Surface Dew Point Temperature Research Articles

Impact of Surface Dew Point Temperature, Precipitable Water and the Lifted Index on the Precipitation over Hyderabad (India).

In this manuscript, we analyze some significant atmospheric parameters relating to precipitation over Hyderabad. For that purpose, we study the relationships between dew point temperature, precipitable water, lifted index with precipitation and the correlation between these parameters. Our analysis includes interpolation, correlation, and regression. For the ten-year average of monthly mean data, the correlation coefficient of dew point temperature with precipitable water is 0.95, the lifted index with precipitable water is (-0.82), the precipitable water with precipitation is 0.96, the lifted index with precipitation is (-0.69). For complete time series monthly mean data, the correlation of dew point temperature with precipitable water is 0.83, the lifted index with precipitable water is (-0.74), the precipitable water with precipitation is 0.78, lifted index with precipitation is (-0.51). Thus, there is positive correlation between some parameters, while negative correlation between others. We have also noticed more precipitation when the precipitable water values range from 40 mm to 60 mm and when the LI is more negative. The degree of relationship between dew point temperature and natural logarithm of Precipitable Water was excellent over Hyderabad and a regression equation relating the two parameters was computed. The probability of precipitation and severe weather occurrence could be identified along with Td, PW and LI. Thus, there is a possibility that LI, Td and PW can be potential parameters to measure the occurrence of precipitation events.

Aerosol invigoration effect in Guilin (China)

AbstractThe data of lightning flash count, rainfall, radar reflectivity, vertical wind shear (WS), surface dew point temperature (DP) and particulate matter up to 10 μm in size (PM10) over Guilin, China from July 2010 to December 2019 were studied to check whether aerosol invigoration effect (AIV) exists in the study area. It was found that convective rainfall fluctuates less when compared with lightning in convective system. A hypothesis was put forward that the difference in fluctuations between convective rainfall and lightning is attributed to AIV. To test this hypothesis, lightning yield, which is defined as the ratio between lightning and rainfall, was analyzed. It was found that lightning yield has a positive correlation with PM10 when WS is low and DP is high for convective precipitation. It was also found that for the weak WS cases, when aerosol conditions are shifted from super pristine to the optimal concentration (Nop), lightning yield increases with increasing PM10; whereas for concentrations greater than Nop, lightning yield decreases with increasing PM10. Nop would be larger for higher DP. The results are in line with the previous studies showing that AIV depends strongly on weak wind shear and/or warm cloud base. This suggests that AIV exists in the study area, and suggests that the hypothesis is reasonable, and lightning yield can be used as a surrogate to study AIV.

Retrospective on the resource for radiative cooling

The history of quantitative measurements of radiative cooling is briefly reviewed, starting with Count Rumford in 1804. The cooling results from upward emission of thermal infrared radiation (wavelengths of 5 to 50 μm) that is not fully offset by downward atmospheric emission. The downward emission is characterized by the apparent atmospheric (sky) emittance and the surface air temperature. In 1984, an equation was published that describes the clear sky emittance as a function of the surface dew point temperature. At the time, this equation was merely one of many empirical relations. Now that time has passed, experimental and theoretical advances support its validity. Further refinements can include improved corrections for time-of-day and the lower air pressure at elevated locations. Complex computer codes for predicting atmospheric radiation have reached quantitative maturity. Given profiles of air temperature, water vapor, CO2, O3, CH4, N2O, and aerosols, they can compute spectral radiances with an accuracy of ∼3 % . The effect of clouds in reducing radiative cooling remains more uncertain.

Relationship Between Surface Dew Point Temperature and Satellite Based Total Water Vapor Content over North Indian Ocean

The dew point temperature is related to the total water vapor content available in the atmosphere column. In this study, Water Vapor Content (WVC) from Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Relative humidity from Research Moored Array for African-Asian-Australian Monsoon Analysis (RAMA) buoy data has been utilized to make a relationship between satellite measured WVC and Dew point temperature. This study focuses on the development of an algorithm to estimate the surface dew point temperature from satellite-based WVC. Regression coefficients are established using 9-years (2004-2012) data of Dew point Temperature computed from Relative humidity and satellite measured WVC. 1594 data points are observed weekly, mean monthly collocated data points are considered to examine the relationship between Dew point temperature and WVC.

