Changes In Solar Flux Research Articles

The Ionospheric Response to the 2013 SSW Event Over the Asian‐Australian Sector

AbstractThis study investigates the response of the Asian‐Australian low‐latitude ionosphere to the 2013 Sudden Stratospheric Warming (SSW) event. The equatorial ionization anomaly structures were built from the latitudinal distribution of Total Electron Content (TEC) measured from 10 Global Positioning System receivers along 115°E in the Asian‐Australian sector. A pair of magnetometers and NASA Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite airglow instrument were also employed to measure the equatorial electrojet strength (inferred E × B drift) and to unveil the changes in the neutral thermospheric O/N2 ratio during the SSW event, respectively. The relocation of the northern crests to higher latitudes during the SSW compared to the non‐SSW periods was mainly attributed to the combined effect of enhanced magnetometer‐inferred upward‐directed E × B drift and increasing solar flux. The local time shift in the thermospheric O/N2 ratio, a slight enhancement in the magnitude of the semi‐diurnal magnetometer‐inferred upward‐directed E × B drift, and changes in solar flux were primarily responsible for the hemispheric TEC enhancement during mid‐January compared to SSW onset. Additionally, the photo‐ionization effect due to increasing solar flux further enhances the TEC magnitude during the relaxing phase. On the other hand, the strong thermospheric equatorward wind played a crucial role in moving the plasma to lower latitudes during the zonal wind transition phases. A moderate geomagnetic storm of 17 January 2013 did not perturb the Asian‐Australian ionosphere. However, on 18 January 2013, the storm had a significant impact and greatly diminished the effect of the SSW.

Role of eddy diffusion in the delayed ionospheric response to solar flux changes

Abstract. Simulations of the ionospheric response to solar flux changes driven by the 27 d solar rotation have been performed using the global 3-D Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) physics-based numerical model. Using the F10.7 index as a proxy for solar extreme ultraviolet (EUV) variations in the model, the ionospheric delay at the solar rotation period is well reproduced and amounts to about 1 d, which is consistent with satellite and in situ measurements. From mechanistic CTIPe studies with reduced and increased eddy diffusion, we conclude that the eddy diffusion is an important factor that influences the delay of the ionospheric total electron content (TEC). We observed that the peak response time of the atomic oxygen to molecular nitrogen ratio to the solar EUV flux changes quickly during the increased eddy diffusion compared with weaker eddy diffusion. These results suggest that an increase in the eddy diffusion leads to faster transport processes and an increased loss rate, resulting in a decrease in the ionospheric time delay. Furthermore, we found that an increase in solar activity leads to an enhanced ionospheric delay. At low latitudes, the influence of solar activity is stronger because EUV radiation drives ionization processes that lead to compositional changes. Therefore, the combined effect of eddy diffusion and solar activity leads to a longer delay in the low-latitude and midlatitude region.

Anomalies and Fluctuations of Near-surface Air Temperature at Tianhuangping (Zhejiang), China, Produced by the Longest Total Solar Eclipse of the 21st Century Under Cloudy Skies

During a total eclipse of the Sun, the solar disk blocked by the lunar disk produces an instant and strong decline of energy at the surface. This loss of energy leads to a decreasing air temperatures near the surface. Anyone under a completely clear sky, with a total solar eclipse (TSE) in progress, feels a cooling, whose minimum is reached a few minutes after totality. This drop in temperature is known as an anomaly and this delay is called thermal lag. During a TSE air temperature changes appreciably not only in magnitude but also in timing, depending on weather and geographical conditions. If the eclipse is partially or totally obscured by clouds, some effects are produced on the thermal lag. Under clear skies, the temperature response lags behind the change in solar flux as one expects in TSE; however, under cloudy skies, the lag can reverse in early and/or late stages of partial phases. The normal heating of the surface by the Sun, which drives turbulent motion in the air layer near the surface, is disrupted during the eclipse. The 2009 TSE in China provided an opportunity to have a look at these kinds of perturbations caused by this eclipse. In this paper, the second of a series of three, we analyze the near-surface air temperature response, at three different heights over the ground, recorded by the Williams College expedition under meteorological conditions characterized by cloudy skies during the longest total solar eclipse of the 21st century on 2009 July 22, at Tianhuangping (Zhejiang), China. An analysis of the relationship between solar radiation and air temperature was made by applying a study previously published in the first paper of this series in which we evaluated the cloudiness contribution in estimating the impact on global solar radiation throughout this phenomenon at that site. The analysis of this response includes linear and absolute negative anomalies as well as fluctuations, which was undertaken through a statistical study to get information on the convection activity produced by the latter. The fluctuations generated by turbulence were studied by analyzing variance and residuals. The results, indicating a steady decrease and recovery of both perturbations, were consistent with those published by other studies for this total solar eclipse.

