Albedo Contrast Research Articles

Monitoring martian slope streaks in the northeast of Lycus sulci

Slope streaks are dark features found in low-latitude regions of Mars, formed from rapid-duration events in low thermal inertia terrain. The sudden appearance of low reflectance factor (I/F) patches followed by gradual whitening is a planet-relevant environmental indicator. The present work aims to quantify the variation in the fading of slope streaks using HiRISE/MRO images. We carried that out by analyzing I/F contrast of 31 streaks about their surroundings north of Olympus Mount, arranged in 16 images dated from 2007 to 2021, used as a dataset for measuring the formation and brightening of the streaks in the region. For the contrast calculations, we used I/F data points extracted from within the streaks and their brighter surroundings. We conducted a statistical analysis on the contrast distribution of each slope streak to test for normality and homogeneity of variances. Using Welch's t-Test, we found that the average albedo contrast values of the slope streaks were statistically different across all pairwise comparisons between dates. Our study provides some insight on the contrast variation (due to sediment deposition) of the streaks along time and seasonal correlation. The results point out to a possible dry formation process, such as dust avalanches, but are not sufficient to rule out wet mechanisms.

Synchronous Rotation in the (136199) Eris–Dysnomia System

We combine photometry of Eris from a 6 month campaign on the Palomar 60 inch telescope in 2015, a 1 month Hubble Space Telescope WFC3 campaign in 2018, and Dark Energy Survey data spanning 2013–2018 to determine a light curve of definitive period 15.771 ± 0.008 days (1σ formal uncertainties), with nearly sinusoidal shape and peak-to-peak flux variation of 3%. This is consistent at part-per-thousand precision with the P = 15.785 90 ± 0.00005 day sidereal period of Dysnomia’s orbit around Eris, strengthening the recent detection of synchronous rotation of Eris by Szakáts et al. with independent data. Photometry from Gaia are consistent with the same light curve. We detect a slope of 0.05 ± 0.01 mag per degree of Eris’s brightness with respect to illumination phase averaged across g, V, and r bands, intermediate between Pluto’s and Charon’s values. Variations of 0.3 mag are detected in Dysnomia’s brightness, plausibly consistent with a double-peaked light curve at the synchronous period. The synchronous rotation of Eris is consistent with simple tidal models initiated with a giant-impact origin of the binary, but is difficult to reconcile with gravitational capture of Dysnomia by Eris. The high albedo contrast between Eris and Dysnomia remains unexplained in the giant-impact scenario.

Continental drift shifts tropical rainfall by altering radiation and ocean heat transport.

Shifts in the position of the intertropical convergence zone (ITCZ) have great importance for weather, climate, and society. The ITCZ shifts have been extensively studied in current and future warmer climate; however, little is known for its migration in the past on geological time scales. Using an ensemble of climate simulations over the past 540 million years, we show that ITCZ migrations are controlled primarily by continental configuration through two competing pathways: hemispheric radiation asymmetry and cross-equatorial ocean heat transport. The hemispheric asymmetry of absorbed solar radiation is produced mainly by land-ocean albedo contrast, which can be predicted using only the landmass distribution. The cross-equatorial ocean heat transport is strongly associated with the hemispheric asymmetry of surface wind stress, which is, in turn, controlled by the hemispheric asymmetry of ocean surface area. These results allow the influence of continental evolution on global ocean-atmosphere circulations to be understood through simple mechanisms that depend primarily on the latitudinal distribution of land.

Mapping Lunar Swirls with Machine Learning: The Application of Unsupervised and Supervised Image Classification Algorithms in Reiner Gamma and Mare Ingenii

