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By analyzing COSMIC data, Sharma et al. (2010) found more than 50% reduction in electron density during a solar eclipse at the F2-layer and above, with the peak of similar to 70% at 370 km. So great eclipse effect on topside ionosphere was very abnormal and much different from previous studies. However, by comparing the cosmic data with IRI results, we find that the abnormal reduction comes mainly from the significant local time variation at sunrise, not from the eclipse effect. Furthermore, we simulated the eclipse effect by using a theoretical model to confirm our analysis. (C) 2011 Elsevier Ltd. All rights reserved.

This short note is a reply to the comments by Le et al. (accepted for publication) on the paper by Sharma et al. (2010) that is concerned with the eclipse time observation of ionospheric TEC and electron density.

By combining Solar Cycle Lengths (SCL) and CO2 this paper predicts a global average surface temperature (GAST) anomaly of 1.5K in the year 2100 compared to 0.42K in 1996–2006. This assumes a continuing CO2 increase of 2 ppm per year and our derived form of Transient Climate Response (TCR), whose value 1.93 ± 0.26 K (K) per CO2 doubling would be 1.23 times higher if the Sun were ignored. After the CO2 effect has been subtracted out, the SCL explains a healthy 55% of the remaining variance. It also estimates that 37% of the recent warming from 1980 to 2001 was due to solar effects. We then compare with models created from Scafetta (2010, 2013) (the first of which has the best fit of all) and from radiative forcings estimated by Myhre et al. (2001) and Skeie et al. (2011). The latter confirms the solar contribution to 1980–2001 warming as 33%, in contrast to the negligible value given by Benestad & Schmidt (2009). It also gives a TCR of 1.3K if only CO2 continues to rise, and 2.0K if CH4 and NO2 also rise proportionately. Likewise this model estimates the ratio between the sensitivities of forcings from the Sun and greenhouse gases as 2.9 (versus 1.0 for Benestad & Schmidt (2009)). We develop a negative exponential model for post-forced warming to derive a ratio between Equilibrium Climate Sensitivity (ECS) and TCR, estimated to be 1.15. Two statistical novelties of the paper are the computation of the exact left tail probability of the Durbin-Watson statistic, and the demonstration of an approximate relationship between the Akaike Information Criterion and the tail probability of the F-statistic.

In this paper, we provide a refined and extended assignment of past and future temperature changes relative to previous analyses and describe and evaluate the relevance of vertical coupling and non-linear and secondary radiative mechanisms for the interpretation of climatic temperature variations in the middle atmosphere. Because of their nature, the latter mechanisms are not adequately accounted for in most regression analyses of temperature trends as a function of local constituent variations. These mechanisms are examined using (1) globally averaged profiles from transient simulations with the Canadian Middle Atmosphere Model (CMAM) forced by changes in greenhouse gases and ozone depleting substances and (2) a one-dimensional radiative-equilibrium model forced using the diagnosed global mean changes in radiatively active constituents as derived from the CMAM model runs. The conditions during the periods 1975 to 1995 and 2010 to 2040 (during which the rates of change in ozone and CO2 differ) provide a suitable contrast for the role of the non-linear and non-local mechanisms being evaluated in this paper to be clearly differentiated and evaluated. Vertical coupling of radiative transfer effects and the influence of secondary absorption bands are important enough to render the results of multiple linear regression analyses between the temperature response and constituent changes misleading. These effects are evaluated in detail using the 1D radiative-equilibrium model using profiles from the CMAM runs as inputs. In order to explain the differences in the CMAM temperature trends prior to and after 2000 these other radiative effects must be considered in addition to local changes in the radiatively active species. The middle atmosphere temperature cools in response to CO2 and water vapor increases, but past and future trends are modulated by ozone changes.

Present paper studies the $\gamma$-ray spectrum observed using NaI(Tl) scintillation detector over a year. The paper reports the presence of a distinct diurnal pattern in the total number of $\gamma$-ray counts detected by the NaI detector. The counts start decreasing after sunrise and show gradual recovery after sunset. The amplitude of this variation is quite significant ( > 10%) at the observation site Tirunelveli, South India. However, further investigation based on different energy ranges reveals that the mentioned diurnal pattern is actually present only in the energies related to the terrestrial background radioactivity. The study demonstrates that the pattern is associated with the radioactivity of isotopes of radon ($^{222}$Rn and $^{220}$Rn) and their daughter radionuclides. The amplitude of the diurnal variation is found to have seasonal dependence, with the lowest amplitude during June-October (~ 2%), and highest in April-May months (~ 14%). The dependence of the amplitude of the diurnal variation on various atmospheric parameters, namely temperature, relative humidity, and vertical wind is examined. The observed diurnal pattern is attributed to the generation of the inversion layer. The distribution of concentration of radon and thoron progenies in an air column changes with the vertical mixing and atmospheric boundary layer (ABL), resulting in the diurnal variation of $\gamma$-rays., Comment: 16 pages, 14 figures, 1 table

Naturally occurring geomagnetic storms have been shown to correlate with changes in organisms׳ biological processes. Changes in the geomagnetic field during a geomagnetic storm are complex and contain both slow changes of the geomagnetic field with frequencies of up to 0.001 Hz, and various geomagnetic pulsations observed in general to be within the range of 0.001–5 Hz. Little is known about what frequency constituent of geomagnetic storms has the strongest effect on living organisms. This paper uses an experimental approach to demonstrate that organisms from different taxa principally respond to slow changes of the geomagnetic field corresponding with the main phase and the initial period of the recovery phase of a geomagnetic storm. Pc1 type pulsations, which are commonly regarded as biologically effective elements of geomagnetic disturbances, did not affect controlled parameters in our experiments. This paper may serve as a starting point for a thorough inquiry into the influence of slow fluctuations of the geomagnetic field on organisms.

The thermal regime of the middle atmosphere is determined to a great extent by the balance between the incoming solar and outgoing infrared radiation. To account for these processes in numerical models of the middle atmosphere, parameterizations that are capable of quickly and accurately calculating infrared cooling and solar heating rates are required. These parameterizations should include the breakdown of local thermodynamic equilibrium (LTE) conditions and allow for feedbacks by ensuring that dependencies on all input parameters are accounted for. This paper discusses the major mechanisms responsible for maintaining the radiative energy budget of the middle atmosphere and presents a brief review of approaches and numerical schemes currently available for use in general circulation models. The main focus of the paper is on the approaches and schemes designed for non-LTE treatment.

Recondensed meteoric material, so-called meteoric smoke, has long been considered the main candidate for condensation nuclei for mesospheric ice formation. Recently however, model studies have shown that meteoric smoke particles are transported away from the polar region, where ice phenomena such as noctilucent clouds occur, before they can grow large enough to serve as ice condensation nuclei. In the accompanying paper it is argued that charging of the meteoric smoke particles may solve this dilemma by significantly altering the efficiency of the particles as condensation nuclei. In the present paper, the feasibility of this idea is investigated more quantitatively, by analysing the time scales of processes such as charging, recombination, and particle growth. Despite large uncertainties, especially in the charging efficiency of the smallest smoke particles, we show that reasonable assumptions yield number densities of charged condensation nuclei that are consistent with what is expected for mesospheric ice phenomena.

