Giant Storm Research Articles

Long-lasting, deep effect of Saturn's giant storms.

Planetary-scale giant storms erupt on Saturn quasiperiodically. There have been at least six recorded occurrences of past eruptions, and the most recent one was in 2010, with its whole life span captured by the Cassini mission. In 2015, we used the Very Large Array to probe the deep response of Saturn's troposphere to the giant storms. In addition to the remnant effect of the storm in 2010, we have found long-lasting signatures of all mid-latitude giant storms, a mixture of equatorial storms up to hundreds of years old, and potentially an unreported older storm at 70°N. We derive an ammonia anomaly map that shows an extended meridional migration of the storm's aftermath and vertical transport of ammonia vapor by storm dynamics. Intriguingly, the last storm in 2010 splits into two distinct components that propagate in opposite meridional directions, leaving a gap at 43°N planetographic latitude.

Microwave observations reveal the deep extent and structure of Jupiter’s atmospheric vortices

Jupiter’s atmosphere has a system of zones and belts punctuated by small and large vortices, the largest being the Great Red Spot. How these features change with depth is unknown, with theories of their structure ranging from shallow meteorological features to surface expressions of deep-seated convection. We present observations of atmospheric vortices using the Juno spacecraft’s Microwave Radiometer. We found vortex roots that extend deeper than the altitude at which water is expected to condense, and we identified density inversion layers. Our results constrain the three-dimensional structure of Jupiter’s vortices and their extension below the clouds.

The depth of Jupiter's Great Red Spot constrained by Juno gravity overflights.

Jupiter’s Great Red Spot (GRS) is the largest atmospheric vortex in the Solar System and has been observed for at least two centuries. It has been unclear how deep the vortex extends beneath its visible cloud tops. We examined the gravity signature of the GRS using data from 12 encounters of the Juno spacecraft with the planet, including two direct overflights of the vortex. Localized density anomalies due to the presence of the GRS caused a shift in the spacecraft line-of-sight velocity. Using two different approaches to infer the GRS depth, which yielded consistent results, we conclude that the GRS is contained within the upper 500 kilometers of Jupiter’s atmosphere.

A complex storm system in Saturn’s north polar atmosphere in 2018

Saturn’s convective storms usually fall in two categories. One consists of mid-sized storms ∼2,000 km wide, appearing as irregular bright cloud systems that evolve rapidly, on scales of a few days. The other includes the Great White Spots, planetary-scale giant storms ten times larger than the mid-sized ones, which disturb a full latitude band, enduring several months, and have been observed only seven times since 1876. Here we report a new intermediate type, observed in 2018 in the north polar region. Four large storms with east–west lengths ∼4,000–8,000 km (the first one lasting longer than 200 days) formed sequentially in close latitudes, experiencing mutual encounters and leading to zonal disturbances affecting a full latitude band ∼8,000 km wide, during at least eight months. Dynamical simulations indicate that each storm required energies around ten times larger than mid-sized storms but ∼100 times smaller than those necessary for a Great White Spot. This event occurred at about the same latitude and season as the Great White Spot in 1960, in close correspondence with the cycle of approximately 60 years hypothesized for equatorial Great White Spots. A series of four storms appeared on Saturn’s northern polar region in 2018, unusually close to each other in space and time. By their dimension and the energy needed to form them, they appear to be a hitherto unobserved kind of storm at Saturn, intermediate between the regional- and the global-sized ones.

Hubble reveals birth of giant storm on Neptune

Hubble reveals birth of giant storm on Neptune

Disrupting the atmospheric beat

The tropical stratospheric temperature and wind field of several planets oscillate quasi-periodically. Recent Cassini observations show that Saturn’s oscillations were disturbed for more than three years by the year-long giant storm that appeared in 2010.

