Atmospheric Specific Humidity Research Articles

Joint Use of Far‐Infrared and Mid‐Infrared Observation for Sounding Retrievals: Learning From the Past for Upcoming Far‐Infrared Missions

AbstractAtmosphere and surface properties are routinely retrieved from satellite measurements and extensively used in weather forecast and climate analysis. Satellite missions dedicated to fill the gap of far‐infrared (far‐IR) observations are scheduled to be launched this decade. To explore mid‐infrared (mid‐IR) and far‐IR joint retrievals for the future far‐IR satellite missions, this study uses an optimal‐estimation‐based method to retrieve atmospheric specific humidity and temperature profiles, surface skin temperature, and surface spectral emissivity from the Infrared Interferometer Sounder‐D (IRIS‐D) measurements in 1970, the only existing spaceborne far‐IR spectral observations with global coverage. Based on a set of criteria, two cases in the Arctic, which are most likely under clear‐sky conditions, are chosen for the retrieval experiments. Information content analysis suggests that the retrieved surface skin temperature and the mid‐IR surface spectral emissivity are highly sensitive to the true values while the retrieval estimates of far‐IR surface emissivity are subject to the variation of water vapor abundance. Results show that radiances based on the retrieved state variables are more consistent with the IRIS‐D observations compared to those based on the reanalysis data. Retrieval estimates of the state variables along with retrieval uncertainties generally fall within reasonable ranges. The relative uncertainties of retrieved state variables decrease compared to the a priori relative uncertainties. In addition, the necessity to retrieve surface emissivity is corroborated by a parallel retrieval experiment assuming a blackbody surface emissivity that has revealed significant distortions of retrieved specific humidity and temperature profiles in the Arctic lower troposphere.

Characteristics of Satellite-Based Ocean Turbulent Heat Flux around the Korean Peninsula and Relationship with Changes in Typhoon Intensity

Ocean-atmosphere energy exchange is an important factor in the maintenance of oceanic and atmospheric circulation and the regulation of meteorological and climate systems. Oceanic sensible and latent heat fluxes around the Korean Peninsula were determined using satellite-based air-sea variables (wind speed, sea surface temperature, and atmospheric specific humidity and temperature) and the coupled ocean-atmosphere response experiment (COARE) 3.5 bulk algorithm for six years between 2014 and 2019. Seasonal characteristics of the marine heat flux and its short-term fluctuations during summer typhoons were also investigated. air-sea variables were produced through empirical relationships and verified with observational data from marine buoys around the Korean Peninsula. Satellite-derived wind speed, sea surface temperature, atmospheric specific humidity, and air temperature were strongly correlated with buoy data, with R2 values of 0.80, 0.97, 0.90, and 0.91, respectively. Satellite-based sensible and latent heat fluxes around the peninsula were also validated against fluxes calculated from marine buoy data, and displayed low values in summer and higher values in autumn and winter as the difference between air-sea temperature and specific humidity increased. Through analyses of spatio-temporal fluctuations in the oceanic turbulent heat flux and variations in intensities of typhoons, this study assessed the possibility of monitoring air-sea energy exchange using satellite-based ocean turbulent heat fluxes during high-impact weather.

Earth Science Theoretical Models for Quantitative Analysis of Global Spatial Data

Geographical space is considered as a dual system of subspace of geophysical coordinates and subspace of component coordinates of the geosystems states. The theoretical and mathematical models of the interaction of these subspaces in terms of vector fields, wave equations and functions, eikonal equations and local sheaves of linear dependencies of meteorological parameters are developed. The climatic zonal norms are reconstructed in the form of points of the global manifold of indicators links according to the positions of the sheaf centers. This model implements the principle of geometrization of geographical knowledge as the chorological approach to justifying the local regularities of the interaction of natural characteristics in the geographical environment. The logical and statistical interrelation of the geographical phenomena of planetary and local levels is studied. Calculations used the average daily values of the scalar fields of atmospheric absolute temperature and specific humidity on the isobaric at-700 hPa surface for different months of 2014 according to logarithmically converted NCEP/NCAR Reanalysis Data. Latitudinal environmental invariants of air temperature and humidity are identified, and a map reflecting the zonal and azonal heterogeneity of the geographical environment is presented. This determines the main theme of earth science as the identification of the projection of space and global cycles onto the local system-forming patterns, which is necessary for the development of the theory, models and methods of scientific analysis of the correlation of scalar fields of geographical characteristics and spatial processes that cause them.

