Latitudinal Temperature Variations Research Articles

Life-history traits of Aedes aegypti (Linnaeus) distributed across a latitudinal range of 23 °N-6 °S.

The growth and associated traits of Aedes aegypti (L.) mosquitoes may adapt and evolve in response to the costs associated with body size in relation to latitudinal variation. We analyzed the life-history traits and energy reserves of field-collected mosquitoes from Taiwan, Thailand, and Indonesia along a latitudinal range spanning from 23°N to 6°S. A U-shaped relationship between body size and latitude was observed. Our study demonstrated the role of latitudinal temperature variations in determining the body size patterns of Ae. aegypti. Notably, the body size of the northern populations (from Taiwan) was significantly larger than those of the tropical populations from Thailand and Indonesia. Models have demonstrated that regional precipitation levels may contribute to body trait variations in certain high-latitude populations in Thailand. However, Indonesian populations have high development rates and large body sizes, indicating the involvement of other physiological traits in determining mosquito body size. The reproductive output of the adult females in this study was positively correlated with body size, but our measure of longevity did not covary significantly with the body size. By contrast, the reproductive output of mosquito-tested populations was in inverse proportion to longevity. Additionally, the mean teneral glycogen levels in the Indonesian and Thai populations were 2.5 times higher than those in the Taiwanese populations. The Indonesian and Thai populations had low mean generation and doubling times, resulting in a high intrinsic rate of increase compared with that of the Taiwanese populations, despite the Taiwanese populations having the highest net reproduction rate.

Continent-wide parallel urban evolution of increased heat tolerance in a common moth.

Urbanization and its urban-heat-island effect (UHI) have expanding footprints worldwide. The UHI means that urban habitats experience a higher mean and more frequent extreme high temperatures than rural habitats, impacting the ontogeny and resilience of urban biodiversity. However, many organisms occupy different microhabitats during different life stages and thus may experience the UHI differently across their development. While evolutionary changes in heat tolerance in line with the UHI have been demonstrated, it is unknown whether such evolutionary responses can vary across development. Here, using common-garden-reared Chiasmia clathrata moths from urban and rural populations from three European countries, we tested for urban evolution of heat shock tolerance in two life stages: larvae and adults. Our results indicate widespread urban evolution of increased heat tolerance in the adult stage only, suggesting that the UHI may be a stronger selective agent in adults. We also found that the difference in heat tolerance between urban and rural populations was similar to the difference between Mid- and North-European regions, suggesting similarity between adaptation to the UHI and natural, latitudinal temperature variation. Our observations incentivize further research to quantify the impact of these UHI adaptations on fitness during urbanization and climate change, and to check whether life-stage-specific adaptations in heat tolerance are typical of other ectothermic species that manage to survive in urbanized settings.

Climate calibration of the Spring Index model for more accurate broad-scale first leaf predictions

Phenological models are needed for forecasting plant and ecosystem responses to climate change. Due to a lack of considering local adaptation induced variations in climatic requirements of plant species for phenological development, traditional uniform/non-spatial models that cover broad geographic regions are susceptible to systematic prediction biases. This study presents a climate calibration method that incorporates climate adaptation patterns of plant species into a widely used Spring Index (SI) First Leaf (FL) model. Multi-year (2009-2021) phenological observation data for a most frequently observed shrub species(common lilac Syringa vulgaris) and a most frequently observed tree species(red maple Acer rubrum) in the eastern USA from the USA-National Phenology Network (USA-NPN) were used to develop and validate the calibrated models. Climatic gradients defined by latitudinal temperature variations were used to predict varied climatic requirements of the populations of each species. Prior to calibration, SI FL predictions showed consistent geographic biases and yielded large prediction errors (especially for red maple, RMSE = 30 d). Calibrated SI FL predictions yielded reduced errors (e.g. RMSE = 16 d for red maple) and were freed from significant geographic biases (α = 0.05) in all cases. The calibration method accounted for both intraspecific and interspecific variations, leading to more accurate broad-scale first leaf predictions for the species tested. The climate-calibrated SI FL allows for more accurate tracking of the onset of spring over extensive geographic areas and would support spatially explicit natural resource and environmental conservation efforts under climate change.