Ionospheric Responses at Low Latitudes to the Annular Solar Eclipse on 21 June 2020

AbstractIn this study, we utilized both ground‐based and space‐borne observations including total electron content (TEC) from Beidou geostationary satellites, two‐dimensional TEC maps from the worldwide dense Global Navigation Satellite System receivers, ionosondes, and in situ electron density (Ne) and electron temperature (Te) from both Swarm and China Seismo‐Electromagnetic Satellite satellites, to investigate the low‐latitude ionospheric responses to the annular solar eclipse on 21 June 2020. The decrease in TEC during the eclipse at low latitudes showed a local time dependence with the largest depletions in the noon and afternoon sectors. It was also found that the TEC depletions at different latitudes in the equatorial ionization anomaly (EIA) region over the East Asian sector cannot solely be explained by the solar flux changes associated with the obscuration rate. The differences in TEC reduction between stations can be more than a factor of 2 at latitudes with the same obscuration rate of over 90%. Compared with TEC variations in the Northern Hemisphere, the TEC also underwent a considerable decrease in the EIA region in the conjugate hemisphere without eclipse shadow. Meanwhile, the hmF2 near the magnetic equator increased around the onset of the eclipse, indicating an enhancement of the eastward equatorial electric field. Furthermore, the TEC decrease during the eclipse in the EIA region in both hemispheres lasted for a long period of more than 7 hr after the eclipse, with a TEC depletion of 2–6 TEC units. The Ne from Swarm and China Seismo‐Electromagnetic Satellite satellites showed a complicated variation after the eclipse, whereas no visible change was observed in Te. The enhanced equatorial electric field, neutral wind changes, and the associated plasma transport act together to generate the observed ionospheric effects at low latitudes during the eclipse. Our results also suggest that the eclipse‐induced perturbations of dynamic processes can continue to impact the ionosphere after the eclipse.

Saturn in Lyman α: A comparison of Cassini and Voyager observations

We analyze Saturn Lyman α system scans observed by the Cassini/UVIS instrument probing non-auroral airglow emissions from Saturn's disk, the ring atmosphere and the Saturn hydrogen torus. We constrain variations in disk brightness with latitude and local time, relating them to models of Saturn's upper atmosphere. We compare these results with Voyager observations of similar viewing geometry. The Cassini disk brightness is almost four time lower than the Voyager brightness. This difference cannot be explained by changes in the solar Lyman α flux or atmospheric structure. The change in solar flux is modest and atmospheric structure retrieved from occultation data is relatively stable over time. The disk brightness observed by Cassini can be explained by resonant scattering of solar Lyman α radiation and the best-fit hydrogen abundance in the thermosphere is consistent with atmospheric structure retrieved from the occultation data as well as photochemical model predictions. Our results support the recently proposed recalibration of the Voyager/UVS instruments that would bring the Voyager disk brightness in line with our model predictions and provide a consistent interpretation of Saturn Lyman α emissions over time. We also explore the extended emission in the Saturn system, centered near the ring plane in edge-on viewing. The extended emission can be explained by a distribution of atomic hydrogen that is symmetric about the ring plane. We do not find evidence for a plume of hot hydrogen atoms escaping from Saturn's sunlit atmosphere that was proposed previously. Instead, the structure earlier interpreted as a plume is most simply explained by solar illumination from below the ring plane during southern summer combined with the edge-on viewing geometry.

