wind variations. The proportion of contribution between synoptic and intraseasonal variations of convection, relative vorticity, and specific humidity is larger over the eastern NTA than over the western NTA. The barotropic energy conversion has a larger part related to climatological mean flows and intraseasonal wind variations over the eastern and western NTA, respectively. There are notable differences between the NTA and the western North Pacific (WNP). One is that the relative contribution of synoptic variations of convection, relative vorticity, and specific humidity is larger over the NTA, whereas that of intraseasonal variations is larger over the WNP. The other is that the barotropic energy conversion related to climatological mean flows and intraseasonal wind variations is comparable over the NTA, whereas that related to climatological mean flows is larger over the WNP.

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Nonmigrating tides inferred from the Mars Odyssey and Mars Global Surveyor aerobraking data

Geophysical Research Letters ◽

10.1029/2006gl027753 ◽

2006 ◽

Vol 33 (23) ◽

Cited By ~ 12

Author(s):

L. Wang ◽

D. C. Fritts ◽

R. H. Tolson

Keyword(s):

Mars Global Surveyor ◽

Nonmigrating Tides ◽

Mars Odyssey

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Geographical Distribution of Variance of Intraseasonal Variations in Western Indochina as Revealed from Radar Reflectivity Data

Journal of Climate ◽

10.1175/2008jcli2153.1 ◽

2008 ◽

Vol 21 (19) ◽

pp. 5154-5161 ◽

Cited By ~ 6

Author(s):

Satoru Yokoi ◽

Takehiko Satomura

Keyword(s):

Geographical Distribution ◽

Coastal Region ◽

Radar Reflectivity ◽

Windward Side ◽

Synoptic Scale ◽

Wind Anomaly ◽

Orographic Rainfall ◽

Intraseasonal Variations ◽

Reflectivity Data ◽

Reflectivity Factor

Abstract This study reveals remarkable differences in the geographical distribution of variance between two types of intraseasonal variations in daily-mean radar reflectivity data in the western part of the Indochina Peninsula. In this region, the Downa Range lies parallel to the coast and separates the inland region from the coastal region. The 30–60-day variation of reflectivity factor dominates most of the coastal region, while its variance in the inland region is less than that of background red noise with the same frequency band. Horizontal gradients in the variance are largest over the range, implying that the mountain range plays a significant role in the geographical contrast. Correlation analysis with reanalysis data shows that the variation only in the coastal region is associated with a synoptic-scale zonal wind anomaly with the same time scale, suggesting the importance of an orographic rainfall process that brings a large amount of precipitation only to the windward side of the Downa Range. In contrast, while the 10–20-day variation of reflectivity factor has larger variance in the inland region than in the coastal region, the variation in both of the regions is correlated with synoptic-scale cyclonic circulation anomaly. A possible reason for the differences between the two types is also discussed in terms of the relationship between synoptic-scale wind anomaly field and the orientation of the Downa Range.

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