The latitude-altitude structure of the double intertropical convergence zone (DITCZ), its zonal variations, annual cycle and interannual variability over tropical oceans, which were least explored so far, are investigated using the long-term (2006–2018) joint analysis of spaceborne cloud radar and lidar observations that can profile all types of clouds. In contrast to satellite imager observations, this analysis can unambiguously discriminate the DITCZ core and the cirrus outflow emanating from them, which enables the characterization of DITCZ features, including their vertical structure, width and strength even when the equatorial region separating the DITCZ bands has overcast clouds or one of the bands is weak. The role of observed surface wind divergence (SWD) and sea surface temperature (SST) in the genesis and annual migration of the DITCZ bands as well as the ability of vertical wind obtained from reanalysis in capturing the observed DITCZ features are evaluated. The DITCZ occurs over the central Pacific throughout the year, while its occurrence is mainly limited to March-April over the eastern Pacific and the Atlantic and in December over the Indian Ocean. Annual variations of the occurrence, vertical extent, strength and latitudinal positions of the DITCZ bands are mainly driven by the combined effect of SWD and SST variations. The significant differential cloud radiative heating between the equator and the DITCZ bands, derived from the profiles of cloud water content, suggests that it would feedback in enhancing the middle and upper tropospheric wind convergence and downdraft over the equator and contribute to sustain the DITCZ.

Radiosonde observations over the Indian Ocean on board ORV Sagar Kanya showed the presence of a sharp thermal inversion layer in the upper troposphere during the onward leg of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) ship cruise in winter 2018 (12° N–2° S, 75° E; 16–24 January 2018). This temperature inversion layer having a thickness of ~ 300 m, referred to as upper tropospheric inversion (UTI) observed near 15 km altitude at 12° N showed a gradual descent towards the equator reaching about 13 km altitude at 2° S. Daily radiosonde observations at a nearby island station Minicoy (8.27° N, 73.05° E) revealed similar UTI structure for about 20 days during the period 5–24 January 2018, indicating that the UTI features observed during the cruise period were temporal in nature. The persistent inversion layer which is situated on the top of a ~ 2 km thick moist layer is characterised by a large vertical gradient in potential temperature, high wind speed, large wind shear and minimum in ozone mixing ratio. The mean magnitude of UTI (~ 1.5 K) and its persistence (life time) is found to be much higher than the temperature inversions reported elsewhere in boreal winter season. Analysis of background meteorological parameters and estimated radiative heating profiles indicates that the presence of the moist layer solemnly could not produce the observed magnitude of thermal inversion. From further analysis, we conjecture that the observed UTI with higher magnitude is a result of the combined influence of radiative cooling due to the tropical moist air and the overlaying warm subtropical air by means of Rossby wave intrusion from the extra-tropics.

The Southern Ocean (SO) marine atmospheric boundary layer (MABL), regulated by continuous air-sea ex-changes, plays a key role in transporting exchanges between tropics and poles. Among SO sectors, the Indian Ocean sector of SO (ISSO) remained least explored in terms of MABL characterization and is examined in this study. In ISSO, occurrence of sharp oceanic thermohaline fronts regulates the vertical thermodynamic structure of MABL, clouds, and inversions. In this study, these properties of ISSO MABL are investigated over three oceanic domains (Sub-Tropical Indian Ocean (STIO), ISSO, and High-Latitude SO (HLSO)). To achieve this, near-sea surface air-sea exchanges along with profiles of meteorological parameters generated between 25 degrees S and 68 degrees S and 57 degrees E to78 degrees E during three field campaigns conducted in the austral summers of 2017, 2018, and 2020 were utilized. Results showed strong SST-Tair variability across the study region. In STIO, positive SST-Tair indicated Low-Level Cold Air Advection (LLCAA)-induced destabilized and coupled MABLs capped by multiple inversions (>3INV's of strength-0.35 K m-1 above-1200 m) and thin mid/high-altitudes clouds (cloud-base-830 m, cloud-top-2309 m, and cloud-thickness-758 m). Over ISSO and northern HLSO, weak and negative SST-Tair indicated Low-Level Warm Air Advection (LLWAA)-induced stratified and decoupled MABLs. Aided by advective mixing of multiple air-masses, low-level thick multilayered clouds (>2 layers, average cloud-base-604 m, cloud -top-2288 m, and cloud-thickness-1314 m) and multiple strong high-level inversions (>2INV's, strength>0.4 K m-1 ,-1836 m) was observed. In HLSO, weakly positive SST-Tair indicated LLCAA-induced weakly destabilized MABLs capped by mid-altitude inversions (strength-0.22 K m-1,-1632 m) and mid-altitude clouds (cloud -base-979 m, cloud-top-2465 m, and cloud-thickness-1263 m) supported by sublimation leading to virga conditions.