Measurements show that the polar mesospheric clouds (PMC) can vary, in the zonal mean, with periods around 1 month [Bailey et al., 2005. Observations of polar mesospheric clouds by the Student Nitric Oxide Explorer. J. Geophys. Res. 110, D13203, doi:10.1029/2004JD005422]. This observation has been the impetus for the present paper, where we describe corresponding temperature oscillations generated by the Numerical Spectral Model (NSM). Our numerical results are taken from the 3D and 2D versions of the NSM, which produce inter-annual and long-term variations in the polar mesopause region, as discussed in the accompanying paper (Part I). In the NSM, the intra-seasonal temperature variations with periods around 2 months are generated by the meridional winds that in turn are accelerated by the momentum deposition from small-scale gravity waves (GW) propagating north/south. The wave-driven dynamical process underlying the oscillations is intrinsically non-linear like that generating the quasi-biennial oscillation (QBO). Our analysis demonstrates that the seasonal annual and semi-annual variations excite the oscillation frequencies through non-linear cascading.

This paper examines the night of 23 May 2002 as observed by a large number of Australian ionosondes (19) as well as others situated in New Guinea, Indonesia and China. The arrival of a solar Coronal Mass Ejection (CME) and subsequent negative Bz turnings in the solar wind resulted in a magnetic storm with two bursts of energy inputs into the auroral zones. The energy depositions produced two successive rise and falls in ionospheric height over a 300 km height range within the period 12.30–21.00 UT. The two events were seen in the night-side hemisphere by all ionosondes at Southeast Asian longitudes in the southern hemisphere, as well as in the northern hemisphere. In this paper, the simultaneity and spatial variability of these events is investigated. The first event, after an initial expansion towards the equator, ended with a retreat in the area of height rise back towards the auroral zone. The second event was of greater complexity and did not show such a steady variation in rise and fall times with latitude. Such events are often described as large-scale travelling atmospheric/ionospheric disturbances (LTADs or LTIDs). In the southern hemisphere, the front of the initial height rise was found to move at a speed up to 1300 m/s as was also measured by Tsugawa et al. [2006. Geomagnetic conjugate observations of large-scale travelling ionospheric disturbances using GPS networks in Japan and Australia. Journal of Geophysical Research 111, A02302] from small changes in GPS TEC. The front was uniform across the widest longitudinal range of observation (52° or 5360 km).The relationship between the subsequent fall in ionospheric height and an associated temporary increase in foF2 was found to be consistent with previous observations. Ionospheric drivers that move ionization up and down magnetic field lines are suggested as the common cause of the relationship between foF2 and height.

Recent studies have demonstrated that ground-based magnetometer observations can be used to infer realistic, daytime vertical E×B drift velocities in the Peruvian and Philippine longitude sectors. It has also been demonstrated that under certain conditions the time variability in the interplanetary electric field (IEF)—minutes to hours—is reflected in the daytime, prompt penetration of high-latitude electric fields to low latitudes. In this paper, we incorporate magnetometer-inferred E×B drift techniques to extend this study to include the Indian sector E×B drift velocities and to investigate the relationships between IEF conditions and daytime, low-latitude electric field observations under both geomagnetically quiet and disturbed conditions. This paper addresses several basic questions related to the relationships between IEF conditions and low-latitude east–west electric fields. (1) When low-latitude electric fields exhibit quiet-time, Sq-type behavior, what are the IEF conditions? (2) Under disturbed conditions, what are the relationships between the IEF parameters and the low-latitude electric fields in the Peruvian, Philippine, and Indian longitude sectors? (3) If the three longitude sector electric field responses are similar under disturbed conditions, is the response consistent with the current ideas put forward at the Millstone Hill Workshop on promptly penetrating electric fields and over-shielding effects at low latitudes? We address the above questions by analyzing magnetometer-inferred E×B drift velocities between January 2001 and December 2004 when there exists more than 500 quiet days and more than 235 geomagnetically disturbed days, defined by daily Ap values greater than 20. It is suggested that the neural network approach that provides realistic E×B drift velocities based on magnetometer observations can be applied at any longitude where appropriately placed magnetometers exist. It is found that: (1) the average quiet, daytime upward E×B drift velocity vs. LT in the Indian sector is comparable to the average velocity vs. LT in the Peruvian sector and both are roughly 3–5 m/s less than the values in the Philippine sector; (2) under quiet conditions, the peak velocity occurs at 1100 LT in the Peruvian sector and at 1000 LT in both the Philippine and Indian sectors; and (3) during disturbed conditions, it is observed that daytime, promptly penetrating electric fields occur, simultaneously, in the Philippine, Indian and Peruvian sectors, in response to fluctuating IEF conditions.

VHF radar observations are used to investigate different regions of the Earth's atmosphere. Strong echoes from the mesosphere are mainly observed during summer months at polar latitudes (polar mesosphere summer echoes [PMSE]), and less often at mid-latitudes (mesosphere summer echoes [MSE]). Interestingly, in recent years similar echoes have been observed during winter months ([polar] mesosphere winter echoes (P)MWE). This paper reports on VHF radar measurements between September and April at Andenes (2001–2005) and Kuhlungsborn (2003–2005) to determine the mean features of (P)MWE at polar and mid-latitudes. The (P)MWE are a rare phenomenon with mean occurrence rates of about 2.9% in polar and only 0.3% in mid-latitudes, with a maximum occurrence height at 70.5 km for daytime and 77.5 km for nighttime echoes. The diurnal variation is characterised by a maximum near noon and minimum during nighttime. The seasonal variation of (P)MWE is weak with some indication of an increased number of PMWE during mid-winter. The occurrence rate of (P)MWE is positively correlated with the ionisation level of the D region of the ionosphere. Mainly high-energetic proton (and electron) fluxes and enhanced X-ray radiation are important for the existence of (P)MWE. The second factor for the existence of (P)MWE are irregularities of the refraction index of half the radar wavelength (about 3 m for the radars used in this paper). Neutral air turbulence due to breaking gravity waves seems to be an important process. Whether charged aerosol particles or partial reflections of infrasound have additionally to be considered to explain (P)MWE is currently a point of discussion in the literature.