Lunar swirls are recognized as broad, bright albedo features in various regions of the Moon. These features are often separated by dark off-swirl lanes or terminate against the dark background, such as lunar maria. Prior mapping of swirls has been done primarily by albedo contrast, which is prone to subjectivity. Closer examination of on-swirl areas shows that they are not uniform, making the boundary between on- and off-swirl difficult to map with certainty. We have applied machine learning techniques to address these issues by identifying the number of swirl units and then mapping them based on actual reflectance, or I/F data. Using LROC NAC paired stereo images that are converted to I/F reflectance at a range of incidence angles, we applied both unsupervised K-means clustering and supervised Maximum Likelihood Classification algorithms to classify and map portions of lunar swirls in Reiner Gamma and Mare Ingenii. Results show that the classification maps are a reasonable match to the representative albedos for the two study regions. A third transitionary swirl unit, termed diffuse-swirl, is present in both the maps and the cumulative distribution plots of the reflectance values. Overall, we find that the use of both algorithms provides independent confirmation of both the number and location of these units and their interrelation. More importantly, the algorithms remove mapping subjectivity by using quantitative information. The data and the statistics generated from the maps also have value in future studies by placing limits for categorizing swirl units in different regions on the Moon.

Charcoal Whirlwinds and Post-Fire Observations in Serengeti National Park Savannahs

Whirlwinds and visible dust devils occur over semi-arid ecosystems and entrain particles from the ground surface. Fires produce abundant charcoal across savannahs and the resulting blackened surfaces create a large albedo contrast. Whirlwinds have been observed associated with active fires; yet, there are few published observations on post-fire landscapes. Spatiotemporal patterns of whirlwinds have been documented for a limited number of regions and have not been made for the ecosystems of eastern Africa. From field-based sightings in the Serengeti National Park, Tanzania, we report on whirlwinds over burned savannah patches that entrained large quantities of charcoal to produce black coloured charcoal devils that lofted charcoal into the atmosphere. Two occurrences of charcoal devils were sighted and photographed, one each in the Western Corridor (Bunda District) and Lamai (Serengeti District), Mara Region. The observations were compared with regional scale meteorological data and remote sensing satellite imagery and albedo estimates of the land cover conditions. Although direct meteorological or particulate matter measurements were not made, the observations show that both charcoal devils differed in colour, funnel shape, height, and savannah land cover types (different woody to grass fuel canopies), and thus different charcoal morphologies. Charcoal laden whirlwinds require further study and characterization to analyse the contribution to local-scale redistribution of matter and regional-to-global fluxes of terrestrially derived atmospheric particulates. Future research focusing on the spatiotemporal patterns of whirlwinds over burned patches of savannah, the formation, duration and dissipation mechanisms, and characterisation of the entrained material would contribute to our understanding of the phenomena. The redistribution of organic and clastic material would contribute to understanding of detrital fluxes to depositional environments, such as lakes, wetlands, and snow.
 Keywords: Atmospheric boundary layer; Convection; Detritus; Dust devils; Fires; Particulate matter.

Comparison of Two Analytic Energy Balance Models Shows Stable Partial Ice Cover Possible for Any Obliquity

Abstract In this study, we compare two analytic energy balance models with an explicit dependence on obliquity to study the likelihood of different stable ice configurations. We compare the results of models with different methods of heat transport and different insolation distributions. We show that stable partial ice cover is possible for any obliquity, provided the insolation distribution is sufficiently accurate. Additionally, we quantify the severity of the transition to the snowball state as different model parameters are varied. In accordance with an earlier study, transitions to the snowball state are more severe for higher values of the albedo contrast and energy transport across latitudes in both models; however, we find that the snowball transition is not equally likely across both models. This work is general enough to apply to any rapidly rotating planet and could be used to study the likelihood of snowball transitions on planets within the habitable region of other stars.

Taxonomy of seasonal and diurnal clear-sky climatology of surface urban heat island dynamics across global cities