The study examines the thermodynamic structure of the marine atmospheric boundary layer (MABL) and its effect on the aerosol dynamics in the Indian Ocean sector of Southern Ocean (ISSO) between 30°S-67°S and 57°E-77°E. It includes observations of aerosols and meteorology collected during the Xth Southern Ocean Expedition conducted in December 2017. The results revealed the effect of frontal-region-specific air-sea coupling on the thermodynamic structure of MABL and its role in regulating aerosols in ISSO. The MABL over the subtropical front was unstable and formed a well-evolved mixed layer (≈2400 m) capped by low-level inversions (≈660 m). Convective activities in the Sub-Antarctic Frontal region were associated with the Agulhas Retroflection Current, which supported the formation of a well-developed mixed layer (≈1860 m). The mean estimates of aerosol optical depth (AOD) and black carbon (BC) mass concentrations were 0.095 ± 0.006 and 50 ± 14 ng m-3, respectively, and the resultant clear sky direct shortwave radiative forcing (DARF) and atmospheric heating rate (HR) were 1.32 ± 0.11 W m-2 and 0.022 ± 0.002 K day-1, respectively. In the polar front (PF) region, frequent mid-latitude cyclones led to highly stabilized MABL, supported low-level multi-layered clouds (>3-layers) and multiple high-level inversions (strength > 0.5 K m-1 > 3000 m). The clouds were mixed-phased with temperatures less than -12 °C at 3000 m altitude. Interestingly, there was higher loading of dust and BC aerosols (276 ± 24 ng m-3), maximum AOD (0.109 ± 0.009), clear sky DARF (1.73 ± 0.02 W m-2), and HR (0.029 ± 0.005 K day-1). This showed an accumulation of long-range advected anthropogenic aerosols within baroclinic-boundaries formed over the PF region. Specifically, in the region south of PF, weak convection caused weakly-unstable MABL with a single low-level inversion followed by no clouds/single-layer clouds. Predominant clean maritime air holding a small fraction of dust and BC accounted for lower estimates of AOD (0.071 ± 0.004), BC concentrations (90 ± 55 ng m-3) and associated clear sky DARF and HR were 1.16 ± 0.06 W m-2 and 0.019 ± 0.001 K day-1, respectively.

This study presents turbulence characteristics of the atmospheric surface layer (ASL) observed during March 2015 to February 2016 over a tropical coastal site in Goa (15.46°N, 73.83°E), India. The primary datasets utilized are the 3D wind components and sonic temperature from sensors mounted on a 32-m meteorological tower at 10 and 20 m heights respectively. Eddy correlation technique has been adopted to study turbulence characteristics and is investigated under the framework of Monin–Obukhov Similarity Theory (MOST). Results revealed that normalized wind variances ( _i=u, v, w/u_* ) follow the ‘1/3’ power law in highly unstable and stable conditions and approach constant values close to near-neutral conditions. In the neutral limit, it is found that _u/u_* >_v/u_* >_w/u_* . The normalized temperature variances ( _T/T_* ) followed (z/L) ^-1/3 during unstable conditions and approach a constant value in the stable limit. The correlation coefficients for momentum (heat) flux with stability were small (high) under strong unstable and stable conditions. Also, the values of momentum flux increased as it approaches neutral conditions which are consistent with studies reported over coastal/urban locations.

