superposed epoch analysis
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MAUSAM ◽  
2022 ◽  
Vol 53 (1) ◽  
pp. 31-44
Author(s):  
Y. E. A. RAJ ◽  
P. V. SANKARAN ◽  
B. RAMAKRISHNAN ◽  
P. L. PADMAKUMAR

Several sea breeze parameters such as time of onset, withdrawal, duration, depth, variation with height, direction etc.  have been derived and studied for Chennai city and Chennai AP observatories in this study, which has been based on a large  data base for the period March-October,1969-83. The monthly and sub monthly values of several sea breeze parameters have been derived. By invoking the concept of superposed epoch analysis the important role played by sea breeze in modulating diurnal variation of surface temperature and relative humidity has been established. The sea breeze at Chennai has been shown to be shallow with a depth of under 1 km. Modal directions of sea breeze and its normal speed have been  derived.


2021 ◽  
Vol 12 (4) ◽  
Author(s):  
Vitalii Degtyarev ◽  
George Popov ◽  
Svetlana Chudnenko

The energy inflow from the solar wind into the magnetosphere and its dissipation in the circular current and auroral ionosphere during maximums of magnetic storm intensity are considered. All magnetic storms with Dst intensities from –18 nT to –422 nT for the period from 1996 to 2014 were divided into groups. For each group, the mean contribution of energy from the solar wind to the magnetosphere and subsequent characteristics of the energy dissipation in the auroral ionosphere and circular current were determined by the superposed epoch analysis method. The nonlinearity of the dependence of the intensity of magnetic storms on the energy coming from the solar wind into the magnetosphere was revealed. Anomalous behavior of magnetic storms with intensity |Dst| > 200 nT was detected. A discussion of the results is given.


2021 ◽  
Author(s):  
Benedikt Gast ◽  
Ales Kuchar ◽  
Gunter Stober ◽  
Christoph Jacobi ◽  
Dimitry Pokhotelov ◽  
...  

<p class="western" align="justify"><span lang="en-GB">Previous studies that analysed the mesosphere and lower thermosphere (MLT) dynamics during sudden stratospheric warmings (SSWs) were limited only to particular SSWs or focused on a particular station representative only for some regions. Here we describe a comprehensive study of the average meteorological conditions during SSWs with a special focus on the general contribution of planetary (PW) and gravity (GW) waves as primary coupling mechanisms between lower and upper atmosphere. The average meteorological conditions in the MLT during SSWs were analyzed using a superposed epoch analysis (Denton et al., 2019) of meteor radar measurements for stations in the northern (NH: Collm, Kiruna, Sodankyla, CMOR) and the southern hemisphere (SH: Rio Grande, Davis, Rothera) for the altitude range of 80–100 km Using the adaptive spectral filtering method (Stober et al., 2021), we study in detail PW and GW characteristics in addition to measured zonal and meridional wind components in a time period from 2000 to 2020.</span></p> <p class="western" align="justify"><span lang="en-GB">In the NH the zonal wind is typically decreasing from around two weeks before the SSW onset, corresponding to an increased PW activity. Around the SSW onset, latitudinal differences in the zonal wind component as well as the PW activity can be seen. In the weeks before the SSW onset, the stations in the NH also show an increased level of GW kinetic energy. The meridional wind at the NH stations fluctuates with a periodicity of about 10 days before and around the onset. In contrast to previous studies (e.g. Yasui et al., 2016), the measurements in the SH are consistent with the inter-hemispheric coupling hypothesis. The expected downward shift of GW drag (Körnich and Becker, 2010) was reproduced by a downward travelling layer of enhanced GW activity at Davis and Rio Grande. Finally, the role of the terdiurnal tide in the GW energy composite is considered.</span></p>