This paper presents results from the TIME-GCM-CCM3 thermosphere–ionosphere–lower atmosphere flux-coupled model, and investigates how well the model simulates known F2-layer day/night and seasonal behaviour and patterns of day-to-day variability at seven ionosonde stations. Of the many possible contributors to F2-layer variability, the present work includes only the influence of ‘meteorological’ disturbances transmitted from lower levels in the atmosphere, solar and geomagnetic conditions being held at constant levels throughout a model year. In comparison to ionosonde data, TIME-GCM-CCM3 models the peak electron density (NmF2) quite well, except for overemphasizing the daytime summer/winter anomaly in both hemispheres and seriously underestimating night NmF2 in summer. The peak height hmF2 is satisfactorily modelled by day, except that the model does not reproduce its observed semiannual variation. Nighttime values of hmF2 are much too low, thus causing low model values of night NmF2. Comparison of the variations of NmF2 and the neutral [O/N2] ratio supports the idea that both annual and semiannual variations of F2-layer electron density are largely caused by changes of neutral composition, which in turn are driven by the global thermospheric circulation. Finally, the paper describes and discusses the characteristics of the F2-layer response to the imposed ‘meteorological’ disturbances. The ionospheric response is evaluated as the standard deviations of five ionospheric parameters for each station within 11-day blocks of data. At any one station, the patterns of variability show some coherence between different parameters, such as peak electron density and the neutral atomic/molecular ratio. Coherence between stations is found only between the closest pairs, some 2500 km apart, which is presumably related to the scale size of the ‘meteorological’ disturbances. The F2-layer day-to-day variability appears to be related more to variations in winds than to variations of thermospheric composition.

We present results from a non-linear, 3D, time dependent numerical spectral model, which extends from the ground up to the thermosphere and incorporates Hines’ Doppler spread parameterization for small-scale gravity waves (GWs). Our focal point is the mesosphere, which is dominated by wave interactions. We discuss diurnal and semi-diurnal tides in the present paper (Part I) and planetary waves (PWs) in a companion paper (Part II). To study the seasonal variations of tides, in particular with regard to GW forcing, numerical experiments are performed that lead to the following conclusions: (1) The large semi-annual variations in the diurnal tide (DT), with peak amplitudes observed around equinox, are produced to a significant extent by GW interactions that involve, in part, PWs. (2) The DT, like PWs, is amplified by GW momentum deposition, which reduces also the vertical wavelength. (3) Variations in eddy viscosity associated with GW interactions may also influence the DT. (4) The semidiurnal tide (SDT), and its phase in particular, is strongly influenced by the zonal mean circulation. (5) Without the DT present, the SDT is amplified by GWs; but the DT filters out GWs such that the wave interaction significantly reduces the amplitude of the SDT during equinox, effectively producing a strong non-linear interaction between the DT and the SDT. (6) PWs generated internally by the baroclinic instability and GW forcing produce large amplitude modulations of the DT and SDT.

The ionospheric electron content (IEC) measured using the VHF Radio Beacon (RB) technique from a geostationary satellite at Guwahati (geographic latitude 26.2 °N, geographic longitude 91.7 °E, geomagnetic latitude 15.2 °N, dip angle 37 °N, magnetic latitude 20.64 °N), during low and high solar activity periods is analysed to examine the influence of solar activity on the IEC near the equatorial ionospheric anomaly crest region, and to assess the predictability of existing ionospheric models such as the International Reference Ionosphere (IRI) and the Semi empirical Low latitude Ionosphere Model (SLIM) on the IEC for different solar activity conditions. The paper shows that the IEC figures derived from models vary widely with solar activity and neither of the models predicts the IEC (within its maximum and minimum deviations) at this station for the entire day. The attempt here is to explain the discrepancy observed between the measured IEC and that derived through the IRI or SLIM models, with the help of the Sheffield University Plasmasphere Ionosphere Model (SUPIM) for a selected solar activity condition. Model IEC values computed from the IRI over a few other anomaly crest stations are also compared; the paper highlights the differences in the observed and model-predicted patterns between 20 ° and 25 °N magnetic latitude.

This paper investigates evolutions of geomagnetic and equatorial electrodynamic responses during three consecutive 27-day recurrent geomagnetic storms (RGSs) in 2007 by using the solar wind plasma, geomagnetic indices, and magnetometer data. The RGSs are classified as corotating interaction regions (CIR)-induced storms and High Intensity Long Duration Continuous AE Activity (HILDCAA). The RGSs show quasi-stable and diverge variabilities in storm-times that critically control the long-lasting and complex electrodynamic responses in equatorial ionosphere, particularly in CIR-storms. The correlations of Auroral Electrojet (AE)/Polar Cap (PC) indices are moderate for CIRs and HILDCAAs during local summer, which suggest to less effective coupling and/or different sources of PC and AE. The correlations of reconnection electric field with AE and Fourier analysis of the north-south component of the interplanetary magnetic field with AE reveal that the solar wind-magnetosphere-ionosphere coupling is more effective in the HILDCAAs than in the CIRs. Results indicate that disturbance electric fields are closely related to storm time evolution of the RGSs and are seasonal dependent. Disturbance dynamo electric fields (DDEFs) are related to each group of HSSs during HILDCAA periods. Justification of storm-time effect or seasonal effects is done. The substantial DDEFs are caused by the storm time effects of enhanced thermospheric wind due to the summer-to-winter winds in the late night sector. DDEFs are effective particularly in the morning-to-prenoon time in the summer, while they are less effective in equinoctial months due to the symmetric meridional winds and in winter months due to restriction of the equatorward motion.

This paper presents the performance of IRI-2016 model in describing the East African sector of equatorial ionosphere during different geomagnetic conditions and time scales. The analysis is carried out by taking six years (2008 and 2011–2015) of the vertical total electron content (vTEC) data from GPS receiver located at Arba Minch (Geographic: 6.06°N and 37.56°E; Geomagnetic: −3.03°N and 109.29°E) in Ethiopia. The IRI-2016 model either underestimates or overestimates observations depending on time of day, months, season, solar and geomagnetic conditions. An underestimation becomes more pronounced from the first to third quartiles, while an overestimation is nearly constant. The diurnal variation pattern of measured vTEC (vTECo) shows a single peak mostly occurring between 1000 and 1400 UT (1230 and 1630 LT), while the modeled vTEC (vTECm) is characterized by two remarkable peak values with the first peak occurring between 0500 and 0700 UT (0730 and 0930 LT), and the second peak occurring between 1300 and 1400 UT (1530 and 16300 LT). The nighttime monthly peak vTECm is lower compared to observations during 2008, but it is reversed during 2011–2015. Seasonally, the vTECo variations show a semiannual variation pattern with maximum values during March equinox and December solstice months and minimum during June solstice and September equinox months. This trend equally explains the semiannual variability noted on the seasonal percentage deviation in vTECm variability. The mean and median annual observations show better agreement with vTECm during daytime, but opposite at nighttime hours (except in 2008). The response of the equatorial ionosphere for storm, which was observed clearly in the observations, did not show in the model results. The vTECo shows a significant relation with both merging and interplanetary electric fields during storm. This suggests that a linkage of those parameters with storm-time vTEC needs to be established for a variety of geophysical conditions to improve the forecasting capability of the model. Generally, the IRI-2016 model shows better agreement with observations during solar minimum compared to other solar activity phases. We suggest that the results from this study would complement in the model improvement towards near real time predictions of different ionospheric parameters over the equatorial and low latitude regions like East Africa.