The height of the atmospheric boundary layer (ABL) plays a crucial role in the vertical transport of energy, moisture, and pollutants from the surface. We investigate the development of the convective ABL (CABL) height over a tropical coastal station and quantify its variations with the shortwave radiative flux, near-surface air temperature (Tair), soil skin temperature, soil moisture content, lower tropospheric thermal structure, and virtual potential temperature lapse rate (VPLR) during onshore and offshore flows, based on multi-year (2012–2017) observations carried out using a microwave radiometer profiler and in situ probes at Thumba (8.5° N, 77° E), located in the south-west of Indian Peninsula. The maximum CABL height increases linearly with the VPLR at the rate of 140 to 200 m per °C km−1 (correlation coefficient of 0.82 to 0.92) during different seasons. The delayed onset of daytime onshore flow results in a greater CABL height as continental conditions persist longer, allowing more CABL growth, whereas the earlier arrival of the onshore flow leads to early development of a thermal internal boundary layer with a lower CABL height. When offshore flow prevails, the CABL develops like the continental CABL, with a peak CABL height greater than that during onshore flow by about 300 m. The onset of onshore flow lowers the daytime increase in Tair by about 2 °C. Such quantifications for distinct flow conditions are very sparse over tropical coastal regions and would be useful for understanding coastal air-pollution dispersal as well as validation and improvements in numerical modelling of the CABL under different wind conditions.

The genesis, dynamics, and impacts of a severe dust storm over the central Himalaya during June 13–17, 2018 have been investigated using in situ measurements, satellite data, and model reanalysis. A low‐pressure system over northern India and prevalence of strong winds (∼20 ms−1) triggered the dust storm leading to poor visibility conditions and five‐fold enhancement in the fine particulate matter (PM2.5) over the central Himalaya. Enhancements in Aerosol Optical Depth (AOD) were observed to be stronger over the Himalayan foothills site (Lumbini) than that over the Indo‐Gangetic Plain (IGP) site‐Gandhi College. The sharp reductions in Angstrom exponent (α) from about 1.2 to 0.3 indicated the dominance of coarse‐mode aerosols during the dust episode. Model results show an enhancement in the dust from 1.5 to 2.5 Tg (∼70%) over the northern Indian subcontinent, with about half of the contribution from the regional source (Thar Desert). Interestingly, dust storm also had significant impacts on turbulent kinetic energy (2.9–9.6 m2 s−2), vertical momentum flux (0.9–3.3 Nm−2), and sensible heat flux (34.8 to −33.9 Wm−2), suggesting turbulent mixing of aerosols and cooling near the surface over the Himalayas. Our study highlights that the large‐scale dust storms exposed to additional dust and pollution from regional sources can profoundly impact the air quality, heat fluxes, and radiative balance over the northern Indian subcontinent. The study would also help in evaluating the results of climate models and to assess the impacts of dust on the hydrological processes and melting Himalayan glaciers.

The sensitive ecosystem of the central Himalayan (CH) region, which is experiencing enhanced stress from anthropogenic forcing, requires adequate atmospheric observations and an improved representation of the Himalaya in the models. However, the accuracy of atmospheric models remains limited in this region due to highly complex mountainous topography. This article delineates the effects of spatial resolution on the modeled meteorology and dynamics over the CH by utilizing the Weather Research and Forecasting (WRF) model extensively evaluated against the Ganges Valley Aerosol Experiment (GVAX) observations during the summer monsoon. The WRF simulation is performed over a domain (d01) encompassing northern India at 15 km × 15 km resolution and two nests (d02 at 5 km × 5 km and d03 at 1 km × 1 km) centered over the CH, with boundary conditions from the respective parent domains. WRF simulations reveal higher variability in meteorology, e.g., relative humidity (RH = 70.3 %–96.1 %) and wind speed (WS = 1.1–4.2 m s−1), compared to the ERA-Interim reanalysis (RH = 80.0 %–85.0 %, WS = 1.2–2.3 m s−1) over northern India owing to the higher resolution. WRF-simulated temporal evolution of meteorological variables is found to agree with balloon-borne measurements, with stronger correlations aloft (r = 0.44–0.92) than those in the lower troposphere (r = 0.18–0.48). The model overestimates temperature (warm bias by 2.8 ∘C) and underestimates RH (dry bias by 6.4 %) at the surface in d01. Model results show a significant improvement in d03 (P = 827.6 hPa, T = 19.8 ∘C, RH = 92.3 %), closer to the GVAX observations (P = 801.4 hPa, T = 19.5 ∘C, RH = 94.7 %). Interpolating the output from the coarser domains (d01, d02) to the altitude of the station reduces the biases in pressure and temperature; however, it suppresses the diurnal variations, highlighting the importance of well-resolved terrain (d03). Temporal variations in near-surface P, T, and RH are also reproduced by WRF in d03 to an extent (r>0.5). A sensitivity simulation incorporating the feedback from the nested domain demonstrates the improvement in simulated P, T, and RH over the CH. Our study shows that the WRF model setup at finer spatial resolution can significantly reduce the biases in simulated meteorology, and such an improved representation of the CH can be adopted through domain feedback into regional-scale simulations. Interestingly, WRF simulates a dominant easterly wind component at 1 km × 1 km resolution (d03), which is missing in the coarse simulations; however, the frequency of southeasterlies remains underestimated. The model simulation implementing a high-resolution (3 s) topography input (SRTM) improved the prediction of wind directions; nevertheless, further improvements are required to better reproduce the observed local-scale dynamics over the CH.

