Abstract: The frequency of cloud detection and the frequency with which these clouds are found in the upper troposphere have been extracted from NOAA High Resolution Infrared Radiometer Sounder (HIRS) polar-orbiting satellite data from 1979 to 2001. The HIRS/2 sensor was flown on nine satellites from the Television Infrared Observation Satellite-Next Generation (TIROS-N) through NOAA-14, forming a 22-yr record. Carbon dioxide slicing was used to infer cloud amount and height. Trends in cloud cover and high-cloud frequency were found to be small in these data. High clouds show a small but statistically significant increase in the Tropics and the Northern Hemisphere. The HIRS analysis contrasts with the International Satellite Cloud Climatology Project (ISCCP), which shows a decrease in both total cloud cover and high clouds during most of this period.

Abstract: [1] We report observations and analysis of a pyro-cumulonimbus event in the midst of a boreal forest fire blowup in Northwest Territories Canada, near Norman Wells, on 3–4 August 1998. We find that this blowup caused a five-fold increase in lower stratospheric aerosol burden, as well as multiple reports of anomalous enhancements of tropospheric gases and aerosols across Europe 1 week later. Our observations come from solar occultation satellites (POAM III and SAGE II), nadir imagers (GOES, AVHRR, SeaWiFS, DMSP), TOMS, lidar, and backscattersonde. First, we provide a detailed analysis of the 3 August eruption of extreme pyro-convection. This includes identifying the specific pyro-cumulonimbus cells that caused the lower stratospheric aerosol injection, and a meteorological analysis. Next, we characterize the altitude, composition, and opacity of the post-convection smoke plume on 4–7 August. Finally, the stratospheric impact of this injection is analyzed. Satellite images reveal two noteworthy pyro-cumulonimbus phenomena: (1) an active-convection cloud top containing enough smoke to visibly alter the reflectivity of the cloud anvil in the Upper Troposphere Lower Stratosphere (UTLS) and (2) a smoke plume, that endured for at least 2 hours, atop an anvil. The smoke pall deposited by the Norman Wells pyro-convection was a very large, optically dense, UTLS-level plume on 4 August that exhibited a mesoscale cyclonic circulation. An analysis of plume color/texture from SeaWiFS data, aerosol index, and brightness temperature establishes the extreme altitude and “pure” smoke composition of this unique plume. We show what we believe to be a first-ever measurement of strongly enhanced ozone in the lower stratosphere mingled with smoke layers. We conclude that two to four extreme pyro-thunderstorms near Norman Wells created a smoke injection of hemispheric scope that substantially increased stratospheric optical depth, transported aerosols 7 km above the tropopause (above ∼430 K potential temperature), and also perturbed lower stratospheric ozone.

Abstract: The microphysical characteristics, radiative impact, and life cycle of a long-lived, surface-based mixed-layer, mixed-phase cloud with an average temperature of approximately −20°C are presented and discussed. The cloud was observed during the Surface Heat Budget of the Arctic experiment (SHEBA) from 1 to 10 May 1998. Vertically resolved properties of the liquid and ice phases are retrieved using surface-based remote sensors, utilize the adiabatic assumption for the liquid component, and are aided by and validated with aircraft measurements from 4 and 7 May. The cloud radar ice microphysical retrievals, originally developed for all-ice clouds, compare well with aircraft measurements despite the presence of much greater liquid water contents than ice water contents. The retrieved time-mean liquid cloud optical depth of 10.1 ± 7.8 far surpasses the mean ice cloud optical depth of 0.2, so that the liquid phase is primarily responsible for the cloud’s radiative (flux) impact. The ice phase, in turn, ...