Uncertainties in modelling the climate impact of irrigation

Irrigation-based agriculture constitutes an essential factor for food security as well as fresh water resources and has a distinct impact on regional and global climate. Many issues related to irrigation’s climate impact are addressed in studies that apply a wide range of models. These involve substantial uncertainties related to differences in the model’s structure and its parametrizations on the one hand and the need for simplifying assumptions for the representation of irrigation on the other hand. To address these uncertainties, we used the Max Planck Institute for Meteorology’s Earth System model into which a simple irrigation scheme was implemented. In order to estimate possible uncertainties with regard to the model’s more general structure, we compared the climate impact of irrigation between three simulations that use different schemes for the land-surface–atmosphere coupling. Here, it can be shown that the choice of coupling scheme does not only affect the magnitude of possible impacts but even their direction. For example, when using a scheme that does not explicitly resolve spatial subgrid scale heterogeneity at the surface, irrigation reduces the atmospheric water content, even in heavily irrigated regions. Contrarily, in simulations that use a coupling scheme that resolves heterogeneity at the surface or even within the lowest layers of the atmosphere, irrigation increases the average atmospheric specific humidity. A second experiment targeted possible uncertainties related to the representation of irrigation characteristics. Here, in four simulations the irrigation effectiveness (controlled by the target soil moisture and the non-vegetated fraction of the grid box that receives irrigation) and the timing of delivery were varied. The second experiment shows that uncertainties related to the modelled irrigation characteristics, especially the irrigation effectiveness, are also substantial. In general the impact of irrigation on the state of the land surface is more than three times larger when assuming a low irrigation effectiveness than when a high effectiveness is assumed. For certain variables, such as the vertically integrated water vapour, the impact is almost an order of magnitude larger. The timing of irrigation also has non-negligible effects on the simulated climate impacts and it can strongly alter their seasonality.

Projecting and Forecasting Winter Precipitation Extremes and Meteorological Drought in California Using the North Pacific High Sea Level Pressure Anomaly

Abstract Large-scale climatic indices have been used as predictors of precipitation totals and extremes in many studies and are used operationally in weather forecasts to circumvent the difficulty in obtaining robust dynamical simulations of precipitation. The authors show that the sea level pressure North Pacific high (NPH) wintertime anomaly, a component of the Northern Oscillation index (NOI), provides a superior covariate of interannual precipitation variability in Northern California, including seasonal precipitation totals, drought, and extreme precipitation intensity, compared to traditional ENSO indices such as the Southern Oscillation index (SOI), the multivariate ENSO index (MEI), Niño-3.4, and others. Furthermore, the authors show that the NPH anomaly more closely reflects the influence of Pacific basin conditions over California in general, over groups of stations used to characterize statewide precipitation in the Sierra Nevada range, and over the southern San Francisco Bay region (NASA Ames Research Center). This paper uses the term prediction to refer to the estimation of precipitation (the predictand) from a climate covariate (the predictor), such as a climate index, or atmospheric moisture. In this sense, predictor and predictand are simultaneous in time. Statistical models employed show the effectiveness of the NPH winter anomaly as a predictor of total winter precipitation and daily precipitation extremes at the Moffett Field station. NPH projected by global climate models is also used in conjunction with atmospheric humidity [atmospheric specific humidity (HUS) at the 850-hPa level] to obtain projections of mean and extreme precipitation. The authors show that future development of accurate forecasts of NPH anomalies issued several months in advance is important for forecasting total winter precipitation and is expected to directly benefit water resource management in California. Therefore, the authors suggest that investigating the lead-time predictability of NPH anomalies is an important direction for future research.

Stratospheric ozone changes under solar geoengineering: implications for UV exposure and air quality

Abstract. Various forms of geoengineering have been proposed to counter anthropogenic climate change. Methods which aim to modify the Earth's energy balance by reducing insolation are often subsumed under the term solar radiation management (SRM). Here, we present results of a standard SRM modelling experiment in which the incoming solar irradiance is reduced to offset the global mean warming induced by a quadrupling of atmospheric carbon dioxide. For the first time in an atmosphere–ocean coupled climate model, we include atmospheric composition feedbacks for this experiment. While the SRM scheme considered here could offset greenhouse gas induced global mean surface warming, it leads to important changes in atmospheric composition. We find large stratospheric ozone increases that induce significant reductions in surface UV-B irradiance, which would have implications for vitamin D production. In addition, the higher stratospheric ozone levels lead to decreased ozone photolysis in the troposphere. In combination with lower atmospheric specific humidity under SRM, this results in overall surface ozone concentration increases in the idealized G1 experiment. Both UV-B and surface ozone changes are important for human health. We therefore highlight that both stratospheric and tropospheric ozone changes must be considered in the assessment of any SRM scheme, due to their important roles in regulating UV exposure and air quality.

