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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#1
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I have just been made aware of this article which seems to suggest something
I had suspected: that lunar tides are linked with jet streams. The article is entitled: "Equatorial Ionospheric Electrodynamic Perturbations During Southern Hemisphere Stratospheric Warming Events" But the abstract says: "We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events." http://onlinelibrary.wiley.com/doi/1...50B B8.d01t04 If SSWs are caused by waves in jet streams breaking, then there is some sort of connection with lunar tides. Cheers, Alastair. |
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Alastair McDonald wrote in message
... I have just been made aware of this article which seems to suggest something I had suspected: that lunar tides are linked with jet streams. The article is entitled: "Equatorial Ionospheric Electrodynamic Perturbations During Southern Hemisphere Stratospheric Warming Events" But the abstract says: "We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events." http://onlinelibrary.wiley.com/doi/1...;jsessionid=F3 9A2C47D3C86E8784D17AA97B850BB8.d01t04 If SSWs are caused by waves in jet streams breaking, then there is some sort of connection with lunar tides. Cheers, Alastair. Why just lunar tides? the solar component of the tides are half as strong as lunar ones |
#3
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![]() "N_Cook" wrote in message ... Alastair McDonald wrote in message ... I have just been made aware of this article which seems to suggest something I had suspected: that lunar tides are linked with jet streams. The article is entitled: "Equatorial Ionospheric Electrodynamic Perturbations During Southern Hemisphere Stratospheric Warming Events" But the abstract says: "We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events." http://onlinelibrary.wiley.com/doi/1...;jsessionid=F3 9A2C47D3C86E8784D17AA97B850BB8.d01t04 If SSWs are caused by waves in jet streams breaking, then there is some sort of connection with lunar tides. Cheers, Alastair. Why just lunar tides? the solar component of the tides are half as strong as lunar ones The solar tides are masked by the effects of solar radiation with which they coincide. Cheers, Alastair. |
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![]() "N_Cook" wrote in message ... Alastair McDonald wrote in message ... I have just been made aware of this article which seems to suggest something I had suspected: that lunar tides are linked with jet streams. The article is entitled: "Equatorial Ionospheric Electrodynamic Perturbations During Southern Hemisphere Stratospheric Warming Events" But the abstract says: "We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events." http://onlinelibrary.wiley.com/doi/1...;jsessionid=F3 9A2C47D3C86E8784D17AA97B850BB8.d01t04 If SSWs are caused by waves in jet streams breaking, then there is some sort of connection with lunar tides. Cheers, Alastair. Why just lunar tides? the solar component of the tides are half as strong as lunar ones Just been alerted to this article, which may answer your question! I am not claiming to understand this at the moment, but I expect in a few years time a simple explanation will become available. Lunar and solar tidal variabilities in mesospheric winds and EEJ strength over Tirunelveli (8.7°N, 77.8°E) during the 2009 major stratospheric warming http://onlinelibrary.wiley.com/doi/1...E93 B9.d01t01 Cheers, Alastair. |
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On Jan 28, 12:47Â*pm, "Alastair McDonald"
wrote: "N_Cook" wrote in message ... Alastair McDonald wrote in message ... I have just been made aware of this article which seems to suggest something I had suspected: that lunar tides are linked with jet streams. The article is entitled: "Equatorial Ionospheric Electrodynamic Perturbations During Southern Hemisphere Stratospheric Warming Events" But the abstract says: "We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events." http://onlinelibrary.wiley.com/doi/1...bstract;jsessi... 9A2C47D3C86E8784D17AA97B850BB8.d01t04 If SSWs are caused by waves in jet streams breaking, then there is some sort of connection with lunar tides. Cheers, Alastair. Why just lunar tides? the solar component of the tides are half as strong as lunar ones Just been alerted to this article, which may answer your question! I am not claiming to understand this at the moment, but I expect in a few years time a simple explanation will become available. Lunar and solar tidal variabilities in mesospheric winds and EEJ strength over Tirunelveli (8.7°N, 77.8°E) during the 2009 major stratospheric warminghttp://onlinelibrary.wiley.com/doi/10.1029/2012JA018236/abstract;jses... Cheers, Alastair.- Hide quoted text - - Show quoted text - Lunarâdependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings B. G. Fejer,1 M. E. Olson,1 J. L. Chau,2 C. Stolle,3 H. LĂŒhr,3 L. P. Goncharenko,4 K. Yumoto,5 and T. Nagatsuma6 Received 13 January 2010; revised 4 March 2010; accepted 12 March 2010; published 28 August 2010. [1] We have used plasma drift and magnetic field measurements during the 2001â2009 December solstices to study, for the first time, the longitudinal dependence of equatorial ionospheric electrodynamic perturbations during sudden stratospheric warmings. Jicamarca radar measurements during these events show large dayside downward drift (westward electric field) perturbations followed by large morning upward and afternoon downward drifts that systematically shift to later local times. Groundâ based magnetometer measurements in the American, Indian, and Pacific equatorial regions show strongly enhanced electrojet currents in the morning sector and large reversed currents (i.e., counterelectrojets) in the afternoon sector with onsets near new and full moons during northern winter warming periods. CHAMP satellite and groundâbased magnetic field observations indicate that the onset of these equatorial afternoon counterelectrojets is longitude dependent. Our results indicate that these large electrodynamic perturbations during stratospheric warming periods are due to strongly enhanced semidiurnal lunar wave effects. The results of our study can be used for forecasting the occurrence and evolution of these electrodynamic perturbations during arctic winter warmings. Citation: Fejer, B. G., M. E. Olson, J. L. Chau, C. Stolle, H. LĂŒhr, L. P. Goncharenko, K. Yumoto, and T. Nagatsuma (2010), Lunarâdependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings, J. Geophys. Res., 115, A00G03, doi:10.1029/2010JA015273. 