Abstract: Cloud overlapping has been a major issue in climate studies owing to a lack of reliable information available over both oceans and land. This study presents the first near-global retrieval and analysis of single-layer and overlapped cloud vertical structures and their optical properties retrieved by applying a new method to the Moderate Resolution Imaging Spectroradiometer (MODIS) data. Taking full advantage of the MODIS multiple channels, the method can differentiate cirrus overlapping lower water clouds from single-layer clouds. Based on newly retrieved cloud products using daytime Terra/MODIS 5-km overcast measurements sampled in January, April, July, and October 2001, global statistics of the frequency of occurrence, cloud-top pressure/temperature (Pc/Tc), visible optical depth (VIS), and infrared emissivity () are presented and discussed. Of all overcast scenes identified over land (ocean), the MODIS data show 61% (52%) high clouds (Pc 500 hPa), 39% (48%) lower clouds (Pc 500 hPa), and an extremely low occurrence (4%) of Pc between 500 and 600 hPa. A distinct bimodal distribution of Pc is found and peaks at 275 and 725 hPa for high and low clouds, thus leaving a minimum in cloud in the middle troposphere. Out of the 61% (52%) of high clouds identified by MODIS, retrievals reveal that 41% (35%) are thin cirrus clouds ( 0.85 and Pc 500 hPa) and the remaining 20% (17%) are thick high clouds ( 0.85). Out of the 41% (35%) of thin cirrus, 29% (27%) are found to overlap with lower water clouds and 12% (8%) are single-layer cirrus. Total low-cloud amount (single-layer plus overlapped) out of all overcast scenes is thus 68% (39% 29%) over land and 75% (48% 27%) over ocean, which is greater than the cloud amounts reported by the MODIS and the International Satellite Cloud Climatology Project (ISCCP). Both retrieved overlapping and nonoverlapping cirrus clouds show similar mean VIS of 1.5 and mean of 0.5. The optical properties of single-layer cirrus and single-layer water clouds agree well with the MODIS standard retrievals. Because the MODIS retrievals do not differentiate between cirrus and lower water clouds in overlap situations, large discrepancies are found for emissivity, cloud-top height, and optical depth for high cirrus overlapping lower water clouds.

Abstract: In situ airborne measurements obtained in convective clouds in the vicinity of the Marshall Islands on 15 days in July and August 1999 are used to determine the microphysical structures and precipitation-producing mechanisms in these clouds. The liquid water contents of the clouds were generally well below adiabatic values, even in newly risen turrets. This is attributed to the entrainment of ambient air and to the very efficient removal of cloud water by the collision and coalescence of drops. The formation of raindrops began when the concentration of droplets with radii <15 µm exceeded ∼3 cm−3 or, equivalently, when the effective cloud drop radius reached ∼ 13 µm. Clouds rained when their depth exceeded ∼1.5 km. Due to rainout, the effective radius of cloud droplets began decreasing ∼2–4 km above cloud base. Extremely high concentrations of ice particles (often >500 litre−1) formed very rapidly at temperatures between −4 and −10 °C. High-resolution imagery of these particles, which were primarily sheaths, needles, frozen drops and irregular ice fragments, indicates that the high concentrations of ice were initiated by the freezing of individual drops, some of which fragmented upon freezing, accompanied by ice splinter production during riming. However, for ice particles < 100 µm in maximum dimension, frozen drops and ice fragments were much more numerous than columnar ice crystals, the latter being indicative of ice splinter production. Narrow (10–50 m wide) streamers of precipitation containing large (<3 mm diameter) solid and liquid particles were often encountered in growing clouds. It is proposed that the particles in these streamers grew rapidly by riming in water-rich zones and, under appropriate conditions, the ice particles produced by both drop fragmentation and riming resulted in exceptionally high localized concentrations of ice. Convective clouds consisting entirely of liquid water produced rain rates that were similar to those from deep convective clouds containing ice. Since the concentration of drizzle and raindrops within a few kilometres of cloud base was highly correlated with cloud depth, and therefore cloud top temperature, the concentration of raindrops in cumulus and cumulo-nimbus clouds over the warm pool of the tropical Pacific Ocean can be inferred from satellite measurements of cloud top temperatures. Copyright © 2005 Royal Meteorological Society.

Abstract: Daily satellite cloud observations and reanalysis dynamical parameters are analyzed to determine how midtropospheric vertical velocity and advection over the sea surface temperature gradient control midlatitude North Pacific cloud properties. Optically thick clouds with high tops are generated by synoptic ascent, but two different cloud regimes occur under synoptic descent. When vertical motion is downward during summer, extensive stratocumulus cloudiness is associated with near-surface northerly wind, while frequent cloudless pixels occur with southerly wind. Examination of ship-reported cloud types indicates that midlatitude stratocumulus breaks up as the boundary layer decouples when it is advected equatorward over warmer water. Cumulus is prevalent under conditions of synoptic descent and cold advection during winter. Poleward advection of subtropical air over colder water causes stratification of the near-surface layer that inhibits upward mixing of moisture and suppresses cloudiness until a...

