Variability of CPT and tropopause characteristics over the Arabian Peninsula

. The climatology of the cold-point tropopause (CPT) and tropopause characteristics in a subtropical area like The Arabian Peninsula is examined using the radiosonde data of the CPT characteristics and NCEP Reanalysis data of the tropopause characteristics. The monthly mean data for January and July are analyzed for three stations, namely Medina, Tabuk and Dammam in Saudi Arabia. The trends of CPT and tropopause characteristics of pressure, height, temperature, temperature anomalies, relative humidity, wind speed and potential temperature are also analyzed. The trends of these characteristics show that they experienced a sharp change during the 1990s and a significant change for the period from 2000 to 2016. For the whole period of study, the month of July, CPT and tropopause pressure decreased for about 5 hPa, whereas the height increased for more than 100 m. The temperature experienced a sudden drop during the beginning of the 1990s and a smooth decrease during the following years in January. Furthermore, a strong correlation is found between the CPT temperature and the Solar Cycle during the ‘90s period then it decreased sharply after this period.

Testing the efficacy of atmospheric boundary layer height detection algorithms using uncrewed aircraft system data from MOSAiC

During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, meteorological conditions over the lowest 1 km of the atmosphere were sampled with the DataHawk2 (DH2) fixed wing uncrewed aircraft system (UAS). Of particular interest is the atmospheric boundary layer (ABL) height, as ABL structure can be closely coupled to cloud properties, surface fluxes, and the atmospheric radiation budget. The high temporal resolution of the UAS observations allows us to subjectively identify ABL height for 65 out of the total 89 flights conducted over the central Arctic Ocean between 23 March and 26 July 2020 by visually analyzing profiles of virtual potential temperature, humidity, and bulk Richardson number. Comparing this subjective ABL height with the ABL heights identified by various previously published objective methods allows us to determine which objective methods are most successful at accurately identifying ABL height in the central Arctic environment. The objective methods we use are the Liu-Liang, Heffter, virtual potential temperature gradient maximum, and bulk Richardson number methods. In the process of testing these objective methods on the DH2 data, numerical thresholds were adapted to work best for the UAS-based sampling. To determine if conclusions are robust across different measurement platforms, the subjective and objective ABL height determination processes were repeated using the radiosonde profile closest in time to each DH2 flight. For both the DH2 and radiosonde data, it is determined that the bulk Richardson number method is the most successful at identifying ABL height, while the Liu-Liang method is least successful.

Atmospheric water vapour and its effect on aerosol Extinction at a coastal station – Visakhapatnam

Integrated atmospheric water vapour content. has been evaluated from the spectral optical depths around the PaT band of water vapour by making directly transmitted solar flux measurements at 800, 935 and 1025 nm. The temporal variation of the total precipitable water vapour shows significant seasonal variation with maximum during~ pre-monsoon and monsoon months and minimum during winter months. The integrated content shows a positive correlation with surface humidity parameters and the correlation is better during monsoon months compared to other seasons. The experimentally derived variations of water vapour are compared with the model variations formulated using radiosonde data. The aerosol extinctions derived from the, multi-spectral solar flux measurements in the visible and near IR regions increase with increasing atmospheric water vapour and this increase shows .a seasonal dependence the surface temperature also seems to affect the, aerosol extinction probably through Its effect on the mixing heights.

Temperature sounding of the atmosphere over the Indian region using satellite data

Capability has been developed at the INSAT Meteorological Data Utilisation Centre (MDUC). New Delhi for making sounding retrievals using data from the U.S. Polar Orbiting Satellites; The International TOYS Processing Package (ITPP) developed by the University of Wisconsin, USA, was used for asking temperature soundings software for front-end processing and input of 1000 hPa analysis data Into the retrieval algorithm was developed at MDUC. In the physical retrieval method regression estimates generated listing stratospheric level HIRS channels and MSU channels were used as Initial guess. For the surface, two options were used, (i) climatological guess, and (ii) 1000 hPa analysis. The paper discusses temperature retrievals over the Indian region made on 13 selected dates from different seasons in 1989-91. Results of comparison of satellite retrievals with colocated radiosonde data are presented. There is good agreement between the two from 700 hPa to 150 hPa levels, with RMSE with 3 C. The error is higher at 850 hPa and near the surface, when climatologic IS used as surface guess, but IS within 3°-4° C when the 1000 hPa analysis is used.

