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Traditional air conditioning systems use lot of energy; thus, dew point evaporative air-cooling systems could be a good alternative. Many experts studied the impact of constructional and operating characteristics on Maisotsenko cycle (M-cycle) to improve its performance. Cooler performance is influenced by the heat exchanger. Heat exchangers were constructed using flat and corrugated plates. The present study proposes the use of geometrically modified trapezoidal corrugated plates for counter flow heat exchanger, which consists of alternate air and water flow passageways. The numerical model is developed to predict the performance under variety of inlet air conditions and channel dimensions. In the standard range of incoming air properties such as relative humidity, the performance parameters assist in making cooler recommendations. Comparison and validation of simulation results are done with published experimental data for corrugated and trapezoidal corrugated plate heat exchangers. For trapezoidal corrugated plates, simulation findings revealed 10% increase in wet bulb efficiency and 7% increase in dew point efficiency over corrugated plates. The efficiency of wet bulb and dew point decreases as channel gap widens. For trapezoidal corrugated plates, the larger channel spacing minimises pressure drop. [ABSTRACT FROM AUTHOR]

In this study, the Atmospheric Infrared Sounder (AIRS) Observations for Model Intercomparison Projects (Obs4MIPs) V2.1 tropospheric air temperature, specific humidity, and relative humidity data are utilized to evaluate the global tropospheric temperature and humidity simulations in the fully coupled global climate models from the Coupled Model Intercomparison Project phases 3, 5, and 6 (CMIP3, CMIP5, and CMIP6), and possible simulation improvement in CMIP6 models in comparison to CMIP3 and CMIP5 models. Our analyses indicate that all three phases of CMIP models share similar tropospheric air temperature, specific humidity, and relative humidity biases in their multi‐model ensemble means relative to AIRS. Cold biases up to 4 K and positive relative humidity biases up to 20% are found in the free troposphere almost globally with maxima over the mid‐latitude storm tracks. Warm biases up to 2 K are seen over the Southern Ocean in the lower troposphere. Positive specific and relative humidity biases exist over the off‐equatorial oceans while negative specific and relative humidity biases are seen near the equator in the tropical free troposphere, which are related to the double‐intertropical convergence zone bias in the models. Both the air temperature and specific humidity biases are important to the relative humidity biases except in the tropical free troposphere where the specific humidity biases dominate. The tropospheric air temperature, specific humidity, and relative humidity biases are reduced from CMIP3 to CMIP5 and to CMIP6 at almost all pressure levels except at 300 hPa for specific humidity and in the boundary layer for relative humidity. Plain Language Summary: In this study, we use the Atmospheric Infrared Sounder (AIRS) data to assess how well the fully coupled global climate models simulate temperature and humidity in the troposphere. We focus on the climate models from the recent three phases of Coupled Model Intercomparison Project (CMIP3, CMIP5, and CMIP6) and investigate if there is any bias reduction in the recent CMIP6 models compared to the earlier CMIP3 and CMIP5 models. To conduct our evaluation, we compare the CMIP model ensemble averages with the AIRS data and find that all three phases of CMIP models exhibit similar biases in tropospheric temperature and humidity. For example, cold biases up to 4 K and positive relative humidity biases up to 20% are seen in the free troposphere over most regions, with the maximum biases over the midlatitudes. Positive specific and relative humidity biases are found over the off‐equatorial oceans while negative specific and relative humidity biases are seen near the equator in the tropical free troposphere. We also note a possible temperature and humidity bias reduction from the CMIP3 models to the CMIP5 models and then to the CMIP6 models at most pressure levels. Key Points: CMIP Phase 3, 5 and 6 climate models share similar tropospheric air temperature, specific and relative humidity biases relative to Atmospheric Infrared SounderCold biases and positive relative humidity biases are prevalent in free troposphere almost globally with maxima over the mid‐latitude oceansDouble‐intertropical convergence zone bias‐related specific and relative humidity biases are evident in tropical free troposphere: positive (negative) off (near) the equator [ABSTRACT FROM AUTHOR]

This study utilizes in situ measurements and numerical weather prediction forecasts curated during the Coupled Air–Sea Processes Electromagnetic Ducting Research (CASPER) east field campaign to assess how thermodynamic properties in the marine atmospheric surface layer influence evaporation duct shape independent of duct height. More specifically, we investigate evaporation duct shape through a duct shape parameter, a parameter known to affect the propagation of X-band radar signals and is directly related to the curvature of the duct. Relationships between this duct shape parameter and air sea temperature difference (ASTD) reveal that during unstable periods (ASTD < 0), the duct shape parameter is generally larger than in near-neutral or stable atmospheric conditions, indicating tighter curvature of the M-profile. Furthermore, for any specific duct height, a strong linear relationship between the near-surface-specific humidity gradient and the duct shape parameter is found, suggesting that it is primarily driven by near-surface humidity gradients. The results demonstrate that an a priori estimate of duct shape, for a given duct height, is possible if the near-surface humidity gradient is known. [ABSTRACT FROM AUTHOR]

Lightning flash rate data measured by the Tropical Rainfall Measuring Mission (TRMM) for the period 1996–2013 over India are analysed to study the spatial and temporal variation of lightning over India during different seasons. The convective available potential energy (CAPE) and other thermodynamic parameters data for the same period are taken for analysis. This study confirms a systematic increase in lightning flash rate density in India during the last two decades. The annual lightning flash rate density is high along the windward side of the Himalayan foothills with two peaks, one over northwestern parts of India (>50 flashes·km−2·year−1) and the other over northeastern parts of India (>40 flashes·km−2·year−1). The pre‐monsoon (March–May) (0.176 flasheskm−2·year−1) and monsoon (June–September) (0.159 flashes·km−2·year−1) lightning trends are the largest contributors in explaining the annual trend of 0.099 flashes·km−2·year−1. All seasons have shown more or less positive trends while post‐monsoon (October–December) has shown a negative trend (−0.013 flashes·km−2·year−1). The seasonal variations show that the lightning is increasing more over northwest India during the monsoon and northeast India during the pre‐monsoon. To further understand the connection between lightning and climate change, a few thermodynamic or microphysical properties are also analysed. This analysis suggests that the high CAPE values together with thermodynamics and cloud microphysical processes are necessary for organized convection and lightning over this region. Additionally, correlation analysis is adopted to identify the main influencing factors and regions contributing to lightning variability. The increase in lightning activity is found to be due to an increase in CAPE, low‐level moisture content and temperature. The increase in temperature and moisture is attributed to the land use land cover (LULC) changes in India. The impact of the above proxies on lightning varies from region to region and season to season. As several regions are undergoing rapid transformation due to human activity, this study provides insights into the need to understand land use related changes to local and regional lightning activity. [ABSTRACT FROM AUTHOR]