The present paper reports a comparative study among two neurocomputing models in the form of Multilayer Perceptron (MLP) models and non-linear regression for the prediction of surface ozone (O3) during pre-monsoon season over Gangetic West Bengal (GWB), India considering NOx, SO2, PM10 and temperature as predictors. Learning the MLPs through gradient descent (GD) with tanhyperbolic and sigmoid nonlinearities, we found that all the models under consideration have almost the same degrees of prediction efficiency for O3 over GWB during pre-monsoon season with the said predictors. However, the MLP model with tanhyperbolic activation function is found to produce a significantly higher correlation and Willmott's index of agreement between actual and predicted O3 than the other models. Finally, MLP with GD learning characterized by tanhyperbolic nonlinearity is identified to have significant efficiency in surface ozone prediction over the region as mentioned above.

Geomorphologies and mechanisms of thermospheric mass density variations caused by geomagnetic storms are still challenging due to limited observations and imprecise models. Recently, precise orbit determination (POD) of Gravity Recovery and Climate Experiment (GRACE) and Swarm satellites is able to estimate thermospheric mass density variations, which may provide data to study thermospheric mass density variations following the storm. In this paper, the thermospheric mass density is estimated from GRACE-A and Swarm-A POD and the distinct thermospheric mass density variations are investigated as function of latitude during the September 2017 geomagnetic storm. Different enhancements in mass density response to the geomagnetic storm are presented for the Northern (GRACE) and the Southern (Swarm) Hemispheres. Swarm observations show symmetric mass density variations between two hemispheres and a slightly stronger enhancement in Southern Hemisphere. GRACE POD and accelerometer observations both show a very strong enhancement in Northern Hemisphere while no corresponding enhancement in Southern Hemisphere. This anomaly may attribute to the effects of vertical winds in high latitude region and plasma drift considering the similar solar zenith angles in both hemispheres.

A Stratosphere-Troposphere (ST) wind profiler radar at 205 MHz is operational at Cochin (10.04 N; 76.44 E), India since January 2017 and is providing accurate three-dimensional wind profiles for an altitude range of 315 m to 20 km. In this paper, we present a method to estimate the tropopause altitude from signal to noise ratio (SNR) profiles obtained from the 205 MHz wind profiler radar. The gradient in SNR is used to estimate the cold point tropopause (CPT) height. The CPT height obtained from the ST radar is validated against co-located radiosonde tropopause height measurements and is found to be in very good agreement. The variability of CPT height during monsoon season was studied and the factors responsible for its variability were investigated. It is found that during monsoon season the Tropical Easterly Jet (TEJ) has an inverse relationship with the CPT height, i.e. CPT height increases as the strength of TEJ diminishes and vice versa. A comparison between TEJ core speed and ice cloud water path (ICWP) which represents the strength of deep convection, shows that ICWP decreases as the strength of TEJ increases. Thus, our analysis shows that TEJ affects the tropopause height through changing the concentration of ice clouds.

Very recently, it has been found that intense anomalies of the mesospheric ozone occur a few days before major earthquakes. This paper explores the credibility of this finding in the case of the last two major earthquakes in Greece. Indeed, the study of the mesospheric ozone vertical distribution showed that unusual anomalies occurred a few days before these two earthquakes. However, at time periods with no significant seismicity the same unusual changes in the mesospheric ozone vertical distribution were observed. Consequently, significant temporal changes of the mesospheric ozone can not be considered as precursors for upcoming significant seismic activity.

In the paper we study the ionosphere response to the March 2015 severe geomagnetic storm according to Eurasian high-middle latitude ionosonde chain. On the basis of the ionosonde chain data we have restored the time/longitude dynamics of the high-middle latitude ionosphere over the Eurasian continent. The data showed that during the main storm phase that developed in the nighttime Siberian sector, a disturbed thermosphere region was created. This region moved westward with 50–70 m/s velocity and which was registered two-three days after the storm in the Eastern and Western Europe. Characteristics of the geomagnetic field variations showed that three active zones occurred during the storm. One is shifted from the geographic pole toward magnetic pole at ∼270° longitude. Two other zones were formed symmetrically opposite to the geomagnetic pole at longitudes ∼40° and ∼130°; the major electron density depletions at these longitudes were observed in the high-middle latitude ionosphere. On the contrary, longitudinal sector ∼80–110° showed electron density maximum in quiet conditions and fast ionosphere restoration after the storm decaying.

In this paper we investigate response of the total ozone column to energetic electron precipitation (EEP) observed by bremsstrahlung effect. The list of EEP events was prepared by members of the balloon experiments of the Lebedev Physical Institute. Here we used superposed epoch analysis and the days with EEP events are registered during winter (November–February) and summer (June–August) months from 1970 to 2012 were chosen as key dates. This period corresponds approximately to three solar cycles. Data of the total ozone column were collected by single coherent total ozone dataset, called the Multi Sensor Reanalysis (MSR). A long series of data of the total ozone column is allowed us to study the response of ozone content to 90 winter and 103 summer EEP events. The obtained ozone sensitivity to the events of energetic electron precipitation is clearly pronounced during local winters in the high latitudes of the Northern and Southern Hemispheres (60–80 NH and 60–80 SH). In the high latitudes of the Northern Hemisphere, during winter months, the total ozone content can be reduced by up to 10 DU after energetic electron precipitation with minimum observed on the first day after EEP events. Response of the total ozone, over high latitudes of the Northern Hemisphere, to EEP events can be opposite during summer months.

The variation of the atmospheric electric field from the ground is analyzed by using an electric field mill sensor for Islamabad, Pakistan. The first early results of atmospheric electric field are presented in this paper. These results are based on fair-weather days for the diurnal, seasonal, and annual variations in Islamabad from 2015 to 2017. The variation in the values of the atmospheric electric field is studied extensively during the monsoon, the pre-monsoon and the winter season. Minimum values are observed during the monsoon season, and maximum values are observed during winter and spring. The measured values of the atmospheric electric field are also compared with the universal standard values of the Carnegie curve. The trend of the diurnal variation shows a sharp single oscillation in fair-weather with a maximum at ∼ 4:00 UT (universal time), which could be due to the influence of local effects such as aerosol.

The ionospheric monitoring satellites aid in correlating the lithospheric variation in ionosphere through Lithosphere-Atmosphere-Ionosphere coupling (LAIC) over the epicenter of future earthquake (EQ). In the present paper, we studied variations in ionosphere associated to two large magnitude EQs (Mw ≥ 6.5) and low epicentral depth EQs of less than 12 km in Plasma Density (PD), Slant Total Electron Content (STEC) and Electron Temperature (ET) of European Space Agency's (ESA) Swarm-three satellites (Swarm-A, -B, and –C). These anomalies are investigated in the Swarm data for 60 days before/after each main shock. The anomalies are detected by statistically implemented median (M) and standard deviation (σ) method within the Dobrovolsky's area. In order to exclude the geomagnetic perturbations, we have selected the ionospheric data in quiet geomagnetic conditions. Anomalous variations in Swarm-A data occur in ET and STEC for the USA event, and similarly, significant perturbation is clear in STEC of Swarm-B before the Mw 6.5, USA. In case of Swarm-C, no clear anomalies associated with the USA event. Furthermore, Swarm-A, -B and –C have abnormal post-seismic PD, STEC and ET responses to the Mw 6.7 Turkey EQ in the form intensive perturbations beyond the upper bound. We also study the atmospheric data over the epicenters in the form of Outgoing Longwave Radiation (OLR), Relative Humidity (RH), Surface Temperature (ST), and Air Temperature (AT) to support the Swarm observations. RH and ST show pre-seismic atmospheric anomalies before the USA EQ in the same anomalous time period as Swarm satellites. While, OLR, ST and AT have post-seismic atmospheric anomalies after the Turkey EQ within 15–20-day period. The precursors chain from the lithosphere to the atmosphere, followed by the ionosphere are highlighted at different altitudes. The variations window for Swarm satellites and atmospheric indices are 5 days prior to USA main shock and one month after the Turkish EQ. Moreover, this study also aims to study the caliber of Swarm satellites for indicating seismo-ionospheric irregularities, which need more studies to delineate the LAIC hypothesis for future EQ.