Abstract: Received 6 June 2004; revised 2 September 2004; accepted 4 October 2004; published 13 April 2005. [1] Current satellite cloud retrievals are usually based on the assumption that all clouds consist of a homogenous single layer despite the frequent occurrence of cloud overlap. As such, cloud overlap will cause large errors in the retrievals of many cloud properties. To address this problem, a multilayered cloud retrieval system (MCRS) is developed by combining satellite visible and infrared radiances and surface microwave radiometer measurements. A two-layer cloud model was used to simulate ice-over-water cloud radiative characteristics. The radiances emanating from the combined low cloud and surface are estimated using the microwave liquid water with an assumption of effective droplet size. These radiances replace the background radiances traditionally used in single-layer cloud retrievals. The MCRS is applied to data from March through October 2000 over four Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) sites. The results are compared to the available retrievals of ice water path (IWP) from radar data and show that the MCRS clearly produces a more accurate retrieval of ice-over-water cloud properties. MCRS yields values of IWP that are closest to those from the radar retrieval. For ice-over-water cloud systems, on average, the optical depth and IWP are reduced, from original overestimates, by approximately 30%. The March–October mean cloud effective temperatures from the MCRS are decreased by 10 ± 12K,whichtranslatestoanaverageheightdifferenceof � 1.4km.Theseresultsindicatethat ice-cloud height derived from traditional single-layer retrieval is underestimated, and the midlevel ice cloud coverage is over classified. Effective ice crystal particle sizes are increased by only a few percent with the new method. This new physically based technique should be robust and directly applicable when data are available simultaneously from a satellite imager and the appropriate satellite or surface microwave sensor.

Abstract: Global space borne lidar profiling of atmospheric clouds and aerosol began in 2003 following the launch of the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite. GLAS obtains nadir profiles through the atmosphere in two wavelength channels, day and night, at a fundamental resolution of 76.8 m vertical and 172 m along track. The 532 nm channel uses photon-counting detectors and resolves profiles of observed backscatter cross sections to 10 -7 l/m-sr. The 1064 nm channel employs analog detection adequate to 10 -6 l/m-sr and with greater dynamic range. By 2005 approximately seven months of global data are available. Processing algorithms produce data products for the corrected lidar signal, cloud and aerosol layer boundaries and optical thickness and extinction and backscatter cross sections. Operational sensitivity is shown by the frequency distribution for cloud optical thickness peaking at approximately 0.02.

Abstract: The three-dimensional structure of clouds is known to be important for determining their radiative effects, but it is difficult to obtain this structure directly from observations In this paper a stochastic model is described that is capable of simulating the structural properties unique to cirrus: fallstreak geometry and shear-induced mixing We first present an analysis of time–height cloud radar sections from southern England to extract the cirrus parameters of interest It is found that horizontal power spectra of the logarithm of ice-water content (estimated from radar reflectivity factor and temperature) typically exhibit a spectral slope of around −5/3 near cloud top that decreases with depth into the cloud, to values as low as −35 in some cases This decrease can be explained by wind shear coupled with a spread of particle fall speeds leading to a homogenization that acts preferentially at smaller scales The power spectra exhibit a distinct scale break, becoming flat at scales larger than around 50 km (the ‘outer scale’) The orientation of the fallstreaks may be predicted from the profile of mean wind and mean ice fall speed We then describe the stochastic model, which takes as input profiles of the mean and fractional standard deviation of ice-water content, spectral slope, outer scale and wind speed It first generates an isotropic 3-D fractal field by performing an inverse 3-D Fourier transform on a matrix of simulated Fourier coefficients with amplitudes consistent with the observed 1-D spectra Random phases for the coefficients allow multiple realizations of a cloud with the same statistical properties to be generated Then horizontal slices from the domain are manipulated in turn to simulate horizontal displacement and changes to the spectra with height Finally the field is scaled to produce the observed mean and fractional standard deviation of ice-water content Vertical 2-D slices extracted from the domain are very similar in appearance to cloud radar observations Radiative-transfer calculations using the independent column approximation are used to show that the different fallstreak orientation resulting from different wind shears can change mean top-of-atmosphere radiative fluxes by in excess of 45 W m−2 in the short-wave and 15 W m−2 in the long-wave The effect of wind shear to induce horizontal mixing causes an additional but smaller radiative effect We also investigate the biases that would be expected from the assumptions made in the radiation schemes of general-circulation models (GCMs) It is found that there is some compensation between the errors arising from the assumptions of horizontal homogeneity and maximum-random overlap; if a GCM were to improve the overlap assumption but still assume clouds to be horizontally homogeneous then the total error in cloud radiative effect would be likely to increase Copyright © 2005 Royal Meteorological Society