Retrieval of Land Surface Model State Variables through Assimilating Screen Level Humidity and Temperature Measurements

This study demonstrates successful variational retrieval of land surface states by assimilating screen level atmospheric measurements of specific humidity and air temperature. To this end, the land surface scheme is first validated against the Oklahoma Atmospheric Surface Layer Instrumentation System measurements with necessary refinements to the forward model implemented. The retrieval scheme involves a 1D land surface-atmosphere model, the corresponding adjoint codes, and a cost function that measures residuals between observed and modeled screen level atmospheric temperature and specific humidity. The retrieval scheme is robust when subjected to observational errors with magnitudes comparable to instrument accuracy and for initial guess errors larger than typical model forecast errors. Using varying assimilation window lengths centered on different periods of a day, the sampling strategy is assessed. The daytime observations are more informative compared to nocturnal observations. An assimilation window as narrow as four hours, if centered on local noon, contains comparable information to an expanded window covering the whole day. There exists an optimal assimilation window length resulting from the contest between degrading forecast accuracy and increasing information content. For an assimilation window less than two days, the “optimal” assimilation window length is inversely proportional to the data ingesting frequency.

Evaluation of CMIP5 climate models in simulating 1979–2005 oceanic latent heat flux over the Pacific

The climatological mean state, seasonal variation and long-term upward trend of 1979–2005 latent heat flux (LHF) in historical runs of 14 coupled general circulation models from CMIP5 (Coupled Model Intercomparison Project Phase 5) are evaluated against OAFlux (Objectively Analyzed air–sea Fluxes) data. Inter-model diversity of these models in simulating the annual mean climatological LHF is discussed. Results show that the models can capture the climatological LHF fairly well, but the amplitudes are generally overestimated. Model-simulated seasonal variations of LHF match well with observations with overestimated amplitudes. The possible origins of these biases are wind speed biases in the CMIP5 models. Inter-model diversity analysis shows that the overall stronger or weaker LHF over the tropical and subtropical Pacific region, and the meridional variability of LHF, are the two most notable diversities of the CMIP5 models. Regression analysis indicates that the inter-model diversity may come from the diversity of simulated SST and near-surface atmospheric specific humidity. Comparing the observed long-term upward trend, the trends of LHF and wind speed are largely underestimated, while trends of SST and air specific humidity are grossly overestimated, which may be the origins of the model biases in reproducing the trend of LHF.

Consistency of Estimated Global Water Cycle Variations over the Satellite Era

Abstract Motivated by the question of whether recent interannual to decadal climate variability and a possible “climate shift” may have affected the global water balance, we examine precipitation minus evaporation (P – E) variability integrated over the global oceans and global land for the period 1979–2010 from three points of view—remotely sensed retrievals and syntheses over the oceans, reanalysis vertically integrated moisture flux convergence (VMFC) over land, and land surface models (LSMs) forced with observations-based precipitation, radiation, and near-surface meteorology. Over land, reanalysis VMFC and P − evapotranspiration (ET) from observationally forced LSMs agree on interannual variations (e.g., El Niño/La Niña events); however, reanalyses exhibit upward VMFC trends 3–4 times larger than P − ET trends of the LSMs. Experiments with other reanalyses using reduced observations show that upward VMFC trends in the full reanalyses are due largely to observing system changes interacting with assimilation model physics. The much smaller P − ET trend in the LSMs appears due to changes in frequency and amplitude of warm events after the 1997/98 El Niño, a result consistent with coolness in the eastern tropical Pacific sea surface temperature (SST) after that date. When integrated over the global oceans, E and especially P variations show consistent signals of El Niño/La Niña events. However, at scales longer than interannual there is considerable uncertainty especially in E. This results from differences among datasets in near-surface atmospheric specific humidity and wind speed used in bulk aerodynamic retrievals. The P variations, all relying substantially on passive microwave retrievals over ocean, also have uncertainties in decadal variability, but to a smaller degree.