This paper studies the electric field parameters of negative cloud-to-ground (CG) lightning flashes in the Bogota savanna (a large plateau located in central Colombia), and its comparison with other regions. This work is the first of its kind in the country where the parameters of lightning-generated electric fields are analyzed in detail. A total of 329 CG lightning flashes had been examined. These flashes were recorded within 4–250 km from the measuring station during the period August–November 2016. From observations, negative CG flashes comprised 93% of total events registered. It has been found that negative lightning discharges occurred along the plateau (4250 km2 at 2550 m altitude) exhibit some different characteristics compared with measurements carried out in several regions (tropical, subtropical and temperate latitudes). In this study, it was found that 64.7% of the negative CG flashes are multiple strokes with an average multiplicity of 2.58 strokes per flash. In addition, the mean interval between 789 negative return strokes (306 first- and 483 subsequent strokes) was 61.3 ± 51.9 ms, while the arithmetic mean of the total duration for 198 multiple-stroke flashes was 149.5 ms. Other lightning flash features such as relation between the interstroke interval and the return stroke order, the ratio of the subsequent stroke peak field to the corresponding first one and the maximum multiplicity are also analyzed.

International audience; This paper is related to analysis of the Weddell Sea Anomaly (WSA) and the Mid-latitude Summer Nighttime Anomaly (MSNA) observed by the low altitude satellite DEMETER during nighttime between 2004 and 2010. This time interval corresponds to the decrease of the solar cycle 23 which was unusually long. It appears that, if these two anomalies have a peak in local summer (December in the Southern hemisphere for the WSA, June in the Northern hemisphere for the MSNA), the anomalies are also observed during the months around December and June with a decreased intensity. But at the end of the solar cycle 23 the summer peaks dramatically decrease and even relatively more quickly than the solar index F10.7. This phenomenon is much more significant for the WSA. It is shown that the mechanism producing the two anomalies (thermospheric neutral winds and magnetic declination effects) is strengthened by the solar ionization which is active during the night above the WSA and the MSNA areas. But at solar minimum, this mechanism is weakened. These results are valid at the satellite altitude (660 km) and may vary at lower altitudes.

The topic of this paper is to investigate whether a solar signal can be identified in the variation of climatic parameters at regional scale. This was done using eight climate parameters recorded in Romania during 1961–2013 which corresponds with four cycles of solar activity. The methodology is based on trend, composite and wavelet analysis. A weak solar influence with a clear spatial pattern was identified, especially during the cold season, on temperature and cloud cover. During the warm season, the influence seems to be spurious. A clear difference between the north-eastern Romania and the rest of the country was found in the response of local climate to solar trigger. The mountain chain induces persistent disparities in the distribution of the most parameters, which supports the fact that orography is an important feature to be considered when analysing solar imprint at regional scale. Possible mechanisms for the solar influence on climate at regional and local scale are proposed.

Distribution of atmospheric water vapor is highly variable in time and space across the Earth; the knowledge of its distribution is essential in climate studies. In Iran, atmospheric water vapor measurements using conventional ground-based methods such as radiosondes are limited. In this paper, a comparison of precipitable water vapor (PWV) estimated by a ground-based sunphotometer (SPM) with atmospheric infrared sounder (AIRS) satellite sensor is presented over Zanjan, a city in northwest Iran for a period from December 2009 to December 2013. The PWV of SPM and AIRS have a good agreement ( R 2 = 93%). The seasonal bias between PWV estimated by SPM and AIRS (PWV SPM - PWV AIRS ) over Zanjan city is − 3.35 , − 5.15 , − 2.27 , − 0.95 mm during spring, summer, autumn, and winter, respectively. Average of AIRS PWV over Iran shows that the largest amount of PWV occurs along the seas (Caspian Sea, Oman Sea, and the Persian Gulf) and its lowest value happens in high altitude mountainous regions of the country. Also, correlation coefficients between AIRS PWV and surface temperature of 29 synoptic stations are calculated over Iran from September 2002 to December 2016. The average of correlation coefficients over the stations is 0.73.

The paper presents the climatology and interannual variability of both eastward- and westward-propagating ∼2-day waves (QTDW) observed in the MLS/Aura geopotential height data for a period of 10 full years (2005–2014). The climatology of the QTDWs has been studied in two steps: (i) by using average 2D-wavelet spectra both the dominant modes of variability and how these modes vary in time and space have been determined, and (ii) by applying a 2D decomposition procedure, where all planetary waves are simultaneously extracted from the data, the average global spatio-temporal distributions of all defined by the 2D-wavelet analysis modes have been obtained. It is found that the westward-propagating waves at mid-high latitudes have zonal wave numbers 2, 3 and 4 and are observed mainly in summer hemisphere. Two different types of eastward-propagating waves have been identified: (i) waves at mid-high latitudes with zonal wave numbers 2 and 3 observed in the winter hemisphere, and (ii) waves observed predominantly over the equator with zonal wave number 2, which do not have a well-defined seasonal variability but show some enhancement in both solstices. While the climatological features of the MLS/Aura QTDWs for the considered period are robust the interannual variations have to be adopted cautiously. The primary reason is that the length of the considered period of 10 years is not enough for finding clear variability pattern. The only long-term variability which appears to have some robustness is that of the W3 wave in the Southern Hemisphere where the influence of the solar cycle has been distinguished.

The paper reports night time observations of ionospheric irregularities made through amplitude scintillation of 251 MHz signal at Kolhapur (16.4°N, 74.2°E), an equatorial Appleton anomaly region using spaced antenna system. Monthly and night time percentage of occurrence of scintillations, during increasing solar cycle from January 2011 to August 2015, is discussed. The parameters such as-maximum cross-correlation function (CI), Fade Rate are also studied. The percentage occurrence is observed to be higher in post sunset period and during equinoctial months than in winter and summer months. Scintillation occurrence is observed to be suppressed during increasing solar activity. CI shows seasonal changes. Percentage of occurrence of CI ≥ 0.5 decreases with increase in solar activity and fade rate also shows solar activity dependence.

