Climate And Weather Of The Sun-Earth System Research Articles

Diurnal variation of the tropospheric water vapour over a coastal and an inland station in Southern Indian Peninsula

Diurnal variation of atmospheric water vapour in the troposphere over two tropical stations Trivandrum (8.5°N, 76.9°E) and Gadanki (13.5°N, 79.2°E) are studied using radiosonde observations for three years (December 2010–March 2014) carried out as part of Tropical Tropopause dynamics (TTD) campaigns under CAWSES (Climate And Weather of the Sun-Earth System) India Phase II program. Trivandrum is a coastal station and Gadanki an inland station in the Indian Peninsula. Even though the absolute value of columnar integrated water vapour content (IWV) is higher over Trivandrum in all the seasons, the amplitude of its diurnal variation is almost the same (∼± 5–8 kg m−2) at both the stations with lower values during the day and higher values during night. Though the absolute humidity decreases exponentially with altitude, the amplitude of normalized diurnal anomaly is more-or-less the same (15–20%) from the surface up to 10 km in all the seasons. There exists a time difference in the peaking hours of water vapour density between the two stations with Gadanki always leading Trivandrum. While the water vapour density maximizes around midnight over Trivandrum, it peaks in the late evening over Gadanki. Harmonic analysis shows that the diurnal and semi-diurnal components together account for almost all the sub-daily variations in IWV and absolute humidity. The contribution of semi-diurnal component is only 25% of that of the diurnal component. Diurnal variation of surface wind speed and direction together with the vertical motion associated with convection regulated by the diurnal variation in temperature seems to play the lead role in causing the diurnal variation in water vapour. While the diurnal variation over Gadanki is mainly controlled by the convectively induced vertical motion, the diurnal variation in the rate of evaporation due to surface wind and local circulation also plays a significant role over Trivandrum.

Two years observations on the diurnal evolution of coastal atmospheric boundary layer features over Thiruvananthapuram (8.5∘ N, 76.9∘ E), India

The atmospheric boundary layer (ABL) over a given coastal station is influenced by the presence of mesoscale sea breeze circulation, together with the local and synoptic weather, which directly or indirectly modulate the vertical thickness of ABL (zABL). Despite its importance in the characterization of lower tropospheric processes and atmospheric modeling studies, a reliable climatology on the temporal evolution of zABL is not available over the tropics. Here, we investigate the challenges involved in determination of the ABL heights, and discuss an objective method to define the vertical structure of coastal ABL. The study presents a two year morphology on the diurnal evolution of the vertical thickness of sea breeze flow (zSBF) and zABL in association with the altitudes of lifting condensation level (zLCL) over Thiruvananthapuram (8.5∘ N, 76.9∘ E), a representative coastal station on the western coastline of the Indian sub-continent. We make use of about 516 balloon-borne GPS sonde measurements in the present study, which were carried out as part of the tropical tropopause dynamics field experiment under the climate and weather of the sun-earth system (CAWSES)–India program. Results obtained from the present study reveal major differences in the temporal evolution of the ABL features in relation to the strength of sea breeze circulation and monsoonal wind flow during the winter and summer monsoon respectively. The diurnal evolution in zABL is very prominent in the winter monsoon as against the summer monsoon, which is attributed to the impact of large-scale monsoonal flow over the surface layer meteorology. For a majority of the database, the zLCL altitudes are found to be higher than that of the zABL, indicating a possible decoupling of the ABL with the low-level clouds.