Thermodynamic effects drive countergradient responses in the thermal performance of Littorina saxatilis across latitude

Thermal performance curves (TPCs) provide a powerful framework to assess the evolution of thermal sensitivity in populations exposed to divergent selection regimes across latitude. However, there is a lack of consensus regarding the extent to which physiological adjustments that compensate for latitudinal temperature variation (metabolic cold adaptation; MCA) may alter the shape of TPCs, including potential repercussion on upper thermal limits. To address this, we compared TPCs for cardiac activity in latitudinally-separated populations of the intertidal periwinkle Littorina saxatilis. We applied a non-linear TPC modelling approach to explore how different metrics governing the shape of TPCs varied systematically in response to local adaptation and thermal acclimation. Both critical upper limits, and the temperatures at which cardiac performance was maximised, were higher in the northernmost (cold-adapted) population and displayed a countergradient latitudinal trend which was most pronounced following acclimation to low temperatures. We interpret this response as a knock-on consequence of increased standard metabolic rate in high latitude populations, indicating that physiological compensation associated with MCA may indirectly influence variation in upper thermal limits across latitude. Our study highlights the danger of assuming that variation in any one aspect of the TPC is adaptive without appropriate mechanistic and ecological context.

Radiative-dynamical Simulation of Jupiter’s Stratosphere and Upper Troposphere

Abstract We present a two-dimensional radiative-dynamical model of the combined stratosphere and upper troposphere of Jupiter to understand its temperature distribution and meridional circulation pattern. Our study highlights the importance of radiative and mechanical forcing for driving the middle atmospheric circulation on Jupiter. Our model adopts a state-of-the-art radiative transfer scheme with recent observations of Jovian gas abundances and haze distribution. Assuming local radiative equilibrium, latitudinal variation of hydrocarbon abundances is not able to explain the observed latitudinal temperature variations in the mid-latitudes. With mechanical forcing parameterized as a frictional drag on zonal wind, our model produces ∼2 K latitudinal temperature variations observed in low to mid-latitudes in the troposphere and lower stratosphere, but cannot reproduce the observed 5 K temperature variations in the middle stratosphere. In the high latitudes, temperature and meridional circulation depend strongly on polar haze radiation. The simulated residual mean circulation shows either two broad equator-to-pole cells or multi-cell patterns, depending on the frictional drag timescale and polar haze properties. A more realistic wave parameterization and a better observational characterization of haze distribution and optical properties are needed to better understand latitudinal temperature distributions and circulation patterns in the middle atmosphere of Jupiter.

The interaction of tectonics, climate and eustasy in controlling dolomitization: A case study of Cenomanian–Turonian, shallow marine carbonates of the Iberian Basin

abstractDuring the Cretaceous, high global sea‐level and low latitudinal temperature variations led to the growth of epeiric carbonate platforms. Platform‐scale dolomitization of these platforms is not common, reflecting the low Mg/Ca ratio of seawater and a humid climate. This study describes the processes governing pervasive dolomitization of a land‐attached carbonate platform within the Iberian Basin. Dolomite is planar to sub‐planar with a geochemical signature consistent with dolomitization from penesaline seawater. Dolomitization was most pervasive during a 1 Myr period in the middle Cenomanian, by repeated reflux of seawater from brine pools formed on the top of a southward‐prograding carbonate platform. Tilting and structural reorganization in the Upper Cenomanian led to a reversal in polarity of the platform, and dolomitization was restarted by the northward reflux of seawater. Rising relative sea‐level and oceanic acidification led to back‐stepping of the platform such that the supply of dolomitizing fluids was cut off. In the Lower Turonian, pervasively dolomitized rudist rudstone facies in the south of the study area indicate that dolomitization restarted, either penecontemporaneously or later, from highly evaporated Campanian–Maastrichtian seawater. A systematic increase in dolomite crystal size up‐section ties broadly, but not entirely, to stratigraphy. It is possible that these textural differences reflect changes in fluid chemistry, limestone permeability or precursor rock texture. However, the lack of stratigraphic conformance, and the preservation of the earliest‐formed dolomite only in the oldest sediments, could indicate a progressive recrystallization of early‐formed dolomite through repeated reflux of brines. As such, the succession appears to preserve a fossilized record of dolomite recrystallization through time during the Cenomanian–Turonian. The results of this study therefore provide a record of the progressive dolomitization of a carbonate platform and demonstrate the important interplay of climate and basin‐scale tectonics on dolomite distribution and crystallinity.