This study investigates the nonlinear dynamics of the stratospheric ozone layer at Pakistan atmospheric region. Ozone considered now the most important issue in the world because of its diverse effects on earth biosphere, including human health, ecosystem, marine life, agriculture yield and climate change. Therefore, this paper deals with total monthly time series data of stratospheric ozone over the Pakistan atmospheric region from 1970 to 2013. Two approaches, basic statistical analysis and Fractal dimension (D) have adapted to study the nature of nonlinear dynamics of stratospheric ozone level. Results obtained from this research have shown that the Hurst exponent values of both methods of fractal dimension revealed an anti-persistent behavior (negatively correlated), i.e. decreasing trend for all lags and Rescaled range analysis is more appropriate as compared to Detrended fluctuation analysis. For seasonal time series all month follows an anti-persistent behavior except in the month of November which shown persistence behavior i.e. time series is an independent and increasing trend. The normality test statistics also confirmed the nonlinear behavior of ozone and the rejection of hypothesis indicates the strong evidence of the complexity of data. This study will be useful to the researchers working in the same field in the future to verify the complex nature of stratospheric ozone.

This paper presents the results of a detailed study on the size characteristics of aerosols at the tropical coastal site Thiruvananthapuram based on the in-situ measurements of size resolved aerosol number density using an aerosol spectrometer, covering a period of 28 months from September 2011 to December 2013. The diurnal pattern of aerosol number density is characterized by day time low and a two-fold increase during nighttime and these changes are closely associated with the strong mesoscale features namely the sea breeze and land breeze prevailing at the site. Aerosol Number Size Distribution (NSD) depicts a multi-modal nature with two prominent modes, one ≤0.1 μm and other ∼1 μm. Two other less pronounced modes are also observed in the NSD, one ∼0.3–0.5 μm and other ∼5–8 μm. The NSDs also exhibited strong seasonal changes linked with the synoptic meteorological feature of this region namely the South Asian monsoon. The seasonal NSDs were parameterized and analyzed. In addition to this, the effects of meteorological parameters temperature, relative humidity, and wind speed and airflow patterns on aerosol number density as revealed by partial correlation analysis were found to be aerosol size dependent.

This paper examines the interannual variability of latent (LE) and sensible (H) heat fluxes over the North Indian Ocean for the summer season (June, July, August), that show positive linear trends during 1958–2017. Using Air-Sea Flux (OAFlux) from NCEP/NCAR reanalysis-I, the variability and trends in LE and H heat fluxes are compared with changes in the position and pressure of the South Asia Low (SAL). Investigation of interactions between the air-sea heat fluxes and SAL pressure center through correlations analysis and with analysis of composites of humidity gradient, temperature gradient and vector wind fields is carried out. The results show that the SAL plays an important role in the variability of air-sea heat fluxes over North Indian Ocean. There is a negative correlation between SAL pressure and its latitude position. A change of the SAL from a north location to a south location induces changes in North Indian Ocean surface winds, humidity and temperature. These, combined with sea surface warming trends, produce trends in summer latent and sensible heat fluxes.

Heavy snowfall is one of the perilous atmospheric phenomena which occurs occasionally in south-west coasts of the Caspian Sea. In this paper, we have simulated the role of sea surface temperature (SST) and lake-air temperature difference on the lake-effect snow in south-west coasts of the Caspian Sea using Weather Research and Forecasting (WRF) model. SST was increased by 2 °C–4 °C and air temperature decrease by 2 °C–4 °C in model simulations and the resulting precipitation was compared to observed values. The results show that the precipitation is significantly sensitive to the SST and lake-air temperature difference. The results indicated that the regions with heavy precipitation correspond with 4 °C increase in SST and 2 °C decrease in air temperature, add about 60 mm to the total precipitation. Furthermore, the increase in SST enhances snowfall along the coastlines. In overall, an increase between 2 °C and 4 °C in SST over 5 days, increases the precipitation between 8.43% and 19.41%, respectively, and decrease air temperature by 2 °C and 4 °C increase precipitation about 24.78% and 0.72%, respectively. Overall, the highest increase in precipitation in the whole region is related to the 2 °C decrease in air temperature and the 4 °C increase in SST. Since other atmospheric parameters such as pressure, wind field, and humidity flux are affected by temperature change, so excessive decrease in air temperature tends to weaken the low pressure and vertical motion and less precipitation occurs. Therefore, the amount of the lake-air temperature difference is a key factor in strengthening the lake-effect precipitation. Additionally, SST increases the latent heat flux and injects additional humidity to the region which further strengthens orographic uplifts and intensifies unstable condition. In the meantime, stronger wind speed caused by unstable boundary layer over the lake and sufficient fetch, accumulate additional humidity in the convergence zone along the south-west coastlines.

In this paper, we report the quasi-two-day wave (QTDW) in daytime only SABER CO2 in January 2003. The QTDW in CO2 of ∼7 ppmv or 3–4% shows double peak structures at mid and low latitudes of both hemispheres. We compare the SABER measured QTDW disturbance in CO2 and temperature to those in the eCMAM (the extended Canadian Middle Atmosphere Model). Good agreement of QTDW CO2 spatial and temporal variations is seen, especially at southern mid-latitudes. eCMAM outputs are further analyzed to show that the QTDW in CO2 mixing ratio is mainly driven by both vertical transport and meridional advection. Because waves in vertical transport can be derived by temperature disturbance via a so-called adiabatic displacement approach, we can estimate the QTDW in CO2 mixing ratio from the SABER QTDW in temperature assuming meridional advection is weak at low and mid-latitudes.

In this paper, we investigate the tidal activity in the mesosphere and lower thermosphere region at 370N using OH Meinel and O2 atmospheric airglow observations from 1998 to 2015. The observations were taken with a Spectral Airglow Temperature Imager (SATI) installed at Sierra Nevada Observatory (SNO) (37.060N, 3.380W) at 2900 m height. From these observations a seasonal dependence of the amplitudes of the semidiurnal tide is inferred. The maximum tidal amplitude occurs in winter and the minimum in summer. The vertically averaged rotational temperatures and vertically integrated volume emission rate (rotational temperatures and intensities here in after), from the O2 atmospheric band measurements and the rotational temperature derived from OH Meinel band measurements reach the maximum amplitude about 1–4 h after midnight during almost all the year except in August–September where the maximum is found 2–4 h earlier. The amplitude of the tide in the OH intensity reaches the minimum near midnight in midwinter, then it is progressively delayed until 4:00 LT in August–September, and from there on it moves again forward towards midnight. The mean Krassovsky numbers for OH and O2 emissions are 5.9 ± 1.8 and 5.6 ± 1.0, respectively, with negative Krassovsky phases for almost all the year, indicating an upward energy transport. The mean vertical wavelengths for the vertical tidal propagation derived from OH and O2 emissions are 35 ± 20 km and 33 ± 18 km, respectively. The vertical wavelengths together with the phase shift in the temperature derived from both airglow emissions indicate that these airglow emission layers are separated by 7 ± 3 km, on average.