Daytime Ionospheric TEC Weather Study Over Latin America

AbstractThe present work is the first of a two‐part weather study of the ionospheric Total Electron Content (TEC), based on data collected by four ground‐based Global Navigation Satellite System networks that cover the whole Latin America from the Patagonia to the north of Mexico. From the best of our knowledge, the maps presented here are the first TEC maps obtained using ground‐based data that covers the entire Latin America region, which represent an advance to the space weather monitoring and forecasting of the ionosphere. This work provides a qualitative and quantitative daytime analysis of the ionospheric TEC variation, which encompasses: (a) the response of TEC to the solar flux at midday; (b) the seasonal variation of TEC in different latitudinal ranges; and (c) the North‐South asymmetry of TEC over Latin America. The response to the solar flux is based on day‐to‐day TEC variations during two periods of different solar activity conditions: 2011 (ascending phase) and 2014 (maximum). The approximations of meridional wind component derived from Horizontal Wind Model‐14 model and hmF2 obtained from International Reference Ionosphere model were used. Equinoctial asymmetries with an opposite configuration in high and moderate solar activity were identified in the TEC variation. For 2011, it was related to the solar flux change. However, in 2014, according to the hmF2 variation, the influence of neutral wind becomes dominant. Among the results, we highlight an absence of winter anomaly in the Northern Hemisphere in 2014 and a stronger annual anomaly for latitudes under −20∘.

Thermal conditions on the International Space Station: Heat flux and temperature investigation of main radiators for the Alpha Magnetic Spectrometer

The investigation on heat flux can clarify the thermal condition and explain temperature behavior on the main radiators of the Alpha Magnetic Spectrometer (AMS). In this paper, a detailed investigation of heat flux on the AMS main radiators is proposed. The heat transfer process of the AMS main radiators is theoretically analyzed. An updated thermal model of the AMS on the International Space Station (ISS) is developed to calculate the external heat flux density on the AMS main radiators. We conclude the ISS components and operations affect on the solar flux density of the AMS main radiators by reflecting or shading solar illumination. According to the energy conservation on the AMS main radiators, the temperature variation mainly depends on the solar flux change. The investigations are conducive to reference for the long-duration thermal control of the AMS, and knowledge for the thermal conditions on the ISS.

Response of the Mars ionosphere to solar flares: Analysis of MGS radio occultation data

AbstractIncreased soft X‐ray irradiance during solar flares produces increased electron densities in the lower ionosphere of Mars, and the relative changes in electron density during a flare are greater for lower altitudes and larger flares. However, this relationship has not been quantified. This has impeded the validation of simulations of the ionospheric response to flares, which are necessary for developing accurate descriptions of the physical processes governing ionospheric behavior under extreme conditions. Here we develop a response function, a mathematical expression for the change in electron density during a solar flare as a function of the change in solar flux and an optical depth proxy. This function is based on analysis of 20 Mars Global Surveyor (MGS) radio occultation electron density profiles measured during solar flares. We find that characterizing the response as a function of optical depth, rather than altitude, provides the best description of ionospheric variability during a flare. A separate response function, determined from analysis of a numerical simulation of the response to a solar flare, was found to be grossly similar to the observationally based response function, though with a weaker dependence on optical depth. We identify 15 MGS profiles with an apparent solar flare response, but no coincident detected solar flare. We suggest that the observed response function can be used to detect flares not visible from Earth and to give an approximation of their strength. Additionally, it can estimate ionospheric electron densities during a flare; however, precision is limited by a small number of observations.

Reduction of measurements of total solar flux to a unified scale and uncertainty in estimating its long-term trends

A comparative analysis of measurements of total solar flux in the active cavity radiometer irradiance monitor (ACRIM) and Physikalisch-Meteorologisches Observatorium Davos (PMOD) scales was performed. An analysis of integrated differences of simultaneous measurements of solar flux made it possible to estimate the systematic differences that can lead to the accumulation large errors with time. The measurements of solar flux in ACRIM and PMOD scales were reduced to an intermediate radiometric scale through data correction for systematic errors. The corrected measurements in the unified scale were consistent and there is a compromise between initial data sets. The measurements in the intermediate scale indicate changes in solar flux between the minima of solar activity in 1986, 1996, and 2008. The amplitude of these variations is comparable with uncertainty in their long-term trends, which questions earlier obtained estimates for secular variations of solar luminosity.

Orbital effects on Mercury’s escaping sodium exosphere

We present results from coronagraphic imaging of Mercury’s sodium tail over a 7° field of view. Several sets of observations made at the McDonald Observatory since May 2007 show a tail of neutral sodium atoms stretching more than 1000 Mercury radii (R m) in length, or a full degree of sky. However, no tail was observed extending beyond 120 R m during the January 2008 MESSENGER fly-by period, or during a similar orbital phase of Mercury in July 2008. Large changes in Mercury’s heliocentric radial velocity cause Doppler shifts about the Fraunhofer absorption features; the resultant change in solar flux and radiation pressure is the primary cause of the observed variation in tail brightness. Smaller fluctuations in brightness may exist due to changing source rates at the surface, but we have no explicit evidence for such changes in this data set. The effects of radiation pressure on Mercury’s escaping atmosphere are investigated using seven observations spanning different orbital phases. Total escape rates of atmospheric sodium are estimated to be between 5 and 13 × 10 23 atoms/s and show a correlation to radiation pressure. Candidate sources of Mercury’s sodium exosphere include desorption by UV sunlight, thermal desorption, solar wind channeled along Mercury’s magnetic field lines, and micro-meteor impacts. Wide-angle observations of the full extent of Mercury’s sodium tail offer opportunities to enhance our understanding of the time histories of these source rates.