Advancing the understanding of the Sun–Earth interaction—the Climate and Weather of the Sun–Earth System (CAWSES) II program

The Scientific Committee on Solar–Terrestrial Physics (SCOSTEP) of the International Council for Science (ICSU) implemented an international collaborative program called Climate and Weather of the Sun–Earth System (CAWSES), which was active from 2004 to 2008; this was followed by the CAWSES II program during the period of 2009–2013. The CAWSES program was aimed at improving the understanding of the coupled solar–terrestrial system, with special emphasis placed on the short-term (weather) and long-term (climate) variability of solar activities and their effects on and responses of Geospace and Earth’s environment. Following the successful implementation of CAWSES, the CAWSES II program pursued four fundamental questions addressing the way in which the coupled Sun–Earth system operates over time scales ranging from minutes to millennia, namely, (1) What are the solar influences on the Earth’s climate? (2) How will Geospace respond to an altered climate? (3) How does short-term solar variability affect the Geospace environment? and (4) What is the Geospace response to variable inputs from the lower atmosphere? In addition to these four major tasks, the SCOSTEP and CAWSES promoted E-science and informatics activities including the creation of scientific databases and their effective utilization in solar–terrestrial physics research. Capacity building activities were also enhanced during CAWSES II, and this represented an important contribution of SCOSTEP to the world’s solar–terrestrial physics community. This introductory paper provides an overview of CAWSES II activities and serves as a preface to the dedicated review papers summarizing the achievements of the program’s four task groups (TGs) and the E-science component.

GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 1: The North American sector

Abstract. The interval of geomagnetic storms of 7–17 March 2012 was selected at the Climate and Weather of the Sun-Earth System (CAWSES) II Workshop for group study of space weather effects during the ascending phase of solar cycle 24 (Tsurutani et al., 2014). The high-latitude ionospheric response to a series of storms is studied using arrays of GPS receivers, HF radars, ionosondes, riometers, magnetometers, and auroral imagers focusing on GPS phase scintillation. Four geomagnetic storms showed varied responses to solar wind conditions characterized by the interplanetary magnetic field (IMF) and solar wind dynamic pressure. As a function of magnetic latitude and magnetic local time, regions of enhanced scintillation are identified in the context of coupling processes between the solar wind and the magnetosphere–ionosphere system. Large southward IMF and high solar wind dynamic pressure resulted in the strongest scintillation in the nightside auroral oval. Scintillation occurrence was correlated with ground magnetic field perturbations and riometer absorption enhancements, and collocated with mapped auroral emission. During periods of southward IMF, scintillation was also collocated with ionospheric convection in the expanded dawn and dusk cells, with the antisunward convection in the polar cap and with a tongue of ionization fractured into patches. In contrast, large northward IMF combined with a strong solar wind dynamic pressure pulse was followed by scintillation caused by transpolar arcs in the polar cap.