Shallow water simulations of Saturn's giant storms at different latitudes

Shallow water simulations are used to present a unified study of three major storms on Saturn (nicknamed as Great White Spots, GWS) at different latitudes, polar (1960), equatorial (1990), and mid-latitude (2010) (Sánchez-Lavega, 2004; Sánchez-Lavega et al., 2011). In our model, the three GWS are initiated by introducing a Gaussian function pulse at the latitude of the observed phenomena with controlled horizontal size and amplitude. This function represents the convective source that has been observed to trigger the storm. A growing disturbance forms when the pulse reacts to ambient winds, expanding zonally along the latitude band of the considered domain. We then compare the modeled potential vorticity with the cloud field, adjusting the model parameters to visually get the closest aspect between simulations and observations. Simulations of the 2010 GWS (planetographic latitude ∼+40º, zonal velocity of the source ∼−30m s−1) indicate that the Coriolis forces and the wind profile structure shape the disturbance generating, as observed, a long region to the east of the convective source with a high speed peripheral anticyclonic circulation, and a long-lived anticyclonic compact vortex accompanied by strong zonal advection on the southern part of the storm forming a turbulent region. Simulations of the equatorial 1990 GWS (planetographic latitude +12º–+5º, zonal velocity of the source 365–400m s−1) show a different behavior because of the intense eastward jet, meridional shear at the equatorial region, and low latitude dynamics. A round shaped source forms as observed, with the rapid growth of a Kelvin-Helmholtz instability on the north side of the source due to advection and to the strong meridional wind shear, whereas at the storm latitude the disturbance grows and propagates eastward. The storm nucleus is the manifestation of a Rossby wave, while the eastward propagating planetary-scale disturbance is a gravity-Rossby wave trapped around the equator. The simulated 1960 GWS disturbance (planetographic latitude +56º, zonal velocity 4m s−1) formed a chain of periodic oval spots that mimic the few available observations of the phenomenon. For the mid and high latitude storms, simulations predict a strong injection of negative relative vorticity due to divergence of the upwelling storm material, which may produce large anticyclones on the anticyclonic side of the zonal profile, and a quick turbulent expansion on the background cyclonic regions. In general, simulations indicate that negative relative vorticity injected by storms determines the natural reaction to zonal winds at latitudes where Coriolis forces are dominant.

Vortices in Saturn's Northern Hemisphere (2008-2015) Observed by Cassini ISS.

We use observations from the Imaging Science Subsystem on Cassini to create maps of Saturn's Northern Hemisphere (NH) from 2008 to 2015, a time period including a seasonal transition (i.e., Spring Equinox in 2009) and the 2010 giant storm. The processed maps are used to investigate vortices in the NH during the period of 2008-2015. All recorded vortices have diameters (east-west) smaller than 6000 km except for the largest vortex that developed from the 2010 giant storm. The largest vortex decreased its diameter from ~11000 km in 2011 to ~5000 km in 2015, and its average diameter is ~6500 km during the period of 2011-2015. The largest vortex lasts at least 4 years, which is much longer than the lifetimes of most vortices (less than 1 year). The largest vortex drifts to north, which can be explained by the beta drift effect. The number of vortices displays varying behaviors in the meridional direction, in which the 2010 giant storm significantly affects the generation and development of vortices in the middle latitudes (25-45°N). In the higher latitudes (45-90°N), the number of vortices also displays strong temporal variations. The solar flux and the internal heat do not directly contribute to the vortex activities, leaving the temporal variations of vortices in the higher latitudes (45-90°N) unexplained.

Unbiased Estimations of Atmosphere Vortices: The Saturn’s Storm by Cassini VIMS-V as Case Study

The size determination of dynamical structures from spectral images poses the question where to fix the shape’s boundary. Here, we propose a method, suitable for nearly elliptical shape, based on the fit of a 2D Gaussian to the pixel intensities of the spectral image. This method has been tested on a vortex structure embedded in the wake of the 2010 Saturn’s giant storm. On January 4th 2012, the Visual and Infrared Mapping Spectrometer (VIMS), onboard Cassini, observed a giant vortex in the Saturn’s northern hemisphere. The structure was embedded in the wake storm system detected on December 2010 by Fletcher et al. [1]. Therefore, all the VIMS observations focused on the Saturn’s storm have been analyzed to investigate its morphology and development. VIMS detected the vortex from May 2011up to January 2012. The evolution of shape and size has been determined for the vortex cloud top, visible at 890 nm. The largest size resulted 4000 km about and seemed to shrinks continuously up to January 2012, while the shape varied in the second half of the year. The vortex oscillated in 2 degrees latitude around 37°N planetocentric latitude, and drifted in longitude by ~0.75 deg/day in westward direction.