The Response of Daily and Sub‐Daily Extreme Precipitations to Changes in Surface and Dew‐Point Temperatures

AbstractExtreme precipitation events are expected to increase in frequency and intensity in the future climate, but the magnitude of these changes remains uncertain. The relationship between extreme precipitation and the surface temperature has been investigated to more robustly assess projected increases in extreme precipitation considering that projected temperature is more adequately simulated. Relationships between extreme precipitation (daily and sub‐daily) and surface air temperature (SAT) or surface dew‐point temperature (SDPT) are analyzed in this study using the 50‐members ensemble from the fifth version of the Canadian Regional Climate Model covering the Northeastern North America region over the period 1956–2099. Temperature‐precipitation scaling rates (TPSRs) were estimated using local SAT and SDPT seasonal anomalies as covariate over both periods for 2–100‐year extreme precipitation events and durations ranging from 1 to 24 h. Contrasting responses were obtained when using SAT or SDPT, especially in the southern part of the domain. Median scaling rates over the entire domain for SDPT were close to the Clausius‐Clapeyron scaling (°C) while they were much smaller for SAT and even negative in southern regions, showing that moisture availability is a key factor for these regions. TPSR based on SDPT is also more robustly constrained and can be used to estimate changes in short‐duration extreme precipitation in a future period from TPSR in the historical period over a large part of the domain.

The Impact of Assimilating GPS Precipitable Water Vapor in Convective-Permitting WRF-ARW on North American Monsoon Precipitation Forecasts over Northwest Mexico

AbstractWe assess the impact of GPS precipitable water vapor (GPS-PWV) data assimilation (DA) on short-range North American monsoon (NAM) precipitation forecasts, across 38 days with weak synoptic forcing, during the NAM GPS Hydrometeorological Network field campaign in 2017 over northwest Mexico. Utilizing an ensemble-based data assimilation technique, the GPS-PWV data retrieved from 18 observation sites are assimilated every hour for 12 hours into a 30-member ensemble convective-permitting (2.5 km) Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model. As the assimilation of the GPS-PWV improves the initial condition of WRF by reducing the root mean square error and bias of PWV across 1200-1800 UTC, this also leads to an improvement in capturing nocturnal convection of mesoscale convective systems (MCSs; after 0300 UTC) and to an increase by 0.1 mm h-1 in subsequent precipitation during the 0300-0600 UTC period relative to no assimilation of the GPS-PWV (NODA) over the area with relatively more observation sites. This response is consistent with observed precipitation from the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement Final Precipitation product. Moreover, compared to the NODA, we find that the GPS-PWV DA decreases cloud top temperature, increases most unstable convective available energy and surface dewpoint temperature, and thus creates a more favorable condition for convective organization in the region.

Effect of warming climate on extreme daily rainfall depth using non-stationary Gumbel model with temperature co-variate

Abstract In this study, non-stationary frequency analysis was carried out to apply non-stationarity of extreme rainfall driven by climate change using the scale parameter of two parameters of the Gumbel distribution (GUM) as a co-variate function. The surface air temperature (SAT) or dew-point temperature (DPT) is applied as the co-variate. The optimal model was selected by comparing AICs, and 17 of 60 sites were found to be suitable for the non-stationary GUM model. In addition, SAT was chosen as the more appropriate co-variate among 13 of the 17 sites. As a result of estimating changes in design rainfall depth with future SAT rises at 13 sites, it is likely to increase by 10% in 2040 and 18% in 2070.

An Improved Covariate for Projecting Future Rainfall Extremes?

AbstractProjection of extreme rainfall under climate change remains an area of considerable uncertainty. In the absence of geographically consistent simulations of extreme rainfall for the future, alternatives relying on physical relationships between a warmer atmosphere and its moisture carrying capacity are projected, scaling with a known atmospheric covariate. The most common atmospheric covariate adopted is surface air temperature, as it exhibits great consistency across climate model simulations into the future and, as per the Clausius‐Clapeyron relationship, has a well‐established link to atmospheric moisture capacity. However, empirical assessments of this relationship show that it varies with latitude, surface temperature, atmospheric temperature, and other factors, suggesting there may be more stable “global” atmospheric covariates that could be used instead. We argue that a better‐suited covariate would be one that captures the relationship between extreme rainfall and temperature but exhibits greater consistency in the relationship across regions as well as climatic zones. Our analysis identifies plausible atmospheric indicators of changes to future extreme rainfall, which now proliferate literature and compare their suitability based on the variability they exhibit across multiple geographical, topographic, and climatic zones within Australia. It is shown that surface air temperature exhibits a regionally inconsistent relationship with extreme rainfall and hence is not suitable for projecting to future conditions. The study identified integrated water vapor and surface dew point temperature as promising alternatives, with the former showing greater consistency in space but at the cost of reduced temporal coverage.