When the sun is located in the observation direction of the ground-based microwave radiometer, the brightness temperature data, especially for those deployed in low latitudes, will increase abnormally due to the influence of solar radiation. The paper collects the observation data of the MWP967KV-type ground-based microwave radiometer set up at Field Experiment Base on Lightning Science of China Meteorological Administration in Guangzhou, from June 1 to July 17, 2017, and May 21 to July 31, 2018. The observation data have been fitted and the fitting parameters have been quantitatively analyzed. The results show that the daily variation characteristics of brightness temperature increment ( Δ T b ( 0 ) ) increase from the end of May or early June, reach the maximum on the summer solstice, and then decline. Higher maximum solar elevation angle ( H s _ max ), greater atmospheric transmittance, and narrower beam width imply greater amplitudes of Δ T b ( 0 ) . The correlation coefficients between the amplitudes of Δ T b ( 0 ) and H s _ max for K-band and V-band in 2017 and 2018 are 0.96, 0.86, 0.98, and 0.94, respectively. And the maximum brightness temperature increment can reach up to 221.21 K. There's a linear relationship between the time of the amplitudes of Δ T b ( 0 ) and the noontime. The correlation coefficients between them for K-band and V-band in 2017 and 2018 are 0.98, 0.90, 0.98, and 0.96, respectively. The longest duration of solar influence is 52.59min and decreases with the observation frequencies due to the beam width.

This paper presents a relationship of lightning activity with maximum air temperature, Bowen ratio, rainfall, cloud ice contents and Aerosol Optical Depth (AOD) over India during transition period from dry to wet seasons. Lightning flash count data and weather parameters are retrieved from the Tropical Rainfall Measuring Mission (Lightning Imaging Sensor - LIS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) satellites for the period of 17 years (1998–2014). The Pearson correlation between lightning flash count and Bowen ratio is found to be coefficient of R = 0.95 for both dry and wet seasons. For dry season, the Pearson correlation of lightning flash count with surface maximum air temperature is found to be coefficient of R = 0.97 whereas, that for wet season negative coefficient of R = −0.89. The comparative analysis of Pearson correlations of lightning flash counts with AOD, rainfall and cloud ice content are found to be coefficients higher by 20%, 28% and 34% for dry season than those of during wet season, respectively. The results of lightning activity and weather parameters in comparative analyses over the Indian region may be useful for better understanding the differential convection characteristics during transition period of dry to wet season. The results are also important for estimations of impact associated with lightning strikes to ground during dry and wet seasons.

Gravity waves play an important role not only in transferring the momentum and energy to the upper atmosphere but also significantly contribute in different global atmospheric phenomenon like Brewer-Dobson circulation along with planetary waves. Larger differences in the gravity wave model parameters with the real observations has recommended more observational studies for better predictions. In this paper, we have launched 80 GPS-radiosondes in different seasons (20 per each season) to parameterize the inertia gravity wave (IGW) characteristics over a tropical station Hyderabad (17.4° N, 78.5 °E). FFT analysis of zonal, meridional winds and temperature fluctuations shows the generation of IGW over this latitude irrespective of the presence of strong tides and Quasi Two Day Wave (QTDW). Monsoon and winter amplitudes are maximized in both tropospheric and stratospheric regions. Hodograph analysis is used to estimate the IGW parameters. No significant seasonal changes are observed in vertical and horizontal wavelengths and are ranged between 2 – 4 km and 100–1700 km respectively. Horizontal group velocities are found to be lesser in tropospheric region than stratospheric one, while the vertical group velocities showed the opposite nature in all the seasons. About 80–90% hodographs show the upward propagation of IGW in stratospheric region and the direction of horizontal wave propagation is not very clear. Vertical wavenumber spectra reveal the isotropic nature of the waves and agreed well with the universal spectrum of power law. The slopes reached canonical values (−3) in both the height regions for all the seasons. Kinetic energy variations in all the seasons show interesting facts about source regions in different seasons. Strong convection and wind shear along with tropical easterly jets are responsible for the generation of these waves in monsoon, whereas, sudden enhancement in meridional wind shear is the source mechanism during winter.

The atmospheric surface layer turbulence statistics and surface fluxes during the winter season over Anantapur, a semi-arid region, are investigated using sonic anemometers mounted 10 m and 18 m above ground level on a 32-m meteorological tower. This paper aims to investigate the applicability of Monin–Obukhov similarity theory and to understand the influence of wind speed on the turbulence intensities. Results reveal that normalized velocity variances follow 1/3 power law in unstable and stable conditions, while approaching constant values in the near-neutral conditions. The qualitative dependency of normalized velocity variances on stability is in agreement with past studies.

As the EISCAT UHF radar system in Northern Scandinavia started its operations in the early 1980s, the collected data cover about three solar cycles. These long time-series provide us the opportunity to study long-term variations and trends of ionospheric parameters in the high latitude region. In the present study we have used the EISCAT Tromso UHF data to investigate variations of the Hall conductivity and ion temperatures in the E-region around noon. Both the ion temperature and the peak altitude of the Hall conductivity are confirmed to depend strongly on solar zenith angle. However, the dependence on solar activity seems to be weak. In order to search for trends in these parameters, the ion temperature and peak altitude of the Hall conductivity data were adjusted for their seasonal and solar cycle dependence. A very weak descent (∼0.2 km/ decade) was seen in the peak altitude of the Hall conductivity. The ion temperature at 110 km shows a cooling trend (∼10 K/ decade). However, other parameters than solar zenith angle and solar activity seem to affect the ion temperature at this altitude, and a better understanding of these parameters is necessary to derive a conclusive trend. In this paper, we discuss what may cause the characteristics of the variations in the electric conductivities and ion temperatures in the high latitude region.

The medium frequency radar deployed at Tirunelveli (8.7°N, 77.8°E), which is located near the southmost tip of peninsular India, have been providing continuous data from the year 1993 to the year 2012 that helped to study the long term tendencies in the lunar tidal variabilities over this geographic location. In the present paper we present the results of seasonal, interannual and long-term variabilities of lunar semi-diurnal tides in the upper mesosphere over Tirunelveli. The present study also includes comparison with model values. The study shows that the tidal amplitudes are larger in the meridional components of the mesospheric winds than the zonal winds. The seasonal variations of the tides are similar in both the components. The tides show maximum amplitudes of about ∼5 m/s in February/March, secondary maximum amplitudes of about ∼3 m/s in September and minimum amplitudes during summer months (May–August). The observed seasonal variation of the lunar tides do not compare well with Vial and Forbes (1994) model values, though it is consistent with earlier observations. The lunar tidal phase in meridional winds leads that in zonal winds from January to June and from September to November, while the latter leads the former during July/August. The lunar tides show large interannual variability. There are unusual amplitude enhancements in the lunar tide in meridional winds during the winters of 2006 and 2009, when major sudden stratospheric warmings (SSW) occurred at high latitude northern hemisphere, whereas zonal lunar tide does not show any clear association with the SSW. Vertical wavelengths of lunar tides in zonal and meridional wind are in the range of 20–90 km. The vertical wavelengths of lunar tides in both zonal and meridional component are smaller in June and larger in November and December. The monthly mean zonal and meridional winds are subjected to regression analysis to study the tidal response to long-period oscillations, namely, quasi-biennial oscillation (QBO), solar cycle variation and El-nino southern oscillation (ENSO). It is found the lunar tide in both zonal and meridional winds show significant QBO response, whereas zonal tide only shows significant negative response to solar cycle and positive response to ENSO. Besides, zonal tide only shows significant long-term increasing trend.