An air-sea interaction field campaign was conducted in September of 2017 within the warm and cold eddy region of the western Northwest Pacific (WNP) (17.5°-20.5°N, 127.5°E-133.5°E). Both near-surface oceanic and atmospheric conditions in addition to ocean heat content (OHC) were examined to better understand the mechanisms governing high heat flux magnitudes responsible for rapidly intensifying tropical cyclones. Observations from this experiment indicate that the latent heat flux (LHF) under modest wind conditions reached 400Wm-2 within the vicinity of a warm eddy, with OHC higher than 100 kJ cm-2 of warm eddy region being 2~3 times as large as that of cold eddy region. These high OHC and a resultant high LHF in the warm eddy, comparable to the magnitude of LHF in the North Equatorial Current, may explain the mechanism of why tropical cyclones over a warm eddy in eddy-rich zones often rapidly intensify in the WNP. A month later typhoon Lan rapidly intensified into a super typhoon, while passing over the boundary region of warm and cold eddies during the observation period. Results from this study illustrate that both the wind-normalized LHF and the difference (Qs-Qa) between the specific humidity at air (Qa) and at the sea surface (Qs), closely correlate with OHC patterns, which suggests that the ocean looks likely to control the spatial pattern of LHF. Overall, both the ocean and weather conditions govern the pattern of specific humidity difference between the air-sea interface, with large OHC over the warm eddy controlling higher Qs and the pattern of Qa depending on the pattern of wind direction. Qa as a factor impacting LHF magnitude is strongly linked to wind direction in the experimental area, that is, the drier northwesterly flow and southeasterly moist wind, resulting in the enhanced contrast of specific humidity at cold eddy region. [ABSTRACT FROM AUTHOR]

Specific humidity (SH) which means the amount of water vapor in 1 kg of air, is used as an indicator of energy exchange between the atmosphere and the Earth's surface. SH is typically computed using microwave satellites. However, the spatial resolution of data for microwave satellite is too low. To overcome this disadvantage, we introduced new methods that applied data collected by the Landsat-8 satellite with high spatial resolution (30 m), a meteorological model, and observation data for South Korea in 2016–2017 to 4 machine learning techniques to develop an optimized technique for computing SH. Among the 4 machine learning techniques, the random forest-based method had the highest accuracy, with a coefficient of determination (R) of 0.98, Root Mean Square Error (RMSE) of 0.001, bias of 0, and Relative Root Mean Square Error (RRMSE) of 11.16%. We applied this model to compute land surface SH using data from 2018 to 2019 and found that it had high accuracy (R = 0.927, RMSE = 0.002, bias = 0, RRMSE = 28.35%). Although the data used in this study were limited, the model was able to accurately represent a small region based on an ensemble of satellite and model data, demonstrating its potential to address important issues related to SH measurements from satellites. [ABSTRACT FROM AUTHOR]

As the Earth's temperatures continue to rise due to increasing greenhouse gases in the atmosphere, a large portion of the warming is due to positive feedbacks from increasing atmospheric water vapor or specific humidity (SH). Some of this water vapor in the boundary layer is transported via deep convection to the upper troposphere (as droplets and ice crystals), moistening the upper troposphere. These small changes in SH in the upper troposphere have a significant impact on the Earth's radiation balance. We compared global daily lightning from the WWLLN data set, and SH data from the ERA5 reanalysis product for 2019, at a spatial resolution of 5°. Our findings show high spatial and temporal correlations between the lightning activity and the SH concentrations in the upper troposphere. The best correlations (r2 = 0.72, p << 0.001) are between lightning activity and UTWV at the 200 mb level (∼12 km altitude), although the correlations with SH at 300 and 400 mb were only slightly lower. Lightning and SH migrate with the seasons north and south of the equator with both parameters showing maxima in the summer hemisphere around 10° latitude. Furthermore, the correlation increases slightly (r2 = 0.73) if a 1‐day lag is considered between the lightning activity and the UTWV. We find that the daily global SH in the upper troposphere can be best estimated using daily global lightning frequency and a power law having an exponent of 0.33. Plain Language Summary: Global warming is amplified by increasing water vapor in the atmosphere, especially water vapor in the upper troposphere. We show that this upper tropospheric water vapor (UTWV) is strongly influenced by global thunderstorm activity, where increases in thunderstorm activity leads to increases the UTWV, with potential feedbacks on surface temperatures. This new analysis shows that lightning and UTWV peak in the northern hemisphere summer, with a positive relationship between daily lightning activity and UTWV concentrations. Key Points: Thunderstorms transport large amounts of water vapor into the upper troposphereThe seasonal dynamics show both lightning and upper tropospheric water vapor peak in the summer hemisphere at 10° latitudeThe global daily lightning activity explains 72% of the variability of global upper tropospheric water vapor [ABSTRACT FROM AUTHOR]

The liquid desiccant cooling system (LDCS) is a viable alternative to conventional air conditioning systems in hot and humid climates because it uses low-grade energy and is environmentally friendly. The critical components of the LDCS are the dehumidifier and regenerator. The focus of the study is to build a compact system by combining a dehumidifier and a regenerator into a single unit. The experimental study of the solar-assisted LDCS is conducted with a CaCl2 concentration of 35%. The impact of inlet air-specific humidity and solution volume flow rate on various system performance parameters has been investigated. This research looks at various system performance parameters such as dehumidification rate, cooling capacity, COP, and effectiveness. It is discovered that the dehumidification rate rises from 0.1268 g/s to 0.2536 g/s when the inlet air-specific humidity rises from 17.4 g/kg to 25.6 g/kg, and the system's maximum COP is 0.324 at 25.6 g/kg specific humidity. It is also discovered that the highest temperature drop is around 4°C at 12.5 LPM solution volume flow rate and 0.07458 kg/s air flow rate. [ABSTRACT FROM AUTHOR]