Space physics and space weather

CAS Key Laboratory of Basic Plasma Physics, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China (qmlu@ustc.edu.cn) Space physics is a subject that has developed since the launch of the first artificial satellite in 1957. It has been promoted by space technology and is related closely with various adjacent disciplines. Space physics covers physical processes and phenomena that occur in the solar atmosphere, interplanetary environment and the Earth’s space environment (including the magnetosphere, ionosphere and upper atmosphere), and considers their relations and evolution. With the development of space and communication technology in the past 20–30 years, people’s daily lives and the efficient running of global economics have become heavily dependent on satellites operating in the space environment. However, hazardous weather events in space, such as coronal mass ejections, solar flares and substorms in the magnetosphere, lead to rapid changes in the space environment and the production of energetic particles. Such events, which are collectively referred to as space weather, damage satellites and space/ground-based technology systems and may even threaten astronauts and adversely affect human health or life on Earth. The study of space weather combines space physics and space/ground-based technology. It regards the solar atmosphere, interplanetary environment and Earth’s space as a complete system. Space weather research detects, studies and predicts the phenomena associated with solar eruptions and the related hazardous space weather events, as well as their effects on space/groundbased technology systems. Reducing the damage caused by space weather events and protecting human life is a further goal. Because of the high demand for advanced technology and national security, space weather is becoming a hot spot of international scientific activity. Since the United States proposed a national space weather program in 1995, more than 10 countries or agencies, such as the European Space Agency, Russia, Canada, Japan and Australia, have drawn up their own space weather programs and launched a series of satellites for research purposes. Additionally, many international organizations are promoting programs such as International Living with a Star (ILWS) and Climate and Weather of the Sun-Earth System (CAWSES). Research on space physics and space weather helps us learn more about hazardous space weather events in the space environment and thus allows us to predict them; this knowledge will serve the astronautics and communications industries. As a multidisciplinary research field, the development of space physics and space weather requires the participation of researchers from different fields. This special issue reviews several selected fronts in research on space physics and space weather: electron dynamics in collisionless magnetic reconnection, high-speed flowing plasmas in the Earth’s plasma sheet, energetic particles in the inner magnetosphere, and solar activity effects of the ionosphere. The main contents are as follows. Magnetic reconnection provides a physical mechanism for fast energy conversion from magnetic energy to plasma kinetic energy. It is closely associated with many explosive phenomena in space plasma. The first paper describes the importance of electron dynamics to the structures of magnetic reconnection, and the acceleration mechanisms of energetic electrons. High-speed flowing plasmas are frequently observed phenomena associated with dramatic changes in magnetic structures in the magnetosphere. The second paper discusses briefly the history of high-speed flows and the proposed mechanisms, the relations between high-speed flows and auroras and their interaction with background plasma. The relationships between high-speed flows and substorms are also summarized in the paper. Energetic particles in the radiation belt are the main space weather threat, and understanding their acceleration mechanisms is one of the major challenges in space physics. The third paper reviews recent progress on the fast acceleration of “killer” electrons and energetic ions by ultrafrequency waves excited in the inner magnetosphere by interplanetary shock. Solar radiation, which varies over multiple temporal scales, is the main cause of remarkable variation in the evolution of the ionosphere. The dependence of the ionosphere on solar activity is a fundamental issue in ionospheric physics, providing information essential to understanding variations in the ionosphere and its processes. Selected recent studies on solar activity effects of the ionosphere are briefly reviewed in the fourth paper. This special issue can be referred to by researchers in related fields.

Research Spotlight: Studying the Sun's effects on Earth's atmosphere

The Sun contributes to climate and weather on Earth through its influence on the atmosphere, and even small variations in solar radiation can affect Earth. Sun‐Earth couplings and interactions can be complex, and natural variability can make it difficult to detect long‐term trends.A variety of studies were undertaken as part of the Climate and Weather of the Sun‐Earth System (CAWSES) project to better understand aspects of the Sun‐Earth system. CAWSES research covered solar input to the atmosphere through radiation and particles and the influence of the Sun on mesospheric ice clouds, ozone concentrations, transport of photochemically active gases, and wave processes including atmospheric tides and sudden stratospheric warming, as well as the variability of these interactions on different time scales.

On the consistency of model, ground‐based, and satellite observations of tidal signatures: Initial results from the CAWSES tidal campaigns

Comparisons between tidal wind signatures diagnosed from satellite and ground‐based observations and a general circulations model for two (September–October 2005, March–April 2007) of the four Climate and Weather of the Sun‐Earth System (CAWSES) Global Tidal Campaign observation periods are presented (CAWSES is an international program sponsored by Scientific Committee on Solar‐Terrestrial Physics). Specific comparisons are made between model (extended Canadian Middle Atmosphere Model), satellite (Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)), meteor, MF and incoherent scatter radar (ISR), and lidar tidal signatures in the mesosphere and lower thermosphere. The satellite and ground‐based signatures are in good agreement and demonstrate for the first time that the tidal wind fields observed by both types of observations are consistent with each other. This is the first time that such agreement has been reported and effectively resolves the long‐standing issue between ground‐based radar and satellite optical measurements of winds. This level of agreement, which has proved elusive in the past, was accomplished by superposing the significant tidal components from the satellite analyses to reconstruct the fields observed by the ground stations. Particularly striking in these comparisons is the extent to which the superposed fields show strong geographic variability. This variability is also seen in the component superpositions generated from the extended Canadian Middle Atmosphere Model (eCMAM), although differences in the geographic patterns are evident.