Knowledge of the temporally continuous dynamics of seasonal and diurnal surface urban heat islands (SUHIs) as well as their underlying determinants is crucial to better understand their variations at multiple time scales. Owing to the orbital limitation of satellites, previous studies primarily focused on SUHI dynamics at limited time-nodes, either in a diurnal or seasonal cycle. However, a joint investigation of the continuous dynamics of seasonal and diurnal SUHIs (hereafter referred to as SUHIsea and SUHIdiu) remains lacking. The comprehensive taxonomy of the patterns of continuous SUHIsea and SUHIdiu dynamics across global cities is also not clear. Using satellite-derived land surface temperature (LST) data, we investigated the prevalent patterns of continuous SUHIsea and SUHIdiu dynamics across global cities by combining annual and diurnal temperature cycle models and the k-means clustering algorithm. Our results showed that: (1) Both SUHIsea and SUHIdiu dynamics exhibited six typical patterns including, single-peak type (SPT), single-valley type (SVT), peak-valley type (PVT), valley-peak type (VPT), two-peak type (TPT), and two-valley type (TVT). (2) The daytime SUHIsea dynamics pattern was closely related to the background climate, with SPT and PVT mainly occurring in cities located in the warm temperate and snow zones, SVT and VPT in the arid zone, and TPT and TVT in the equatorial zone. In contrast, the nighttime SUHIsea dynamics pattern depended more on rural land cover type, with SPT, PVT, and TPT mostly occurring in cities surrounded by barren lands with high albedo and SVT, VPT, and TVT in cities surrounded by dense vegetation with low albedo. We also find a significant negative relationship between daytime SUHIsea dynamics and urban-rural contrast in vegetation and between nighttime SUHIsea dynamics and urban-rural contrast in albedo across cities. (3) For SUHIdiu dynamics, SPT, PVT, and TVT were mainly located in cities with higher vegetation coverage in rural than in urban areas, while SVT, VPT, and TPT were in cities with higher vegetation coverage in urban areas. The SUHIdiu dynamics were found to be synthetically affected by the urban-rural contrast in vegetation and albedo. We consider these findings to be beneficial for deepening the understanding of SUHI dynamics at various time scales.

Stable asymmetric ice belts in an energy balance model of Pluto

In this paper we analyze a latitude-dependent energy balance model with two dynamic ice lines between the north and south poles and consider results for a range of parameter values, of which some may pertain to Pluto. Our analysis shows that for any albedo contrast, there exist stable ice line equilibria where the northern and southern edges are not symmetric about the equator. In particular, stable, asymmetric ice belts can be found within the latitude ranges defined by Sputnik Planitia on Pluto. However, we find that an ice belt with northern and southern edges defined by the northern and southern boundaries of Sputnik Planitia would be flowing to a symmetrical configuration for the parameter values used in this study.

Megaripples at Wau-an-Namus, Libya: A new analog for similar features on Mars

Transverse Aeolian Ridges (TARs) are curious aeolian megaripples on Mars, but there are few sites identified thus far to study as terrestrial analogs. A new terrestrial analog site for TARs has been found in and around an isolated volcano caldera in the Sahara Desert of Libya. The Wau-an-Namus volcano is potentially active and recognizable from space because of its strong albedo contrast. Wau-an-Namus has large dark aeolian megaripple bedforms, with the same horizontal length scales and overall planform patterns as observed for TARs on Mars. Some new patterns for these TAR-like features also have been found at Wau-an-Namus, such as stripe-like and clustered patterns, which may shed new light on the formation of these features on both planets. Other aeolian features such as sand dunes and dust devil tracks are also evident in this region. This is the first terrestrial analog site with dark megaripple features, similar to some TARs on Mars. The dark halo around Wau-an-Namus, visible from space, represents a unique site to study the formation and evolution of these mysterious features, and thereby further our understanding of the probable recent history of the wind regime on Mars.

