Relative Humidity Profiles Research Articles

A detection of atmospheric relative humidity profile by UV Raman lidar

A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N 2 and H 2O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2 km with less than 10% of the uncertainty under the conditions of laser energy of 300 mJ and signal-averaging time of 10 min.

Vertically-resolved particle size distribution within and above the mixing layer over the Milan metropolitan area

Abstract. Vertical aerosol profiles were directly measured over the city of Milan during three years (2005–2008) of field campaigns. An optical particle counter, a portable meteorological station and a miniaturized cascade impactor were deployed on a tethered balloon. More than 300 vertical profiles were measured, both in winter and summer, mainly in conditions of clear, dry skies. The mixing height was determined from the observed vertical aerosol concentration gradient, and from potential temperature and relative humidity profiles. Results show that inter-consistent mixing heights can be retrieved highlighting good correlations between particle dispersion in the atmosphere and meteorological parameters. Mixing height growth speed was calculated for both winter and summer showing the low potential atmospheric dispersion in winter. Aerosol number size distribution and chemical composition profiles allowed us to investigate particle behaviour along height. Aerosol measurements showed changes in size distribution according to mixing height. Coarse particle profiles (dp>1.6 μm) were distributed differently than the fine ones (dp<1.6 μm) were, at different heights of the mixing layer. The sedimentation process influenced the coarse particle profiles, and led to a reduction in mean particle diameter for those particles observed by comparing data above the mixing height with ground data (−14.9±0.6% in winter and −10.7±1.0% in summer). Conversely, the mean particle diameter of fine particles increased above the mixing height under stable atmospheric conditions; the average increase, observed by comparing data above the mixing height with ground data, was +2.1±0.1% in winter and +3.9±0.3% in summer. A hierarchical statistical model was created to describe the changes in the size distribution of fine particles along height. The proposed model can be used to estimate the typical vertical profile characterising launches within pre-specified groups starting from: aerosol size and meteorological conditions measured at ground-level, and a mixing height estimation. The average increase of fine particle diameter, estimated on the basis of the model, was +1.9±0.5% in winter and +6.1±1.2% in summer, in keeping with experimental findings.

Characterizing polar atmospheres and their effect on Rayleigh‐scattering optical depth

A large set of radiosoundings was analyzed to study the dependence of Rayleigh‐scattering optical depth (ROD) on pressure and temperature features of the polar clear‐sky atmosphere. This set consists of 1320 radiosoundings, launched throughout the year at six Arctic sites, and of 940 radiosoundings launched at five Antarctic sites. The vertical profiles of pressure, temperature, and relative humidity given by these radiosoundings were corrected for lag errors and dry biases and then completed up to 120 km altitude, using COSPAR International Reference Atmosphere (CIRA) monthly vertical profiles of pressure and temperature, water vapor mixing ratio data derived from various satellite observations, and standard CO2 vertical profile relative to 2007, when the ground‐level concentration was 380 ppmv. Calculations of the volume Rayleigh‐scattering coefficient were made for all the radiosoundings to study its seasonal variations with height due to pressure and temperature changes occurring in the troposphere and stratosphere. It was found that the surface‐level pressure and temperature conditions can account to a large extent for these seasonal effects. Therefore, average spectral evaluations of ROD were made at 88 selected wavelengths from 0.20 to 4.0 μm for all the radiosoundings, subdivided into eight latitude/altitude site classes, representing 70°N, 75°N, 80°N, 70°S, 75°S, 80°S, and 90°S latitudes, for which the average ground values of air pressure pa and air temperature Ta were defined. The dependence of ROD on the daily ground‐level values of air pressure po and air temperature To measured at each site can be accounted for by using an algorithm in which the pressure dependence is given with good approximation by ratio (po/pa), and the temperature linear dependence is expressed by the difference (Ta − To) multiplied by a spectral slope coefficient k(λ) which varies by site classification. This algorithm was estimated to provide values of ROD with accuracy within ±0.5% at the six sea‐level Arctic sites, ±0.5% at the three Antarctic coastal sites, and ±0.7% at the two Antarctic Plateau sites (Dome C and South Pole). When used to analyze the Sun photometer measurements, the present evaluations of ROD are estimated to provide aerosol optical depth values at visible wavelengths with relative errors of 1%–2% at the Arctic sites, 1%–4% at the coastal Antarctic sites, and 3%–13% at the Antarctic Plateau sites, for background aerosol extinction conditions.