Introduction to special section on Climate and Weather of the Sun Earth System

In the special section on CAWSES (Climate and Weather of the Sun Earth System) a total of 19 papers are published covering several aspects of Sun‐Earth coupling. Six papers concentrate on summer mesospheric ice clouds including detection by satellites, radar‐based derivation of particle properties, and water vapor observations in the mesosphere. Solar radiation affects ice clouds on time scales of the 11 year solar cycle and 27 days. Stratospheric shrinking contributes significantly to long‐term trends of ice clouds. The seasonal variability of smoke particles is confirmed to be impacted by global circulation. Six papers address the external forcing of the atmosphere caused by the Sun. The relevance of radionuclei and solar radiation spectral irradiance is presented. The impact of precipitating energetic solar particles on trace gas concentrations is studied. Ion chemistry and electron production can be important to destroy ozone in the mesosphere and upper stratosphere. Strong solar events can reduce ice clouds on short time scales owing to dynamical feed back mechanisms. The 27 day solar signal is identified in ozone concentration using satellite measurements. Model studies show that the dynamical response of the stratospheric polar vortex to solar cycle forcing depends on the phase of the quasi‐biennial oscillation. The year 2009 was a remarkable exception from this rule reinforcing natural variability. Regarding centennial time scales it is shown that changes in the stratosphere can influence tropospheric circulation. Tides have extensively been studied within CAWSES. As is demonstrated, nonmigrating tides originating in the troposphere can propagate into the thermosphere.

Impact of strong geomagnetic storms on total ozone at southern higher middle latitudes

The effects of space weather on the magnetosphere-ionosphere-atmosphere system have been broadly studied within the program CAWSES (Climate and Weather of the Sun-Earth System) and project COST724. Here we show that strong geomagnetic storms do not affect total ozone at higher middle latitudes of the Southern Hemisphere contrary to the Northern Hemisphere, where an effect is observed under specific conditions.

Diurnal changes in middle atmospheric H2O and O3: Observations in the Alpine region and climate models

In this paper we investigate daily variations in middle atmospheric water vapor and ozone based on data from two ground‐based microwave radiometers located in the Alpine region of Europe. Temperature data are obtained from a lidar located near the two stations and from the SABER experiment on the TIMED satellite. This unique set of observations is complemented by three different three‐dimensional (3‐D) chemistry‐climate models (Monitoring of Stratospheric Depletion of the Ozone Layer (MSDOL), Laboratoire de Météorologie Dynamique Reactive Processes Ruling the Ozone Budget in the Stratosphere (LMDz‐REPROBUS), and Solar Climate Ozone Links (SOCOL)) and the 2‐D atmospheric global‐scale wave model (GSWM). The first part of the paper is focused on the first Climate and Weather of the Sun‐Earth System (CAWSES) tidal campaign that consisted of a period of intensive measurements during September 2005. Variations in stratospheric water vapor are found to be in the order of 1% depending on altitude. Meridional advection of tidal nature is likely to be the dominant driving factor throughout the whole stratosphere, while vertical advection becomes more important in the mesosphere. Observed ozone variations in the upper stratosphere and lower mesosphere show amplitudes of several percent in accordance with photochemical models. Variations in lower stratospheric ozone are not solely governed by photochemistry but also by dynamics, with the temperature dependence of the photochemistry becoming more important. The second part presents an investigation of the seasonal dependence of daily variations. Models tend to underestimate the H2O diurnal amplitudes, especially during summer in the upper stratosphere. Good agreement between models and observations is found for ozone in the upper stratosphere, which reflects the fact that the O3 daily variations are driven by the photochemistry that is well modeled.

DIVISION II / WORKING GROUP INTERNATIONAL COLLABORATION IN SPACE WEATHER

The IAU Division II WG on International Collaboration in Space Weather has as its main goal to help coordinate the many activities related to space weather at an international level. The WG currently includes the international activities of the International Heliospheric Year (IHY), the International Living with a Star (ILWS) program, the CAWSES (Climate and Weather of the Sun-Earth System) Working Group on Sources of Geomagnetic Activity, and Space Weather Studies in China. The coordination of IHY activities within the IAU is led by Division II under this working group. The focus of this half-day meeting was on the activities of the IHY program. About 20 people were in attendance. The Chair of the WG, David F. Webb, gave a brief introduction noting that the meeting would have two parts: first, a session on IHY activities emphasizing IHY Regional coordination and, second, a general discussion of the other programs of the WG involving international Space Weather activities.