Diurnal variation of cloud radiative forcing (CRF) is a major factor that controls the global radiation balance. This study presents multi-year seasonal mean diurnal variations of longwave cloud radiative forcing (LWCRF) and daytime shortwave cloud radiative forcing (SWCRF) at the top of atmosphere over tropics, derived from the broadband radiation measurements made by ScaRaB/3 onboard the low-inclination Megha-Tropiques satellite. The largest LWCRF (60–80 Wm−2) occurs over the oceanic regions of the east equatorial Indian Ocean and the western Pacific during all seasons, as well as the South Pacific Convergence Zone, the northeast Bay of Bengal, Amazon region, central and southern Africa and north Indian landmass (monsoon trough) during the local summer. Diurnal variations of 15–25 Wm−2 in LWCRF (20–35% of the mean) are observed with peak values occurring at 18–21 local time (LT) over continents and 00–06 LT over oceans. The minimum LWCRF occurs at 09–12 LT throughout the tropics. Over convective regions, SWCRF maximizes at 12–15 LT (− 220 to − 300 Wm−2) and has a higher magnitude over continents due to early convection occurrence, indicating the importance of diurnal phase. Certain specific features including the CRF associated with the double inter-tropical convergence zone, day-night changes in net CRF, and the effect of El Ni$$\stackrel{\sim }{\mathrm{n}}$$o on CRF are also presented. The net CRF and its zonal variations are strikingly similar during the normal and El Ni$$\stackrel{\sim }{\mathrm{n}}$$o periods because the changes in LWCRF and SWCRF are mutually compensated.

The growth of the daytime convective atmospheric boundary layer, which plays a pivotal role in the vertical mixing and dispersal of water vapour and pollutants, is modulated by cloud radiative effects. Assessment of this cloud effect is sparse in any geographical region and non-existent over tropical coastal regions. We investigate the effect of clouds on the diurnal evolution of boundary-layer height over tropical coastal location Thumba (8.5°N, 77°E) during onshore and offshore flow using multi-year (2010–2016) microwave radiometer profiler observations. The boundary-layer height during both cloudy and clear-sky periods increases rapidly from 0800 LT (local time = UTC + 5.1 h) to attain a daytime peak around noon (400–1500 m). The seasonal mean noontime boundary layer height during cloudy periods is lower than that during clear-sky periods by > 900 m (> 400 m) when offshore (onshore) flow prevails during winter and pre-monsoon seasons. The forenoon growth rate of the boundary-layer height during clear-sky offshore flow is rapid (> 380 m h−1) compared to that during cloudy offshore (160 m h−1), clear-sky onshore (160–250 m h−1), and cloudy onshore (> 100 m h−1) flow. Effects of shortwave cloud radiative forcing and soil temperature on the noontime boundary-layer height and their interdependencies are presented. These observations reveal the contrasting and significant effect of clouds on the growth of the daytime boundary layer during onshore and offshore flow, and the coupled effects of cloud radiative forcing and soil temperature on boundary-layer height over tropical coastal regions, which provide essential constraints for evaluating model simulations.