Key variables analysis of a novel continuous biodrying process for drying mixed sludge

A novel continuous biodrying process has been developed whose goal is to increase the dry solids content of the sludge to economic levels rendering it suitable for a safe and economic combustion operation in a biomass boiler. The sludge drying rates are enhanced by the metabolic bioheat produced in the matrix of mixed sludge. The goal of this study was to systematically analyze the continuous biodrying reactor. By performing a variable analysis, it was found that the outlet relative humidity profile was the key variable in the biodrying reactor. The influence of different outlet relative humidity profiles was then evaluated using biodrying efficiency index. It was found that by maintaining the air outlet relative humidity profile at 85/85/96/96% in the four compartments of the reactor, the highest biodrying efficiency index can be achieved, while economic dry solids level (>45% w/w) are guaranteed.

Observed development of the vertical structure of the marine boundary layer during the LASIE experiment in the Ligurian Sea

Abstract. In the marine environment, complete datasets describing the surface layer and the vertical structure of the Marine Atmospheric Boundary Layer (MABL), through its entire depth, are less frequent than over land, due to the high cost of measuring campaigns. During the seven days of the Ligurian Air-Sea Interaction Experiment (LASIE), organized by the NATO Undersea Research Centre (NURC) in the Mediterranean Sea, extensive in situ and remote sensing measurements were collected from instruments placed on a spar buoy and a ship. Standard surface meteorological measurements were collected by meteorological sensors mounted on the buoy ODAS Italia1 located in the centre of the Gulf of Genoa. The evolution of the height (zi) of the MABL was monitored using radiosondes and a ceilometer on board of the N/O Urania. Here, we present the database and an uncommon case study of the evolution of the vertical structure of the MABL, observed by two independent measuring systems: the ceilometer and radiosondes. Following the changes of surface flow conditions, in a sequence of onshore – offshore – onshore wind direction shifting episodes, during the mid part of the campaign, the overall structure of the MABL changed. Warm and dry air from land advected over a colder sea, induced a stably stratified Internal Boundary Layer (IBL) and a consequent change in the structure of the vertical profiles of potential temperature and relative humidity.

Surface Aerodynamic Temperature Modeling over Rainfed Cotton

Evapotranspiration (ET) or latent heat flux (LE) can be spatially estimated as an energy balance (EB) residual for land surfaces using remote sensing inputs. The EB equation requires the estimation of net radiation (Rn), soil heat flux (G), and sensible heat flux (H). Rn and G can be estimated with an acceptable accuracy. In computing H, radiometric surface temperature (Ts) is often used instead of surface aerodynamic temperature (To), as To is neither measured nor easily estimated. This may cause an underestimation of ET because H will be overestimated as Ts is typically larger than To for unstable atmospheric conditions. The objectives of this study were to (1) model To to improve the estimation of H and consequently ET for advective environments in the semi-arid Texas High Plains, and (2) assess the accuracy of the To model using three different methods (aerodynamic profile, lysimeter, and eddy covariance). A 6.5 m tower platform was used to measure profiles of wind speed, air temperature, and relative humidity in and above cotton canopy near a large weighing lysimeter managed under rainfed conditions at the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas. The To was modeled using H as a residual from the EB at the lysimeter location. Results indicated that To was better modeled as a linear function of Ts, air temperature, and surface aerodynamic resistance. Modeled To showed a very small estimation error (0.1% mean bias error and 3.8% root mean square error) when compared to To values measured using the aerodynamic profile data. Even though excellent results were found in this study, the model is only valid for dryland cotton with a leaf area index ranging from 0.2 to 1.3 m2 m-2. Furthermore, more research is needed to expand the To model to cover cotton grown under irrigated conditions and showing larger crop percent cover and leaf area index values, and under different environmental and atmospheric conditions.