1. Introduction [2] The quiet time lowâlatitude ionospheric electric fields are generated by dynamo action of thermospheric neutral winds [e.g., Richmond, 1995a; Heelis, 2004]. In the equatorial region the zonal electric fields drive strong daytime lower E region eastward currents, called equatorial electrojets, in narrow latitudinal bands centered at the dip equator [e.g., Richmond, 1995b]. The zonal electric fields also drive equatorial E and F region vertical plasma drifts which have been studied extensively using radar and satellite measurements [e.g., Fejer, 1997]. [3] The initial geomagnetic field measurements near the magnetic equator have already indicated the large variability of the equatorial electrojet intensity. Bartels and Johnston [1940] reported the occasional occurrence of afternoon depressions in the electrojet horizontal magnetic field component (DH) below their nighttime values during geomagnetic quiet days. They suggested that the largest variations, on soâcalled âbig L days,â were due to the superposition of highly magnified lunar tides on the normal quiet time variation. Morning and afternoon quiet time anomalous equatorial electrojet current reversals, called counterelectrojets, have been extensively studied since the nineteen sixties [e.g., Gouin, 1962; Gouin and Mayaud, 1967; Hutton and Oyinloye, 1970; Rastogi, 1973]. Comprehensive reviews of these studies were by published by Mayaud [1977] and Marriott et al. [1979]. The quiet time current reversals are confined to the equatorial electrojet region and are most common during low solar activity years [Rastogi, 1974b]. They can occur for a week or so, but not necessarily on the same days, at longitudes separated by more than a few hours. Afternoon counterelectrojets occur mainly near new and full moons (lunar ages 0000 and 1200); morning counterelectrojets are most common after the lower and upper transits (lunar ages 9 and 21) [Onwumechilli and Akasofu, 1972; Hutton and Oyinloye, 1970; Rastogi, 1974a, 1975]. [4] In the Indian sector, counterelectrojets are most frequent in the afternoon hours of the June solstices; in the American sector, counterelectrojets are most common in the morning hours of December solstices [Patil et al., 1990]. However, as pointed out by Mayaud [1977], it is remarkable that all published examples of magnetically quiet time very large 1Center for Atmospheric and Space Sciences, Utah State University, Logan, Utah, USA. 2Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Lima, Peru. 3Helmholtz Centre Potsdam,GeoForschungsZentrum, Potsdam,Germany. 4Haystack Observatory,Massachusetts Institute of Technology, Westford, Massachusetts, USA. 5Space Environment Research Center, Kyushu University, Fukuoka, Japan. 6Applied Electromagnetic Research Center, National Institute of Information and Communications Technology, Tokyo, Japan. Copyright 2010 by the American Geophysical Union. 0148â0227/10/2010JA015273 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, A00G03, doi: 10.1029/2010JA015273, 2010 A00G03 1 of 9 counterelectrojet events are from the December solstice. Several studies suggested that these events result from the superposition of the lunar semidiurnal wave over the solar daily wave, but they also noted that highly enhanced lunar tides would be required to explain the occasionally observed very large semidiurnal current perturbations since lunar tides can normally account only for much smaller variations. Bhargava and Sastri [1977] derived a semidiurnal magnetic field component with a maximum around 1000 LT and a minimum near 1500 LT superposed on the electrojet horizontal field during afternoon counterelectrojet events, and Alex et al. [1986] suggested that these perturbations were due to lunarâsolar tidal waves. Lunar controlled counterelectrojets persist for several days, exhibit a systematic change in the diurnal pattern, and tend to occur over longer longitudinal ranges [Rangarajan and Rastogi, 1993]. [5] Numerous studies examined the effects of lower atmospheric processes on equatorial electric fields and currents. Stening [1977] suggested an association of equatorial counterelectrojets and stratospheric warmings. Chen [1992] showed 2 day oscillations in the intensity of the equatorial ionization anomaly, which is driven by the vertical plasma drift (zonal electric field). Forbes and Leveroni [1992] identified a quasi 16 day oscillation on the electrojet DH intensity during a large northern winter stratospheric disturbance possibly due to the upward penetration of a free Rossby mode excited in the winter stratosphere. Somayajulu et al. [1993] reported westward meteor zonal winds in the altitude region of 90â105 km at Trivandrum (8.5°N, 77°E) during five afternoon counterelectrojet days in January 1987, and eastward winds during normal electrojet days. Stening et al. [1996] pointed out that this and other counterelectrojet events during northern winter were accompanied by eastwardâtoâwestward upper atmosphere wind reversals at a height of 99 km at Saskatoon, Canada (35°S, 107°W), and that they generally occurred during sudden stratospheric warming (SSW) periods. On the other hand, northern summer counterelectrojet events at Trivandrum, sometimes persisting for several days, were not associated with changes in the Saskatoon winds. Stening [1989] and Gurubaran [2002] pointed out that equatorial counterelectrojet events could result from the dynamo effects of global wind changes. Stening et al. [1997] used numerical simulations to show that lunar tidal amplitudes and phases undergo large changes during stratospheric warmings. Rastogi [1999] suggested that quiet time counterelectrojet events during low solar activity northern winter months result from changes in the ionospheric wind system associated with stratospheric warmings. [6] Sudden stratospheric warming (SSW) is a largeâscale meteorological process in the winter polar region caused by the rapid growth of quasiâstationary planetary waves and their interaction with the