This study utilizes in situ measurements and numerical weather prediction forecasts curated during the Coupled Air–Sea Processes Electromagnetic Ducting Research (CASPER) east field campaign to assess how thermodynamic properties in the marine atmospheric surface layer influence evaporation duct shape independent of duct height. More specifically, we investigate evaporation duct shape through a duct shape parameter, a parameter known to affect the propagation of X-band radar signals and is directly related to the curvature of the duct. Relationships between this duct shape parameter and air sea temperature difference (ASTD) reveal that during unstable periods (ASTD < 0), the duct shape parameter is generally larger than in near-neutral or stable atmospheric conditions, indicating tighter curvature of the M-profile. Furthermore, for any specific duct height, a strong linear relationship between the near-surface-specific humidity gradient and the duct shape parameter is found, suggesting that it is primarily driven by near-surface humidity gradients. The results demonstrate that an a priori estimate of duct shape, for a given duct height, is possible if the near-surface humidity gradient is known.

Monitoring water consumption dynamics across the geographic range of an ecosystem may indicate the possible variation and stress in a biome. Here, model output data based on remote sensing (1979–2022) were used to examine the water consumption dynamics and effects on cone production in three geographic margins in the longleaf pine's range (i.e., Bladen Lake State Forest, Escambia Experimental Forest, and Kisatchie National Forest) under varying climatic conditions. Results indicated that the mean annual transpiration at Escambia was approximately 431 mm and that at Bladen and Kisatchie was 500 mm. Mean monthly transpiration peaked twice (June and October) at Escambia but only once (August) at Bladen and Kisatchie. The mean annual evapotranspiration ranged from approximately 900 mm at Kisatchie to about 791 mm at Escambia and Bladen. The mean annual transpiration/evapotranspiration ratio was about 0.65 at Bladen and 0.55 at Escambia and Kisatchie. A significant correlation existed between evapotranspiration and specific humidity across the sites on a monthly scale but not on a yearly scale. Significant negative relationships existed between precipitation and the ratios of transpiration/precipitation and evapotranspiration/precipitation on the yearly scale across the sites. Negative power relationships were observed between precipitation and the specific humidity/precipitation ratio on monthly and yearly scales. Cone production was generally highest in years with moderate water consumption. These results provide baseline information on how hydrological and ecological processes of longleaf pine forests interact with climate across broad spatial and temporal scales. [ABSTRACT FROM AUTHOR]

This study identifies quantitatively the dominant contributions of meteorological factors on the development of the boundary layer heights (BLH) in the European region, based on 32 years (1990−2021) of radiosonde observations. The spatial variability of the BLH is further discussed by location, by classifying recording stations as inland, coastal, or bay. We find that the BLH in Europe varies considerably from day to night and with the seasons. Nighttime BLH is higher in winter and lower in summer, with the highest BLH recorded at coastal stations. Daytime BLH at coastal stations shows a bimodal structure with peaks in spring and autumn; at inland and bay stations, daytime BLH is lower in winter and higher in summer. The daily amplitudes of BLH at the inland and bay stations are stronger than those at coastal stations. Based on our multiple linear regression analysis and our decoupling analysis of temperature and specific humidity, we report that the development of the nighttime BLH at all types of stations is strongly dominated by the variations of surface wind speed (and, at coastal stations, wind directions). The main contributors to daytime BLH are the near-surface temperature variability at most coastal and inland stations, and, at most bay stations, the variation of the near-surface specific humidity.

Specific humidity (SH) which means the amount of water vapor in 1 kg of air, is used as an indicator of energy exchange between the atmosphere and the Earth’s surface. SH is typically computed using microwave satellites. However, the spatial resolution of data for microwave satellite is too low. To overcome this disadvantage, we introduced new methods that applied data collected by the Landsat-8 satellite with high spatial resolution (30 m), a meteorological model, and observation data for South Korea in 2016–2017 to 4 machine learning techniques to develop an optimized technique for computing SH. Among the 4 machine learning techniques, the random forest-based method had the highest accuracy, with a coefficient of determination (R) of 0.98, Root Mean Square Error (RMSE) of 0.001, bias of 0, and Relative Root Mean Square Error (RRMSE) of 11.16%. We applied this model to compute land surface SH using data from 2018 to 2019 and found that it had high accuracy (R = 0.927, RMSE = 0.002, bias = 0, RRMSE = 28.35%). Although the data used in this study were limited, the model was able to accurately represent a small region based on an ensemble of satellite and model data, demonstrating its potential to address important issues related to SH measurements from satellites.

Warm blobs are persistently warmer-than-normal seawaters over the Northeast Pacific (NEP), which cause substantial impacts on marine ecosystems and climate. Recently, the warm blobs occurred consecutively in spring and summer of 2021 and 2022. The warm blob in 2021 was mostly located east of 155°W, while it shifted to west of 155°W in 2022. Based on a mixed-layer heat budget analysis, we find that atmospheric processes positively and dominantly contributed in May 2021 and July 2022. Specifically, less latent heat loss from the ocean caused by reducing background westerlies and evaporation intensified the 2021 warm blob, while more shortwave radiation heating due to decreased low clouds intensified the one in 2022. However, the positive contribution of the atmospheric processes cannot maintain a season due to their strong internal variability. The seasonal persistence of the warm blobs, instead, is owing to the offset between the atmospheric and oceanic processes. We highlight the importance of atmospheric processes in the evolution of the NEP warm blobs in spring and summer, which lacks sufficient investigation but can provide more potential predictability for the NEP warm blobs.