A general framework for understanding the response of the water cycle to global warming over land and ocean

Abstract. Climate models project increases in globally averaged atmospheric specific humidity that are close to the Clausius–Clapeyron (CC) value of around 7% K−1 whilst projections for mean annual global precipitation (P) and evaporation (E) are somewhat muted at around 2% K−1. Such global projections are useful summaries but do not provide guidance at local (grid box) scales where impacts occur. To bridge that gap in spatial scale, previous research has shown that the "wet get wetter and dry get drier" relation, Δ(P − E) ∝ P − E, follows CC scaling when the projected changes are averaged over latitudinal zones. Much of the research on projected climate impacts has been based on an implicit assumption that this CC relation also holds at local (grid box) scales but this has not previously been examined. In this paper we find that the simple latitudinal average CC scaling relation does not hold at local (grid box) scales over either ocean or land. This means that in terms of P − E, the climate models do not project that the "wet get wetter and dry get drier" at the local scales that are relevant for agricultural, ecological and hydrologic impacts. In an attempt to develop a simple framework for local-scale analysis we found that the climate model output shows a remarkably close relation to the long-standing Budyko framework of catchment hydrology. We subsequently use the Budyko curve and find that the local-scale changes in P − E projected by climate models are dominated by changes in P while the changes in net irradiance at the surface due to greenhouse forcing are small and only play a minor role in changing the mean annual P − E in the climate model projections. To further understand the apparently small changes in net irradiance we also examine projections of key surface energy balance terms. In terms of global averages, we find that the climate model projections are dominated by changes in only three terms of the surface energy balance: (1) an increase in the incoming long-wave irradiance, and the respective responses (2) in outgoing long-wave irradiance and (3) in the evaporative flux, with the latter change being much smaller than the former two terms and mostly restricted to the oceans. The small fraction of the realised surface forcing that is partitioned into E explains why the hydrologic sensitivity (2% K−1) is so much smaller than CC scaling (7% K−1). Much public and scientific perception about changes in the water cycle has been based on the notion that temperature enhances E. That notion is partly true but has proved an unfortunate starting point because it has led to misleading conclusions about the impacts of climate change on the water cycle. A better general understanding of the potential impacts of climate change on water availability that are projected by climate models will surely be gained by starting with the notion that the greater the enhancement of E, the less the surface temperature increase (and vice versa). That latter notion is based on the conservation of energy and is an underlying basis of climate model projections.

Atmospheric teleconnection mechanisms of extratropical North Atlantic SST influence on Sahel rainfall

Extratropical North Atlantic cooling has been tied to droughts over the Sahel in both paleoclimate observations and modeling studies. This study, which uses an atmospheric general circulation model (GCM) coupled to a slab ocean model that simulates this connection, explores the hypothesis that the extratropical North Atlantic cooling causes the Sahel droughts via an atmospheric teleconnection mediated by tropospheric cooling. The drying is also produced in a regional climate model simulation of the Sahel when reductions in air temperature (and associated geopotential height and humidity changes) from the GCM simulation are imposed as the lateral boundary conditions. This latter simulation explicitly demonstrates the central role of tropospheric cooling in mediating the atmospheric teleconnection from extratropical North Atlantic cooling. Diagnostic analyses are applied to the GCM simulation to infer teleconnection mechanisms. An analysis of top of atmosphere radiative flux changes diagnosed with a radiative kernel technique shows that extratropical North Atlantic cooling is augmented by a positive low cloud feedback and advected downstream, cooling Europe and North Africa. The cooling over North Africa is further amplified by a reduced greenhouse effect from decreased atmospheric specific humidity. A moisture budget analysis shows that the direct moisture effect and monsoon weakening, both tied to the ambient cooling and resulting circulation changes, and feedbacks by vertical circulation and evaporation augment the rainfall reduction. Cooling over the Tropical North Atlantic in response to the prescribed extratropical cooling also augments the Sahel drying. Taken together, they suggest a thermodynamic pathway for the teleconnection. The teleconnection may also be applicable to understanding the North Atlantic influence on Sahel rainfall over the twentieth century.

A critical humidity threshold for monsoon transitions

Abstract. Monsoon systems around the world are governed by the so-called moisture-advection feedback. Here we show that, in a minimal conceptual model, this feedback implies a critical threshold with respect to the atmospheric specific humidity qo over the ocean adjacent to the monsoon region. If qo falls short of this critical value qoc, monsoon rainfall over land cannot be sustained. Such a case could occur if evaporation from the ocean was reduced, e.g. due to low sea surface temperatures. Within the restrictions of the conceptual model, we estimate qoc from present-day reanalysis data for four major monsoon systems, and demonstrate how this concept can help understand abrupt variations in monsoon strength on orbital timescales as found in proxy records.