Saturn's giant storm and global radiant energy

AbstractWe analyze the relationship between Saturn's radiant energies and the 2010 giant storm with the Cassini observations. The storm increased the emitted power in a wide latitudinal band (20–55°N) with a maximum change of 9.2 ± 0.1% around 45°N from 2010 to 2011. Such a regional change caused the global‐average emitted power to increase by ~2.0 ± 0.2%. Saturn's giant storm occurs quasiperiodically (i.e., period approximately one Saturnian year), so it is possible that giant storms continuously modify the emitted power if the storm modification has a lifetime close to one Saturnian year. The hemispheric‐average emitted power in the southern hemisphere, which was mainly affected by the seasonal change, decreased by 8.5 ± 0.3% from 2004 to 2013. Our estimates also imply that the 2010 giant storm significantly modified the absorbed solar power of Saturn. The significant temporal variations of radiant powers should be considered in reexamining the value of Saturn's internal heat flux.

Moist convection in hydrogen atmospheres and the frequency of Saturn’s giant storms

A giant storm erupted on Saturn in December 2010. It produced intense lightning and cloud disturbances and encircled the planet in six months. Six giant storms—also called Great White Spots—have been observed on Saturn since 1876, recurring every 20 to 30 years and alternating between mid-latitudes and the equator. Here we use thermodynamic arguments to demonstrate that the quasi-periodic occurrence of Saturn’s giant storms can be explained by a water-loading mechanism, in which moist convection is suppressed for decades owing to the relatively large molecular weight of water in a hydrogen–helium atmosphere. We find that the interaction between moist convection and radiative cooling in the troposphere above the cloud base produces an oscillation that leads to giant storm generation with a period of approximately 60 years for either mid-latitudes or the equator, provided the mixing ratio of water vapour in the troposphere exceeds 1.0%. We use a two-dimensional axisymmetric dynamic model and a top-cooling convective adjustment scheme to apply our conceptual model to Saturn. For a water vapour mixing ratio of 1.1%, simulated storms show a recurrence interval, ammonia depletion and tropospheric warming that are consistent with 2010 observations. Jupiter’s atmosphere is more depleted in water than Saturn, which may explain its lack of planet-encircling storms.

The global vortex analysis of Jupiter and Saturn based on Cassini Imaging Science Subsystem

Presented in this manuscript are observations exploring vortices with diameters larger than 1000km on Jupiter and Saturn. These images are taken from the Imaging Science Subsystem onboard the Cassini Spacecraft. The analyses of Saturn’s vortices show that there are significantly more vortices in the Southern Hemisphere (SH) than in the Northern Hemisphere (NH) during the time from 2004 to 2010. In particular, the concentration of vortices are completely different between the two hemispheres, especially in the latitude band around 40°N where the 2010 giant storm occurred. In the SH, the latitude band around 40°S has the highest concentration of vortices on Saturn. Contrasting results show that vortices are lacking in the latitudinal band around 40°N in the NH before the eruption of the 2010 giant storm, although zonal wind characteristics are similar at both locations. Global maps of Saturn at different times suggest that the total numbers of large vortices dramatically decreased from 29±1 to 11±2 in the SH and from 11±2 to 7±1 in the NH during this time period (2004–2010), just before the eruption of the giant storm at the end of 2010. The goal here is to present observational trends and evaluate if the temporal variation in the total number of vortices is related to the eruption of the 2010 giant storm. The comparison of jovian and saturnian vortices shows that the contrast of the two hemispheres is different between the two giant planets, likely due to the different obliquities, hence different seasonal cycles on the two planets. Jovian vortices tend to display a near equal distribution of vortices across hemispheres, while saturnian vortices are distributed unevenly. The comparison also reveals that on both planets, there is a correlation between the highest number of vortices and the westward jet peaks. This suggests that atmospheric instabilities play a critical role in generating vortices on both planets.

Magnetic disturbance generation during the historic magnetic storm in September 1859

The model calculation of a magnetic disturbance, which was registered at Colaba observatory (India) during the historic giant magnetic storm on September 1–2, 1859, is illustrated. The calculation demonstrates that the observed, unusually fast, 2-h main phase of this storm, when the negative amplitude of the geomagnetic field vector H component was −1600 nT, and an extremely fast (1.5-h) initial field recovery phase from the maximum to the −110 nT amplitude can be generated. The following models of the magnetospheric current systems were used in the calculations: the ring current (DR), the magnetospheric magnetopause current (DCF), the magnetotail current system (DT), and the high-latitude current system (DP). The unusual time variation in the registered geomagnetic disturbance is related to the probable fast and considerable equatorward shift of the high-latitude currents during the main phase of the analyzed giant storm and to the same fast backward motion of these currents during the initial field recovery phase. The unusually large amplitude of the registered geomagnetic disturbance could have been caused by the total contribution of the indicated magnetospheric current systems during the time when the storm was generated as a result of the interaction between the magnetosphere and the solar plasma ejected during the gigantic solar flare before the storm.