A One-Dimensional Cloud Model with Trimodal Convective Outflow

Abstract The author describes a one-dimensional cloud model designed to investigate the relationships between stratiform downdrafts, congestus outflow, stability, and relative humidity in the tropical lower troposphere. In the tropics, the climatological lapse rate varies with height below the melting level in a way that is inconsistent with the assumptions of either moist pseudoadiabatic or reversible adiabatic ascent. This anomalous variation is referred to as the melting-level stability anomaly (MLSA). It is argued that the MLSA is caused by a transition from static to dynamic downdrafts at the melting level. Above the melting level, evaporation of precipitation cools and moistens the tropical atmosphere but does not generate downdraft parcels with sufficient negative buoyancy to descend between model levels. Below the melting level, the evaporative cooling associated with stratiform precipitation is strong enough to overcome the stability of the atmosphere and generate a convective-scale circulation. The vertical descent within these downdrafts induces a compensatory ascent in the background atmosphere that changes the overall cooling-to-moistening downdraft ratio. The inclusion of this stratiform downdraft circulation brings the modeled lapse rate and relative humidity profiles into simultaneous agreement with observations. The transition from static to dynamic downdrafts is triggered, in the model, by imposed increases in the amount of rain falling outside clouds, in the out-of-cloud rain rate, and in the vertical coherence of the rain shafts. The destabilization of the lower tropical atmosphere triggered by the stratiform circulation affects the development of convective clouds. In particular, the melting-level stability anomaly increases detrainment near the melting level and gives rise to the congestus mode.

Comparison of atmospheric infrared sounder temperature and relative humidity profiles with NASA African Monsoon Multidisciplinary Analyses (NAMMA) dropsonde observations

The 2006 NASA African Monsoon Multidisciplinary Analyses (NAMMA) field campaign was conducted to investigate the Saharan Air Layer (SAL) activity and its influence on Atlantic tropical cyclones. During the field campaign, 197 dropsonde soundings were collected from 13 research flights over the eastern Atlantic (10°N–22°N, 16°W–34°W) between 19 August and 12 September 2006 which provide a valuable data set to examine the uncertainty of the temperature and relative humidity profiles retrieved from the Atmospheric Infrared Sounder (AIRS) data in the SAL region. Comparing AIRS retrievals with the dropsonde observations indicates that AIRS profiles have a RMS difference of 1.35°C in temperature at the eight standard pressure levels and a RMS difference of 13.8% in relative humidity on seven standard pressure layers from 1000 hPa to 300 hPa. In particular, the RMS differences of temperature and relative humidity range from 0.79°C to 1.61°C and from 10.1% to 15.3%, respectively, from 1000 hPa to 300 hPa. Note that the uncertainty is estimated under sky conditions with active cloud activity because many NAMMA dropsondes were released in the cloud clusters or in the circulation of named tropical cyclones. This study suggests that in the SAL or the region with cloud activity the AIRS relative humidity/temperature has the RMS error within/approaching the design expectation for clear sky conditions.

The Effect of Imposed Drying on Parameterized Deep Convection

AbstractThis paper examines the influence of imposed drying, intended to represent horizontal advection of dry air, on parameterized deep convection interacting with large-scale dynamics in a single-column model framework. Two single-column models, one based on the NASA Goddard Earth Observing System general circulation model version 5 (GEOS5) and the other developed by Bony and Emanuel, are run in weak temperature gradient mode. Drying is imposed by relaxation of the specific humidity field toward zero within a specified vertical layer. The strength of the drying is controlled by specifying either the relaxation time scale or the vertically integrated drying tendency; results are insensitive to which specification is used.The two models reach very different solutions for the same boundary conditions and model configuration. Even when adjustments to the boundary conditions and model parameters are made to render the precipitation rates similar, large differences in the profiles of relative humidity and large-scale vertical velocity persist. In both models, however, drying in the middle troposphere is more effective, per kg m−2 s−1 (or W m−2) of imposed drying, in suppressing precipitation than is drying in the lower troposphere. Even when compared at equal relaxation time (corresponding to weaker net drying in the middle than lower troposphere), middle-tropospheric drying is comparably effective to lower-tropospheric drying. Upper-tropospheric drying has a relatively small effect on precipitation, although large drying in the upper troposphere cannot be imposed as a steady state because of the lack of moisture there. Consistent with the other model differences, the gross moist stabilities of the two models are quite different and vary somewhat differently as a function of imposed drying, but in both models the gross moist stability increases as the drying is increased when it is less than around 30 W m−2 and located in the middle troposphere. For lower-tropospheric drying, the gross moist stability either decreases with increased drying or increases more slowly than for middle-tropospheric drying.

Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part II: Column Model Simulations

Abstract This study employed a nondynamic microphysical column model to evaluate the degree to which the microphysical processes of sublimation, melting, and evaporation alone can explain the evolution of the relative humidity (RH) and latent cooling profiles within the trailing stratiform region of mesoscale convective systems observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). Simulations revealed that observations of a sharp change in the profile of RH, from saturated air with respect to ice above the melting layer to subsaturated air with respect to water below, developed in response to the rapid increase in hydrometeor fall speeds from 1–2 m s−1 for ice to 2–11 m s−1 for rain. However, at certain times and locations, such as the first spiral descent on 29 June 2003 within the notch of lower reflectivity, the air may remain subsaturated for temperatures (T) < 0°C. Sufficiently strong downdrafts above the melting level, such as the 1–3 m s−1 downdrafts observed in the notch of lower reflectivity on 29 June, could enable this state of sustained subsaturation. Sensitivity tests, where the hydrometeor size distributions and upstream RH profiles were varied within the range of BAMEX observations, revealed that the sharp contrast in the RH field across the melting layer always developed. The simulations also revealed that latent cooling from sublimation and melting resulted in the strongest cooling at altitudes within and above the melting layer for locations where hydrometeors did not reach the ground, such as within the rear anvil region, and where sustained subsaturated air is present for T < 0°C, such as is observed within downdrafts. Within the enhanced stratiform rain region, the air is typically at or near saturation for T < 0°C, whereas it is typically subsaturated for T > 0°C; thus, evaporation and melting result in the primary cooling in this region. The implications of these results for the descent of the rear inflow jet across the trailing stratiform region are discussed.

Doppler Lidar Estimation of Mixing Height Using Turbulence, Shear, and Aerosol Profiles

Abstract The concept of boundary layer mixing height for meteorology and air quality applications using lidar data is reviewed, and new algorithms for estimation of mixing heights from various types of lower-tropospheric coherent Doppler lidar measurements are presented. Velocity variance profiles derived from Doppler lidar data demonstrate direct application to mixing height estimation, while other types of lidar profiles demonstrate relationships to the variance profiles and thus may also be used in the mixing height estimate. The algorithms are applied to ship-based, high-resolution Doppler lidar (HRDL) velocity and backscattered-signal measurements acquired on the R/V Ronald H. Brown during Texas Air Quality Study (TexAQS) 2006 to demonstrate the method and to produce mixing height estimates for that experiment. These combinations of Doppler lidar–derived velocity measurements have not previously been applied to analysis of boundary layer mixing height—over the water or elsewhere. A comparison of the results to those derived from ship-launched, balloon-radiosonde potential temperature and relative humidity profiles is presented.