Vertical Moist Thermodynamic Structure of the Madden–Julian Oscillation in Atmospheric Infrared Sounder Retrievals: An Update and a Comparison to ECMWF Interim Re-Analysis

Abstract The large-scale vertical moist thermodynamic structure of the Madden–Julian oscillation (MJO) was documented using the first 2.5 yr (2002–05) of version 4 atmospheric specific humidity and temperature profiles from the Atmospheric Infrared Sounder (AIRS). In this study, this issue is further examined using currently available 7-yr version 5 AIRS data (2002–09) to test its dependence on the AIRS data record lengths, AIRS retrieval versions, and MJO event selection and compositing methods employed. The results indicate a strong consistency of the large-scale vertical moist thermodynamic structure of the MJO between different AIRS data record lengths (2.5 vs 7 yr), different AIRS retrieval versions (4 vs 5), and different MJO analysis methods [the extended empirical orthogonal function (EEOF) method vs the multivariate empirical orthogonal function (MEOF) method]. The large-scale vertical moist thermodynamic structures of the MJO between the AIRS retrievals and the ECMWF Interim Re-Analysis (ERA-Interim) products are also compared. The results indicate a much better agreement of the MJO vertical structure between AIRS and ERA-Interim than with the NCEP–NCAR reanalysis, although a significant difference exists in the magnitude of moisture anomalies between ERA-Interim and AIRS. This characterization of the vertical moist thermodynamic structure of the MJO by AIRS and ERA-Interim offers a useful observation-based metric for general circulation model diagnostics.

Anthropogenic-induced changes in twenty-first century summertime hydroclimatology of the Northeastern US

Potential changes in summertime hydroclimatology over the northeastern (NE) region of the USA induced by increases in greenhouse gas (GHG) concen- trations are investigated using a state-of-the-art regional climate modeling system. Results for a higher emissions scenario illustrate changes that may occur if depen- dence on fossil fuels continues over the coming century. Summertime precipitation is projected to decrease across much of the central NE, but increase over the southernmost and northernmost portions of the domain. Evaporation is expected to increase across the entire domain. The balance between these two results in a decrease in soil moisture content across most of the domain (by approximately 10 mm) and an increase in the summertime soil-moisture depletion rate (by ap- proximately 10 mm/month). At the same time, an increase in both atmospheric near-surface specific and saturation specific humidity is projected, resulting in an increase in relative humidity across the southern portion of the domain, with slight decreases over the northern portion. Combined with an average increase in summer temperatures of 3.5 ◦ C, the projected increase in relative humidity results in a marked increase in the average daily maximum heat index for the region on the order of 3.9 ◦ C, as well as a 350-400% increase in the number of days with heat index values exceeding 32.2 ◦ C( 90 ◦ F)—the level of "extreme caution". Taken together, these high-resolution, dynamically-generated projections confirm the potential for

Spectral optical atmospheric thickness dependence on the specific humidity in the presence of continental and maritime air masses

Atmospheric and spectral solar irradiation data, measured at the Atmospheric Physics Laboratory of the University of Patras (38°17′N, 21°47′E, 64 m a.s.l.), are used to determine the water vapor dependence of the spectral optical atmospheric thickness. The amount of the atmospheric water vapor is being described by the atmospheric specific humidity. The values of the spectral optical atmospheric thickness are being regressed with the simultaneous values of the atmospheric specific humidity and on the wavelength of the spectral solar irradiation, during the occurrence of continental and maritime air masses. The data analysis indicates the decrease of spectral optical atmospheric thickness with increase of the wavelength of the solar beam irradiation and, mainly, the major role of the amount of atmospheric water vapor on the spectral optical atmospheric thickness due to continental or maritime aerosols. The water vapor interaction with the particles of the insoluble continental dust results to the partial wetting and growing of the dust particles. In the atmospheric specific humidity minimum, which is observed in the dry and cold season, the spectral optical atmospheric thickness is minimized with the prevalence of continental air mass. In the atmospheric specific humidity maximum, which is observed in the wet and warm season, the spectral optical atmospheric thickness is maximized with the continental air mass prevalence, too. The water vapor interaction with the soluble sea-salt crystals of maritime aerosol is opposite from this with the insoluble continental dust and results in the complete dissolution of the sea-salt crystals in the wet season. During the presence of maritime air masses, the included sea-salt aerosols are dissolved by the atmospheric water vapor and the spectral optical atmospheric thickness takes intermediate values in the near violet and visible spectral regions of the solar spectrum. The observational data analysis results in two families of regression curves of the spectral optical atmospheric thickness with the atmospheric specific humidity, one corresponding to the continental and one to the maritime aerosol. The aim of this work is the explanation of the physical phenomenon of the hot sunrays during some winter days and of the weak sunrays during summer days.