MAUSAM ◽  
2021 ◽  
Vol 49 (3) ◽  
pp. 309-320
Author(s):  
Y. E. A. RAJ

The withdrawal dates of northeast monsoon over coastal Tamil Nadu for the 90-year period (1901-90) have been objectively derived. The methodology of determination was generally based on an index based on the spatial distribution of daily rainfall over stations of coastal Tamil Nadu, over a 5-day pentad for the six month period, September- February. The normal withdrawal date thus obtained was 27 December with a standard deviation of 13.6 days and range 23 November-28 January. The duration of northeast monsoon was distributed with mean 67.5 days, standard deviation 14.9 days and range 26-102 days. During 36.7 % of years the withdrawal spilled over to January of next year. The daily normal rainfall and its difference filter have been discussed with reference to the normal date of withdrawal. The average decrease of rainfall at the time of withdrawal has been derived by application of superposed epoch analysis. It has further been shown that during years when the withdrawal took place in January the intensity of northeast monsoon prior to withdrawal was as intense as in years when withdrawal occurred in December. A few cases of northeast monsoon withdrawal have been illustrated with diagrams. As no definite dynamic or thermodynamic features could be uniquely identified which are associated with the withdrawal, this technique is basically statistical, considering the behaviour of the daily normal rainfall as the sole criterion. Unique thermodynamic and dynamic features are not identifiable which are associated with the withdrawal of northeast monsoon over coastal Tamilnadu.


2021 ◽  
Author(s):  
Philippa Ann Higgins ◽  
Jonathan Gray Palmer ◽  
Chris S. M. Turney ◽  
Martin Sogaard Andersen ◽  
Fiona Johnson

Abstract. Much of our knowledge about the impacts of volcanic events on climate comes from proxy records. However, little is known about the impact of volcanoes on trees from the Southern Hemisphere. We investigated whether volcanic signals could be identified in ring widths from eight New Zealand dendrochronological species, using superposed epoch analysis. We found that most species are good recorders of volcanic dimming and that the magnitude and persistence of the post-event response can be broadly linked to plant life history traits. Across species, site-based factors, particularly altitude and exposure to prevailing conditions, are more important determinants of the strength of the volcanic response than the species. We then investigated whether proxy selection impacts the magnitude of post-volcanic cooling in tree-ring based temperature reconstructions by developing two new multispecies reconstructions of New Zealand summer (December–February) temperature. Both reconstructions showed temperature anomalies remarkably consistent with studies based on instrumental temperature, and with the ensemble mean response of climate models, demonstrating that New Zealand ring widths are reliable indicators of regional volcanic climate response. However, we also found that volcanic response is complex, with positive, negative, and neutral responses identified – sometimes within the same species group. Species-wide composites thus tend to underestimate the volcanic response. The has important implications for the development of future tree ring and multiproxy temperature reconstructions from the Southern Hemisphere.


MAUSAM ◽  
2021 ◽  
Vol 67 (2) ◽  
pp. 357-376
Author(s):  
B. AMUDHA ◽  
Y. E. A. RAJ ◽  
R. ASOKAN

Characteristics of the northeast monsoon (NEM) have been studied utilising the outgoing long wave radiation (OLR) data derived over the north Indian Ocean and south peninsular India (SPI) from the series of Indian geostationary satellites. The contrasting feature of movement of the equatorial cloud zone from southeast to northwest direction during the onset phase of NEM has been reiterated using 1° × 1° gridded high resolution OLR data for the period 2000-2012.  Presence of OLR values less than 180 Wm-2 over a large part of coastal Tamil Nadu on the date of onset and the simultaneous commencement of rainfall with clouding approaching SPI from southeast is clear from the study of superposed epoch analysis of the data. Triad means of OLR also substantiate this inference. During active spells of NEM which succeed prolonged dry spells, replication of the south to north movement of clouding by the OLR contours and the plausible reasons for such a movement have been brought out. The active monsoon situation existing over Sri Lankan region during the withdrawal phase of NEM over SPI is demonstrated with the depiction of the movement of OLR contours less than 230 Wm-2 over the region.  