Recent high resolution temperature measurements by resonance lidar occasionally showed a sudden mesopause altitude increase by ∼5 km and an associated mesopause temperature decrease by ∼10 K at Davis (69°S). In this paper we present further observations which are closely related to this ‘mesopause jump’, namely the increase of mean height of polar mesospheric summer echoes (PMSE) observed by a VHF radar, very strong westward winds in the upper mesosphere measured by an MF radar, and relatively large eastward winds in the stratosphere taken from reanalysis. We present a detailed explanation of mesopause jumps. They occur only when stratospheric winds are moderately eastward and mesospheric winds are strongly westward. Under these conditions, gravity waves with comparatively large eastward phase speeds can pass the stratosphere and propagate to the lower thermosphere because their vertical wavelengths in the mesosphere are rather large which implies enhanced dynamical stability. When finally breaking in the lower thermosphere, these waves drive an enhanced residual circulation that causes a cold and high-altitude mesopause. The conditions for a mesopause jump occur only in the Southern Hemisphere (SH) and are associated with the late breakdown of the polar vortex. Mesopause jumps are primarily, but not only, observed prior and close to solstice. Our study also shows that during the onset of PMSE in the SH, stratospheric zonal winds are still eastward (up to 30 m/s), and that the onset is not closely related to the transition of the stratospheric circulation. Unlike previously published results with polar mesospheric clouds, we find an overall poor correlation between PMSE onset and the date of the vortex breakdown.

This paper discusses the transport of water vapour in the tropopause region over the Tibetan Plateau, where high water vapour mixing ratio is observed during the Northern Hemisphere (NH) summer-monsoon period. The Weather Research and Forecasting (WRF) model has been used to study the two contrasting cases i.e. when water vapour is high and low at 100 hPa (close to tropopause). The composite distribution of water vapour shows two key results (a) the water vapour appears be transported to the Tibetan plateau region from the extra-tropics under the influence of stronger northwesterly winds and (b) the vertical water vapour flux is relatively higher over the Tibetan Plateau region during the period when water vapour amount at this level is higher. This suggests that in addition to the horizontal transport from the extra-tropics, the local convection occurring over the Tibetan Plateau also contributes to the increase in the water vapour over this region. The differences in the circulation during high and low water vapour cases suggest that a cyclonic circulation difference over the central Indian region limit the transport of water vapour from the Bay of Bengal to the Tibetan Plateau region.

This paper presents an algorithm for deriving the effective droplet radius and optical depth of liquid water clouds using ground-based measurements, aircraft observations and an adiabatic model of cloud liquid water. The algorithm derives cloud effective radius and cloud optical depth over a tropical site at Omkoi (17.80°N, 98.43°E), Thailand. Monthly averages of cloud optical depth are highest in April (54.5), which is the month with the lowest average cloud effective radius (4.2 μm), both occurring before the start of the rainy season and at the end of the high contamination period. By contrast, the monsoon period extending from May to October brings higher cloud effective radius and lower cloud optical depth to the region on average. At the diurnal scale there is a gradual increase in average cloud optical depth and decrease in cloud effective radius as the day progresses.

This paper uses the sunspot number (SSN) index and the El Nino modoki index (EMI) to examine the possible modulation of El Nino Modoki events by variations in solar activity. A significant positive correlation was found between SSN and EMI with a lag of two years, and both SSN and EMI have an obvious period of about 11–12 years. The evolution of El Nino Modoki events was investigated using composite analysis. There was a clear evolution of El Nino Modoki events in the three years after the solar peak year. An ocean mixed layer heat budget diagnostic method is used to investigate the contributor to the anomalous patterns in the three years after the solar peak. The atmosphere radiation fluxes are confirmed as the major contributor to the warming response in the central tropical Pacific. Two possible mechanisms are proposed, one is the direct mechanism that the solar radiation warms up the tropical pacific with a geographical difference, due to the cloud distribution. The warming response in the central Pacific is amplified by the coupled positive feedback between the ocean and atmosphere with 1–2 years lag. Another possible way can be described as follows: the solar heating effect propagating from the upper atmosphere modulates the strength and variation of atmospheric anomaly at high and mid-latitudes in the northern hemisphere winter, which results in an anomalous subtropical cyclone over the northeastern Pacific in the winter seasons following the solar peak years. The anomalous cyclone reduces the cloud cover over the northeastern Pacific and enhances the local input of solar radiation. As a result, a positive sea surface temperature (SST) anomaly occurs over the northeastern Pacific and extends towards the central tropical Pacific along the path of anomalous southwesterly winds, which may trigger an El Nino Modoki event in the following years.

In this paper, the effects of a minor sudden stratospheric warming (SSW) event of 2012 in the ionosphere over South American and African sectors have been studied using C/NOFS satellite data and GPS observations. Also, the magnetometer measurements obtained at two stations in the equatorial and low-latitude regions in the South American sector are presented. There were significant Vertical Total Electron Content (VTEC) depletions in the afternoon in both South American and African sectors during the 2012 minor SSW event. A novel feature of the present study is the reduction of the quasi 16-day oscillation (periods ranging from 11 to 20 days) in the daily averaged VTEC in the Brazilian and African sector during an SSW event. Also, the results for the Brazilian sector show an amplification of the ~2–6 day period in the daily averaged VTEC at equatorial and low-latitude regions, after the SSW temperature peak. This investigation shows that a minor SSW can affect the irregularities at ionospheric heights in the Brazilian and African sectors. Ground-based magnetometer measurements in the American sector shows strongly enhanced equatorial electrojet (EEJ) after the SSW temperature peak.

In this paper, the spatial patterns and vertical structure of atmospheric temperature anomalies, in both the tropics and the extratropical latitudes, associated with the El Nino-Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO) in the upper troposphere and stratosphere are investigated using global positioning system (GPS) radio occultation (RO) measurements from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Formosa Satellite Mission 3 mission from July 2006 to February 2014. We find that negative correlations between the atmospheric temperature in the tropics and ENSO are observed at 17–30 km in the lower stratosphere at a lag of 1–4 months and at a lead of 1 month. Out-of-phase temperature variation is observed in the troposphere over the mid-latitude band and in-phase behaviour is observed in the lower stratosphere. Interestingly, we also find that there is a significant negative correlation at a lag of 1–3 months from 32 km to 40 km in the mid-latitude region of the Northern Hemisphere. The atmospheric temperature variations over mid-latitude regions in both hemispheres are closely related to the QBO. There are also two narrow zones over the subtropical jet zone where the QBO signals are strong in both hemispheres, approximately parallel to the equator. Finally, we develop a new robust index to describe the strength of the ENSO and QBO signal.