Saturn’s visible lightning, its radio emissions, and the structure of the 2009–2011 lightning storms

Visible lightning on Saturn was first detected by the Cassini camera in 2009 at ∼35° South latitude. We report more lightning observations at ∼35° South later in 2009, and lightning in the 2010–2011 giant lightning storm at ∼35° North. The 2009 lightning is detected on the night side of Saturn in a broadband clear filter. The 2011 lightning is detected on the day side in blue wavelengths only. In other wavelengths the 2011 images lacked sensitivity to detect lightning, which leaves the lightning spectrum unknown.The prominent clouds at the west edge, or the “head” of the 2010–2011 storm periodically spawn large anticyclones, which drift off to the east with a longitude spacing of 10–15° (∼10,000km). The wavy boundary of the storm’s envelope drifts with the anticyclones. The relative vorticity of the anticyclones ranges up to −f/3, where f is the planetary vorticity. The lightning occurs in the diagonal gaps between the large anticyclones. The vorticity of the gaps is cyclonic, and the atmosphere there is clear down to level of the deep clouds. In these respects, the diagonal gaps resemble the jovian belts, which are the principal sites of jovian lightning.The size of the flash-illuminated cloud tops is similar to previous detections, with diameter ∼200km. This suggests that all lightning on Saturn is generated at similar depths, ∼125–250km below the cloud tops, probably in the water clouds. Optical energies of individual flashes for both southern storms and the giant storm range up to 8×109J, which is larger than the previous 2009 equinox estimate of 1.7×109J. Cassini radio measurements at 1–16MHz suggest that, assuming lightning radio emissions range up to 10GHz, lightning radio energies are of the same order of magnitude as the optical energies.Southern storms flash at a rate ∼1–2per minute. The 2011 storm flashes hundreds of times more often, ∼5times per second, and produces ∼1010W of optical power. Based on this power, the storm’s total convective power is of the order 1017W, which is uncertain by at least an order of magnitude, and probably is underestimated. This power is similar to Saturn’s global internal power radiated to space. It suggests that storms like the 2010–2011 giant storm are important players in Saturn’s cooling and thermal evolution.

New results on planetary lightning

We present the latest observations from spacecraft and ground-based instruments in search for lightning activity in the atmospheres of planets in the solar system, and put them in context of previous research. Since the comprehensive book on planetary atmospheric electricity compiled by Leblanc et al. (2008), advances in remote sensing technology and telescopic optics enable detection of additional and new electromagnetic and optical emissions, respectively. Orbiting spacecraft such as Mars Express, Venus Express and Cassini yield new results, and we highlight the giant storm on Saturn of 2010/2011 that was probably the single most powerful thunderstorm ever observed in the solar system. We also describe theoretical models, laboratory spark experiments simulating conditions in planetary mixtures and map open issues.

Cloud structure of Saturn’s 2010 storm from ground-based visual imaging

We present a study of the vertical cloud structure for the initial stage of the Great White Spot (GWS), a giant storm that developed in Saturn in December 2010, using ground-based visual images. We focus in the characterization of the undisturbed atmosphere preceding the storm and the disturbed region in the wake of the GWS. The observations were taken at Calar Alto (Spain) and Pic du Midi (France) observatories on 27 December 2010 and 13 January 2011, about 1month after the detection of the outbreak. They cover a spectral range from the ultraviolet at 375nm to the near infrared at 954nm, including the deep methane absorption band at 890nm and a number of increasingly weaker methane absorption bands. Limb to limb scans of the absolute reflectivity of the regions preceding and following the storm at different wavelengths are compared to those produced by a radiative transfer model atmosphere. Our model assumes three layers of gas and particles: stratospheric and tropospheric hazes and a deep cloud. We find that the most notorious changes in the wake of the GWS occurred in the top level of the semi-infinite bottom cloud which ascended from an altitude level P>1bar in the undisturbed region to P=300+300-100mbar in the stormy area, representing a rise of more than 40km. The density of the tropospheric haze does not change substantially but tropospheric particles are found to be more reflectant at all wavelengths, suggesting that they are coated by fresh material, putatively coming from deeper levels of the atmosphere.