stratospheric mean circulation [Matsuno, 1971]. These events strongly affect the background wind, temperature, chemistry and wave activity of the middle atmosphere, as well as the vertical thermodynamic coupling in a large range of altitudes and latitudes [e.g., Labitzke, 1981; Andrews et al., 1987; Liu and Roble, 2002; Hoffmann et al., 2002; Shepherd et al., 2007; Pancheva et al., 2008]. [7] Lowâlatitude mesospheric and lower thermospheric effects associated with polar stratospheric warmings have been the subject of intense recent scientific interest [e.g., Vineeth et al., 2007; Sridharan and Sathishkumar, 2008]. Recently, Chau et al. [2009] reported a unique semidiurnal signature lasting for several days on equatorial F region vertical plasma drifts measured at the Jicamarca Radio Observatory (11.9°S, 76.8°W; dip latitude 1°N) during a minor SSW event in January 2008. Vineeth et al. [2009] suggested that SSWs lead to higher occurrence of quasi 16 day periodicity of equatorial counterelectrojets and that stronger counterelectrojets are associated with more intense warmings. Sridharan et al. [2009] used magnetic field and mesospheric wind measurements in the Indian region to show that major arctic SSW events affect the dayâtoâday variability of equatorial counterelectrojets through the enhancement of semidiurnal tides. [8] In this study, we use Jicamarca radar measurements and global satellite and groundâbased magnetic field observations during 2001â2009 northern winters to study, for the first time, the longitudeâdependent equatorial electrodynamic perturbations during SSW events. Our results suggest that these large electrodynamic perturbations most likely result from strong sudden enhancements of longitudeâdependent lunar tidal wave effects during stratospheric warmings. 2. Data [9] We have used vertical plasma drifts obtained from Doppler radar measurements of 150 km echoes by the Jicamarca Unattended Longâterm Ionosphere and Atmosphere (JULIA) radar system at the Jicamarca Radio Observatory (11.9°S, 76.8°W; 0.8°N magnetic), near Lima, Peru. These measurements are generally made between about 0900 and 1600 LT with a time resolution of 5 min and also provide accurate estimates of the F region vertical plasma drifts and ionospheric zonal electric fields [e.g., Kudeki and Fawcett, 1993; Chau and Woodman, 2004]. However, they were only made during a relatively small number of days during our 2001â2009 northern winter periods of interest. [10] We have determined the strength of the equatorial electrojets in the American, Indian, and Japanese sectors from the difference of the horizontal magnetic fields measured at pairs of stations, one close to the geomagnetic equator and another a few degrees off. These stations are Jicamarca and Piura (5.2°S, 80.6°W; 6.8° magnetic) in the American sector, Tirunelveli (8.7°N, 77.8°E; 0.5°S magnetic) and Alibag (18.6°N, 72.9°E; 10°N magnetic) in the Indian region, and Yap (9.3°N, 138.5°E; 0.5°N magnetic) and Biak (1.1°S, 136.0°E; 9.7°S) in the Pacific sector. We have also used the magnetic field measurements in the Peruvian region to estimate ionospheric vertical plasma drifts (zonal electric fields) using the methodology developed by Anderson et al. [2002]. These derived drifts are generally in good agreement with the vertical drifts measured by the Jicamarca radar, except between dawn and about 1000 LT, when they often underestimate the measured upward drifts. [11] The polarâorbiting Challenging Minisatellite Payload (CHAMP) satellite has been making highâquality magnetic field (accuracy of about 0.1 nT)measurements since July 2000. The satellite has an orbital period of 93 min and advances about 23° westward from orbit to orbit. Equatorial electrojet current distributions are determined from CHAMP measurements by first removing magnetic field contributions from other sources, and then using a very general current model which makes the results independent of the satellite altitude A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 2 of 9 and ambient field geometry [e.g., LĂŒhr et al., 2004; Manoj et al., 2006]. In this study, we present CHAMP equatorial magnetic field measurements in the afternoon sector from late December 2002 through January 2003. 3. Results 3.1. Electrodynamic Effects During December 2002 and January 2003 [12] Figure 1 shows the development of the December 2002 to January 2003 minor stratospheric warming events. The top plots present the zonal mean temperatures at 10 hPa (about 32 km) at 90°N, the mean zonal winds averaged over 60°N, and the corresponding 30 year mean temperatures and zonal winds obtained from the National Center for Environmental Prediction (NCEP). The bottom plots give the daily solar decimetric flux and the 3 h Kp indices. [13] Figure 1 indicates that the December 2002 highlatitude stratospheric temperatures and zonal winds were mostly above and below their 30 year mean values, respectively. The temperature started to increase rapidly on 28 December, reached its maximum on 31 December, and then slowly decreased until about 12 January; the second and third warmings started on 14 and 24 January and reached peak values on 16 and 26 January. During the first two warmings, the longitudinal averaged eastward winds decreased by about 10 and 30 m/s below their average values, respectively. [14] Figure 2 shows the daytime vertical plasma drifts obtained from Doppler measurements of 150 km echoes over Jicamarca during the first 2002â2003 warming and the corresponding quiet time averages. Figure 2 shows large downward drift (westward electric field) perturbations during 30 December to 1 January, which is indicative of an abnormally large reduction in the ionospheric daytime eastward electric fields. This was followed by a very large and sudden increase in the morning upward drifts on 2 January. The resulting very large semidiurnal drift perturbations (upward in the morning and downward in the afternoon) shifted gradually to later local times from 2 January through 6 January. Incoherent scatter radar measurements during the stronger January 2008 SSW event presented by Chau et al. [2009] show basically an identical perturbation drift pattern after about 0900 LT, and even larger upward drift enhancements in the early morning period. [15] The vertical drifts derived from Jicamarca and Piura magnetic field