We investigate surface-layer characteristics over a mountainous ridge in the Central Himalayas, utilizing tower-based fast-response micrometeorological observations (at 12 and 27 m above ground level) for the winter months November 2013–January 2014. During this period, the site generally experienced clear skies and weak synoptic flow (wind speed < 2 m s−1), favouring a strong diurnal evolution of the atmospheric boundary layer. The observations show a regular change in wind direction from north-easterly during the night-time to westerly during the daytime throughout the season, indicating the systematic development of a mountain circulation due to changes in heating of the mountain slopes as the day advances. Considering the variations in wind direction and topography of the site, the tilt corrections are implemented sector-wise by segregating the data into three sectors, thus estimating three sets of coefficients for the tilt correction. Observations during fair-weather conditions (59 days only) are analyzed with the sensible heat flux (H) showing large diurnal variations, which are in-phase with the mean vertical velocity. The afternoon peak value of H is found to be ≈ 116 ± 80 W m−2. In contrast, diurnal variations of momentum flux and turbulent kinetic energy are less prominent with rather weak maxima occurring between 0900 and 1300 IST, the period when wind direction changes over the ridge. Variations of the dimensionless standard deviations of the vertical velocity component and temperature are found to scale with the stability parameter z/L under convective conditions, while taking into account the effect of self-correlation. The constancy of fluxes with height, slope-flow buoyancy and stress divergence are also analyzed to provide a rigorous evaluation of Monin–Obukhov similarity theory based on two-level turbulence measurements.

Atmospheric boundary layer (ABL) is the lower part of the troposphere which directly responds to the instantaneous changes in surface forcing within a typical time scale of less than an hour. The turbulent eddies provides a major pathway for the vertical mixing of aerosols, water vapour and pollutants in the ABL and vertical flux of energy and momentum which make ABL distinct from the other atmospheric layers. ABL is characterized by the remarkable strong diurnal variation of its vertical extent, turbulent intensity and meteorological parameters which is mainly driven by surface energy balance arising from incoming solar flux, emitted thermal radiation, heat transfer and the ground energy flux. The diurnal evolution of ABL is also significantly modulated by the background meteorological conditions and geography of the region. The boundary layer height (BLH) is a key parameter that determines the vertical extent of mixing and dispersal of atmospheric constituents. Even though various techniques exist for measuring BLH, they are not sufficient to study the diurnal evolution of BLH (due to the rapid development of convective boundary layer) under all-weather conditions (due to cloud cover). Microwave Remote sensing serves as the best method for studying diurnal cycle of BLH under clear and cloudy conditions since microwaves are capable of penetrating clouds.

Seasonal variation of sea breeze (SB) characteristics and its effect on turbulence spectra at Visakhapatnam (17.7°N, 83.3°E) located at east coast of Peninsular India are investigated by considering 244 sea breeze events during December 2012 to March 2014. The delayed onset of backdoor SB during winter occurs due to the southward component of shore-parallel background winds while the prevailing northward component of background wind enable the early onset of corkscrew SB during pre-monsoon and summer monsoon. The turbulence spectral peak of horizontal winds shifts to higher frequency side after SB onset.

The ScaRaB payload onboard Megha-Tropiques (MT) satellite has been making observations of radiative fluxes at the top of the atmosphere (TOA) for different local time (LT) of the day. This provides a unique opportunity to investigate the diurnal variation of the regional instantaneous cloud radiative Forcing (CRF) at TOA. Using direct observations of radiative fluxes from ScaRaB, seasonal mean diurnal variations of CRF at TOA are investigated during July 2012-Decemeber 2016. Such observations are essential to investigate and quantify the regional differences in the longwave CRF (LWCRF) diurnal cycle and daytime variations of shortwave CRF (SWCRF) over deep convective regions and subsidence zones of the Hadley and Walker circulation cells. One of the most remarkable features observed is the significantly large diurnal variation of LWCRF over deep convective regions, with distinctly different phases over the continents and open oceans. Results show that the magnitude of the diurnal variation of LWCRF is largest over the continental deep convective regions of Brazil and Africa, where the peak-to-trough amplitude of the diurnal cycle of LWCRF is in the range of 20 to 30 Wm -2 , which is about 30-45% of their diurnal mean values. Peak-to-trough amplitude of the diurnal cycle of LWCRF over the oceanic regions are mostly in the range of ~15 to 25Wm -2 which are about 20 to 35% of the diurnal mean values of LWCRF over these regions. The least diurnal variation of LWCRF over the ITCZ generally occurs over the eastern Pacific (peak-to-trough amplitude <;15 Wm-2 ). The diurnal maxima of LWCRF over the continental regions occur during 1521 LT while the minima occur at ~03-09 LT. Over the deep convective regions of open oceans, the diurnal cycle of LWCRF attains broad maximum during 21-06 LT while the minimum occurs at ~09-12 LT. Further, this study indicates that the magnitudes of shortwave CRF (SWCRF) are largest around ~12-15 LT, mainly due to the largest incoming solar flux and phase of the diurnal variation of cloud development. Though significant shift in the location of deep convection occurs during El Nino periods (which also introduces corresponding shift in the spatial variations of LWCRF and SWCRF), zonal variations of the average net CRF (NCRF) during the El Nino and normal periods are remarkably similar during all seasons.