A global analysis of geographical features of vertical profiles of specific air humidity and concentrations of sulfur dioxide and sulfate aerosols is carried out based on the CAMS reanalysis data, as well as the height of the planetary boundary layer (PBL) based on the ERA5 reanalysis data for 2003–2020. The scale height HY, i.e., the height at which the concentration of the substance Y decreases by a factor of e, is used as a characteristic of the aforesaid profiles. The maximal heights of the upper PBL boundary are observed in regions of the prevailing cyclonic gyre—in storm tracks and in regions of monsoonal circulation in summer. For the vertical scale of the specific humidity profile, minima are identified in the regions of the subtropical gyre with prevailing large-scale subsidence of air masses. The scale height of SO2 is characterized by spatial minima associated with oxidation of this substance. For , a spatial minimum over the ocean near southeast Asia is found. A statistically significant negative correlation between the PBL thickness and the vertical scale of the specific humidity profile in humid regions of the tropics is revealed, as well as a positive correlation between scale heights of sulfur dioxide and sulfates, most significantly manifested in regions with acute pollution of the lower troposphere by these substances. [ABSTRACT FROM AUTHOR]

Monitoring water consumption dynamics across the geographic range of an ecosystem may indicate the possible variation and stress in a biome. Here, model output data based on remote sensing (1979–2022) were used to examine the water consumption dynamics and effects on cone production in three geographic margins in the longleaf pine’s range (i.e., Bladen Lake State Forest, Escambia Experimental Forest, and Kisatchie National Forest) under varying climatic conditions. Results indicated that the mean annual transpiration at Escambia was approximately 431 mm and that at Bladen and Kisatchie was 500 mm. Mean monthly transpiration peaked twice (June and October) at Escambia but only once (August) at Bladen and Kisatchie. The mean annual evapotranspiration ranged from approximately 900 mm at Kisatchie to about 791 mm at Escambia and Bladen. The mean annual transpiration/evapotranspiration ratio was about 0.65 at Bladen and 0.55 at Escambia and Kisatchie. A significant correlation existed between evapotranspiration and specific humidity across the sites on a monthly scale but not on a yearly scale. Significant negative relationships existed between precipitation and the ratios of transpiration/precipitation and evapotranspiration/precipitation on the yearly scale across the sites. Negative power relationships were observed between precipitation and the specific humidity/precipitation ratio on monthly and yearly scales. Cone production was generally highest in years with moderate water consumption. These results provide baseline information on how hydrological and ecological processes of longleaf pine forests interact with climate across broad spatial and temporal scales.

The satisfactory performance of indirect evaporative cooling techniques (IEC) is governed significantly by the structural and design arrangement of heat and mass exchange devices. The experimental performance of the dew point evaporative cooler has been investigated in the present work with the geometrically modified flow passages for air and water. Conventionally, these passages are formed by either flat or corrugated plates. The trapezoidal corrugated plate has been used to form these passages for air and water. The laboratory trials were conducted for the different combinations of intake air temperature, specific humidity, and air velocity. The performance in terms of dew point and wet bulb efficiency is presented based on laboratory trials. The experimental results achieved dew point and wet bulb efficiencies ranging between 52% and 82% and 74% and 126%, respectively. The geometrically modified flow passages increase the heat exchange area for the same volume of a similar heat exchange device and achieve an increased thermal performance of the proposed cooler.

Global Navigation Satellite System (GNSS) radio occultation (RO) technology has been widely used in Earth atmospheric detection and has a significant impact on numerical weather prediction (NWP), climate detection, and other fields. Cosmic-2 LEO-1 (C2E1) is a well-known RO data provider; however, its observations are confined to 45°S and 45°N. Recently, the Binhu meteorological observation test satellite (BH) has provided global coverage of RO data, including refractivity, specific humidity, and temperature data. In this study, RO data from BH and C2E1 are analyzed and compared from 8 February 2022 to 17 February 2022. Employing the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-5) data as a reference, both BH and C2E1 RO data agree with the ERA data, with the refractivity, temperature, and specific humidity profiles reflecting the real conditions of the natural atmosphere. In addition, BH data are comparable to C2E1 data at low and middle latitudes (0–45°), and BH data at middle and high latitudes (45–90°) are of better quality than those at low and middle latitudes (0–45°). For example, without considering the errors introduced by the interpolation of the ERA-5 data for comparative analysis, the BH refractivity profiles show a mean absolute bias of 0.73 N at low and middle latitudes and only 0.23 N at middle and high latitudes, and that for BH specific humidity profiles at middle and high latitudes is 0.015 g/kg, which is only half of that at low and middle latitudes. The BH temperature and specific humidity data show promising data accuracy. Therefore, BH RO data may provide important supplementary data at higher latitudes and may improve future NWPs through assimilation. [ABSTRACT FROM AUTHOR]

The marine atmospheric boundary layer (MABL) has a profound impact on sensible heat and moisture exchanges between the surface and the free troposphere. The goal of this study is to develop an alternative technique for retrieving MABL-specific humidity (q) using GNSS-RO data in deep-refracted signals. The GNSS-RO signal amplitude (i.e., signal-to-noise ratio or SNR) at the deep straight-line height (HSL) was been found to be strongly impacted by water vapor within the MABL. This study presents a statistical analysis to empirically relate the normalized SNR (SRO) at deep HSL to the MABL q at 950 hPa (~400 m). When compared to the ERA5 reanalysis data, a good linear q–SRO relationship is found with the deep HSL SRO data, but careful treatments of receiver noise, SNR normalization, and receiver orbital altitude are required. We attribute the good q–SRO correlation to the strong refraction from a uniform, horizontally stratiform and dynamically quiet MABL water vapor layer. Ducting and diffraction/interference by this layer help to enhance the SRO amplitude at deep HSL. Potential MABL water vapor retrieval can be further developed to take advantage of a higher number of SRO measurements in the MABL compared to the Level-2 products. A better sampled diurnal variation of the MABL q is demonstrated with the SRO data over the Southeast Pacific (SEP) and the Northeast Pacific (NEP) regions, which appear to be consistent with the low cloud amount variations reported in previous studies. [ABSTRACT FROM AUTHOR]

Advanced and accurate forecasting of COVID-19 cases plays a crucial role in planning and supplying resources effectively. Artificial Intelligence (AI) techniques have proved their capability in time series forecasting non-linear problems. In the present study, the relationship between weather factor and COVID-19 cases was assessed, and also developed a forecasting model using long short-term memory (LSTM), a deep learning model. The study found that the specific humidity has a strong positive correlation, whereas there is a negative correlation with maximum temperature, and a positive correlation with minimum temperature was observed in various geographic locations of India. The weather data and COVID-19 confirmed case data (1 April to 30 June 2020) were used to optimize univariate and multivariate LSTM time series forecast models. The optimized models were utilized to forecast the daily COVID-19 cases for the period 1 July 2020 to 31 July 2020 with 1 to 14 days of lead time. The results showed that the univariate LSTM model was reasonably good for the short-term (1 day lead) forecast of COVID-19 cases (relative error <20%). Moreover, the multivariate LSTM model improved the medium-range forecast skill (1-7 days lead) after including the weather factors. The study observed that the specific humidity played a crucial role in improving the forecast skill majorly in the West and northwest region of India. Similarly, the temperature played a significant role in model enhancement in the Southern and Eastern regions of India. [ABSTRACT FROM AUTHOR]

