Clouds atop atmospheric boundary layer over an urban location have been studied using a ground-based Raman LIDAR (RL), supported by radiosonde, INSAT-3D & Meteosat-7 geostationary satellite, and ERA5 reanalysis datasets. The low-level clouds over Ahmedabad (23.02°N, 72.57°E) have been formed from the outflow of a large-scale convergence zone extending from the East-West Indian region. The persistence of these clouds throughout the day has been aided by the transport of moisture to cloud heights by turbulent updrafts. The cloud cover broke off with the entrainment of free tropospheric air with the deepening of the boundary layer, disrupting the surface moisture supply. The consecutive two days (10 and 11 June 2016) observations from the RL showed a unique sensitivity of these clouds to the diurnal variation of the atmospheric boundary layer due to the strong coupling between the clouds and the boundary layer. Ground-based LIDARs provide a better platform for studying the low-level boundary layer clouds and their sensitivity to surface forces due to high accuracy and high temporal resolution. Thus, increasing ground-based observations of such boundary layer clouds is essential for a better understanding of climate sensitivity.

The present work is an effort to investigate possible radial variations in the solar coronal rotation by analyzing the solar radio emission data at 15 different frequencies (275-1755 MHz) for the period starting from July 1994 to May 1999. We used a time series of disk-integrated radio flux recorded daily at these frequencies through radio telescopes situated at Astronomical Observatory of the Jagellonian University in Cracow. The different frequency radiation originates from different heights in the solar corona. Existing models, indicate its origin at the height range from nearly ∼ 12, 000 km (for emission at 275 MHz), below up to ∼ 2, 400 km (for emission at 1755 MHz). There are some data gaps in the time series used for the study, so we used statistical analysis using the Lomb-Scargle Periodogram (LSP). This method has successfully estimated the periodicity present in time series even with such data gaps. The rotation period estimated through LSP shows variation in rotation period, which is compared with the earlier reported estimate using auto correlation technique. The present study indicates some similarity as well as contradiction with studies reported earlier. The radial and temporal variation in solar rotation period are presented and discussed for the whole period analyzed.

ABSTRACT This paper examines long-term (more than four solar cycles) temporal and spatial fluctuations in the solar rotation by investigating radio-emission escapes from various layers of the solar atmosphere during the years 1967–2010. The flux modulation approach can also be used to investigate variations in solar rotation, which is a contentious topic in solar physics. This study makes use of a time-series of radio flux data at various frequencies (245–15 400 MHz) obtained at Sagamore Hill Solar Radio Observatory in Massachusetts, USA, and at other observatories from 1967 to 2010. The periodicity present in the temporal variation of the time-series is estimated through a Lomb–Scargle periodogram. The rotation period estimated for five radio emissions (606, 1415, and 2695 MHz from the corona, and 4995 and 8800 MHz from the transition region) through a statistical approach shows continuous temporal and spatial variations throughout the years. The smoothed rotation period shows the presence of periodic ∼22-yr and ∼11-yr components. The 22-yr component could be linked to the reversal of the solar magnetic field (Hale) cycle, while the 11-yr component is most likely related to the sunspot (Schwabe) cycle. In addition to these two components, random components are also prominently present in the analysed data. The cross-correlation between the sunspot number and the rotation period obtained shows a strong correlation with the 11-yr Schwabe and 22-yr Hale cycle. The corona rotates faster or slower than the transition region in different epochs. The alternation of the faster rotation speed between the corona and transition region also follows the 22-yr cycle.

We present the results of variation in the rotational profile of solar corona for the period from 2012 to 2017, covering the peak and descending phases of the Solar Cycle 24. There is a clear evidence of North-South asymmetry in the solar coronal rotation. For this work, we used flux modulation method analysis for the solar full disk images (SFD) obtained at 211 Å by the Atmospheric Imaging Assembly (AIA) telescope on board Solar Dynamics Observatory (SDO) space mission. The SDO has three scientific instruments namely, the Extreme Ultraviolet Variability Experiment (EVE), the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA). SDO mission was launched by NASA on 11 February 2010 aimed to study the dynamics of Sun's surface and its atmosphere. AIA filters cover 10 different wavelength bands, chosen to reveal key aspects of solar activity at different heights in the solar atmosphere. Solar full disc (SFD) images obtained at the extreme ultraviolet wavelength (EUV) 211 Å by AIA are available in different sizes: 512 × 512, 1024 × 1024 and others with a very less data gap.