Application of AIRS Soundings to Afternoon Convection Forecasting and Nowcasting at Airports

In Taiwan, the frequency of afternoon convection increases in summer (July and August), and the peak hour of afternoon convection occurs at 1500–1600 local solar time (LST). Afternoon convection events are forecasted based on the atmospheric stability index, as computed from the 0800 LST radiosonde data. However, the temporal and spatial resolution and forecast precision are not satisfactory. This study used the observation data of Aqua satellite overpass near Taiwan around 1–3 h before the occurrence of afternoon convection. Its advantages are that it improves the prediction accuracy and increases the data coverage area, which means that more airports can use results of this research, especially those without radiosondes. In order to determine the availability of Atmospheric Infrared Sounder (AIRS) in Taiwan, 2010–2016 AIRS and radiosonde-sounding data were used to determine the accuracy of AIRS. This study also used 2017–2018 AIRS data to establish K index (KI) and total precipitable water (TPW) thresholds for the occurrence of afternoon convection of four airports in Taiwan. Finally, the KI and TPW were calculated using the independent AIRS atmospheric sounding (2019–2020) to forecast the occurrence of afternoon convection at each airport. The average predictive accuracy rate of the four airports is 84%. Case studies at Hualien Airport show the average predictive accuracy rate of this study is 81.8%, which is 9.1% higher than that of the traditional sounding forecast (72.7%) during the same period. Research results show that using AIRS data to predict afternoon convection in this study could not only increase data coverage area but also improve the accuracy of the prediction effectively.

Rapid change in surface-based temperature inversions across the world during the last three decades

Surface-based inversions (SBIs) are significant and common natural phenomena in the planetary boundary layer, and they play essential roles in weather and climate. This study used radiosonde data from 493 radiosonde stations worldwide from the Integrated Global Radiosonde Archive (IGRA) during 1989–2019 to investigate the variations in surface-based inversions from a global perspective. The results indicated that from 1989 to 2019, the SBI frequency increased, and the SBI strength variations with fluctuations and SBI depth decreased over the study period. However, the spatial distribution of frequency, strength, and depth did not have consistent trends. Compared with the Southern Hemisphere, SBIs in the Northern Hemisphere occurred more frequently and were stronger and deeper. In terms of stations over land and the ocean, we found that the SBI frequency over the ocean has increased faster than that over land in the past 15 years, and the SBI strength over land was almost twice that of the ocean. The amplitudes of the annual cycle of SBI characteristics over land were greater than over the ocean in both hemispheres, and the frequency, strength, and depth were greater over land. This study investigated surface-based inversions from a global perspective and filled a gap in the current research on SBIs.

An idealized 1½-layer isentropic model with convection and precipitation for satellite data assimilation research. Part II: model derivation

In this part II paper we present a fully consistent analytical derivation of the ‘dry’ isentropic 1½-layer shallow water model described and used in part I of this study, with no convection and precipitation. The mathematical derivation presented here is based on a combined asymptotic and slaved Hamiltonian analysis which is used to resolve an apparent inconsistency arising from the application of a rigid-lid approximation to an isentropic two-layer shallow water model. Real observations based on radiosonde data are used to justify the scaling assumptions used throughout the paper, as well as in part I. Eventually, a fully consistent isentropic 1½-layer model emerges from imposing fluid at rest (v1 = 0) and zero Montgomery potential (M1 = 0) in the upper layer of an isentropic two-layer model.