Geographical variation in bill size provides evidence for Allen’s rule in a cosmopolitan raptor

AbstractAimAvian beak morphology is a good example of how anatomical structures have evolved in response to different selective pressures, such as diet and vocalizations, but also thermoregulation. The last of these functions was neglected until recently, but convincing evidence has been provided regarding the capacity of birds to regulate heat dissipation through their highly vascularized bills. According to this adaptive function and coherently with the ecogeographical “Allen's rule”, which predicts smaller body appendages in colder climates, large beaks should be favoured in warm environments. Here, we tested this prediction in the cosmopolitan common barn owl group.LocationWorld.Time period1809–2017.Major taxa studiedTyto alba species complex.MethodsWe analysed the variation in bill length relative to body size according to temperature, latitude and elevation in 7,619 barn owls. The specimens were collected by 140 museums and represent three distinct evolutionary lineages that occur in geographically separated regions and cover the entire distributional range of the species complex: the Afro‐Palaearctic Tyto alba, the Australasian Tyto javanica and the American Tyto furcata.ResultsIn the three lineages, the bill becomes larger with increasing temperature. This convergent pattern of evolution of smaller bills in colder climates is associated with a latitudinal variation in temperature, because small‐billed individuals occurred at higher latitudes than conspecifics living closer to the Equator. Moreover, in T. furcata, large‐billed birds mostly occurred at lower elevations closer to the Equator, with bill length decreasing progressively with concomitant increase in latitude and elevation.DiscussionThese findings provide evidence for the repeated evolution of bill size on a global scale that is compatible with Allen's rule. These results suggest a role of the bill as a potential heat‐exchange surface in nocturnal raptors, which are not directly exposed to solar radiation and whose bill shape evolved primarily to hunt and consume animal prey.

A large predatory reef fish species moderates feeding and activity patterns in response to seasonal and latitudinal temperature variation

Climate-driven increases in ocean temperatures are expected to affect the metabolic requirements of marine species substantially. To mitigate the impacts of increasing temperatures in the short-term, it may be necessary for ectothermic organisms to alter their foraging behaviour and activity. Herein, we investigate seasonal variation in foraging behaviour and activity of latitudinally distinct populations of a large coral reef predator, the common coral trout, Plectropomus leopardus, from the Great Barrier Reef, Australia. P. leopardus exhibited increased foraging frequency in summer versus winter time, irrespective of latitude, however, foraging frequency substantially declined at water temperatures >30 °C. Foraging frequency also decreased with body size but there was no interaction with temperature. Activity patterns were directly correlated with water temperature; during summer, the low-latitude population of P. leopardus spent up to 62% of their time inactive, compared with 43% for the high-latitude population. The impact of water temperature on activity patterns was greatest for larger individuals. These results show that P. leopardus moderate their foraging behaviour and activity according to changes in ambient temperatures. It seems likely that increasing ocean temperatures may impose significant constraints on the capacity of large-bodied fishes to obtain sufficient prey resources while simultaneously conserving energy.