Abstract: [1] Three gravity-wave-induced clouds and a glaciating altocumulus layer were continuously monitored with lidar at Leipzig, Germany, on 21 November 2003. The midtropospheric clouds formed in Saharan dust at heights from 3.5 km (−9°C) to 6.5 km (−27°C). Distinct ice formation in the altocumulus was triggered by the gravity wave. For the first time, an aerosol/cloud study presents height profiles of temperature, water vapor mixing ratio, relative humidity, dust, and cloud optical properties (volume extinction and backscatter coefficients, lidar ratio, depolarization ratio) within the same air column, solely derived from lidar data. The three gravity-wave-induced clouds did not show any sign of ice formation. The aged dust particles below 4.5-km height were probably partly coated and mixed with hygroscopic material and thus deactivated concerning ice nucleation. Ice crystals were generated in isolated air parcels at the cloud edges of a young, optically thin altocumulus layer between 5- and 6.5-km height. An aged altocumulus deck composed of a geometrically thin liquid water layer at cloud top and an extended ice crystal layer (ice virga) was observed 2 hours later in the same height range. Strong ice formation occurred in the altocumulus during the downdraft induced by the gravity wave. Contact freezing was probably the main reason for the observed ice formation on dust particles. Ice depolarization ratios were relatively low with values from 10 to 15% in the altocumulus and indicate plate-like crystals.

Abstract: The frequent occurrence of high cirrus overlapping low water cloud poses a major challenge in retrieving their optical properties from spaceborne sensors. This paper presents a novel retrieval method that takes full advantage of the satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The main objectives are identification of overlapped high cirrus and low water clouds and determination of their individual optical depths, top heights, and emissivities. The overlapped high cloud top is determined from the MODIS CO2-slicing retrieval and the underlying low cloud top is determined from the neighboring MODIS pixels that are identified as single-layer low clouds. The algorithm applies a dual-layer cloud radiative transfer model using initial cloud properties derived from the MODIS CO2-slicing channels and the visible (0.65 m) and infrared (11 m) window channels. An automated iterative procedure follows by adjusting the high cirrus and low water cloud optical depths until computed radiances from the dual-layer model match with observed radiances from both the visible and infrared channels. The algorithm is valid for both single-layer and dual-layer clouds with the cirrus optical depth 4 (emissivity 0.85). For more than two-layer clouds, its validity depends on the thickness of the upper-layer cloud. A preliminary validation is conducted by comparing against ground-based active remote sensing data. Pixel-by-pixel retrievals and error analyses are presented. It is demonstrated that retrievals based on a single-layer assumption can result in systematic biases in the retrieved cloud top and optical properties for overlapped clouds. Such biases can be removed or lessened considerably by applying the new algorithm.

Abstract: . A 3-minute 3-km rapid scan of the METEOSAT Second Generation geostationary satellite over southern Africa was applied to tracking the evolution of cloud top temperature (T) and particle effective radius (re) of convective elements. The evolution of T-re relations showed little dependence on time, leaving re to depend almost exclusively on T. Furthermore, cloud elements that fully grew to large cumulonimbus stature had the same T-re relations as other clouds in the same area with limited development that decayed without ever becoming a cumulonimbus. Therefore, a snap shot of T-re relations over a cloud field provides the same relations as composed from tracking the time evolution of T and re of individual clouds, and then compositing them. This is the essence of exchangeability of time and space scales, i.e., ergodicity, of the T-re relations for convective clouds. This property has allowed inference of the microphysical evolution of convective clouds with a snap shot from a polar orbiter. The fundamental causes for the ergodicity are suggested to be the observed stability of re for a given height above cloud base in a convective cloud, and the constant renewal of growing cloud tops with cloud bubbles that replace the cloud tops with fresh cloud matter from below.