Evaluating and improving the Community Land Model's sensitivity to land cover

Abstract. Modeling studies have shown the importance of biogeophysical effects of deforestation on local climate conditions but have also highlighted the lack of agreement across different models. Recently, remote-sensing observations have been used to assess the contrast in albedo, evapotranspiration (ET), and land surface temperature (LST) between forest and nearby open land on a global scale. These observations provide an unprecedented opportunity to evaluate the ability of land surface models to simulate the biogeophysical effects of forests. Here, we evaluate the representation of the difference of forest minus open land (i.e., grassland and cropland) in albedo, ET, and LST in the Community Land Model version 4.5 (CLM4.5) using various remote-sensing and in situ data sources. To extract the local sensitivity to land cover, we analyze plant functional type level output from global CLM4.5 simulations, using a model configuration that attributes a separate soil column to each plant functional type. Using the separated soil column configuration, CLM4.5 is able to realistically reproduce the biogeophysical contrast between forest and open land in terms of albedo, daily mean LST, and daily maximum LST, while the effect on daily minimum LST is not well captured by the model. Furthermore, we identify that the ET contrast between forests and open land is underestimated in CLM4.5 compared to observation-based products and even reversed in sign for some regions, even when considering uncertainties in these products. We then show that these biases can be partly alleviated by modifying several model parameters, such as the root distribution, the formulation of plant water uptake, the light limitation of photosynthesis, and the maximum rate of carboxylation. Furthermore, the ET contrast between forest and open land needs to be better constrained by observations to foster convergence amongst different land surface models on the biogeophysical effects of forests. Overall, this study demonstrates the potential of comparing subgrid model output to local observations to improve current land surface models' ability to simulate land cover change effects, which is a promising approach to reduce uncertainties in future assessments of land use impacts on climate.

Correlation Analysis of the Urban Heat Island Effect and Its Impact Factors in China

Urban heat islands (UHIs), which are urban areas with higher surface or air temperatures than surrounding rural areas, can further enhance the heat stress already exacerbated by global warming. This poses great challenges to human health and sustainable development. China has been burdened with heavy air pollution in recent years, and the effect of haze pollution on UHIs is still far less well understood. This study investigated the spatial variations of daytime, nighttime, and seasonal surface UHI effects in China during 2003-2013, based on MODIS land surface temperature data, and analyzed the correlations between the UHI effect and its impact factors from both biophysical and biochemical perspectives. Our results show that MODIS-derived annual nighttime UHI effect (3.4 K±0.2 K, mean±1 s.e.) is higher than the annual mean daytime UHI effect (2.1 K±0.3 K). The daytime UHI effect is strongest in summer and weakest in winter but contrasts with the seasonal variation characteristics of nighttime UHI effect. During daytime, UHI effects in humid and semi-humid regions are much more obvious than those in semi-arid/arid regions; during nighttime, the UHI effect in semi-humid and semi-arid/arid regions is much stronger than that in humid regions. A Daytime Urban Cool Island effect exists in semi-arid/arid regions during spring, autumn, and winter seasons. Population, vegetation activity, and irrigation are three factors controlling annual mean daytime UHI effect. The nighttime UHI is significantly influenced by latitude, albedo, precipitation, and aerosol concentrations. We provide evidence for a long-held hypothesis that the biogeochemical effect of urban aerosols is an important contributor to the UHI effect. The important role played by rural background environment in calculating the UHI effect is further discussed in terms of surface aerodynamic roughness and the contrast in albedo between urban and rural areas. Mitigation of haze pollution has a co-benefit of reducing the UHI effect and heat stress for urban dwellers. It is also conducive to reducing negative impacts of regional and global climate change.

Evidence for ice-ocean albedo feedback in the Arctic Ocean shifting to a seasonal ice zone

Ice-albedo feedback due to the albedo contrast between water and ice is a major factor in seasonal sea ice retreat, and has received increasing attention with the Arctic Ocean shifting to a seasonal ice cover. However, quantitative evaluation of such feedbacks is still insufficient. Here we provide quantitative evidence that heat input through the open water fraction is the primary driver of seasonal and interannual variations in Arctic sea ice retreat. Analyses of satellite data (1979–2014) and a simplified ice-upper ocean coupled model reveal that divergent ice motion in the early melt season triggers large-scale feedback which subsequently amplifies summer sea ice anomalies. The magnitude of divergence controlling the feedback has doubled since 2000 due to a more mobile ice cover, which can partly explain the recent drastic ice reduction in the Arctic Ocean.