Global climate change is a change in the planetary energy (E) balance. It is usually expressed as a change in near‐surface air temperature (Ta), but changes in energy content due to Ta (ET) represent only part of the near‐surface energy balance, which also includes E changes due to specific humidity (ESH). We analyzed MERRA‐2 and ERA5 reanalysis data and 15 CMIP6 Atmospheric Model Intercomparison Project (AMIP) models from 1980 to 2014. Some 44%, 39%, and 50% of MERRA‐2 pixels showed significant increases in ET, ESH, and E, respectively. The average increase in ET (ESH) was 16.9 (13.6) J kg−1 year−1, but AMIP models estimated larger average ET (21.6 J kg−1 year−1) and ESH (16.7 J kg−1 year−1). Global Ta would have increased at nearly double the observed rate if energy was not partitioned into latent heat. Results demonstrate the critical role that specific humidity plays in recent climate changes. Plain Language Summary: Greenhouse gases trap longwave radiation, making it more difficult for energy to leave Earth. This increases air temperatures, but there is much more to global climate change than air temperature alone. Most of the excess energy caused by the increase in greenhouse gases has entered the ocean, because it takes a lot of energy to heat water. The water vapor content of the atmosphere near the surface has also increased, and it takes energy to heat and evaporate this water. We find that the energy needed to evaporate the extra water that has entered the atmosphere has helped buffer increases in global air temperatures, which would have increased by nearly double if this energy was used to increase air temperatures alone. Global climate models can simulate many aspects of these energy changes, but struggle in regions where regional climate is complex. Many of the largest increases in atmospheric energy have occurred in populous regions of the globe while the greatest temperature increases are near the poles. It is important to understand that global change is a change in the planetary energy balance, and that near surface air temperature alone is only a small (but important) part of this energy change. Key Points: The temperature and specific humidity of the near‐surface atmosphere are increasingBoth imply an increase in atmospheric energy content, and climate models often struggle to simulate regional changesThe rate of air temperature increase would have more than doubled without specific humidity change, all else being equal [ABSTRACT FROM AUTHOR]

The representation of water vapour in numerical weather prediction models is still subject to significant uncertainties, which are partly due to the lack of observations of water vapour in the lower troposphere over land and sea-ice areas. There are now several satellite datasets of total column water vapour available, which make use of the reflected radiances from the surface in the near-infrared spectral region where there are water vapour absorption bands. The ocean and land cover imager (OLCI) on the Sentinel-3A and 3B satellites measures the top of atmosphere radiances in the near infrared, and a total column water vapour product is retrieved and made available in near real time. Comparisons of the total column water vapour from OLCI with NWP model 6-h forecasts, collocated ground-based GNSS measurements and radiosonde profiles have been undertaken to determine the accuracy of the product. Following the monitoring, some experiments were made to assimilate the OLCI total column water vapour over land using the Met Office 4D-Var assimilation system. A 5-month trial assimilating the OLCI data has shown consistently positive impacts on the forecast scores with some changes to the water vapour distribution in the model. [ABSTRACT FROM AUTHOR]

© 2015 Elsevier Inc. Using GPS radio occultation refractivity data collected over the period of 2002-2013, we present a new method for identification of the intertropical convergence zone (ITCZ). The ITCZ is identified by estimating the maximum in the monthly meridional refractivity and specific humidity field by applying a Gaussian fit at each longitude. The interannual variability and climatology of the ITCZ is presented from 12. years of refractivity data. This new method captures all the general features of ITCZ extent and its variability. We also examine the effects of the ITCZ vertically during different seasons. The ITCZ is observed mostly at eastern Pacific in May month, and it is zonally distributed in the September and October months of each year. The zonal variability is large between lower and higher levels, particularly over the Indian monsoon and western Pacific. The latitudinal difference in the vertical extent between 850. hPa and higher levels is larger during the northern hemisphere (NH) summer than NH winter.

Abstract The representation of water vapour in numerical weather prediction models is still subject to significant uncertainties, which are partly due to the lack of observations of water vapour in the lower troposphere over land and sea‐ice areas. There are now several satellite datasets of total column water vapour available, which make use of the reflected radiances from the surface in the near‐infrared spectral region where there are water vapour absorption bands. The ocean and land cover imager (OLCI) on the Sentinel‐3A and 3B satellites measures the top of atmosphere radiances in the near infrared, and a total column water vapour product is retrieved and made available in near real time. Comparisons of the total column water vapour from OLCI with NWP model 6‐h forecasts, collocated ground‐based GNSS measurements and radiosonde profiles have been undertaken to determine the accuracy of the product. Following the monitoring, some experiments were made to assimilate the OLCI total column water vapour over land using the Met Office 4D‐Var assimilation system. A 5‐month trial assimilating the OLCI data has shown consistently positive impacts on the forecast scores with some changes to the water vapour distribution in the model.

© 2015 Elsevier Inc. Using GPS radio occultation refractivity data collected over the period of 2002-2013, we present a new method for identification of the intertropical convergence zone (ITCZ). The ITCZ is identified by estimating the maximum in the monthly meridional refractivity and specific humidity field by applying a Gaussian fit at each longitude. The interannual variability and climatology of the ITCZ is presented from 12. years of refractivity data. This new method captures all the general features of ITCZ extent and its variability. We also examine the effects of the ITCZ vertically during different seasons. The ITCZ is observed mostly at eastern Pacific in May month, and it is zonally distributed in the September and October months of each year. The zonal variability is large between lower and higher levels, particularly over the Indian monsoon and western Pacific. The latitudinal difference in the vertical extent between 850. hPa and higher levels is larger during the northern hemisphere (NH) summer than NH winter.