Seasonality of tropospheric ozone and water vapor over Delhi, India: a study based on MOZAIC measurement data

Tropospheric distributions of ozone (O3) and water vapor (H2O) have been presented based on the Measurements of OZone and water vapor by Airbus In-Service AirCraft (MOZAIC) data over the metro and capital city of Delhi, India during 1996–2001. The vertical mixing ratios of both O3 and H2O show strong seasonal variations. The mixing ratios of O3 were often below 40 ppbv near the surface and higher values were observed in the free troposphere during the seasons of winter and spring. In the free troposphere, the high mixing ratio of O3 during the seasons of winter and spring are mainly due to the long-range transport of O3 and its precursors associated with the westerly-northwesterly circulation. In the lower and middle troposphere, the low mixing ratios of ∼20–30 ppbv observed during the months of July–September are mainly due to prevailing summer monsoon circulation over Indian subcontinent. The summer monsoon circulation, southwest (SW) wind flow, transports the O3-poor marine air from the Arabian Sea and Indian Ocean. The monthly averages of rainfall and mixing ratio of H2O show opposite seasonal cycles to that of O3 mixing ratio in the lower and middle troposphere. The change in the transport pattern also causes substantial seasonal variation in the mixing ratio of H2O of 3–27 g/kg in the lower troposphere over Delhi. Except for some small-scale anomalies, the similar annual patterns in the mixing ratios of O3 and H2O are repeated during the different years of 1996–2001. The case studies based on the profiles of O3, relative humidity (RH) and temperature show distinct features of vertical distribution over Delhi. The impacts of long range transport of air mass from Africa, the Middle East, Indian Ocean and intrusions of stratospheric O3 have also been demonstrated using the back trajectory model and remote sensing data for biomass burning and forest fire activities.

Physical and isotopic characterization of evaporation from Sphagnum moss

Summary Evaporation from and water transfer within living and dead (but undecomposed) Sphagnum mosses is important biologically and hydrologically, but understanding of the internal mass-transfer mechanisms remains incomplete. A column experiment was conducted to characterize liquid and vapour fluxes and the profiles of relative humidity, temperature and the hydrogen- and oxygen-isotope composition of Sphagnum pore waters evaporating under controlled conditions. A constant water table at 20 cm depth was established in six identical columns fed by a common water reservoir (δ18O = −13.0‰; δ2H = −85.8‰). Evaporation from the columns averaged 4.5 mm d−1 at the average chamber temperature and relative humidity of 20.7 °C and 27.1%, respectively. The columns developed upward-convex profiles of relative humidity and isotopic composition within the first day that persisted throughout the experiment. Isotopic data from columns sampled after 1, 2, 4, 7 and 15 days were strongly constrained by an evaporation line with the linear relation δ2H = 3.8δ18O −36.1 (R2 = 0.99; n = 25), consistent with the expected evaporative-enrichment trajectory under chamber conditions. Calculated vapour flux accounted for only ∼1% of the total mass flux within the columns, reflecting the dominance of liquid-phase capillary flow. While this calculated vapour flux was small, it decreased markedly near the surface, where evaporative cooling may have resulted in condensation of vapour, simultaneously increasing the liquid water content of the surface mosses. The presence of a vapour pressure deficit down to about 15 cm below the surface indicate that both evaporation and upward vapour diffusion were occurring at depth within the Sphagnum columns, but modelling shows that in situ fractionation alone within the columns cannot explain the extent of the observed enrichment. Rather, the enrichment of the heavy isotopes wherever evaporation is occurring and their consequent downward diffusion are needed to explain the observed profiles. Coupled advection–diffusion modelling of these profiles yielded estimates of the effective liquid-phase diffusivities in Sphagnum pore waters of 2.380 (±0.020) × 10−5 cm2 s−1 for 1H1H18O and 2.415 (±0.015) × 10−5 cm2 s−1 for 1H2H16O, in good agreement with accepted values.

Microclimatic profiles in soybean- pearl millet intercropping systems

A field experiment was conducted during kharif season of 2003-2004 at research farm of department of Agril Meteorology, CCS HAU, Hisar located at 29º102 N lat75º462 E. long and 215.2 m above the MSL The experiment comprising eight treatments was laid out in a RBD with three replications. The crop was sown as rain fed in the last week of June. The temperature and relative humidity profiles were measured at four phenophases using Assmann’s psychrometer. Air temperature profiles in all treatments were inverse throughout the day in comparison to the bare field. Relative humidity was higher in the crop canopy than above crop canopy in all the treatments but after harvest of pearl millet, the slope was less than that in the earlier growth phase. Leaf area index, dry biomass accumulation, test weight, yield and harvest index were reported for all the treatments.