Abstract: Boundary-layer measurements made from the Swedish icebreaker Oden during the Arctic Ocean Experiment 2001 (AOE-2001) are analysed. They refer mainly to ice drift in the central Arctic during the period 2-21 August 2001. On board Oden a remote sensing array with a wind profiler, cloud radar and a scanning microwave radiometer, and a regular weather station operated continuously; soundings were also released during research stations. Tur- bulence and profile measurements on an 18-m mast were deployed on the ice, along with two sodar systems, a microbarograph array and a tethered sounding system. Surface flux and meteorological stations were also deployed on nearby ice floes. There is a clear diurnal cycle in radiation and also in wind speed, cloud base and visibility. It is absent in temperature and humidity, probably due to the very strong control by melting/ freezing ice and snow. In the advection of warm air, latent heat of melting maintains the surface temperature at 0 � C, while with a negative energy balance the latent heat of freezing of the salty ocean water acts to maintain the surface temperature >)2 � C. The constant presence of water at the surface maintains a relative humidity close to 100%, and this is also often facilitated by an increasing specific humidity through the capping inversion, making entrainment a moisture source. This ensures cloudy conditions, with low cloud and fog prevailing most of the time. Intrusions of warm and moist air from beyond the ice edge are frequent, but the local Arctic boundary layer remains at a relatively constant temperature, and is shallow and well mixed with strong capping inversions. Power spectra of surface-layer wind speed sometimes show large variance at low frequency. A scanning radiometer provides a monitoring of the vertical thermal structure with a spatial and temporal resolution not seen before in the Arctic. There are often two inversions, an elevated main inversion and a weak surface inversion, and occasionally additional inversions occur. Enhanced entrainment across the main inversion appears to occur during frontal passages. Variance of the scanning radiometer temperatures occurs in large pulses rather than varying smoothly, and the height to the maximum variance appears to be a reasonable proxy for the boundary-layer depth.

Abstract: Retrievals of cloud properties from satellite imagery often invoke the assumption that the fields of view are overcast when cloud-contaminated, even though a significant fraction are only partially cloud-covered. The overcast assumption leads to biases in the retrieved cloud properties: cloud amounts and droplet effective radii are typically overestimated, while visible optical depths, cloud altitudes, cloud liquid water amounts, and column droplet number concentrations are typically underestimated. In order to estimate these biases, a retrieval scheme was developed to obtain the properties of clouds for partially covered imager fields of view. The partly cloudy pixel retrieval scheme is applicable to single-layered cloud systems and invokes the assumption that clouds that only partially cover a field of view are at the same altitude as nearby clouds from the same layer that completely cover imager pixels. The properties of the retrieval are illustrated through its application to 2-km Visible and...

Abstract: Three gravity-wave-induced clouds and a glaciating altocumulus layer were continuously monitored with lidar at Leipzig, Germany, on 21 November 2003. The midtropospheric clouds formed in Saharan dust at heights from 3.5 km (-9°C) to 6.5 km (-27°C). Distinct ice formation in the altocumulus was triggered by the gravity wave. For the first time, an aerosol/cloud study presents height profiles of temperature, water vapor mixing ratio, relative humidity, dust, and cloud optical properties (volume extinction and backscatter coefficients, lidar ratio, depolarization ratio) within the same air column, solely derived from lidar data. The three gravity-wave-induced clouds did not show any sign of ice formation. The aged dust particles below 4.5-km height were probably partly coated and mixed with hygroscopic material and thus deactivated concerning ice nucleation. Ice crystals were generated in isolated air parcels at the cloud edges of a young, optically thin altocumulus layer between 5- and 6.5-km height. An aged altocumulus deck composed of a geometrically thin liquid water layer at cloud top and an extended ice crystal layer (ice virga) was observed 2 hours later in the same height range. Strong ice formation occurred in the altocumulus during the downdraft induced by the gravity wave. Contact freezing was probably the main reason for the observed ice formation on dust particles. Ice depolarization ratios were relatively low with values from 10 to 15% in the altocumulus and indicate plate-like crystals.