Global Navigation Satellite System (GNSS) radio occultation (RO) technology has been widely used in Earth atmospheric detection and has a significant impact on numerical weather prediction (NWP), climate detection, and other fields. Cosmic-2 LEO-1 (C2E1) is a well-known RO data provider; however, its observations are confined to 45°S and 45°N. Recently, the Binhu meteorological observation test satellite (BH) has provided global coverage of RO data, including refractivity, specific humidity, and temperature data. In this study, RO data from BH and C2E1 are analyzed and compared from 8 February 2022 to 17 February 2022. Employing the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-5) data as a reference, both BH and C2E1 RO data agree with the ERA data, with the refractivity, temperature, and specific humidity profiles reflecting the real conditions of the natural atmosphere. In addition, BH data are comparable to C2E1 data at low and middle latitudes (0–45°), and BH data at middle and high latitudes (45–90°) are of better quality than those at low and middle latitudes (0–45°). For example, without considering the errors introduced by the interpolation of the ERA-5 data for comparative analysis, the BH refractivity profiles show a mean absolute bias of 0.73 N at low and middle latitudes and only 0.23 N at middle and high latitudes, and that for BH specific humidity profiles at middle and high latitudes is 0.015 g/kg, which is only half of that at low and middle latitudes. The BH temperature and specific humidity data show promising data accuracy. Therefore, BH RO data may provide important supplementary data at higher latitudes and may improve future NWPs through assimilation.

Water vapour is among the most critical variables that shape the Earth's energy balance and hydrologic cycle. Surface relative humidity (RH) and specific humidity (SH) are the main measures of atmospheric moisture. Long‐term changes in these variables in South Korea vary regionally as well as locally, but have not been explored using long‐term observation data. This study analyzes the annual trends of the means and SD of RH, surface air temperature, and SH in South Korea at 55 stations for the period 1973–2018. Three trend detection tests based on the Mann–Kendall test have been performed to detect trends at the 5% significance level for the annual and monthly statistics (means and SD) of these variables. Significant decreasing and increasing trends have been detected in the annual means of RH and air temperature, while the annual mean of SH has remained nearly constant. Overall, the surface air in South Korea has become drier over the study period, particularly in winter. The trend in RH and SH varies widely according to months to result in the increase in the SD over the annual cycle. The monthly SD of RH, SH, and surface air temperature show especially large positive trends for March and September, when the transition from winter to spring and summer to fall, respectively, occurs. [ABSTRACT FROM AUTHOR]

The marine atmospheric boundary layer (MABL) has a profound impact on sensible heat and moisture exchanges between the surface and the free troposphere. The goal of this study is to develop an alternative technique for retrieving MABL-specific humidity (q) using GNSS-RO data in deep-refracted signals. The GNSS-RO signal amplitude (i.e., signal-to-noise ratio or SNR) at the deep straight-line height (HSL) was been found to be strongly impacted by water vapor within the MABL. This study presents a statistical analysis to empirically relate the normalized SNR (SRO) at deep HSL to the MABL q at 950 hPa (~400 m). When compared to the ERA5 reanalysis data, a good linear q–SRO relationship is found with the deep HSL SRO data, but careful treatments of receiver noise, SNR normalization, and receiver orbital altitude are required. We attribute the good q–SRO correlation to the strong refraction from a uniform, horizontally stratiform and dynamically quiet MABL water vapor layer. Ducting and diffraction/interference by this layer help to enhance the SRO amplitude at deep HSL. Potential MABL water vapor retrieval can be further developed to take advantage of a higher number of SRO measurements in the MABL compared to the Level-2 products. A better sampled diurnal variation of the MABL q is demonstrated with the SRO data over the Southeast Pacific (SEP) and the Northeast Pacific (NEP) regions, which appear to be consistent with the low cloud amount variations reported in previous studies.

Introduction: Based on the research and assessment carried out during the Climate Change Enabling Activity Project under United Nations Framework Convention on Climate Change (UNFCCC) and using the scenarios proposed by IPCC, it is estimated that if the CO2 concentration doubles by the year 2100, the average temperature in Iran will increase by 1.5-4.5°C which will cause significant changes in water resources, energy demand, agricultural products and coastal zones. The present study is aimed to investigate the characteristics of climate change in Iran and some parts of the neighboring countries. Identifying the spatio-temporal changes in three atmospheric variables comprising perceptible water (PW), specific humidity (SH) and vector wind (VW, U and V components) over 1960-2017 was the main themes of the study. Materials and Methods: Monthly values of these variables during wintertime (January to March) were extracted from the CDC/Reanalysis 2/NOAA in 2.5 * 2.5 grids for the period of 1960-2017. The study area locates between 20o to 45o N and 30o to 70o E. After averaging monthly data into seasonal series, as first step, significant changes in the considered series were investigated between two equal periods having 29 years of data (1960-1988 and 1989-2017). In the second step, the 58 years of the study period were divided into five successive decades (1960-2009) and a period with eight years (2010-2017). The Kolmogorov-Smirnov (K-S) field significant test was used for assessing the spatio-temporal difference between the obtained maps associated with various decades. Results and Discussion: According to Figures 1 and 2, for both of the 29-year time-scales (1960-1988 and 1989-2017), PW was maximum (12 to 17 kg/m2) alongside the northern coasts of the Persian Gulf and the Oman Sea. After this, PW had the highest values over the southern coasts of the Caspian Sea (10 to 12 kg/m2). Oppose to these coastal areas, minimum values of this variable with about 6 to 10 kg/m2 were associated with the Zagros mountains. In general, PW exhibited an inverse relationship with elevation. In contrast to PW, SH maximized (4.2 to 5 g/kg) over the Zagros ranges and its relationship with elevation was generally positive. The lowest value of the SH data was about 3.5 g/kg suggesting relatively low variation in the SH data within the country. Compared to the 1960-1988 period, a significant decline was observed in the values of PW and SH in 1989-2017. Although this decline was obvious over all parts of the country, it was slightly significant for the southwestern (northwestern) districts. Compared to the first half of the study period (1960-1989), PW (or SH) decreased by about 2.5 kg/m2 (or 0.6 g/kg) in southwestern and 0.3 kg/m2 (or 0.15 g/kg) in northwestern parts of Iran for the recent half (1989-2017). Differences between wind data during these two time-periods were mostly either northerly or easterly suggesting a significant decrease in the rain-bearing southerly or westerly circulation over 1989-2017. Anomalies of the near-surface wintertime winds were mostly found to be southerly or westerly during 1960-1988 implicating the possibility of moisture transport from the Persian Gulf, the Oman Sea, the Mediterranean Sea, and the Red Sea into the most parts of Iran. Conversely, the anomalies were either northerly or easterly in1989-2017 suggesting less moisture transport into Iran for this recent period. In the decadal time-scale, maximum values of PW, SH, as well as southerly or westerly circulations, were observed during 1960-1969. The given results suggest that the enhanced (or suppressed) values of PW and SH are generally harmonized with the strengthened southerly and westerly (or northerly and easterly) wind anomalies. For this period, prevailing of southeasterly winds over the Caspian Sea enhanced or suppressed the measure of PW, SH over the western or eastern coasts of the Sea, respectively. Even though the mentioned atmospheric circulation patterns were generally similar for the 1960-1969 and 1970-1979 decades, positive anomalies of PW and SH, as well as the westerly and southerly airflows, were slightly suppressed for the second decade. The anomalies of westerly and southerly winds decreased by about one-fifth for 1980-1989 as compared with that in 1960-1969 resulting in a significant decrease in the PW and SH data for this decade. Although these anomalies were slightly positive over most parts of Iran, their weakness did not allow significant improvement in the PW and SH values. The period of 2000-2009 was evaluated as the driest decade of the study period for which the negative anomalies of PW and SH, as well as westerly and southerly circulations, were maximized (in absolute values). In spite of the fact that these undesirable conditions have recovered during the period of 2010-2017, PW and SH were still very low for this recent period. With the exception of the 1990-1999 decade, PW and SH have continuously decreased for the decades after 1970. The rain-bearing southerly and westerly winds have been gradually replaced with dry northerly or easterly wind during the recent periods. Conclusion: The findings showed that the PW and SH distribution patterns are close together in the 29-year periods, the measures were, however, significantly smaller in the second period than in the first. The wind anomalies, which were mostly southerly and westerly in 1960-1988, have been changed to northerly and easterly in 1989-2017. Since the southerly and westerly winds play an influential role in moisture transfer to Iran, their reduction in the second period is consistent with the observed decrease in PW and SH. Among the ten-year periods, the highest positive PW and SH abnormalities are associated with the 1960 and 1969 decade. This positive anomaly decreased over the time. Since a positive trend is observed for 2010-2017, it can be concluded that 2000-2010 is the driest decade of the study period. The positive anomalies of westerlies (easterlies) and southerlies (northerlies) increased (decreased) the magnitudes of PW and SH. [ABSTRACT FROM AUTHOR]