AbstractSolar rotation is still one of the unresolved concern of solar physics. We performed time series analysis on the bins formed on equally separated latitude regions on the soft X-ray images. These images are observed with the X-ray telescope (XRT) on board the Hinode satellite. The flux modulation method traces the passage of X-ray feature over the solar disc and statistical analysis of the time series data of the SXR images (one per day) for the period extends from year 2015 to 2017 gives the coronal rotation period as a function of latitude. The investigation provided quite systematic information of the solar rotation and its variability.

Rayleigh lidars at Gadanki (13.5° N, 79.2° E), a tropical site, and at Mt. Abu (24.5° N, 72.7° E), a subtropical site, in India were operated simultaneously during the months of March, April, and May 2004. Significant differences are found in the temperatures over both the locations. Higher temperature, ~10–20 K, in the altitude region of 40–65 km is found during March 2004 over Mt. Abu. The mean stratopause temperature during March 2004 is found ~284 K at an altitude of 48 km over Mt. Abu, which is 18 K higher than the observed stratopause temperature of ~266 K over Gadanki. During April and May 2004, the temperatures over Mt. Abu are higher in the entire altitude range of 30–70 km than over Gadanki. Lidar-observed temperatures, over both the locations, are compared with the temperatures observed by SABER (Sounding of the Atmosphere using Broadband Emission Radiometry; onboard TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics)) and HALOE (Halogen Occultation Experiment; onboard UARS (Upper Atmosphere Research Satellite)). It is found that the lidar-observed temperatures are in qualitative agreement with the temperature observed by satellites, though quantitatively there are significant differences. Wave types of fluctuations have been noted in the upper stratosphere and in the lower mesosphere over both the locations.

The coronal rotation has been estimated using radio emissions at 2.8 GHz for the period 1947 to 2005. These measurements show a long term variability of the coronal rotation period. There are three components in this variability; irregular component, 11 year variation which is related to the sunspot number and 22 year component which may be related to solar magnetic field reversal or Hale effect.

The solar images at 17 GHz by Nobeyama Radio Heliograph and in X-ray by soft X-ray telescope (SXT) on board Yohkoh satellite have been of particular interest for the estimation of solar coronal rotation using flux modulation approach. These studies established that the solar corona rotates differentially. The radio images estimate equatorial rotation period lower than those estimated by the X-ray images. The latitude profiles of the coronal rotation have temporal variability. The space-time plots of sidereal rotation period, interestingly, display clear North-South asymmetry. The asymmetry appears to change its sign in odd and even activity cycles of the Sun.

The aim of this paper is to study the latitudinal variation in the solar rotation in soft X-ray corona. The time series bins are formed on different latitude regions of the solar full disc (SFD) images that extend from 80°S to 80°N. These SFD images are obtained with the soft X-ray telescope (SXT) on board the Yohkoh solar observatory. The autocorrelation analyses are performed with the time series that track the SXR flux modulations in the solar corona. Then for each year, extending from 1992 to 2001, we obtain the coronal sidereal rotation rate as a function of the latitude. The present analysis from SXR radiation reveals that: (i) the equatorial rotation rate of the corona is comparable to the rotation rate of the photosphere and the chromosphere, (ii) the differential profile with respect to the latitude varies throughout the period of the study; it was more in the year 1999 and least in 1994, and (iii) the equatorial rotation period varies systematically with sunspot numbers and indicates its dependence on the phases of the solar activity cycle.

The coronal sidereal rotation rate as a function of latitude for each year, extending from 1992 to 2001 for soft X-ray images and from 1998 - 2005 for radio images are obtained. The present analysis reveals that the equatorial rotation rate of the corona is comparable to the photosphere and the chromosphere, However, at the higher latitudes, the corona rotation quite differently than the photosphere and chromosphere. The latitude differential obtained by both radio and X-ray images is quite variable throughout the period of the study. The equatorial rotation period seems to vary almost systematically with sunspot numbers which indicates its dependence on the phases of the solar activity cycle.

In the present work, we perform time-series analysis on the latitude bins of the solar full disc (SFD) images of Nobeyama Radioheliograph (NoRH) at 17 GHz. The flux modulation method traces the passage of radio features over the solar disc and the autocorrelation analysis of the time-series data of SFD images (one per day) for the period 1999-2001 gives the rotation period as a function of latitude extending from 60 degrees S to 60 degrees N. The results show that the solar corona rotates less differentially than the photosphere and chromosphere, i.e. it has smaller gradient in the rotation rate.