Analysis of Atmospheric Energy Transport in ERA-40 and Implications for Simple Models of the Mean Tropical Circulation

Abstract An analysis of atmospheric energy transport in 22 years (1980–2001) of the 40-yr ECMWF Re-Analysis (ERA-40) is presented. In the analyzed budgets, there is a large cancellation between divergences of dry static and latent energy such that the total energy divergence is positive over all tropical oceanic regions except for the east Pacific cold tongue, consistent with previous studies. The west Pacific and Indian Oceans are characterized by a balance between diabatic sources and mean advective energy export, with a small eddy contribution. However, in the central and eastern Pacific convergence zone, total energy convergence by the mean circulation is balanced by submonthly eddies, with a small diabatic source. Decomposing the mean advective tendency into terms due to horizontal and vertical advection shows that the spatial variation in the mean advection is due largely to variations in vertical advection; these variations are further attributed to variations in the vertical profile of the vertical velocity. The eddy energy export, due almost exclusively to eddy moisture export, does not exhibit any significant seasonal variation. The relationship between the eddies and the mean circulation is examined. Large-scale moisture diffusion is correlated with eddy moisture export on (500 km)2 spatial scales, implying that eddy activity preferentially dries narrow convergence zones over wide ones. Eddy moisture export is further linked to the depth of mean convection in large-scale convergence zones with larger eddy export associated with shallower circulations. This suggests a mechanism that could contribute to the observed variation in mean divergence profiles across the northern tropical Pacific whereby sea surface temperature gradients set the width of convergence zones and eddy activity modulates the tropospheric relative humidity and divergence profile. The importance of variations in the vertical profile of the vertical velocity and eddies in closing the energy budget implies that simple models of the mean tropical circulation should include these effects.

Hygrothermal performance study of an innovative interior thermal insulation system

An innovative interior thermal insulation system on the basis of hydrophilic mineral wool which can serve as an alternative solution to the commonly used systems with water vapor barrier is presented in the paper. At first, the process of materials design is described. Then, the hygrothermal performance of the designed insulation system is tested in the difference climate conditions that correspond to the winter climate in Middle Europe. In the experiment, the profiles of temperature, relative humidity and liquid moisture content are monitored. Measured temperature profiles demonstrate the proper thermal insulation function of the system. The hygric function can also be considered very good as no water condensation during the whole testing period of five months appears in the insulation layer. Therefore, the basic requirements for the successful application of the system in building practice are met.

Impact of consistent boundary layer mixing approaches between NAM and CMAQ

Discrepancies in grid structure, dynamics and physics packages in the offline coupled NWS/NCEP NAM meteorological model with the U.S. Environmental Protection Agency Community Multiscale Air Quality (CMAQ) model can give rise to inconsistencies. This study investigates the use of three vertical mixing schemes to drive chemistry tracers in the National Air Quality Forecast Capability (NAQFC). The three schemes evaluated in this study represent various degrees of coupling to improve the commonality in turbulence parameterization between the meteorological and chemistry models. The methods tested include: (1) using NAM predicted TKE-based planetary boundary height, h, as the prime parameter to derive CMAQ vertical diffusivity; (2) using the NAM mixed layer depth to determine h and then proceeding as in (1); and (3) using NAM predicted vertical diffusivity directly to parameterize turbulence mixing within CMAQ. A two week period with elevated surface O3 concentrations during the summer 2006 has been selected to test these schemes in a sensitivity study. The study results are verified and evaluated using the EPA AIRNow monitoring network and other ozonesonde data. The third method is preferred a priori as it represents the tightest coupling option studied in this work for turbulent mixing processes between the meteorological and air quality models. It was found to accurately reproduce the upper bounds of turbulent mixing and provide the best agreement between predicted h and ozonesonde observed relative humidity profile inferred h for sites investigated in this study. However, this did not translate into the best agreement in surface O3 concentrations. Overall verification results during the test period of two weeks in August 2006, did not show superiority of this method over the other 2 methods in all regions of the continental U.S. Further efforts in model improvement for the parameterizations of turbulent mixing and other surface O3 forecast related processes are warranted.