Solar Physics ◽  
2021 ◽  
Vol 296 (12) ◽  
Author(s):  
Scott W. McIntosh ◽  
Robert J. Leamon ◽  
Ricky Egeland ◽  
Mausumi Dikpati ◽  
Richard C. Altrock ◽  
...  

AbstractWe investigate the occurrence of the “extended solar cycle” (ESC) as it occurs in a host of observational data spanning 140 years. Investigating coronal, chromospheric, photospheric, and interior diagnostics, we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) and previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder’s butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of $55^{\circ }$ 55 ∘ latitude in the evolution, and possible production, of solar magnetism.


2021 ◽  
Vol 922 (2) ◽  
pp. 216
Author(s):  
Miho Janvier ◽  
Pascal Démoulin ◽  
Jingnan Guo ◽  
Sergio Dasso ◽  
Florian Regnault ◽  
...  

Abstract Interplanetary coronal mass ejections (ICMEs) are known to modify the structure of the solar wind as well as interact with the space environment of planetary systems. Their large magnetic structures have been shown to interact with galactic cosmic rays (GCRs), leading to the Forbush decrease (FD) phenomenon. We revisit in the present article the 17 yr of Advanced Composition Explorer spacecraft ICME detection along with two neutron monitors (McMurdo and Oulu) with a superposed epoch analysis to further analyze the role of the magnetic ejecta in driving FDs. We investigate in the following the role of the sheath and the magnetic ejecta in driving FDs, and we further show that for ICMEs without a sheath, a magnetic ejecta only is able to drive significant FDs of comparable intensities. Furthermore, a comparison of samples with and without a sheath with similar speed profiles enable us to show that the magnetic field intensity, rather than its fluctuations, is the main driver for the FD. Finally, the recovery phase of the FD for isolated magnetic ejecta shows an anisotropy in the level of the GCRs. We relate this finding at 1 au to the gradient of the GCR flux found at different heliospheric distances from several interplanetary missions.


2021 ◽  
Author(s):  
Scott William McIntosh ◽  
Robert J Leamon ◽  
Ricky Egeland ◽  
Mausumi Dikpati ◽  
Richard C Altrock ◽  
...  

Abstract We investigate the occurrence of the ``extended solar cycle'' (ESC) as it occurs in a host observational data spanning 140 years. Investigating coronal, chromospheric, photospheric and interior diagnostics we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) using previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder's butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of 55\degree\ latitude in the evolution, and possible production, of solar magnetism.


Forests ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1433
Author(s):  
Annette Debel ◽  
Wolfgang Jens-Henrik Meier ◽  
Achim Bräuning

Since recent drought events have already caused severe damage to trees and droughts in the near future are expected to occur even more frequently, this study investigated the response of forest ecosystems to changing climate conditions in the topographically complex region of Bavaria, southeast Germany. For this purpose, climate–growth relationships of important European deciduous and coniferous tree species were investigated over the past 50 years at three middle mountain ranges and corresponding basins. A response analysis between tree-ring width and climate variables was applied to detect modifications in tree responses comparing two 25-year periods at individual forest sites. Furthermore, tree responses to climatic extreme years and seasons were analyzed using a superposed epoch analysis. The results showed that Scots pine (Pinus sylvestris) proved to be the most vulnerable and least drought-resistant of all investigated tree species. Likewise, Norway spruce (Picea abies) and European beech (Fagus sylvatica) revealed a higher drought sensitivity over the past 25 years, even though an extended growing season partially improved tree growth at high-elevation sites. In conclusion, all studied tree species were affected by drought events, even at humid high-elevation sites. Correlations with daily climate variables confirmed that even short-term weather conditions could strongly influence trees’ radial growth. Tree responses to climate conditions have shifted significantly between past and present periods but vary considerably among sites and are generally stronger in humid regions than in already dry areas.


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