This study proposed that due to their high standing water tables that peatlands would be cold humid islands within their landscape, and especially so relative to farmland on mineral soils. To test this hypothesis, we measured air temperature and humidity at 17 locations along a 7.8 km transect across the UK's largest lowland raised bog from February 2018 to January 2019. Air temperature and humidity were measured hourly for 1 year and supported with spot albedo measurements. The study represented a factorial experiment with respect to sites of measurement, the type of land use (peat vs. arable land) and time of sampling over both the seasonal and diurnal cycles. We show that: (a) That although mean annual temperature was not significantly different between arable and peatlands, the arable land showed a decreased amplitude to its seasonal cycle – this is the reverse of the expected pattern. (b) The albedo of the peatland was significantly lower than that of arable land showing that vegetated peatland still absorbed more solar radiation. (c) The specific humidity was lower on the peatland than on the surrounding arable land. The study showed that while shrubby vegetation exists over a peatland then energy budgets are more likely to be dominated by the lower aerodynamic resistance and lower albedo of the vegetated peatland relative to arable land. Thus, shrub‐dominated peatlands will not be a cold humid island in their landscape. [ABSTRACT FROM AUTHOR]

The tropical cyclones (TCs) frequently occur in the North Atlantic Ocean Basin, which is adjacent to West Africa, the largest global source of atmospheric dust. However, few studies have conducted systematic observational research of how dust affects the genesis conditions of TCs at large scales which includes sea surface temperature (SST), vorticity, vertical wind shear, and specific humidity. This study focused on the period from June–September in the years 2000 to 2018 to investigate the horizontal and vertical distributions of aerosol optical depth (AOD) (dust) and meteorological parameters. Dust can be transported at 600 hPa upward and is mixed well within the troposphere over land, while it is mainly distributed in the lower troposphere over the ocean. The SST is significantly suppressed by dust due to direct radiation effects, but the atmospheric temperature is warmer at 20–40°W between 700 and 850 hPa. The vertical distributions of temperature and specific humidity are similar. Dust decreases specific humidity in the lower troposphere over the ocean, especially in high AOD regions, but enhances midlevel moisture. Dust heats the lower troposphere and favors the development of convection and positive vorticity at heights of approximately 800–1,000 hPa. The warming effect of dust on the lower atmosphere over land and the nearby oceans results in strengthened West African monsoons and vertical wind shear. Thus, dust suppresses the SST and low‐level specific humidities and favors wind shear and positive relative vorticity, which further influence environmental conditions in the TC genesis region. Key Points: The effects of dust on the TC genesis environment are investigated by examining the changes of TC‐related meteorological variables at large scalesDust suppresses SSTs and low‐level humidities, enhances midlevel moisture, and favors wind shear and positive relative vorticityThe influence of dust on the TC‐related meteorology occurs in the troposphere and is most evident at altitudes between 700 and 850 hPa [ABSTRACT FROM AUTHOR]

Based on the atmospheric temperature and dew point temperature difference series of mandatory levels in the arid region of northwest China, we calculated the specific humidity of stations at 200, 300, 400, 500, 700, and 850 hPa and analyzed the spatial and temporal distribution. The specific humidity of radiosonde is compared with two sets of reanalysis data (ERA-interim from European Centre for Medium Range Weather Forecasts and Modern Era Retrospective Analysis for Research and Applications: MERRA-2). The annual specific humidity and summer specific humidity show a positive trend in the vertical atmospheric levels during the period 1958–2018. Taking the middle of the 1980s and 2002 as boundaries, the selected levels show the trend of “declining-gentle rising-fluctuation rising”. The maximum specific humidity is observed at the level of 850–700 hPa during the warm months of the year, and the most vertical expansion in specific humidity is in July. In terms of spatial distribution, the specific humidity is greatly influenced by the topography and underlying surface at lower levels. The characteristics of spatial distribution of the trend are well described by the two sets of reanalysis data in the middle and upper levels, but there are some deficiencies in depicting the trend in the lower levels.