Toward Spectroscopically Detecting the Global Latitudinal Temperature Variation on the Solar Surface

A very slight rotation-induced latitudinal temperature variation (presumably on the order of several Kelvin) on the solar surface is theoretically expected. While recent high-precision solar brightness observations reported its detection, confirmation by an alternative approach using the strengths of spectral lines is desirable, for which reducing the noise due to random fluctuation caused by atmospheric inhomogeneity is critical. Towards this difficult task, we carried out a pilot study of spectroscopically investigating the relative variation of temperature (T) at a number of points in the solar circumference region near to the limb (where latitude dependence should show up if any exists) based on the equivalent widths (W) of 28 selected lines in the 5367--5393A and 6075--6100A regions. Our special attention was paid to i) clarifying which kind of lines should be employed and ii) how much precision would be accomplished in practice. We found that lines with strong T-sensitivity (|log W/log T|) should be used and that very weak lines should be avoided because they inevitably suffer large relative fluctuations (Delta_W/W). Our analysis revealed that a precision of Delta_T/T ~ 0.003 (corresponding to ~15K) can be achieved at best by a spectral line with comparatively large |log W/log T|, though this can possibly be further improved if other more suitable lines are used. Accordingly, if many such favorable lines could be measured with sub-% precision of Delta_W/W and by averaging the resulting Delta_T/T from each line, the random noise would eventually be reduced down to <~1K and detection of very subtle amount of global T-gradient might be possible.

Influence of a coronal envelope as a free boundary to global convective dynamo simulations

We explore the effects of an outer stably stratified coronal envelope on rotating turbulent convection, differential rotation, and large-scale dynamo action in spherical wedge models of the Sun. We solve the compressible magnetohydrodynamic equations in a two-layer model with unstable stratification below the surface, representing the convection zone, and a stably stratified coronal envelope above. The interface represents a free surface. We compare our model to models that have no coronal envelope. The presence of a coronal envelope is found to modify the Reynolds stress and the $\Lambda$ effect resulting in a weaker and non-cylindrical differential rotation. This is related to the reduced latitudinal temperature variations that are caused by and dependent on the angular velocity. Some simulations develop a near-surface shear layer that we can relate to a sign change in the meridional Reynolds stress term in the thermal wind balance equation. Furthermore, the presence of a free surface changes the magnetic field evolution since the toroidal field is concentrated closer to the surface. In all simulations, however, the migration direction of the mean magnetic field can be explained by the Parker--Yoshimura rule, which is consistent with earlier findings. A realistic treatment of the upper boundary in spherical dynamo simulations is crucial for the dynamics of the flow and magnetic field evolution.

Update of the Venus density and temperature profiles at high altitude measured by SOIR on board Venus Express

The SOIR instrument on board Venus Express regularly sounds the Venus atmosphere using the solar occultation technique. The density and temperature profiles are inferred from SOIR spectra recorded in the infrared. The method has been described in a previous publication (Mahieux et al., 2012. J. Geophys. Res. 117. doi:10.1029/2012JE004058.). This paper is devoted to the update of the VAST (Venus Atmosphere from SOIR measurements at the Terminator) compilation that was initiated in the above cited work, which gives the mean CO2 number density and temperature profiles for different latitude bins. The method has been improved and has been applied to more data. The new compilation which is given on the same latitudinal grid now distinguishes between the two sides of the terminator. The compilation also confirms the main thermal layering characteristics that were identified in the earlier version: the succession of a warm layer (230±30K, 1−σ standard deviation) at a pressure level of 3.2×10−7mbar (~140km), a very cold layer (125±32K) at 2.5×10−5mbar (~123km), a warm layer (204±17K) at 0.01mbar (~102km) and finally a colder layer at 0.4mbar (171±34K, ~87km). The layering of all the temperature profiles is explained by radiative rather than dynamical processes. The temporal temperature variation is larger than the mean latitudinal temperature variation. VAST is compared with temperature profiles obtained from other Venus Express instruments, VeRa and SPICAV–UV, and ground based measurements.