measurements during December 2002 to January 2003 are presented in Figure 3. The slant line indicates the local times of the equatorial crossings of the CHAMP satellite. The December data show large drift dayâtoâday variability. Figure 3 also shows small upward morning and large downward afternoon drifts during 29â31 December, large sudden increase in the upward morning and downward afternoon drifts on 2 January, and the gradual shift of the semidiurnalâlike perturbation drift pattern to later local times Figure 1. Stratospheric polar zonally averaged temperature, zonal wind (positive eastward), from the National Center for Environmental Prediction, and decimetric solar flux and Kp indices for December 2002 to January 2003. The median values are shown as black circles. Figure 2. Vertical plasma drift velocities of 150 km radar echoes measured with the Jicamarca Unattended Longâterm Ionosphere and Atmosphere system. The smooth curve denotes the mean drifts. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 3 of 9 over a period of a few days leading to increased upward drifts in the afternoon and decreased or reversed drifts in the morning. A smaller but weaker perturbation drift pattern also occurred during 19â25 January after an interval of much smaller daytime drifts on 15â18 January. Figure 3 also show relatively large 2 day modulations on the vertical drifts. [16] Figure 4 shows the daytime DH, which reflects the intensity of the equatorial electrojet, in the Peruvian, Indian, and Pacific sectors between 1 December 2002 and 29 January 2003. In this period, new moons occurred on 4 December and 2 January, and full moons occurred on 19 December and 18 January. The December data illustrate the typical dayâtoday variability of the daytime electrojet currents with the absence of correlated large temporal perturbation drift patterns in these longitudinal sectors. After the late December warming onset, the electrojet intensities first weakened for about 2 days and then, around new moon, suddenly developed very similar multiday perturbation patterns with largely enhanced morning eastward and afternoon westward currents that systematically shifted to later local times. Strong morning counterelectrojets were seen around the first and last quarters (10 and 25 January). The morning and afternoon current perturbations occurred first and were strongest in the American sector and developed last and were weakest (particularly in the afternoon) in the Pacific sector. Similar, but weaker, current perturbations developed near full moon after the second warming, when the highâlatitude wind perturbations were even larger. These perturbation events are about 14 days apart, as expected for the lunar semimonthly tide [Stening, 1989]. [17] Figure 5 illustrates in more detail the longitudedependent daytimemagnetic field perturbations during the first SSW episode. We can see again that the afternoon counterelectrojets occurred first and were strongest in the American sector and the shift of the perturbation current pattern to later local times. In particular, there is a clear increase in the time of the counterelectrojet minimum as the days progress. Figure 5 also shows the effect of geomagnetic activity on the electrojet intensity, which was strongest during 3â4 January. [18] The onset of strong semidiurnal electrojet intensity perturbations close to new and full moons and the shifts of the current perturbation patterns to later local times with lunar age suggest the occurrence of highly enhanced lunar semidiurnal wave effects over a broad range of longitudes during these SSW events. The shift of the current perturbation patterns are consistent with the difference in the lengths of the solar and lunar days. [19] Figure 4 also shows the occurrence of strong 2 day wave perturbations on the strength of the electrojet currents Figure 3. Vertical plasma drift velocities (positive upward) over Jicamarca derived from magnetic field observations. The slant line indicates the local time coverage of the CHAMP satellite. Figure 4. Equatorial horizontal magnetic field components in three longitudinal sectors and highâlatitude zonally averaged stratospheric temperatures and zonal winds during December 2002 and January 2003. The days of new and full moons are indicated by open and solid circles, respectively. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 4 of 9 in our three longitudinal sectors. These perturbations appear to be strongest during SSW events. Pancheva et al. [2006] studied in detail the global occurrence of 2 day wave activity during this period, and Aveiro et al. [2009] reported their signatures on the equatorial electrojet and E region electric fields in the Brazilian sector. [20] The polarâorbiting CHAMP satellite made equatorial electrojet magnetic field measurements in the afternoon sector between late December 2002 and midâFebruary 2003. These measurements made with an orbital period of 93 min provided about 18 equatorial daytime crossings. Figure 6 presents the equatorial electrojet current densities in the afternoon sector between late 27 December 2002 and 30 January 2003. The horizontal lines denote the average longitudes of the ground stations used in our study. We note that the CHAMP electrojet current densities, obtained by fitting the full latitudinal profile of the geomagnetic field data, provide more accurate estimates of the electrojet intensities than derived from geomagnetic data from pairs of stations. We note that the current maxima are about 14 days apart. Figure 6 indicates that following the first warming, afternoon counterelectrojets occurred at all longitudes and that their onset times increased toward the east, which is in good agreement with our groundâbased data. Figure 6 also shows more irregular occurrence of afternoon counterelectrojets during the second warming, which could be partly due to the precession of the satellite to earlier to local times. 