Solar Cycle Signal of Tropospheric Ozone over the Tibetan Plateau

AbstractTropospheric column ozone data during 1979 to 1992 over the Tibetan Plateau and solar flux F10.7 index data at the same period, are used to study the relationship between tropospheric ozone variation and solar flux change. It is shown that there exists a solar cycle changing trend in the tropospheric ozone at this region. The estimated changes in tropospheric and stratospheric and column total ozone over a solar cycle are respectively 1.31, 4.97 and 6.628 Dobson units (DU), or 4.07%, 2.04% and 2.28% from solar minimum to solar maximum. This is quite different from that trend over tropical Pacific region discovered by Chandra et al 1999. In the tropic Pacific region, a negative changing trend was found. There are at least two aspects should be put into consideration in explaining the difference. One is the different components of NOX and water vapor in the background atmosphere over those two regions. The other is the frequent exchange and transmission of stratosphere‐troposphere atmospheric substances over the Tibetan plateau, which may result in some ozone sent to troposphere from stratosphere.

Solar cycle variability of Mars dayside exospheric temperatures: Model evaluation of underlying thermal balances

The response of the Mars dayside exospheric temperatures to short and long term solar flux changes was recently established. Characterization of the relative importance of various thermospheric heating and cooling mechanisms for maintaining these Mars exospheric temperatures requires the systematic application of modern global dynamical models that capture both lower and upper atmosphere thermal and dynamical processes. Coupled Mars General Circulation Model (MGCM) plus Mars Thermospheric General Circulation Model (MTGCM) simulations are utilized for this study, closely matching conditions during Mars Global Surveyor drag measurements. Simulations confirm the major balance of EUV heating and thermal heat conduction at dayside exospheric altitudes. However, the influence of variable Martian global winds is significant and must be carefully considered when investigating the global regulation of Mars exospheric temperatures over the solar cycle and Martian seasons. Finally, the present MGCM‐MTGCM heating and cooling processes suggests that an EUV‐UV heating efficiency of 19% yields net heating in accord with MGS exospheric temperatures.

Development of a Fabry–Perot interferometer for ultra-precise measurements of column CO2

Progress on a passive Fabry–Perot-based instrument for detecting column CO2 through absorption measurements at 1.58 µm is described. In this design, solar flux reaches the instrument platform and is directed through two channels. In the first channel, transmittance fringes from a Fabry–Perot interferometer are aligned with CO2 absorption lines so that absorption due to CO2 is primarily detected. The second channel encompasses the same frequency region as the first, but is comparatively more sensitive to changes in the solar flux than absorption due to CO2. The ratio of these channels is sensitive to changes in the total CO2 column, but not to changes in solar flux. This inexpensive instrument will offer high precision measurements (error <1%) in a compact package. Design of this instrument and preliminary ground-based measurements of column CO2 are presented here as well as strategies for deployment on aircraft and satellite platforms.

Geophysical Fluid Dynamics Laboratory general circulation model investigation of the indirect radiative effects of anthropogenic sulfate aerosol