Spatial Heterogeneity of the Soil Moisture Content and Its Impact on Surface Flux Densities and Near-Surface Meteorology

Using a subgrid distribution for the soil moisture content derived from a macroscale hydrologic model, it is investigated how lateral subgrid variations in the soil moisture content impact both the daily and the seasonal cycle of the spatially averaged surface flux densities and near-surface meteorology. In agreement with earlier studies it is found that in wet conditions the use of one uniform volumetric soil moisture content, referred to as the bulk approach, gives larger estimates of the latent heat flux density than a quasi-distributed approach where the lateral variation in the volumetric soil moisture content is taken into account. In dry conditions the bulk approach gives lower estimates of the latent heat flux density than the quasi-distributed approach. In this study, the differences between the flux density estimates obtained by both approaches appear even when the developing convective boundary layer is allowed to feed back on the surface. It is also shown that differences in the estimated surface flux densities lead to differences between the predicted atmospheric specific humidity and the predicted near-surface temperature. The differences due to the subgrid variations in the soil moisture content appear to impact the seasonal hydrologic balance. Especially for dry climates, the quasi-distributed approach predicts a more gradual decrease of the evapotranspiration during the dry season, resulting in a larger cumulative evapotranspiration over the dry season. Thus, taking account of the spatial heterogeneity of the soil moisture content is a prerequisite for a proper representation of the seasonal hydrological cycle within largescale atmospheric models.

A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period

A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times.

Feedbacks in the Land-Surface and Mixed-Layer Energy Budgets

A mixed-layer model of the surface energy budget and the planetary boundary layer (PBL) is developed, based on the prognostic equations for soil temperature, mixed layer potential temperature and specific humidity and the growth and abrupt collapse of the PBL. Detailed parameterizations of the longwave radiative fluxes are included. The feedbacks in the uncoupled (i.e. surface energy budget with non-responding PBL) and coupled land surface and atmospheric mixed-layer energy budgets are examined. A simplified, time continuous, version of the model, in which the specific humidity budget is the balance of evapotranspiration and dry-air entrainment, and the PBL height is given by the lifted condensation level, is shown to be in good agreement with the complete model. By forcing the simplified model with daily mean rather than periodic solar radiation, an equilibrium model state is achieved where the fluxes are in close agreement with the daily mean fluxes corresponding to the periodic forcing. The model also agrees favorably with measurements from the FIFE field experiment. Feedbacks are examined using the equilibrium model state. The uncoupled and coupled model sensitivities with respect to the minimal stomatal resistance and the atmospheric specific humidity not only differ in magnitude, but in sign as well. This results puts into question the extent to which uncoupled land-surface models that are forced with atmospheric variables may be used in sensitivity studies.

Evaluation of global and diffuse solar irradiation in Ibadan from specific humidity and relative sunshine

SYNOPSIS A multiple regression analysis has been carried out on the monthly-mean global and diffuse solar irradiation data in Ibadan, Nigeria having the atmospheric specific humidity or water vapour content Wat and the relative sunshine (n/N) as dependent variables, with the resulting equations: The standard error of estimate on the coefficients of the dependent variables is less than 0.03.

Tropospheric rivers: A one‐year record and a possible application to ice core data

The morphology of tropospheric rivers has been examined for the period June 1991–May 1992 from atmospheric specific humidity and wind velocity data. Vertically integrated water vapor flux vectors are subjected to harmonic analysis and the high frequency components (periods less than 3 days) show large amplitude values in the North Atlantic, North Pacific, South Atlantic, South Indian Ocean and South Pacific plus small amplitude occurrences in the Red Sea‐Arabian Sea region in the December–February season. In June–August the latter is replaced with a large amplitude monsoon‐related region over South‐East Asia. Maximum intensities increase slightly in altitude with latitude. The correspondence between rivers, frontal boundaries and storm tracks is noted.Sometimes rivers originating over the North Pacific cross North America and reach Greenland while at other times they pass polewards over the North Atlantic, raising the possibility that water vapor involved in ice core formation may have evaporated from surface water bodies with different temperature and salinity characteristics. Changes in oxygen isotope variations at a point may therefore reflect changes in the dynamics of tropospheric rivers in addition to local temperature changes.