3.2. Observations During Other Periods [21] We have examined the currently available Jicamarca vertical drifts and magnetic field groundâbased measurements in the Peruvian and Indian equatorial regions during the other December solstices from 2001 to 2009. In these periods, there were only very limited radar drift measurements. Strong stratospheric warmings occurred during 2001â 2002, 2003â2004, 2005â2006, and 2008â2009, with the last being by far the strongest, and there were occurrences of minor warmings during the other northern winter periods except for 2004â2005. [22] Figure 7 shows the equatorial DH data from the Peruvian and Indian sectors, and the highâlatitude temperatures and winds at 10 hPa from 10 December 2001 to 23 January 2002. Moderate geomagnetic activity on 16, 21, 24 and 31 December and on 10, 11, and 19 January resulted in noticeable shortâterm (less then a few hours)DH electrojet variability, especially in the Peruvian region. Figure 7 shows large DH perturbations with strongly enhanced morning eastward and afternoon westward currents starting near new moon and about nine days after the warming onset, and the shift of the perturbation patterns to local times. [23] Figure 8 shows the DH data from Peru and the corresponding highâlatitude temperatures and zonal winds during the magnetically quiet period from 20 December 2008 to 28 February 2009. In this period, new moons occurred on Figure 5. Equatorial horizontal magnetic field components close to the 2 January new moon period during the first December 2002 to January SSW event. The smooth curves denote the quiet time values before the SSW onset. Figure 6. Equatorial electrojet afternoon current density measurements by the CHAMP satellite and highâlatitude stratospheric parameters between late December 2002 and January 2003. The horizontal lines denote the longitudes of our groundâbased stations. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 5 of 9 27 December and 26 January and full moons on 11 January and 9 February. The highâlatitude data indicate the occurrence of a very strong large SSW event from midâJanuary through midâFebruary. The equatorial data do not show any unusual DH perturbations prior to the SSW onset. After the warming, however, there were again very large decreases in the electrojet morning and afternoon currents on 23â24 January, followed by large sudden increases in the morning eastward and afternoon westward currents and a continuous shift of the current reversals to later local times after the new moon on 27 January. [24] Figure 9 shows the DH data from the Peruvian region during 24â28 January 2009 and the corresponding average values prior to the SSW event. Figure 9 illustrates in more detail the very large increase in the intensity of the early morning electrojet intensities from 26 to 27 January and the following gradual shift of the current reversal times. Jicamarca incoherent scatter radar measurements (not shown) indicate that the F region upward drift velocity at about 0900 LT increased from about 20 m/s on 25 January to about 50 m/s on 27 January. [25] The morphology of Jicamarca vertical plasma drift during the January 2008 SSW event reported by Chau et al. [2009] is fully consistent with the results presented above. In that event full moon occurred on 22 January, the Jicamarca morning upward plasma drifts strongly increased on 22â23 January. One day later, the Indian DH data (not shown) show small increases in intensity of the morning electrojet and strong afternoon counterelectrojet conditions. The same sequence of events appears to have occurred during the strong 2003 and 2004 warming period, although in this case there were no plasma drift measurements and the Peruvian magnetometer data are less reliable partly due to geomagnetic effects. The morphology of equatorial DH perturbations described above has also been inferred from equatorial measurements during the 2006â2007 SSW event. [26] We have seen that during SSW events large semidiurnal perturbations in equatorial plasma drifts and electrojet currents are associated with lunar tidal wave effects. It is important to note, however, that lunar tidal effects frequently modulate the equatorial electric fields and current as reported in earlier studies. During northern winter, these effects are seen more often in the Peruvian than in the Indian sector, as reported in earlier studies. Figure 10 shows the equatorial DH data from the Peruvian and Indian sectors and the highâlatitude stratospheric temperatures and winds during December 2004 and January 2005, a northern winter period without stratospheric warmings. In this case, the shortâterm enhancements in the intensities of the electrojet currents were associated with increase geomagnetic activity. Figure 10 shows afternoon counterelectrojets and shifts of the perturbation patterns occurred around the time of the new moon period on 9 January, and perhaps also close to the new Figure 8. Equatorial horizontal magnetic field measurements in the Peruvian sector and highâlatitude stratospheric parameters during December 2008 and January 2009. The days of new and full moons are also shown. Figure 7. Equatorial horizontal magnetic field measurements in the Indian and Peruvian sectors and highâlatitude stratospheric parameters during December 2001 and January 2003. The days of new and full moons are also shown. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 6 of 9 moon period on 24 January. However, these semidiurnal current perturbations had only fairly small magnitudes. 4. Discussion [27] We have shown large temporal electrodynamic perturbations in the equatorial vertical drifts (zonal electric fields) and electrojet intensities in three widely spaced longitudinal sectors during SSWevents from the end of December through early February. These large semidiurnal like perturbations were preceded by about two days of largely reduced eastward electric fields and electrojet intensities. The sudden onset of the large semidiurnal perturbations occurred during the SSW events and close to the new and full moons (lunar ages 00 and 12 h) and systematically shifted to later local times with lunar age. Later, large electric field and electrojet current reversals in the morning occurred near the first and last quarters (lunar ages 0600 and 1800 h). In the absence of SSW events, the electric field and current had much smaller perturbations. These results indicate the large amplification of lunar tidal wave effects in the equatorial zonal electric fields and electrojet intensities during arctic stratospheric warmings. [28] The large electrojet current perturbations during SSW events shown above occurred first in the American and last in the Pacific sector. This is consistent