Assessing models for ionospheric weather specifications over Australia during the 2004 Climate and Weather of the Sun-Earth-System (CAWSES) campaign

[1] The Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) program is developing assimilation models to specify ionospheric weather. In this study the Gauss Markov Kalman Filter (GMKF) GAIM model was used. The period 20 March through 19 April 2004, which spanned the Climate and Weather of the Sun-Earth-System (CAWSES) first study period, has been extensively studied to validate the performance of the GAIM model. Although the USU-GAIM model has both regional and global capabilities and can assimilate data from a wide variety of ionospheric observations, for this study the GMKF model was run in a global mode using data only from 162 ground-based GPS slant total electron content (TEC) stations and in situ measurements from three satellites. Using measurements from the 11 ionosonde stations of the Australian Department of Defence sounder network as an independent bottomside ground-truth, the International Reference Ionosphere (IRI), Ionospheric Forecast Model (IFM), and GMKF were compared for (1) monthly mean climatology and (2) the day-to-day weather during the 31 day period. A skill score was developed for the day-to-day weather by defining the IRI as the reference model. IFM is found to be a 10% improvement, while the GMKF is 39% more capable to capture weather variability. However, the study also identifies that this global version of GMKF has difficulty around sunrise, during which time the GMKF performance can be poorer than IRI. Excluding this interval from the skill score analysis increases the GMKF ability to track weather to 48%. The use of more data and different data types should further increase the GMKF's ability to capture weather variations.

Science rationale for CAWSES (Climate and Weather of the Sun–Earth System): SCOSTEP’s interdisciplinary program for 2004–2008

An international program called Climate and Weather of the Sun–Earth System (CAWSES) has been developed by the Scientific COmmittee on Solar–TErrestrial Physics (SCOSTEP) for the study of integrated Sun–Earth system science to be conducted over the period 2004–2008. This program aims to significantly enhance our understanding of the space environment and its impacts on life and society. The main functions of CAWSES are: (a) to help coordinate international activities in observations, modeling and theory crucial to achieving this understanding; (b) to encourage involvement of scientists in both developed and developing countries in such efforts; and (c) to provide educational opportunities for students at all levels. Such multi-nation, multi-technique studies are absolutely essential for an understanding of the short term (space weather) and the long term (space climate) variability throughout the entire solar–terrestrial domain, for its societal applications and for tracking global changes in climate and ozone. The CAWSES program has been organized under four science Themes: (i) Solar Influence on Climate; (ii) Space Weather: Science and Applications; (iii) Atmospheric Coupling Processes; (iv) Space Climatology. Progress on some of these Themes can only be achieved through conducting carefully planned experimental campaigns with the data being assimilated in coupled physics based models. An end-to-end modeling capability is the ultimate goal of solar–terrestrial science. We hope these aspects will help us also in our Capacity Building efforts which is the fifth Theme under the CAWSES program – particularly in developing countries. In this paper, we will highlight some of the aspects of CAWSES science and attempt to discuss how different specialities in various research fields can be brought together with a well-defined purpose of understanding the interdependencies of the Sun–Earth system as a single entity.

Climate and weather of the Sun–Earth system: CAWSES

SCOSTEP's mission is to implement research programs in solar-terrestrial physics that can benefit from international participation and involve at least two of its participating ICSU bodies. Some past SCOSTEP programs have been comprehensive in nature such that virtually all of SCOSTEP's energy was dedicated to the implementation of one large program. Examples of these were SCOSTEP's STEP program in 1990–1995, the MAP program in 1982–1985, and the IMS in 1976–1979. This document sets forth the case for a major future SCOSTEP program called CAWSES (Climate and Weather of the Sun–Earth System), to be implemented in the period 2004–2008.