Climate zones on Pluto and Charon

We give an explanatory description of the unusual “climate zones” on Pluto that arise from its high obliquity (mean 115°) and high amplitude (±12°) of obliquity oscillation over a 2.8 million year period. The zones we describe have astronomically defined boundaries and do not incorporate atmospheric circulation. For such a high mean obliquity, the lines of tropics (greatest latitudes where the Sun can be overhead) cycle closer to each pole than does each arctic circle, which in turn cycle nearly to the equator. As a consequence in an astronomical context, Pluto is more predominantly “tropical” than “arctic.” Up to 97% of Pluto's surface area can experience overhead Sun when the obliquity cycle is at its minimum of 103°. At this same obliquity phase (most recently occurring 0.8Myr ago), 78% of Pluto's surface experienced prolonged intervals without sunlight or “arctic winter” (and corresponding “arctic summer”). The intersection of these climate zones implies that a very broad range of Pluto's latitudes (spanning 13–77° in each hemisphere; 75% of the total surface area) are both tropical and arctic. While some possible correlations to these climate zones are suggested by comparison with published maps of Pluto and Charon yielded by the New Horizons mission, in this work we present a non-physical descriptive analysis only. For example, the planet-wide dark equatorial band presented by Stern et al. (2015; Science, 350, 292–299) corresponds to Pluto's permanent “diurnal zone.” In this zone spanning latitudes within ±13° of the equator, day-night cycles occur each Pluto rotation (6.4 days) such that neither “arctic winter” nor “arctic summer” has been experienced in this zone for at least 20 million years. The stability of this and other climate zones may extend over several Gyr. Temperature modeling shows that the continuity of diurnal cycles in this region may be the key factor enabling a long-term stability for the high albedo contrast between Tombaugh Regio adjacent to the dark Cthulhu Regio (Earle et al. (2017) Icarus, special issue, submitted). (All names are informal.) Charon's synchronous alignment with Pluto dictates that both bodies in the binary pair have the same climate zone structure, but any effects on Charon's morphology may be limited if volatile transport there is minimal or absent. Cold-trapped methane-rich volatiles on top of its water ice surface may be responsible for forming Charon's dark red north polar cap (Grundy et al., 2016b), and we note the most concentrated area of this feature resides almost entirely within the permanent “polar zone” (above 77° latitude) where the Sun never reaches the overhead point and arctic seasons have been most consistently experienced over at least tens of millions of years. Pluto is not alone among bodies in the Kuiper belt (and uranian satellites) in having high obliquities, overlapping tropical and arctic zones, and latitude bands that remain in a continuous diurnal cycle over long terms.

The spectral albedo of sea ice and salt crusts on the tropical ocean of Snowball Earth: 1. Laboratory measurements

AbstractThe ice‐albedo feedback mechanism likely contributed to global glaciation during the Snowball Earth events of the Neoproterozoic era (1 Ga to 544 Ma). This feedback results from the albedo contrast between sea ice and open ocean. Little is known about the optical properties of some of the possible surface types that may have been present, including sea ice that is both snow‐free and cold enough for salts to precipitate within brine inclusions. A proxy surface for such ice was grown in a freezer laboratory using the single salt NaCl and kept below the eutectic temperature (−21.2°C) of the NaCl‐H2O binary system. The resulting ice cover was composed of ice and precipitated hydrohalite crystals (NaCl · 2H2O). As the cold ice sublimated, a thin lag‐deposit of salt formed on the surface. To hasten its growth in the laboratory, the deposit was augmented by addition of a salt‐enriched surface crust. Measurements of the spectral albedo of this surface were carried out over 90 days as the hydrohalite crust thickened due to sublimation of ice, and subsequently over several hours as the crust warmed and dissolved, finally resulting in a surface with puddled liquid brine. The all‐wave solar albedo of the subeutectic crust is 0.93 (in contrast to 0.83 for fresh snow and 0.67 for melting bare sea ice). Incorporation of these processes into a climate model of Snowball Earth will result in a positive salt‐albedo feedback operating between −21°C and −36°C.