A multiscale analysis of the tornadoes of 30–31 May 2019 in south-central Chile

Abstract On 30 and 31 May 2019, tornadoes occurred in the cities of Los Angeles and Talcahuano/Concepcion in south-central Chile, in a region where tornado activity is not common. The main goal of this study was to analyze these tornadoes across multiple scales: synoptic, mesoscale, and subseasonal. On the synoptic scale, the tornadoes were associated with an anomalous 500-hPa trough and associated surface cyclone to the west of Chile. A strong (20+ m s−1) low-level jet accompanied this trough, potentially enhanced by flow blocking by the Andes. A relatively warm and saturated surface layer combined with cold upper-level temperatures in the trough to yield 200–500 J kg−1 of CAPE on both days. This CAPE was accompanied by high levels of both deep-layer and low-level shear. Storm motions inferred by lightning swaths and GOES-IR imagery, along with estimates of storm motion and updraft helicity from a high-resolution WRF simulation, suggested this CAPE-shear combination was sufficient for the tornadic thunderstorms to be supercells. Finally, anomalies of sea level pressure, 500-hPa height, and surface dew point temperature from 27 to 31 May 2019 resembled long-term composite anomalies for MJO phases 1 and 2, suggesting a subseasonal link between the extreme event in Chile and convection in the tropics.

The relationship of atmospheric air temperature and dew point temperature to extreme rainfall

To understand the expected changes of extreme rainfalls due to climate change, the sensitivity of rainfall to surface temperature is often calculated. However, as surface temperatures may not be a good indicator of atmospheric moisture, an alternative is to use atmospheric temperatures, but the use of atmospheric temperatures lacks precedent. Using radiosonde atmospheric temperature data at a range of geopotential heights from 34 weather stations across Australia and its territories, we examine whether atmospheric temperature can improve our understanding of rainfall-temperature sensitivities. There is considerable variability in the calculated sensitivity when using atmospheric air temperature, while atmospheric dew point temperature showed robust positive sensitivities, similar to when surface dew point temperature measurements were used. We conclude atmospheric dew point temperature may be a promising candidate for future investigations of empirically calculated sensitivities of rainfall to temperature but does not appear superior to the use of surface dew point temperature measurements.

Contrasting the responses of extreme precipitation to changes in surface air and dew point temperatures

The Clausius–Clapeyron (C–C) relationship is a thermodynamic relationship between saturation vapor pressure and temperature. Based on the C–C relationship, the scaling of extreme precipitation with respect to surface air temperature (i.e., extreme precipitation scaling) has been widely believed to quantify the sensitivity of these extremes to global surface warming under climate change. However, the extreme precipitation scaling rate in the observations produces counter-intuitive results, particularly in the tropics (i.e., strong negative scaling in the tropical land) possibly associated with limitations in moisture availability under the high-temperature bands. The trends in extreme precipitation based on station data are mixed with decreases in most of the tropics and subtropics and increases in most of the USA, western Europe, Australia, and a large portion of Asia. To try to reconcile these results, we examine the extreme precipitation scaling using dew point temperature and extreme precipitation and compare these results with those obtained from surface air temperature and extreme precipitation using station-based data, reanalysis data, and climate model simulations. We find that this mix of increases and decreases in the trends of extreme precipitation across the planet is more similar to the changes in surface dew point temperature rather than the actual temperature across the station-based data, reanalysis data, and the historical experiments with the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5 (CAM5). These findings suggest that dew point temperature is a better and more realistic metric for the responses of extreme precipitation to temperature increases. Therefore, the risk of having extreme precipitation is higher than what was obtained using surface air temperature, particularly in the tropics and subtropics (e.g., South Asia), areas of the world characterized by extremely high population density and severe poverty.

Variations of Thunderstorm Charge Structures in West Texas on 4 June 2012

AbstractThis study documents an environment for which small changes therein significantly impacted electrification and for which current theories of electrification lacked the ability to discriminate storm polarity. Thirty single‐cell and multicell storms from 1900 to 2200 UTC on 4 June 2012 over a 150‐ by 100‐km West Texas region were examined. Some of these storms had anomalous charge structures (primarily positive charge in the midlevels at −10 °C to −30 °C or 6.3 to 8.8 km above MSL locally) and some normal (primarily negative at midlevels), even though they existed concurrently and did not statistically differ in overall flash sizes, flash rates, radar volume, or echo top height. Overall, the normal storms ingested lower equivalent potential temperature surface air and were estimated to experience lower convective available potential energy than the anomalous storms, as observed in other studies. They were, however, estimated to have smaller warm cloud depth and surface dew point temperatures, contrary to expectations. Significant overlap between the storm environments suggested that lower instability may have contributed to some storms becoming normally electrified, but it was not a sufficient condition. Additionally, there had been previous convection in the region dominated by normal‐polarity storms. A Weather Research and Forecasting ensemble suggested that the previous convection moistened the midlevels of the atmosphere near cloud base. We propose that future studies investigate dry‐air entrainment as an additional, intertwined environmental factor that could decrease droplet sizes and effective warm rain processes, promoting positive graupel charging in the midlevels and anomalous charge structures.