In this study, the variation and trend of specific humidity (SH) of the troposphere (1,000–500 hPa) over Iran was analysed using the monthly European Center for Medium Range Weather Forecasting (ECMWF) Re‐Analysis Interim (ERA‐Interim) gridded data from January 1979 to December 2016. By using nonparametric modified Mann–Kendall test, the trend of values for each gridded point was tested in eight different atmospheric levels at 95% confidence level. The Sen's slope estimator test was used to estimate the change rate. The findings showed that the annual trend of SH is decreasing in most of Iran and is only increasing on the northern and southern coast of the country. The highest increasing trend of the SH is observed on the southern coast of Iran in 1,000 hPa. The regression line fitting on the standardized time series of Iran's area average SH showed that the highest decreasing rate occurred in the first layer (1,000–850 hPa) and only the third layer (600–500 hPa) has had a significant increase of SH trend over Iran. Area average annual anomaly of the tropospheric cross sections indicates that the studied period is divided into two periods: a wet period (1979–1998) and a dry period (1999–2016). [ABSTRACT FROM AUTHOR]

A new boundary-layer method is proposed to estimate sensible and latent heat fluxes on a monthly scale, based on hourly surface observations of temperature and specific humidity, as well as their vertical profile in the morning. It assumes that advective effects may be neglected over such a time scale, so that temporal tendencies of temperature and specific humidity are controlled solely by the vertical flux convergence over the mixed layer. The growth of the mixed layer in the model is driven by the sensible heat flux and opposed by the mean thermal stratification observed by upper-air soundings over that month. The method is tested for three sites, where the flux estimates are compared to eddy-covariance observations. No filtering of days based on synoptic condition, cloudiness or other external conditions is applied, providing realistic monthly estimates. In the three cases, the flux estimates approach closely the eddy-covariance observations, indicating that the method may be applied to estimate the fluxes at places where only weather station data are available. [ABSTRACT FROM AUTHOR]

Abstract The effects of humidity, wind, and InterTropical Discontinuity (ITD) movement on seasonal distribution of atmospheric aerosols were assessed over different ecological zones in Nigeria. Satellite-observed aerosol optical depth (AOD), humidity, wind speed, and precipitation/ITD data were used. The Moderate Resolution Imaging Spectroradiometer (MODIS) AOD time series of dataset were used. The MODIS AOD retrievals were at the wavelength of 550 nm and AOD data was re-scaled and sub-divided into seasonal and annual distributions to investigate the variations in Aerosol. Kriging spatial interpolation model was used to analyze the aerosol seasonal distribution. Correlations analysis was used to evaluate the degree of influence of humidity, wind speed, and precipitation/ITD on the seasonal distribution of aerosol over six ecological zones; Sahel, Sudan, Guinea, Rainforest, Freshwater, and Mangrove zones in Nigeria. The results show that the AOD over Nigeria is influenced by meteorological factors, but much more influenced by dust source outside the country. AOD appears much more during Harmattan season than Wet and Dry seasons; with AOD ≥0.46, with considerable concentration in Sahel ecological zone than other ecological zones. The results show a strong significant relationship between aerosol distribution and meteorological, principally humidity with R2 ≥ 0.65 @ p < 0.05. The study reveals that for daily variation of AOD, wind speed, humidity and precipitation as well as spatial distribution of dust source in and outside the country are important drivers. Highlights • Influence of humidity, wind and ITD on atmospheric aerosols distribution were examined. • MODIS Terra time series of dataset were used. • Aerosol distributions was extraordinary in Harmattan season. • Much more atmospheric aerosols concentration in Sahel compared to other ecological zone. [ABSTRACT FROM AUTHOR]

This study investigated the feasibility of partitioning the available energy between sensible (H) and latent (LE) heat fluxes via variational assimilation of reference-level air temperature and specific humidity. For this purpose, sequences of reference-level air temperature and specific humidity were assimilated into an atmospheric boundary layer model (ABL) within a variational data assimilation (VDA) framework to estimate H and LE. The VDA approach was tested at six sites (namely, Arou, Audubon, Bondville, Brookings, Desert, and Willow Creek) with contrasting climatic and vegetative conditions. The unknowns of the VDA system were the neutral bulk heat transfer coefficient (CHN) and evaporative fraction (EF). EF estimates were found to agree well with observations in terms of magnitude and day-to-day fluctuations in wet/densely vegetated sites but degraded in dry/sparsely vegetated sites. Similarly, in wet/densely vegetated sites, the variations in the CHN estimates were found to be consistent with those of the leaf area index (LAI) while this consistency deteriorated in dry/sparely vegetated sites. The root mean square errors (RMSEs) of daily H and LE estimates at the Arou site (wet) were 25.43 (Wm−2) and 55.81 (Wm−2), which are respectively 57.6% and 45.4% smaller than those of 60.00 (Wm−2) and 102.21 (Wm−2) at the Desert site (dry). Overall, the results show that the VDA system performs well at wet/densely vegetated sites (e.g., Arou and Willow Creek), but its performance degrades at dry/slightly vegetated sites (e.g., Desert and Audubon). These outcomes show that the sequences of reference-level air temperature and specific humidity have more information on the partitioning of available energy between the sensible and latent heat fluxes in wet/densely vegetated sites than dry/slightly vegetated sites.

A theoretical model is developed to simulate the convective air-drying process of an unsaturated porous plate using the representative elementary volume (REV) approach. The model considers a variety of transport mechanisms and uses the specific humidity (mass fraction) as the convective mass transfer driving potential, which is thought to suit for modeling of non-isothermal water evaporation into air fluid. The partial differential equations included in the model are discretized and solved fully implicitly using the predicator-corrector method. Calculations are performed with two water vapor concentrations including the specific humidity and vapor density as the mass transfer driving potential to clarify how the potential selection will affect the drying characteristics. Calculations are performed for plate thickness of 15 mm and air temperatures of 320.15, 333.15 and 348.15 K. The results show that use of the vapor density as the driving potential causes underestimations of the wet surface temperature and plate moisture content, and this tendency becomes more conspicuous for a lower air temperature. It is recommended to use the specific humidity as the mass transfer driving potential to better describe the moisture and heat transfer during the convective drying of an unsaturated porous medium. [ABSTRACT FROM AUTHOR]