with the longitudinal dependence of afternoon counterelectrojet onsets inferred from the 2002â2003 CHAMP data. Magnetometer derived vertical plasma drifts during the 2002â2003 and 2003â2004 SSW events also indicate the earlier occurrence of large perturbations in the Peruvian than in the Philippine sector (D. Anderson, private communication, 2009). On the other hand, magnetic field measurements during the January 1989 SSW event studied by Rangarajan and Rastogi [1993] suggest the occurrence of large electrojet current perturbations earlier in the Indian than in the American sector. This indicates that detailed additional studied are needed to fully characterize the longitudinal dependence of SSW associated equatorial electrodynamic disturbances. [29] Our data suggest that the electric field and current perturbations are most pronounced during December, but there are indications that SSWâenhanced electrodynamic perturbations also occur during equinoctial periods [e.g., Stening et al., 1996]. Figure 5 of Fejer and Scherliess [2001], for example, shows an unusually large increase in the morning Figure 9. Horizontal magnetic field measurements in the Peruvian equatorial region during the very large 2009 SSW event. The smooth curve denotes the average values before the SSW onset. Figure 10. Equatorial horizontal magnetic field measurements in the Indian and Peruvian sectors and highâlatitude stratospheric parameters during December 2004 and January 2005, which was a period without SSW events. The days of new and full moons are also shown. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 7 of 9 and early afternoon F region upward plasma drifts over Jicamarca from 17 to 18 March 1988. This large quiet time drift increase also occurred on a new moon during a SSW event and the enhanced upward drifts lasted for at least three days (the radar measurements ended on 20 March). In this case, however, there were only very small decreases in the afternoon drifts relative to their average values. This suggests that the equatorial electrodynamic signatures of SSW events might change with season. We note that over Jicamarca, afternoon vertical drift reversals and corresponding counterelectrojet events are less frequent during equinox than during the December solstice. [30] Simulation studies using the NCAR TIMEâGCM show that, owing to their nonlinear interaction with quasistationary planetary waves, both the migrating and nonmigrating tides have largest changes at low latitudes and in the ionospheric E region [Liu et al., 2010]. They also indicate that equatorial plasma drifts and, therefore, equatorial electrojet intensity changes are longitudeâ and localâtimeâdependent with large upward drift (i.e., eastward electric field) perturbations near 0500 LT around 70°W, and largest downward drift perturbations around 70°E at the same local time. Our observations consistently show larger morning eastward electric field perturbations in the American than in the Indian sector in good agreement with these simulations. We note, however, that the large variability of the electrodynamics of the lowâlatitude ionosphere during SSW events often also involve strong gravity, 2 day and longer period planetary wave effects [e.g., Sathishkumar and Sridharan, 2009; Abdu et al., 2006]. [31] The equatorial vertical plasma drifts and electrojet intensities exhibit sudden distinctive signatures during SSW events which can also be identified in earlier observations. This suggests that the study of historic global equatorial magnetic field measurements, which now go back over a century, could provide additional information on the equatorial electrodynamic effects of SSWs over several decades. We note that the meteorological analysis of arctic winter SSW data extends back only to 1978â1979 and that the historical stratospheric temperature data presented by Manney et al. [2005] extends to 1958â1959. The use of global equatorial magnetic field measurements to infer the occurrence of SSW events during other seasons and earlier periods will be a subject of a future study. 5. Summary [32] We have studied Jicamarca vertical plasma drift and global equatorial magnetic field measurements during 2001â 2009 arctic SSW events. Our observations show that this strong highâlatitude meteorological process gives rise to large global equatorial electrodynamic perturbations lasting for several days. These equatorial perturbations are longitude dependent and have distinctive magnetic field signatures which have been reported for several decades. Our results indicate that lunar semidiurnal tidal wave effects highly enhanced during SSW events are the most likely source of these unusual electrodynamic perturbations. [33] Acknowledgments. We thank A. Bhattacharyya and the Indian Institute of Geomagnetism for the Tirunelveli and Alibag data. We thank NICT for the Yap data and the Solar Terrestrial Environmental Laboratory, Nagoya University, for managing the database of the 210 MM magnetic observations. We also thank D. Siskind and S. Larson for useful discussions. The work at Utah State University was supported by the Aeronomy Program, Division of Atmospheric Sciences, through grant ATMâ0534038 and by the NASA Living With a Star (LWS) Program through grant NNX06AC44G. The Jicamarca Radio Observatory is a facility of the Instituto Geofisico del Peru, Ministry of Education, and is operated with support from the NSF cooperative agreement ATMâ0432565 through Cornell University. [34] Robert Lysak thanks Robert Stening and another reviewer for their assistance in evaluating this paper. References Abdu, M. A., et al. (2006), Planetary wave signatures in the equatorial atmosphereâionosphere system and mesosphereâE and F region coupling, J. Atmos. Sol. Terr. Phys., 68, 509â522, doi:10.1016/j.jastp. 