CONVECTIVE BURSTS AND THE COUPLING OF SATURN'S EQUATORIAL STORMS AND INTERIOR ROTATION

Temporal variations of Saturn's equatorial jet and magnetic field hint at rich dynamics coupling the atmosphere and the deep interior. However, it has been assumed that rotation of the interior dynamo must be steady over tens of years of modern observations. Here we use a numerical convection model and scaling estimates to show how equatorial convective bursts can transfer angular momentum to the deeper interior. The numerical model allows angular momentum transfer between a fluid outer spherical shell and a rigid inner sphere. Convection drives a prograde equatorial jet exhibiting quasiperiodic bursts that fill the equatorial volume outside the tangent cylinder. For each burst strong changes in the equatorial surface velocity are associated with retrograde torque on the inner sphere. Our results suggest that Saturn's Great White Spot, a giant storm that was observed to fill the equatorial region in 1990, could mobilize a volume of fluid carrying roughly 15% of Saturn's moment of inertia. Conservation of angular momentum then implies that a 20% change in the equatorial jet angular velocity could change the average interior rotation rate by about 0.1%-roughly an order of magnitude less than the apparent rotation rate changes associated with Saturn's kilometric radio (SKR) signal. However,more » if the SKR signal originates outside the liquid metal core in a 'planetary tachocline' that separates the layer of fast zonal flow from the magnetically controlled and slowly convecting deep interior, then convective bursts can provide a possible mechanism for the observed {approx}1% SKR changes.« less

Statistical study on great geomagnetic storms during solar cycle 23

Characteristics of great geomagnetic storms during solar cycle 23 were statistically investigated. Firstly, we focused on the uniqueness of solar cycle 23 by analyzing both the great storm number and sunspot number from 1957 to 2008. It was found that the relationship between the sunspot number and great storm number weakened as the activity of the storms strengthened. There was no obvious relationship between the annual sunspot number and great storm number with Dst≤−300 nT. Secondly, we studied the relationship between the peak Dst and peak Bz in detail. It was found that the condition Bz≤−10 nT is not necessary for storms with Dst≤−100 nT, but seems necessary for storms with Dst≤−150 nT. The duration for Bz≤−10 nT has no direct relationship with the giant storm. The correlation coefficient between the Dst peak and Bz peak for the 89 storms studied is 0.81. After removing the effect of solar wind dynamic pressure on the Dst peak, we obtained a better correlation coefficient of 0.86. We also found the difference between the Dst peak and the corrected Dst peak was proportional to the Dst peak.

Storm-clouds brooding on towering heights

Springtime on Saturn came in with a bang last December, when a massive storm erupted in its north temperate zone. This rare event has been observed in unprecedented detail from the ground and from space. See Letters p.71 & p.75 Six Great White Spot (GWS) events have been observed in the atmosphere of Saturn since 1876. These giant convective storms occur roughly once every Saturnian year (equal to 29.5 Earth years). The sixth GWS erupted in December 2010 and has been the subject of intense observation. Two papers in this issue present the details of some of these observations. Sanchez-Lavega et al. report that the storm developed at northern latitudes in the peak of a weak westward jet during early northern springtime. The storm head moved faster than the jet and triggered a disturbance that circled the planet. Numerical simulations show that Saturn's winds extend without decay deep down into the weather layer. Fischer et al. report that the storm reached a width of 10,000 kilometres within three weeks. Its lightning flash rates are an order of magnitude greater than those seen in previous storms, peaking at more than 10 flashes per second.

Local differences in great magnetic storms observed at middle and low latitudes

Abstract The dependence of the storm-time amplitude on longitude and latitude was analyzed by statistically investigating great magnetic storms observed at different observatories. First, we compared the storm-time ranges observed at Beijing Observatory (BJI) and San Juan Observatory (SJG) to reveal their longitudinal dependence. It was found that the difference between BJI and SJG could be fitted by the 4-order Fourier series approximation, and the storm-time H ranges at dawn were less than those at dusk. Second, we carried out a case study of two typical storms, and analyzed the focused local time when peak storm-time H ranges occurred. The results confirmed the above conclusion. Third, a statistical study was conducted for all magnetic storms observed at the 120°E magnetic chain in eastern China for 1995–2004 to reveal the latitudinal dependence of storm-time ranges. It was found the relationship depended on the activity of analyzed storms and became complicated for giant storms with Dst ≤ −300 nT.