Evaluating biases in simulated land surface albedo from CMIP5 global climate models

AbstractLand surface albedo is a key parameter affecting energy balance and near‐surface climate. In this study, we used satellite data to evaluate simulated surface albedo in 37 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). There was a systematic overestimation in the simulated seasonal cycle of albedo with the highest bias occurring during the Northern Hemisphere's winter months. The bias in surface albedo during the snow‐covered season was classified into that in snow cover fraction (SCF) and albedo contrast (β1). There was a general overestimation of β1 due to the simulated snow‐covered albedo being brighter than the observed value; negative biases in SCF were not always related to negative albedo biases, highlighting the need for realistic representation of snow‐covered albedo in models. In addition, models with a lower leaf area index (LAI) tend to produce a higher surface albedo over the boreal forests during the winter, which emphasizes the necessity of improving LAI simulations in CMIP5 models. Insolation weighting showed that spring albedo biases were of greater importance for climate. The removal of albedo biases is expected to improve temperature simulations particularly over high‐elevation regions.

Inferring planetary obliquity using rotational and orbital photometry

The obliquity of a terrestrial planet is an important clue about its formation and critical to its climate. Previous studies using simulated photometry of Earth show that continuous observations over most of a planet's orbit can be inverted to infer obliquity. However, few studies of more general planets with arbitrary albedo markings have been made and, in particular, a simple theoretical understanding of why it is possible to extract obliquity from light curves is missing. Reflected light seen by a distant observer is the product of a planet's albedo map, its host star's illumination, and the visibility of different regions. It is useful to treat the product of illumination and visibility as the kernel of a convolution. Time-resolved photometry constrains both the albedo map and the kernel, the latter of which sweeps over the planet due to rotational and orbital motion. The kernel's movement distinguishes prograde from retrograde rotation for planets with non-zero obliquity on inclined orbits. We demonstrate that the kernel's longitudinal width and mean latitude are distinct functions of obliquity and axial orientation. Notably, we find that a planet's spin axis affects the kernel -- and hence time-resolved photometry -- even if this planet is East-West uniform or spinning rapidly, or if it is North-South uniform. We find that perfect knowledge of the kernel at 2-4 orbital phases is usually sufficient to uniquely determine a planet's spin axis. Surprisingly, we predict that East-West albedo contrast is more useful for constraining obliquity than North-South contrast.

Extensive computation of albedo contrast between martian dust devil tracks and their neighboring regions

We have developed a method to compute the albedo contrast between dust devil tracks and their surrounding regions on Mars. It is mainly based on Mathematical Morphology operators and uses all the points of the edges of the tracks to compute the values of the albedo contrast. It permits the extraction of more accurate and complete information, when compared to traditional point sampling, not only providing better statistics but also permitting the analysis of local variations along the entirety of the tracks. This measure of contrast, based on relative quantities, is much more adequate to establish comparisons at regional scales and in multi-temporal basis using imagery acquired in rather different environmental and operational conditions. Also, the substantial increase in the details extracted may permit quantifying differential depositions of dust by computing local temporal fading of the tracks with consequences on a better estimation of the thickness of the top most layer of dust and the minimum value needed to create dust devils tracks. The developed tool is tested on 110 HiRISE images depicting regions in the Aeolis, Argyre, Eridania, Noachis and Hellas quadrangles. As a complementary evaluation, we also performed a temporal analysis of the albedo in a region of Russell crater, where high seasonal dust devil activity was already observed before, comprising the years 2007–2012. The mean albedo of the Russell crater is in this case indicative of dust devil tracks presence and, therefore, can be used to quantify dust devil activity.

Land–Ocean Warming Contrast over a Wide Range of Climates: Convective Quasi-Equilibrium Theory and Idealized Simulations

Abstract Surface temperatures increase at a greater rate over land than ocean in simulations and observations of global warming. It has previously been proposed that this land–ocean warming contrast is related to different changes in lapse rates over land and ocean because of limited moisture availability over land. A simple theory of the land–ocean warming contrast is developed here in which lapse rates are determined by an assumption of convective quasi-equilibrium. The theory predicts that the difference between land and ocean temperatures increases monotonically as the climate warms or as the land becomes more arid. However, the ratio of differential warming over land and ocean varies nonmonotonically with temperature for constant relative humidities and reaches a maximum at roughly 290 K. The theory is applied to simulations with an idealized general circulation model in which the continental configuration and climate are varied systematically. The simulated warming contrast is confined to latitudes below 50° when climate is varied by changes in longwave optical thickness. The warming contrast depends on land aridity and is larger for zonal land bands than for continents with finite zonal extent. A land–ocean temperature contrast may be induced at higher latitudes by enforcing an arid land surface, but its magnitude is relatively small. The warming contrast is generally well described by the theory, although inclusion of a land–ocean albedo contrast causes the theory to overestimate the land temperatures. Extensions of the theory are discussed to include the effect of large-scale eddies on the extratropical thermal stratification and to account for warming contrasts in both surface air and surface skin temperatures.