The Geophysical Fluid Dynamics Laboratory (GFDL) atmosphere general circulation model, with its new cloud scheme, is employed to study the indirect radiative effect of anthropogenic sulfate aerosol during the industrial period. The preindustrial and present‐day monthly mean aerosol climatologies are generated from running the Model for Ozone And Related chemical Tracers (MOZART) chemistry‐transport model. The respective global annual mean sulfate burdens are 0.22 and 0.81 Tg S. Cloud droplet number concentrations are related to sulfate mass concentrations using an empirical relationship (Boucher and Lohmann, 1995). A distinction is made between “forcing” and flux change at the top of the atmosphere in this study. The simulations, performed with prescribed sea surface temperature, show that the first indirect “forcing” (“Twomey” effect) amounts to an annual mean of −1.5 W m−2, concentrated largely over the oceans in the Northern Hemisphere (NH). The annual mean flux change owing to the response of the model to the first indirect effect is −1.4 W m−2, similar to the annual mean forcing. However, the model's response causes a rearrangement of cloud distribution as well as changes in longwave flux (smaller than solar flux changes). There is thus a differing geographical nature of the radiation field than for the forcing even though the global means are similar. The second indirect effect, which is necessarily an estimate made in terms of the model's response, amounts to −0.9 W m−2, but the statistical significance of the simulated geographical distribution of this effect is relatively low owing to the model's natural variability. Both the first and second effects are approximately linearly additive, giving rise to a combined annual mean flux change of −2.3 W m−2, with the NH responsible for 77% of the total flux change. Statistically significant model responses are obtained for the zonal mean total indirect effect in the entire NH and in the Southern Hemisphere low latitudes and midlatitudes (north of 45°S). The area of significance extends more than for the first and second effects considered separately. A comparison with a number of previous studies based on the same sulfate‐droplet relationship shows that, after distinguishing between forcing and flux change, the global mean change in watts per square meter for the total effect computed in this study is comparable to existing studies in spite of the differences in cloud schemes.

Response of peak electron densities in the martian ionosphere to day-to-day changes in solar flux due to solar rotation

Photochemical Chapman theory predicts that the square of peak electron density, N m , in the dayside ionosphere of Mars is proportional to the cosine of solar zenith angle. We use Mars Global Surveyor Radio Science profiles of electron density to demonstrate that this relationship is generally satisfied and that positive or negative residuals between observed and predicted values of N m 2 are caused by periods of relatively high or low solar flux, respectively. Understanding the response of the martian ionosphere to changes in solar flux requires simultaneous observations of the martian ionosphere and of solar flux at Mars, but solar flux measurements are only available at Earth. Since the Sun's output varies both in time and with solar latitude and longitude, solar flux at Mars is not simply related to solar flux at Earth by an inverse-square law. We hypothesize that, when corrected for differing distances from the Sun, solar fluxes at Mars and Earth are identical when shifted in time by the interval necessary for the Sun to rotate through the Earth–Sun–Mars angle. We perform four case studies that quantitatively compare time series of N m at Mars to time series of solar flux at Earth and find that our hypothesis is satisfied in the three of them that used ionospheric data from the northern hemisphere. We define a solar flux proxy at Mars based upon the E 10.7 proxy for solar flux at Earth and use our best case study to derive an equation that relates N m to this proxy. We discuss how the ionosphere of Mars can be used to infer the presence of solar active regions not facing the Earth. Our fourth case study uses ionospheric observations from the southern hemisphere at latitudes where there are strong crustal magnetic anomalies. These profiles do not have Chapman-like shapes, unlike those of the other three case studies. We split this set of measurements into two subsets, corresponding to whether or not they were made at longitudes with strong crustal magnetic anomalies. Neither subset shows N m responding to changes in solar flux in the manner that we observe in the three other case studies. We find many similarities in ionospheric responses to short-term and long-term changes in solar flux for Venus, Earth, and Mars. We consider the implications of our results for different parametric equations that have been published describing this response.

Cirrus cloud horizontal and vertical inhomogeneity effects in a GCM

A set of the inhomogeneity factor for high-level clouds derived from the ISCCP D1 dataset averaged over a five-year period has been incorporated in the UCLA atmospheric GCM to investigate the effect of cirrus cloud inhomogeneity on climate simulation. The inclusion of this inhomogeneous factor improves the global mean planetary albedo by about 4% simulated from the model. It also produces changes in solar fluxes and OLRs associated with changes in cloud fields, revealing that the cloud inhomogeneity not only affects cloud albedo directly, but also modifies cloud and radiation fields. The corresponding difference in the geographic distribution of precipitation is as large as 7 mm day−1. Using the climatology cloud inhomogeneity factor also produces a warmer troposphere related to changes in the cloudiness and the corresponding radiative heating, which, to some extent, corrects the cold bias in the UCLA AGCM. The region around 14 km, however, is cooler associated with increase in the reflected solar flux that leads to a warmer region above. An interactive parameterization for mean effective ice crystal size based on ice water content and temperature has also been developed and incorporated in the UCLA AGCM. The inclusion of the new parameterization produces substantial differences in the zonal mean temperature and the geographic distribution of precipitation, radiative fluxes, and cloud cover with respect to the control run. The vertical distribution of ice crystal size appears to be an important factor controlling the radiative heating rate and the consequence of circulation patterns, and hence must be included in the cloud-radiation parameterization in climate models to account for realistic cloud processes in the atmosphere.