Neural Network Based Retrieval of Atmospheric Temperature Profile Using AMSU-A Observations

The present study describes artificial neural network (ANN) based approach for the retrieval of atmospheric temperature profiles from AMSU-A microwave temperature sounder. The nonlinear relationship between the temperature profiles and satellite brightness temperatures dictates the use of ANN, which is inherently nonlinear in nature. Since latitudinal variation of temperature is dominant one in the Earth’s atmosphere, separate network configurations have been established for different latitudinal belts, namely, tropics, mid-latitudes, and polar regions. Moreover, as surface emissivity in the microwave region of electromagnetic spectrum significantly influences the radiance (or equivalently the brightness temperature) at the satellite altitude, separate algorithms have been developed for land and ocean for training the networks. Temperature profiles from National Center for Environmental Prediction (NCEP) analysis and brightness temperature observations of AMSU-A onboard NOAA-19 for the year 2010 have been used for training of the networks. Further, the algorithm has been tested on the independent dataset comprising several months of 2012 AMSU-A observations. Finally, an error analysis has been performed by comparing retrieved profiles with collocated temperature profiles from NCEP. Errors in the tropical region are found to be less than those in the mid-latitude and polar regions. Also, in each region the errors over ocean are less than the corresponding ones over land.

Geographic variation in range size and beta diversity of groundwater crustaceans: insights from habitats with low thermal seasonality

AbstractAimThree broad mechanisms have been proposed to explain geographic variation in species range size: habitat area/heterogeneity, climate seasonality and long‐term climate variability. However, it has proved difficult to disentangle their relative role, particularly as temperature seasonality often covaries with the amplitude of long‐term temperature oscillations. Here, we shed new light onto this debate by providing the first continental‐scale analysis of range size and beta diversity in groundwater habitats, where taxa are not exposed to latitudinal variation in temperature seasonality.LocationEurope.MethodsWe compiled and mapped occurrence data for 1570 groundwater crustacean species. Generalized regression models were used to test for latitudinal variation in geographic range size and to assess the relative role of the three broad mechanisms in shaping present‐day patterns of range size. We partitioned beta diversity into its spatial turnover and nestedness components and analysed their latitudinal variation across Europe.ResultsMedian range size increases with latitude above 43° N and the range size of individual species is positively correlated to latitude, even after accounting for phylogenetic effects. Long‐term temperature variability accounted for a substantially higher variation in median range size of groundwater crustaceans across Europe than precipitation seasonality and habitat heterogeneity, including aquifer area, elevation range, climatic rarity and productive energy. Spatial turnover contributes significantly more to beta diversity in southern regions characterized by stable historic climates than it does in northern Europe.Main conclusionsOur findings add support to the historic climate hypothesis which suggests that patterns of increasing range size and decreasing species turnover at higher latitudes in the Palaearctic region are primarily driven by long‐term temperature oscillations rather than by climatic seasonality and the availability and heterogeneity of habitats.

Pan-tropical distribution of the Jurassic ostreid bivalves

Globally, the Jurassic cemented ostreid bivalves from northern Tibet, SW China, have a pan-tropical distribution pattern between palaeolatitudes of 60° South and North. Ostreid bivalves have tiny to large larvae, and nearly all of them have a cemented mode of life during their adult stage. The distribution pattern and the habits of the Jurassic ostreid bivalves revealed that, in the Jurassic time interval, all seas and oceans were interconnected, and ostreid bivalves were very capable of dispersion through their planktonic larval stage or as pseudoplankton during the post-larval stage, and even were able to cross the palaeo-Pacific Ocean from east to west. However, latitudinal temperature variation limited the distribution of these thermophilous bivalves to the lower and middle latitudes.