Abstract: Algorithms for cloud detection (cloud mask) and classification (cloud type) at high and midlatitudes using data from the Advanced Very High Resolution Radiometer (AVHRR) on board the current NOAA satellites and future polar Meteorological and Operational Weather Satellites (METOP) of the European Organisation for the Exploitation of Meteorological Satellites have been extensively validated over northern Europe and the adjacent seas. The algorithms have been described in detail in Part I and are based on a multispectral grouped threshold approach, making use of cloud-free radiative transfer model simulations. The thresholds applied in the algorithms have been validated and tuned using a database interactively built up over more than 1 yr of data from NOAA-12, -14, and -15 by experienced nephanalysts. The database contains almost 4000 rectangular (in the image data)-sized targets (typically with sides around 10 pixels), with satellite data collocated in time and space with atmospheric data from a short-range NWP forecast model, land cover characterization, elevation data, and a label identifying the given cloud or surface type as interpreted by the nephanalyst. For independent and objective validation, a large dataset of nearly 3 yr of collocated surface synoptic observation (Synop) reports, AVHRR data, and NWP model output over northern and central Europe have been collected. Furthermore, weather radar data were used to check the consistency of the cloud type. The cloud mask performs best over daytime sea and worst at twilight and night over land. As compared with Synop, the cloud cover is overestimated during night (except for completely overcast situations) and is underestimated at twilight. The algorithms have been compared with the more empirically based Swedish Meteorological and Hydrological Institute (SMHI) Cloud Analysis Model Using Digital AVHRR Data (SCANDIA), operationally run at SMHI since 1989, and results show that performance has improved significantly.

Abstract: [1] Global climate models typically do not correctly simulate cloudiness associated with midlatitude synoptic systems because coarse grid spacing prevents them from resolving dynamics occurring at smaller scales and there exist no adequate parameterizations for the effects of these subgrid-scale dynamics. Comparison of modeled and observed cloud properties averaged over similar regimes (e.g., compositing) aids the diagnosis of simulation errors and identification of meteorological forcing responsible for producing particular cloud conditions. This study uses a k-means clustering algorithm to objectively classify satellite cloud scenes into distinct regimes based on grid box mean cloud fraction, cloud reflectivity, and cloud top pressure. The spatial domain is the densely instrumented southern Great Plains site of the Atmospheric Radiation Measurement Program, and the time period is the cool season months (November–March) of 1999–2001. As a complement to the satellite retrievals of cloud properties, lidar and cloud radar data are analyzed to examine the vertical structure of the cloud layers. Meteorological data from the constraint variational analysis is averaged for each cluster to provide insight on the large-scale dynamics and advective tendencies coincident with specific cloud types. Meteorological conditions associated with high and low subgrid spatial variability are also investigated for each cluster. Cloud outputs from a single-column model version of the GFDL AM2 atmospheric model forced with meteorological boundary conditions derived from observations and a numerical weather prediction model were compared to observations for each cluster in order to determine the accuracy with which the model reproduces attributes of specific cloud regimes.

Abstract: . Radar cloud-top heights were retrieved at both the Chilbolton Facility for Atmospheric and Radio Research, UK (CFARR) and the ARM Southern Great Plain site, USA (SGP), using millimetre wave cloud radars and identical algorithms. The resulting cloud-top heights were used for comparison with MODIS and MISR retrieved cloud-top heights, from March 2000 to October 2003. Both imaging instruments reside on the NASA Earth Observing System (EOS) Terra platform launched in 1999. MODIS and MISR cloud-top products were from the recent collections (4 and 3, respectively) that cover the entire mission. The cloud characteristics are different at each ground site, with clouds generally residing at higher altitudes at SGP, but with a greater occurrence of broken or multilayered clouds at CFARR. A method is presented to automatically eliminate scenes where clouds are of a broken nature, since it is difficult in these conditions to ensure that ground-based and satellite measurements refer to the same cloud deck. The intercomparison between MODIS and radar cloud-top heights reveals that MODIS cloud-top heights agree with radar within about 1km for mid- and high-level clouds. However, this accuracy is degraded to nearly 3 km for low-level clouds. MISR cloud-top heights are found to agree with radar cloud-top heights to within 0.6 km, which is in line with theoretical expectations. In single-level cloud situations MODIS and MISR cloud-top heights tend to agree within 1 km. This comparison also reveals that the loss of radar sensitivity during 2001 resulted in the CFARR instrument being less accurate for high-level cloud-top height measurements. Keywords. Atmospheric composition and structure (Instruments and techniques)

Abstract: High-resolution infrared radiance spectra obtained from near nadir observations provide atmospheric, surface, and cloud property information. A fast radiative transfer model, including cloud effects, is used for atmospheric profile and cloud parameter retrieval. The retrieval algorithm is presented along with its application to recent field experiment data from the NPOESS Airborne Sounding Testbed - Interferometer (NAST-I). The retrieval accuracy dependence on cloud properties is discussed. It is shown that relatively accurate temperature and moisture retrievals can be achieved below optically thin clouds. For optically thick clouds, accurate temperature and moisture profiles down to cloud top level are obtained. For both optically thin and thick cloud situations, the cloud top height can be retrieved with an accuracy of approximately 1.0 km. Preliminary NAST-I retrieval results from the recent Atlantic-THORPEX Regional Campaign (ATReC) are presented and compared with coincident observations obtained from dropsondes and the nadir-pointing Cloud Physics Lidar (CPL).