Precipitating Snow Retrievals from Combined Airborne Cloud Radar and Millimeter-Wave Radiometer Observations

Abstract An algorithm for retrieving snow over oceans from combined cloud radar and millimeter-wave radiometer observations is developed. The algorithm involves the use of physical models to simulate cloud radar and millimeter-wave radiometer observations from basic atmospheric variables such as hydrometeor content, temperature, and relative humidity profiles and is based on an optimal estimation technique to retrieve these variables from actual observations. A high-resolution simulation of a lake-effect snowstorm by a cloud-resolving model is used to test the algorithm. That is, synthetic observations are generated from the output of the cloud numerical model, and the retrieval algorithm is applied to the synthetic data. The algorithm performance is assessed by comparing the retrievals with the reference variables used in synthesizing the observations. The synthetic observation experiment indicates good performance of the retrieval algorithm. The algorithm is also applied to real observations from the Wakasa Bay field experiment that took place over the Sea of Japan in January and February 2003. The application of the retrieval algorithm to data from the field experiment yields snow estimates that are consistent with both the cloud radar and radiometer observations.

Relation between temperature sensitivity to doubled carbon dioxide and the distribution of clouds in current climate models

The paper considers a relation between equilibrium global warming at doubled carbon dioxide (climate sensitivity) and the distribution of clouds and relative humidity in 18 state-of-the-art climate models. There is a strong correlation among three indices: (1) model climate sensitivity, (2) mean cloud amount change due to global warming, and (3) the difference in cloud amount between the tropics and midlatitudes. In the simulation of the present-day current, models with high sensitivity produce smaller clouds amounts in the tropics and larger cloud amounts over midlatitude oceans than models with low sensitivity. The relative humidity in the tropics is smaller in models with high sensitivity than in models with low sensitivity. There is a similarity between vertical profiles of cloud amount and relative humidity under global warming and vertical profiles of the difference in these quantities averaged over the tropics and midlatitudes. Based on the correlations obtained and observations of cloud amount and relative humidity, an estimate is made of the sensitivity of a real climate system.

A physical model to estimate snowfall over land using AMSU‐B observations

In this study, we present a physical model to retrieve snowfall rate over land using brightness temperature observations from NOAA's Advanced Microwave Sounder Unit‐B (AMSU‐B) at 89 GHz, 150 GHz, 183.3 ± 1 GHz, 183.3 ± 3 GHz, and 183.3 ± 7 GHz. The retrieval model is applied to the New England blizzard of 5 March 2001 which deposited about 75 cm of snow over much of Vermont, New Hampshire, and northern New York. In this physical model, prior retrieval assumptions about snowflake shape, particle size distributions, environmental conditions, and optimization methodology have been updated. Here, single scattering parameters for snow particles are calculated with the discrete‐dipole approximation (DDA) method instead of assuming spherical shapes. Five different snow particle models are considered. Snow particle size distributions are assumed to vary with air temperature and to follow aircraft measurements described by previous studies. Brightness temperatures at AMSU‐B frequencies for the New England blizzard are calculated using these DDA calculated single scattering parameters and particle size distributions. The vertical profiles of pressure, temperature, relative humidity and hydrometeors are provided by MM5 model simulations. These profiles are treated as the a priori database in the Bayesian retrieval algorithm. In algorithm applications to the blizzard data, calculated brightness temperatures associated with selected database profiles agree with AMSU‐B observations to within about ±5 K at all five frequencies. Retrieved snowfall rates compare favorably with the near‐concurrent National Weather Service (NWS) radar reflectivity measurements. The relationships between the NWS radar measured reflectivities Ze and retrieved snowfall rate R for a given snow particle model are derived by a histogram matching technique. All of these Ze‐R relationships fall in the range of previously established Ze‐R relationships for snowfall. This suggests that the current physical model developed in this study can reliably estimate the snowfall rate over land using the AMSU‐B measured brightness temperatures.