On the persistent spread in snow-albedo feedback

Snow-albedo feedback (SAF) is examined in 25 climate change simulations participating in the Coupled Model Intercomparison Project version 5 (CMIP5). SAF behavior is compared to the feedback’s behavior in the previous (CMIP3) generation of global models. SAF strength exhibits a fivefold spread across CMIP5 models, ranging from 0.03 to 0.16 W m−2 K−1 (ensemble-mean = 0.08 W m−2 K−1). This accounts for much of the spread in 21st century warming of Northern Hemisphere land masses, and is very similar to the spread found in CMIP3 models. As with the CMIP3 models, there is a high degree of correspondence between the magnitudes of seasonal cycle and climate change versions of the feedback. Here we also show that their geographical footprint is similar. The ensemble-mean SAF strength is close to an observed estimate of the real climate’s seasonal cycle feedback strength. SAF strength is strongly correlated with the climatological surface albedo when the ground is covered by snow. The inter-model variation in this quantity is surprisingly large, ranging from 0.39 to 0.75. Models with large surface albedo when these regions are snow-covered will also have a large surface albedo contrast between snow-covered and snow-free regions, and therefore a correspondingly large SAF. Widely-varying treatments of vegetation masking of snow-covered surfaces are probably responsible for the spread in surface albedo where snow occurs, and the persistent spread in SAF in global climate models.

A quantitative analysis of KALPANA-1 derived water vapor winds and its impact on NWP model

The coverage of satellite derived winds over the Indian region including Indian Ocean has improved by the operation of India’s first dedicated satellite for meteorology, KALPANA-1 since 12 September 2002. Atmospheric motion vectors (AMVs) are being derived at the India Meteorological Department (IMD), New Delhi on a routine operational basis. The AMV is recognized as an important source of information for numerical weather prediction (NWP) and is particularly suited for tracking the low and middle level clouds mainly because of the good contrast in albedo between target and background, whereas the upper level moisture pattern can be better tracked by water vapor winds (WVW) using water vapor (WV) channel (5.7–7.1 μm). The WVWs proved to be a very useful wind product for predicting the future track position of cyclones, well marked low pressure areas or heavy rainfall warnings in advance and so, often these types of weather systems are steered by the upper level winds. In the present study, the quantitative as well as qualitative analyses of KALPANA-1 WVW have been carried out. The primary change introduced is making use of first guess (FG) forecast fields obtained from National Center for Environmental Prediction (NCEP) and Global Forecast System (GFS), at a resolution of 1° × 1° with T-382/L64 instead of forecasts of operational limited area model (LAM) of IMD. The overall results showed a consistent improvement after using improved FG wind fields from NCEP instead of LAM with a significantly increasing number of good qualities of KALPANA-1 derived WVWs. The quantitative error analysis has also been carried out for the validation of WVWs using collocated radiosonde observations for the period from May 2008 to December 2009 and the available mid-upper level winds derived from METEOSAT-7 data for the period from October to December 2008. The analysis shows that after modification, the RMSE and bias of KALPANA-1 WVWs have reduced considerably. Further, to assess the impact of these winds, a high resolution mesoscale model WRF 3DVAR system is used in the present study for the analysis of tropical cyclone ‘Sidr’. The results show that the wind assimilation experiments (analysis at 200 hPa) using upper level KALPANA-1 WVW have great potential for improving the NWP analysis. The impact of additional wind data in the model is found to be positive and beneficial.