Abstract: The Geoscience Laser Altimeter System (GLAS), a nadir pointing lidar on the Ice Cloud and land Elevation Satellite (ICESat) launched in 2003, now provides important new global measurements of the relationship between the height distribution of cloud and aerosol layers. GLAS data have the capability to detect, locate, and distinguish between cloud and aerosol layers in the atmosphere up to 40 km altitude. The data product algorithm tests the product of the maximum attenuated backscatter coefficient b'(r) and the vertical gradient of b'(r) within a layer against a predetermined threshold. An initial case result for the critical Indian Ocean region is presented. From the results the relative height distribution between collocated aerosol and cloud shows extensive regions where cloud formation is well within dense aerosol scattering layers at the surface. Citation: Hart, W. D., J. D. Spinhime, S. P. Palm, and D. L. Hlavka (2005), Height distribution between cloud and aerosol layers from the GLAS spaceborne lidar in the Indian Ocean region,

Abstract: Data from the National Oceanic and Atmospheric Administration’s (NOAA’s) Advanced Very High Resolution Radiometer (AVHRR) instrument are used to provide the mean July and January global daytime distributions of multilayer cloud, where multilayer cloud is defined as cirrus overlapping one or more lower layers. The AVHRR data were taken from multiple years that were chosen to provide data with a constant local equator crossing time of 1430–1500 local time. The cloud overlap detection algorithm is used in NOAA’s Extended Clouds from AVHRR (CLAVR-x) processing system. The results between 60°N and 60°S indicated that roughly 20% of all clouds and roughly 40% of all ice clouds were classified as cirrus overlapping lower cloud (cirrus overlap). The results show a strong July–January pattern that is consistent with the seasonal cycle in convection. In some regions, cirrus overlap is found to be the dominant type of cloud observed. The distributions of overlapping cirrus cloud presented here are compared ...

Abstract: Long-term measurements from Advanced Very High Resolution Radiometer (AVHRR) onboard the National Oceanic and Atmospheric Administration satellites were evaluated to assess variability in cloud-top temperatures over central and eastern Europe that saw radical infrastructural changes after the fall of the East Bloc in 1989 that has affected the pollution levels and hence cloud albedo. Four years in the late 1980s (1985-1988) and in the late 1990s (1997-2000) were chosen, as these are distinctively marked as episodes of very high and lower air pollution (sulphates and particulate matter). During the late 1980s, low- and medium-level clouds were colder by more than 2 K and convective clouds even by 4 K. Cloud-tops over and around polluted regions are higher, and their temperatures showed stronger variability, suggesting an indirect aerosol effect in the thermal spectral range as well.

Abstract: Algorithms are now currently used for the retrieval of cloud optical thickness and droplet effective radius from multispectral radiance measurements. This paper extends their application to the retrieval of cloud droplet number concentration, cloud geometrical thickness, and liquid water path in shallow convective clouds, using an algorithm that was previously tested with airborne measurements of cloud radiances and validated against in situ measurements of the same clouds. The retrieval is based on a stratified cloud model of liquid water content and droplet spectrum. Radiance measurements in visible and near-infrared channels of the Moderate Resolution Imaging Spectroradiometer (MODIS), which is operated from the NASA platforms Terra and Aqua, are analyzed. Because of uncertainties in the simulation of the continental surface reflectance, the algorithm is presently limited to the monitoring of the microphysical structure of boundary layer clouds over the ocean. Two MODIS scenes of extended cloud fields over the North Atlantic Ocean trade wind region are processed. A transport and dispersion model (the Hybrid Single-Particle Lagrangian Integrated Trajectory Model, HYSPLIT4) is also used to characterize the origin of the air masses and hence their aerosol regimes. One cloud field formed in an air mass that was advected from southern Europe and North Africa. It shows high values of the droplet concentration when compared with the second cloud system, which developed in a more pristine environment. The more pristine case also exhibits a higher geometrical thickness and, thus, liquid water path, which counterbalances the expected cloud albedo increase of the polluted case. Estimates of cloud liquid water path are then compared with retrievals from the Special Sensor Microwave Imager (SSM/I). SSM/I-derived liquid water paths are in good agreement with the MODIS-derived values.