2005.03.019. Alex, S., A. Patil, and R. G. Rastogi (1986), Equatorial counter electrojet solution of some dilemma, Indian J. Radio Space Phys., 15, 114â118. Anderson, D., A. Anghel, K. Yumoto, M. I****suka, and E. Kudeki (2002), Estimating daytime vertical ExB drift velocities in the equatorial Fâ region using groundâbased magnetometer observations, Geophys. Res. Lett., 29(12), 1596, doi:10.1029/2001GL014562. Andrews, D., J. R. Holton, and C. B. Leovy (1987), Middle Atmosphere Dynamics, pp 259â294, Elsevier, New York. Aveiro, H. C., C. M. Denardini, and M. A. Abdu (2009), Signatures of 2âday wave in the E region electric fields and their relationship to winds and ionospheric currents, Ann. Geophys., 27, 631â638. Bartels, J., and H. F. Johnston (1940), Geomagnetic tides in horizontal intensity at Huancayo, Terr. Magn. Atmos. Electr., 45, 269â308, doi:10.1029/ TE045i003p00269. Bhargava, B. N., and N. S. Sastri (1977), A comparison of days with and without occurrence of counter electrojet afternoon events in the Indian region, Ann. Geophys., 33, 329â333. Chau, J. L., and R. F. Woodman (2004), Daytime vertical and zonal velocities from 150âkm echoes: Their relevance to F region dynamics, Geophys. Res. Lett., 31, L17801, doi:10.1029/2004GL020800. Chau, J. L., B. G. Fejer, and L. P. Goncharenko (2009), Quiet variability of equatorial E x B drifts during a stratospheric warming event, Geophys. Res. Lett., 36, L05101, doi:10.1029/2008GL036785. Chen, P.âR. (1992), Twoâday oscillation of the equatorial ionization anomaly, J. Geophys. Res., 97, 6343â6357, doi:10.1029/91JA02445. Fejer, B. G. (1997), The electrodynamics of the lowâlatitude ionosphe Recent results and future challenges, J. Atmos. Sol. Terr. Phys., 59, 1465â1482, doi:10.1016/S1364-6826(96)00149-6. Fejer, B. G., and L. Scherliess (2001), On the variability of equatorial F region vertical plasma drifts, Atmos. Sol. Terr. Phys., 63, 893â897. Forbes, J. M., and S. Leveroni (1992), Quasiâ16 day oscillation in the ionosphere, Geophys. Res. Lett., 19, 981â984, doi:10.1029/92GL00399. Gouin, P. (1962), Reversal of the magnetic daily variations at Addis Abbaba, Nature, 193, 1145â1146, doi:10.1038/1931145a0. Gouin, P., and P. N. Mayaud (1967), A propos de lâexistence possible dâun contre electrojet aux latitudes magnetiques equatorials, Ann. Geophys., 23, 41â47. Gurubaran, S. (2002), The equatorial electrojet: Part of a worldwide current system, Geophys. Res. Lett., 29(9), 1337, doi:10.1029/2001GL014519. Heelis, R. A. (2004), Electrodynamics in the low and middle latitude ionosphe A tutorial, J. Atmos. Sol. Terr. Phys., 66, 825â838, doi:10.1016/ j.jastp.2004.01.034. Hoffmann, P., W. Singer, and D. Keuer (2002), Variability of the mesospheric wind field at middle and arctic latitudes in winter and its relationship to stratospheric circulation disturbances, J. Atmos. Sol. Terr. Phys., 64, 1229â1240, doi:10.1016/S1364-6826(02)00071-8. Hutton, R., and J. O. Oyinloye (1970), The counterâelectrojet in Nigeria, Ann. Geophys., 26, 921â926. Kudeki, E., and C. D. Fawcett (1993), High resolution observations of 150 km echoes at Jicamarca, Geophys. Res. Lett., 20, 1987â1990, doi:10.1029/93GL01256. Labitzke, K. (1981), Stratosphericâmesospheric midwinter disturbances: A summary of observed characteristics, J. Geophys. Res., 86, 9665â9678, doi:10.1029/JC086iC10p09665. Liu, H.âL., and R. G. Roble (2002), A study of a selfâgenerated stratospheric sudden warming and its mesosphericâlower atmospheric impacts using the coupled TIMEâGCM/CCM3, J. Geophys. Res., 107(D23), 4695, doi:10.1029/2001JD001533. Liu, H.âL., W. Wang, A. D. Richmond, and R. G. Roble (2010), Ionospheric variability due to planetary waves and tides for solar minimum conditions, J. Geophys. Res., 115, A00G01, doi:10.1029/2009JA015188. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 8 of 9 LĂŒhr, H., S. Maus, and M. Rother (2004), Noonâtime equatorial electrojet: Its spatial features as determined by the CHAMP satellite, J. Geophys. Res., 109, A01306, doi:10.1029/2002JA009656. Manney, G. L., K. Kruger, J. L. Sabutis, S. A. Sena, and S. Pawson (2005), The remarkable 2003â2004 winter and other recent warm winters in the Arctic stratosphere since late 1960, J. Geophys. Res., 110, D04107, doi:10.1029/2004JD005367. Manoj, C., H. LĂŒhr, S. Maus, and N. Nagarajan (2006), Evidence for short spatial correlation lengths of the noontime equatorial electrojet inferred from a comparison of satellite and ground based magnetic data, J. Geophys. Res., 111, A11312, doi:10.1029/2006JA011855. Marriott, R. T., A. D. Richmond, and S. V. Venkateswaran (1979), The quiet time equatorial electrojet and counterâelectrojet, J. Geomagn.. Geoelectr., 31, 311â340. Matsuno, T. (1971), A dynamical model of the stratospheric sudden warming, J. Atmos. Sci., 28, 1479â1494, doi:10.1175/1520-0469(1971)0281479: ADMOTS2.0.CO;2. Mayaud, P. N. (1977), The equatorial counterâelectrojet: A review of its geomagnetic aspects, J. Atmos. Terr. Phys., 39, 1055â1070, doi:10.1016/ 0021-9169(77)90014-9. Onwumechilli, A., and S.âI. Akasofu (1972), On the abnormal depression of Sq(H) under the equatorial electrojet in the afternoon, J. Geomagn. Geoelectr., 24, 161â173. Pancheva, D. V., et al. (2006), Twoâday wave coupling of the lowâ latitude atmosphereâionosphere system, J. Geophys. Res., 111, A07313, doi:10.1029/2005JA011562. Pancheva, D. V., et al. (2008), Latitudinal wave coupling of the stratosphere and mesosphere during the major stratosphere and mesosphere during the major stratospheric warming in 2003/2004, Ann. Geophys., 26, 467â483. Patil, A. R., D. R. K. Rao, and R. G. Rastogi (1990), Equatorial electrojet strengths in the Indian and American sector: Part I. During low solar activity, J. Geomagn. Geoelectr., 42, 801â823. Rangarajan, G. K., and R. G. Rastogi (1993), Longitudinal difference in magnetic field variations associated with quiet day counter electrojet, J. Geomagn. Geoelectr., 45, 649â656. Rastogi, R. G. (1973), Counter equatorial electrojet currents in the Indian zone, Planet. Space Sci., 21, 1355â1365, doi:10.1016/0032-0633(73) 90228-6. Rastogi, R. G. (1974a), Lunar effects in the counterâelectrojet near the magnetic equator, J. Atmos. Terr. Phys., 36, 167â170, doi:10.1016/ 0021-9169(74)90074-9. http://www.haystack.mit.edu/ssw/wp-c..._Fejer_SSW.pdf That's the way to do it! Rastogi, R. G. (1974b), Westward equatorial electrojet during daytime hours, J. Geophys. Res., 79, 1503â1512, doi:10.1029/JA079i010p01503.. Rastogi, R. G. (1975), Is the Moon the cause of the equatorial counter electrojet currents?, Curr. Sci., 44, 251â252. Rastogi, R. G. (1999), Morphological aspects of a new type of counter electrojet event, Ann. Geophys., 17, 210â219, doi:10.1007/s00585-999-0210-6. Richmond, A. D. (1995a), The ionospheric wind dynamo: Effects of its coupling with different atmospheric regions, in The Upper Mesosphere and Lower Thermosphe A Review of Experiment