Abstract. In situ measurements of lower stratospheric water vapour employing Cryogenic Frost point Hygrometer (CFH) over two tropical stations, Trivandrum (8.53 °N, 76.87 °E) and Hyderabad (17.47 °N, 78.58 °E) over the Indian subcontinent are conducted as part of Tropical Tropopause Dynamics (TTD) monthly campaigns under GARNETS program. The annual variation of lower stratosphere (LS) water vapour clearly depicts the so called tape recorder effect at both the stations. The ascent rate of water vapour compares well with the velocity of Brewer-Dobson circulation and is slightly higher over the equatorial station when compared to the off-equatorial station. The column integrated water vapour in the LS varies in the range 1.5 to 4 g/m2 with low values during winter and high values during summer monsoon and post monsoon seasons and its variability shows the signatures of local dynamics. The variation in water vapour mixing ratio (WVMR) at the cold point tropopause (CPT) exactly follows the variation in CPT temperature. The difference in WVMR between the stations shows a semi-annual variability in the altitude region 18–20 km region with high values of WVMR during summer monsoon and winter over Hyderabad and during pre-monsoon and post-monsoon over Trivandrum. This difference is related to the influence of the variations in local CPT temperature and deep convection. The monsoon dynamics has a significant role in stratospheric water vapour distribution in summer monsoon season.

This paper assesses the performance of water vapor measurements by Sondeur Atmosphérique du Profild’ Humidité Intertropicale par Radiométrie (SAPHIR), microwave limb sounder (MLS), and the global reanalysis water vapor data [Modern Era Retrospective analysis for Research and Applications (MERRA) and European Center for Medium-Range Weather Forecasts reanalysis (ERA) interim] by comparing with water vapor-measured in situ by cryogenic frost-point hygrometer (CFH) at two tropical stations, Trivandrum (8.5°N, 76.9°E) and Hyderabad (17.47°N, 78.58°E). The iMet-1 radiosonde though overestimates frost-point temperature (3%–5%) in the 4–10-km altitude region with respect to CFH, it agrees well with CFH observations in the upper troposphere and the lower troposphere with a mean difference <2% and ~1%, respectively. SAPHIR–CFH intercomparison is done for the troposphere region, and MLS, MERRA, and ERA interim are compared with CFH in the lower stratosphere region. SAPHIR and CFH comparison shows a reasonable agreement between both the datasets with a relative humidity difference of about 15% in the lower and middle troposphere and a dry bias of ~40% in the upper troposphere. Intercomparison between CFH and MLS water vapor mixing ratios (WVMRs) shows a small wet bias (−10% to −20%) for the MLS in the lower stratospheric region between 100 and 50 hPa and a small dry bias (<10%) above that region. This paper shows that the MLS always underestimates when the CFH WVMR is greater than 6 ppmv and overestimates when the WVMR is less than 2 ppmv. The intercomparison of CFH with MERRA and ERA interim specific humidity shows results similar to that with MLS.

Day-night changes in the altitudinal distribution of tropical clouds are examined using multi-year analyses of CloudSat and CALIPSO data. The combined occurrence of all cloud types maximizes in the nighttime throughout the middle and upper troposphere. In contrast to the nighttime maxima in the appearance of optically thick tropical clouds in the ~5–12km altitude band, the occurrence of such clouds exhibit a pronounced daytime enhancement in the upper troposphere (>12km). This arises from the more frequent occurrence of thick cirrus and deeper penetration of daytime convective clouds to the upper troposphere, as evidenced from more frequent daytime occurrence of clouds with thickness >9km. Apart from the afternoon convection over land and remnant cirrus from nighttime convection over ocean, the daytime cloud enhancement observed above 12km altitude might be also driven by the larger tropospheric net cloud radiative heating and its vertical gradient during the daytime.