Calibration of water vapor Raman lidar measurements by use of radiosonde and microwave radiometer measurements

<p>Water vapor profiles with high vertical and temporal resolution were determined by use of the Raman lidar PollyXT within the MOSAiC campaign in the Arctic during the winter time 2019 – 2020. These measurements need a calibration. Usually, radiosonde data are utilized to calibrate the lidar data by the profile or the linear fit method, respectively. The radiosonde is drifting with the wind; thus, it is often measuring different atmospheric volumes compared to the lidar observations.</p> <p>The period 5-7 February 2020 is used to demonstrate the results. The correlation coefficient of the linear fit between the radiosonde and the lidar data varies with the different atmospheric conditions. The calibration results from the profile method coincide with those of the linear fit method, but the selection of the appropriate calibration setup is not straightforward. The varying correlation of the calibration results is attributed to the partly too low data-variability of the water vapor mixing ratio in the respective heights.  Moreover, the drift of the radiosondes with the wind and hence measurements of atmospheric volumes with lateral distances will have decreased the correlation between the lidar and the radiosonde measurements.</p> <p>During MOSAiC a microwave radiometer was collocated close to the lidar. This system was measuring the same atmospheric vertical column. Its product, the integrated water vapor, might be useful for the calibration of the lidar.</p> <p>Hence, the contribution will analyze the error of the lidar retrieved water vapor mixing ratio that includes the calibration with the radiosonde data and the microwave radiometer product.</p> <p> </p>

Some statistical characteristics of occurrence of fog over Patna airport

bl 'kks/k i= esa o"kZ 2000 ls 2010 rd 10 o"kksZa ds uoacj ls Qjojh ekg dh vof/k ds vk¡dMksa dk mi;ksx djrs gq, iVuk gokbZ vMMs ij Nkus okys dqgjs dh lkaf[;dh; fo’ks"krkvksa tSls & dksgjk Nkus dh ckjEckjrk] Nkus dk le;] vof/k] l?kurk rFkk folfjr gksus ds le; dk v/;;u fd;k x;k gSA bl v/;;u ls izkIr gq, ifj.kke ls irk pyk gS fd foxr 10 o"kksZa ds nkSjku iVuk gokbZ vMMs ij pkjksa gh eghuksa esa dqgjs dh ckjEckjrk esa o"kZ 1961&90 rFkk 1951&80 ds tyok;fodh esa miyC/k flukWfIVd rFkk rRdkfyd ekSkle izs{k.kksa dh rqyuk esa fo’ks"k :i ls o`f) gqbZ gSA iVuk gokbZ vMMs ij dqgjk Nkus dk lcls vuqdwy eghuk fnlEcj vkSj mlds ckn tuojh dk ekuk x;k gsA fnlacj vkSj tuojh ds eghuksa esa 5 ?kaVsa ls vf/kd vof/k rd dqgjk Nkus dh vko`fRr dh izfr’kr~rk vf/kdre jgh gS tcfd uoacj ,oa Qjojh ds eghuksa esa 2 ?kaVs ls de vof/k dh vko`fRr lcls vf/kd jgh gSA dqgjk dk cuuk vDlj 0000&0200 ;w-Vh-lh- ds nkSjku vkSj bldk {k; gksuk 0200&0500 ;w- Vh- lh- ds nkSjku ns[kk x;k gSA cgqr ?kus dqgjs dh vf/kdre vko`fRr & izfr’krrk uoacj ekg esa ns[kh xbZ gSA fnlacj vkSj tuojh ds eghuksa dh vf/kdrj fLFkfr;ksa esa 1200 ;w-Vh-ij vxyh jkr@lqcg ds le; iMs+ dksgjs ds jsfM;ksa lkSans ds vk¡dMksa ds vk/kkj ij rS;kj fd, x, dqgjk LFkkf;Ro lwpdkad ¼,Q-,l-vkbZ-½ 40 ls de ik;k x;k gSA In this paper some statistical characteristics of fog, such as frequencies of occurrence, time of onset, duration, intensity and time of dispersal over Patna airport are studied making use of 10 years data for the period November-February, 2000-2010. The result shows that during the last ten years frequency of fog over Patna airport has increased significantly in all the four months as compared to the climatology based on available synoptic and current weather observations during 1961-90 and 1951-80. The most favourable month for occurrence of fog over Patna airport has been identified as December followed by January. Percentage frequency is highest for duration of fog for more than 5 hours in the months of December and January whereas in the months of November and February frequency is highest for duration less than 2 hours. The formation of fog mostly observed during 0000-0200 UTC and dissipation during 0200-0500 UTC. Percentage frequency of very thick fog was found to be highest in the month of November. In the months of December and January in most of the cases Fog Stability Index (FSI) based on 1200 UTC radiosonde data leading to occurrence of fog during following night/morning has been found to be less than 40.