and Theory, Geophys. Monogr. Ser., vol. 87, edited by R. M. Johnson and T. L. Killeen, pp. 49â65, AGU, Washington, D.C. Richmond,A. D. (1995b), Ionospheric electrodynamics, inHandbook of Atmospheric Electrodynamics, vol. 2, edited by H. Volland, pp. 249â290, CRC Press, Boca Raton, Fla. Sathishkumar, S., and S. Sridharan (2009), Planetary and gravity wave in the mesosphere and lower thermosphere over Tirunelveli (8.7°N, 77.8°E) during stratospheric warming events, Geophys. Res. Lett., 36, L07806, doi:10.1029/2008GL037081. Shepherd, M. G., et al. (2007), Stratospheric warming effects on the tropical mesospheric temperature field, J. Atmos. Sol. Terr. Phys., 69, 2309â 2337, doi:10.1016/j.jastp.2007.04.009. Somayajulu, V. V., L. Cherian, K. Rajeev, G. Ramkumar, and C. Ragnava Reddi (1993), Mean winds and tidal components during counter electrojet events, Geophys. Res. Lett., 20, 1443â1446, doi:10.1029/93GL00088. Sridharan, S., and S. Sathishkumar (2008), Seasonal and interannual variations of gravity wave activity in the lowâlatitude mesosphere and lower thermosphere over Tirunelveli (8.7°N, 77.8°E), Ann. Geophys., 26, 3215â3223. Sridharan, S., S. Sathishkumar, and S. Gurubaran (2009), Variabilities of mesospheric tides and equatorial electrojet strength during major stratospheric warming events, Ann. Geophys., 27, 4125â4130. Stening, R. J. (1977), Electron density profile changes associated with the equatorial electrojet, J. Atmos. Terr. Phys., 39, 157â164, doi: 10.1016/ 0021-9169(77)90109-X. Stening, R. J. (1989), A diurnal modulation of the lunar tide in the upper atmosphere, Geophys. Res. Lett., 16, 307â310, doi:10.1029/GL016i004p00307. Stening, R. J., C. E. Meek, and A. H. Manson (1996), Upper atmosphere wind system during reverse equatorial electrojet events, Geophys. Res. Lett., 23, 3243â3246, doi:10.1029/96GL02611. Stening, R. J., J. M. Forbes, M. E. Hagan, and A. D. Richmond (1997), Experiments with lunar atmospheric tidal model, J. Geophys. Res., 102, 13,465â13,471, doi:10.1029/97JD00778. Vineeth, C., T. K. Pant, C. V. Devasia, and R. Sridharan (2007), Highly localized cooling in daytime mesopause temperature over the dip equator during counterâelectrojet events: First results, Geophys. Res. Lett.., 34, L14101, doi:10.1029/2007GL030298. Vineeth, C., T. Kumar Pant, and R. Sridharan (2009), Equatorial counter electrojets and polar stratospheric sudden warmings: A classical example of high latitudeâlow latitude coupling?, Ann. Geophys., 27, 3147â3153. J. L. Chau, Radio Observatorio de Jicamarca, Instituto Geofisico del Peru Apartado 13â0207, Lima 13, Peru 2. B. G. Fejer and M. E. Olson, Center for Atmospheric and Space Sciences, Utah State University, Logan, UT 84222â4405, USA. ) L. P. Goncharenko, Haystack Observatory, Massachusetts Institute of Technology, Westford, MA 01886â1299, USA. H. LĂŒhr and C. Stolle, Helmholtz Centre Potsdam, GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany 3. T. Nagatsuma, Applied Electromagnetic Research Center, National Institute of Information and Communications Technology, Tokyo 184â8795, Japan.. K. Yumoto, Space Environment Research Center, Kyushu University, Fukuoka 812â8581, Japan. A00G03 FEJER ET AL.: EQUATORIAL STRATWARM EFFECT A00G03 9 of 9 |
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On Jan 28, 10:52*am, "Alastair McDonald"
wrote: "N_Cook" wrote in message ... Alastair McDonald wrote in message ... I have just been made aware of this article which seems to suggest something I had suspected: that lunar tides are linked with jet streams. The article is entitled: "Equatorial Ionospheric Electrodynamic Perturbations During Southern Hemisphere Stratospheric Warming Events" But the abstract says: "We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events." http://onlinelibrary.wiley.com/doi/1...bstract;jsessi... 9A2C47D3C86E8784D17AA97B850BB8.d01t04 If SSWs are caused by waves in jet streams breaking, then there is some sort of connection with lunar tides. Cheers, Alastair. Why just lunar tides? the solar component of the tides are half as strong as lunar ones The solar tides are masked by the effects of solar radiation with which they coincide. The Blocking Highs of the North Atlantic follow a seasonal cycle of 2 1/2, 3, 4 and 2 1/2 month intervals, with the peak in January and August (IIRAoT.) Also, IIRC, the peaks coincide with the movement of the ITCZ and the North Atlantic hurricane season (though I forget why and how.) The sequence of events on the sea level chart is a couter clockwise rotation of a multiple Low system. This is followed by a large magnitude earthquakes of a value comparable to the overall pressures in the system, a tropical storm -similarly appointed and then the block. Highs in winter tend to be very high pressure and those in summer almost flaccid. I have the impression that the summer stuff is due to the lack of Polar air and the abundance of exrta tropical air. The retrograde motion strikes me as having something in common with the work of Astrology -bearing in mind that there was once no difference in the term and the astronomy scholars regarded as cutting edge scientists even today. spitFor a given definition of the term scientist/spit I have no idea how to cast an horological chart though if anyone here could help I'd be grateful. (Unless you are Dawlish, that is. I rather suspect the tit might In which case, I'd rather not know.) The occurrence of SSWs in something approaching multidecadal timescales has flummoxed research since the following ones are not usually of the same or similar value. This is likely to be due to the cause being a signicant event that occurs only once in a while rather in the manner of a Saros cycle as opposed to something as the incremantal steps seen with something such as the solar declination (and lunar declination which is slightly more complex but again, is of multistepped increments.) What the other planets do to accomplish this I can't say. Apparently it's the cobined resultant of the solar system that keeps the moon in its place. (Which incidentally explains why the earth is still in its present orbit and why the earth and moon have not moved off to pasture new -not will they.) I have the impression it must be the way they focus the solar winds and earths "bow shock". But I point no fingo. |
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