Reproductive Strategies of the Eastern OysterCrassostrea virginica(Gmelin 1791) in Tropical Lagoons of the Mexican Gulf of Mexico

The oyster fishery is 1 of the most important coastal fisheries in Mexico. Management is based on a minimum legal size of 80 mm and several seasonal bans that vary along the coast of the Gulf of Mexico. We describe the gonad development cycle of Crassostrea virginica (Gmelin 1791) along the Mexican coast of the Gulf of Mexico for 5 lagoons for the years 2000 and 2004, between latitudes 2141'16.75'' N and 1823'51.08'' N. Significant differences in duration and intensity were observed among reproductive stages associated with different environmental conditions. Gametogenesis and mature stages correlated positively with temperature and total chlorophyll, respectively. Spawning correlated negatively with salinity in both years. Maturity correlated positively with total chlorophyll levels. The reproductive stages varied from seasonal, a few months, to continuous throughout the year. Recovery, expressed as the number of organisms in postspawning and resting stages, was fast for populations that presented constant gametogenesis and spawning, with less than 50% of the population in postspawning and resting stages. Environmental fluctuations in total chlorophyll are the regulating factors for gametogenic activity, rather than latitudinal temperature variations. This makes monitoring environmental conditions in the lagoons or gonad development a necessity to predict reproduction and recruitment for proper management of the oyster resource.

Intersatellite Differences of HIRS Longwave Channels Between NOAA-14 and NOAA-15 and Between NOAA-17 and METOP-A

Intersatellite differences of the High-Resolution Infrared Radiation Sounder (HIRS) longwave channels (channels 1-12) between National Oceanic and Atmospheric Administration 14 (NOAA-14) and NOAA-15 and between NOAA-17 and METOP-A are examined. Two sets of colocated data are incorporated in the examination. One data set is obtained during periods when equator crossing times of two satellites are very close to each other, and the data set is referred to as global simultaneous nadir overpass observation (SNO). The other data set is based on multiyear polar SNOs. The examination shows that intersatellite differences (ISDs) of temperature-sounding channels from lower stratosphere to lower troposphere, i.e., channels 3-7, are correlated with their corresponding lapse rate factors. Many of the channels also vary with respect to channel brightness temperatures; however, for the upper tropospheric temperature channel (channel 4), the patterns of ISDs from low latitudes and high latitudes are very different due to the fact that the latitudinal variation of brightness temperature does not necessarily follow the latitudinal variation of the temperature lapse rate. The differences between observations in low latitudes and high latitudes form “fork” patterns in scatter plots of ISDs with respect to brightness temperatures. A comparison of ISDs derived from short-term global SNOs and those derived from multiyear polar SNOs reveals the advantage and the limitation of the two data sets. The multiyear polar SNO generally provides larger observation ranges of brightness temperatures in channels 1-4. The global SNO extends the brightness temperature observations to the warm sides for channels 5-12 and captures the occurrences of larger ISDs for most longwave channels.

Latitudinal distributions of atmospheric MSA and MSA/nss‐SO42− ratios in summer over the high latitude regions of the Southern and Northern Hemispheres

To characterize the spatial distributions of methane‐sulfonic acid (MSA) as represented by measured aerosol methane sulfonate (MS) and its relationships with non‐sea‐salt (nss) sulfate (SO42−) in the marine atmospheric boundary layer over high‐latitude regions, bulk aerosol samples were collected during eight cruises during the Chinese National Antarctic and Arctic Research Expeditions from 1998 to 2008. The concentrations of MSA (an indicator of marine biogenic sulfur production), sulfate, sodium and chloride in samples were analyzed using ion chromatography. Increases in the aerosol MSA concentrations and MSA/nss‐SO42− ratios were observed as functions of latitudes in the Pacific Ocean, more abruptly near high southern latitudes as compared to those in high northern latitudes. The MSA concentrations increased from 0.011 μg m−3 near the equator to 0.26 μg m−3 at 63°S, 23°W and from 0.0013 μg m−3 at northern midlatitudes to 0.19 μg m−3 at 58°N, 175°E. However, MSA decreased in the latitudes north of 58°N in the Pacific, where air temperature was lower. MSA/nss‐SO42− ratios increased from 0.024 near the equator to 0.93 at 62°S, 4°E and from 0.0031 around northern midlatitudes to 0.39 at 68°N, 169°W. The MSA concentrations were more correlated with MSA/nss‐SO42− (R2 = 0.43, n = 60) in Southern Hemisphere than Northern Hemisphere (R2 = 0.091, n = 40). No significant correlation was found between MSA/nss‐SO42− and air temperature at high latitudes, indicating latitudinal temperature variations were not a main factor responsible for the MSA/nss‐SO42− variation in those regions. Substantial increases in the concentrations of MSA in coastal Antarctica may indicate additional sources of biogenic S besides the emissions of dimethylsulfide from the sea.