Decadal-Scale Climate and Ecosystem Interactions in the North Pacific Ocean

Decadal-scale climate variations in the Pacific Ocean wield a strong influence on the oceanic ecosystem. Two dominant patterns of large-scale SST variability and one dominant pattern of large-scale thermocline variability can be explained as a forced oceanic response to large-scale changes in the Aleutian Low. The physical mechanisms that generate this decadal variability are still unclear, but stochastic atmospheric forcing of the ocean combined with atmospheric teleconnections from the tropics to the midlatitudes and some weak ocean-atmosphere feedbacks processes are the most plausible explanation. These observed physical variations organize the oceanic ecosystem response through large-scale basin-wide forcings that exert distinct local influences through many different processes. The regional ecosystem impacts of these local processes are discussed for the Tropical Pacific, the Central North Pacific, the Kuroshio-Oyashio Extension, the Bering Sea, the Gulf of Alaska, and the California Current System regions in the context of the observed decadal climate variability. The physical ocean-atmosphere system and the oceanic ecosystem interact through many different processes. These include physical forcing of the ecosystem by changes in solar fluxes, ocean temperature, horizontal current advection, vertical mixing and upwelling, freshwater fluxes, and sea ice. These also include oceanic ecosystem forcing of the climate by attenuation of solar energy by phytoplankton absorption and atmospheric aerosol production by phytoplankton DMS fluxes. A more complete understanding of the complicated feedback processes controlling decadal variability, ocean ecosystems, and biogeochemical cycling requires a concerted and organized long-term observational and modeling effort.

Comparison of solar variability effects with the surface radiative forcing of CO 2

In this paper we provide a comparison of the change in the solar flux with the surface forcing from greenhouse gases, particularly that of carbon dioxide which is increasing in the atmosphere due to fossil fuel combustion processes. This comparison shows that the maximum changes in the clear sky solar flux since the time of the approximate onset of the industrial period is comparable to the corresponding carbon dioxide surface forcing. In comparison with the forcing from all of the other major greenhouse gases combined, the solar contribution may be about 20–60% as strong. This comparison indicates that over the past few hundred years, the surface temperature change impact from solar variability can rival that from the anthropogenic increase in greenhouse gases.

Modifications to the Titheridge upper ionosphere and plasmasphere temperature model

In 1998, J. E. Titheridge presented a computationally simple, yet accurate, model for the electron and ion temperatures (Te and Ti) in the topside ionosphere and plasmasphere. The model is centered on a theoretically based equation with only two free parameters at a base height of 400 km: the electron temperature (To) and electron temperature gradient (Go). Titheridge fitted this equation to satellite Te observations to determine the mean day and night variations in To and Go as functions of latitude and also estimated corrections for changes in solar flux, geomagnetic activity, and diurnal variations. Here we augment the satellite Te data originally fitted by Titheridge with results from a more recent satellite‐based empirical model and use the enlarged Te data base to determine new functions for the day and night latitudinal variations in To and Go. In addition, the solar flux correction has been modified so that increasing F10.7 now corresponds to decreasing To rather than to increasing To. This modification yields better agreement with incoherent radar observations and the predictions of a theoretical model. Furthermore, corrections for seasonal variations and the separation of geographic and geomagnetic coordinates are introduced. All of the above modifications have been incorporated to improve the functional forms of the To and Go expressions, without noticeably decreasing the computational speed and elegance of the original Titheridge model.

Solar variability, coupling between atmospheric layers and climate change.

One of the enduring puzzles of atmospheric physics is the extent to which changes in the Sun can influence the behaviour of the climate system. While solar-flux changes tend to be relatively modest, a number of observations of atmospheric parameters indicates a disproportionately large response. Global-scale models of the coupled middle and upper atmosphere have provided new insights into some of the mechanisms that may be responsible for the amplification of the solar signal. In particular, modification of the transport of heat and chemicals such as ozone by waves during periods of solar activity has been shown to make an important contribution to the climate of the stratosphere and mesosphere. In this paper, a review of some of the recent advances in understanding the coupling between atmospheric layers and how this work relates to Sun-weather relations and climate change in the troposphere will be presented, along with a discussion of some of the challenges that remain.