Abstract: [1] Radiative heating and cooling occurs throughout most of a stratocumulus cloud layer. Shortwave (SW) heating of individual drops can be strong enough that drop temperatures at equilibrium deviate by as much as 6°C from the surrounding environment. These large temperature differences lead to substantial errors when the classical equation for vapor growth is used. A new form of the vapor growth equation is derived for cases of strong radiative heating. The new equation is used to assess the equilibrium supersaturation (seq) state of drops and cloud condensation nuclei (CCN) within a stratocumulus cloud. Longwave (LW) cloud top cooling has two primary effects on seq. It tends to reduce seq for large drops to values as low as −6%, providing for drop growth at subsaturations. It also tends to reduce the critical supersaturation and size at which larger CCN activate to become growing cloud drops. In contrast, LW heating of cloud base suppresses the growth of cloud drops and CCN. Larger CCN (sizes between 0.5 and 5 μm) lose their Kohler curve maximum, indicating restricted CCN growth. Solar heating produces seq up to 20% for drops with sizes between 500 and 1000 μm, indicating strong evaporation of drizzle drops. Since solar absorption increases more slowly with drop size than LW emission, a minimum appears in the Kohler curves at sizes between 20 and 100 μm, suggesting a preferred size range for vapor growth in SW heated clouds. Like LW heating, SW heating causes suppression of growth for larger CCN.

Abstract: [1] To fully attribute differences in cloud forcing between regions, or between models and observations, requires separation of the effects of different cloud types. This can only be achieved using data which resolve both day to day and diurnal variations. Here we propose a method which takes advantage of the high temporal resolution of geostationary data to estimate the contribution of individual cloud types to the monthly mean and monthly time-step mean cloud forcing in each grid-box. Details of the method are outlined, and data from the Meteosat-8 satellite for June 2004 are used to demonstrate its benefits.

Abstract: INTRODUCTION Satellite Meteorology Overview of Numerical Weather Prediction Modeling Evolution of Observational Data for Numerical Weather Prediction Modeling Additional Applications of Meteorological Satellite Data METEOROLOGICAL SATELLITE SYSTEMS Evolution of Satellites and Sensors The National Polar-Orbiting Operational Environmental Satellite System (NPOESS) VIIRS IMAGERY DESIGN ANALYSIS VIIRS Environmental Data Record Requirements Overview VIIRS Imagery Requirements Cloud Applications-Related Imagery Requirements Value of Manually Generated Cloud Analyses VIIRS IMAGERY REQUIREMENTS ANALYSIS Theoretical Basis for Manual Cloud Analyses Overview of Approach to Instrument Design Cloud Truth Data Sets to Flowdown Sensor Requirements Derivation of Sensing Requirements from Analysis Requirements Overview of VIIRS Hardware Design PRINCIPLES IN IMAGE INTERPRETATION Introduction VIIRS Imagery Data VIIRS Imagery Assist Data MULTICOLOR COMPOSITES OF MULTISPECTRAL IMAGERY Introduction Color Composites of (0.645-mm, 0.865-mm, and 12.0-mm) Surface Vegetation and Cloud Classifications Color Composites (3.7-mm albedo, 0.865- mm, 12.0- mm) for Snow Detection Color Composites of (0.645-mm, 0.645-mm, 3.7-mm albedo) Snow Mapping Through Thin Cirrus Clouds Color Composites of (0.412-mm, 0.865-mm, and 0.645-mm) Clouds Over Arid Regions CASE STUDIES IN THE USE OF MULTICOLOR COMPOSITES FOR SCENE INTERPRETATION Overview MODIS Airborne Simulation Data Over Alaska MODIS Airborne Simulation Success Data Collected Over Colorado AUTOMATED 3-D CLOUD ANALYSES FROM NPOESS Architecture for 3-D Cloud Analyses Automated Cloud Detection Cloud Top Phase Classifications Cloud Optical (Thickness and Particle Size) Properties Cloud Top (Temperature, Pressure, and Height) Parameters Cloud Base Heights REFERENCES INDEX