Influence of seasonal and latitudinal temperature variation on early life-history traits of a coral reef fish

Temporal and latitudinal gradients in ocean temperature may be useful for predicting the likely responses of marine species to accelerating global warming. Here, we examined seasonal variations in early life-history traits of the reef fish Pomacentrus moluccensis at Lizard Island on the Great Barrier Reef (GBR). Latitudinal variations were then compared among three locations from Kimbe Bay in Papua New Guinea to the southern GBR (18° latitude). At Lizard Island, a 4°C temperature rise from spring to summer was correlated with a 0.13 mm day−1 increase in pre-settlement growth rates and a 3.28-day decrease in pelagic larval duration (PLD). The latitudinal comparison revealed a non-linear relationship where growth rate and settlement size declined and PLD increased at Kimbe Bay where temperature was the highest of all the study sites. Furthermore, the slopes of latitudinal variations in life-history traits as a function of temperature within the GBR were significantly steeper than those in the temporal analysis. These latitudinal patterns were likely to be shaped by (1) the species thermal reaction norm, (2) local adaptation or (3) location-specific environmental and demographic characteristics. The significant correlations of early life-history traits with natural temperature gradients emphasise the potential sensitivity of reef fish larvae to global warming.

Linkages between the cold summer mesopause and thermospheric zonal mean circulation

We present the first results from the NCAR thermosphere/ionosphere/electrodynamics general circulation model (TIE‐GCM) coupled to a weather forecast/assimilation system of the lower and middle atmosphere. Our results emphasize the importance of a proper representation of the latitudinal temperature variation at the base of the thermosphere for calculating zonal mean zonal winds in the thermosphere. The inclusion of a realistic cold summer mesopause yields significantly improved agreement with climatology in the calculated thermospheric winds in the summer hemisphere. Having established this link between the temperature structure of the mesosphere and the thermospheric circulation, we next present observational evidence that the year‐to‐year variability of thermospheric winds can be linked to analogous variations in the onset of the cold summer mesopause season. Since these mesopause variations have previously been ascribed to stratospheric weather variability, by extension, our results suggest a new mode of coupling between the stratosphere and thermosphere.

An algorithm for the estimation of upper tropospheric humidity from Kalpana observations: Methodology and validation

[1] This study presents a methodology for estimating the upper tropospheric humidity (UTH) for a layer between 500 and 200 hPa from observations in the water vapor channel (5.6–7.2 μm) of the Indian geostationary satellite, Kalpana. Radiative transfer simulations for different UTH conditions have been used to develop the relationship between water vapor channel radiances and UTH. A new technique has been described to include the normalized reference pressure in the algorithm, to account for latitudinal variation of temperature that is derived from a diverse radiosonde profiles data set and is a polynomial function of the latitude for different months. This has an advantage that the forecast or analysis profiles from the operational numerical weather prediction model are not required to compute the normalized reference pressure. The operationally retrieved UTH products have been extensively compared and validated for the period of 1 March to 1 May 2009, using Meteosat-7 UTH products over the Indian Ocean and the UTH computed from the radiosonde profiles. The results suggest that UTH estimates from Kalpana match very well with the Meteosat-7 UTH products having RMS difference of ∼6%. Validation with the UTH computed from the radiosonde observed relative humidity shows that the RMS error of Kalpana UTH is 9.6% and the mean bias is −3.0%. Similar validation of Meteosat-7 UTH with the same set of radiosonde derived UTH shows an RMS error of 13.3% and the bias of −6.5%, which is higher in comparison to the Kalpana UTH.