Multi-technique analysis of precipitable water vapor estimates in the sub-Sahel West Africa

Precipitable water vapor (PWV) is an important climate parameter indicative of available moisture in the atmosphere; it is also an important greenhouse gas. Observations of precipitable water vapor in sub-Sahel West Africa are almost non-existent. Several Aerosol Robotic Network (AERONET) sites have been established across West Africa, and observations from four of them, namely, Ilorin (4.34° E, 8.32° N), Cinzana (5.93° W, 13.28° N), Banizoumbou (2.67° E, 13.54° N) and Dakar (16.96° W, 14.39° N) are being used in this study. Data spanning the period from 2004 to 2014 have been selected; they include conventional humidity parameters, remotely sensed aerosol and precipitable water information and numerical model outputs. Since in Africa, only conventional information on humidity parameters is available, it is important to utilize the unique observations from the AERONET network to calibrate empirical formulas frequently used to estimate precipitable water vapor from humidity measurements. An empirical formula of the form PWV=aTd+b where Td is the surface dew point temperature, a and b are constants, was fitted to the data and is proposed as applicable to the climatic condition of the sub-Sahel. Moreover, we have also used the AERONET information to evaluate the capabilities of well-established numerical weather prediction (NWP) models such as ERA Interim Reanalysis, NCEP-DOE Reanalysis II and NCEP-CFSR, to estimate precipitable water vapor in the sub-Sahel West Africa; it was found that the models tend to overestimate the amount of precipitable water at the selected sites by about 25 %.

Relationship of extreme precipitation, dry-bulb temperature, and dew point temperature across Australia

Precipitation extremes are expected to intensify due to an increased moisture holding capacity in the atmosphere with higher temperatures; according to the Clausius–Clapeyron (CC) relation this increase is approximately 7% for every degree increase in temperature. Contrary to expectation, the relationship between precipitation extremes and surface temperature often differs from 7%/°C. Here, we explore this relationship further by estimating the sensitivity of precipitation with both dry-bulb temperature and dew point temperature across Australia.A much better correspondence to the CC relation is obtained when surface dew point temperature is used for the calculation of precipitation-temperature sensitivities instead of surface dry-bulb temperature with most sites exhibiting sensitivities close to, or in excess of, the CC relation. The sensitivity obtained using dew point temperature is more consistent across climatic region, precipitation duration, and precipitation percentile. We conclude that dew point temperature is a better measure of precipitation changes due to increases in atmospheric moisture than dry-bulb temperature.

Severe weather over the Highveld of South Africa during November 2016

November months are notorious for severe weather over the Highveld of South Africa. November 2016 was no exception and a large number of severe events occurred. Very heavy rainfall, large hail and tornadoes were reported. The aim of this paper is to compare the synoptic circulation of November 2016 with the long-term mean November circulation and to investigate some sounding derived parameters. Furthermore, a few of the severe weather events are described in detail. The surface temperatures and dewpoint temperatures were found to be higher than normal resulting in increased conditional instability over the Highveld. Low-level moisture originated over the warm Mozambique Channel and the 500 hPa temperature trough was located favourably over the Highveld; further east than normal. The combination of these factors and weak steering winds resulted in flash flooding on the 9th while favourable wind shear conditions caused the development of a tornado on 15 November. The favourable circulation patterns and moisture gave rise to an atmosphere in which severe weather was a possibility, and the awareness of such factors is used as one of many tools when considering the severe weather forecast. The consideration of the daily variables derived from sounding data were good precursors for the prediction of severe thunderstorm development over the Highveld during November 2016. It is recommended that an operational meteorologist incorporates upper air sounding data into the forecasting process and not to rely on numerical prediction models exclusively.

Investigation of factors affecting condensation on soiled PV modules

Condensation contributes to soiling of photovoltaic modules by trapping dust particles and, in certain conditions, leaving a material bridge between particles and the surface after evaporating. This study investigated the effects of four parameters on condensation on soiled surfaces: (i) relative humidity (RH), (ii) surface–dew point temperature difference, (iii) hygroscopic dust content, and (iv) surface wettability. Natural and synthetic dust mixtures of various compositions were studied via water adsorption isotherms, XRD, ion chromatography and optical microscopy, on hydrophilic and hydrophobic surfaces, in the lab and field. It was found that water uptake by surface dust was strongly dependent on its content of hygroscopic material, and such material allowed microscopic condensation droplets to exist on a soiled glass coupon even when it was significantly warmer than the dew point. A hydrophobic PTFE surface did not greatly retard the onset of condensation, compared to a glass surface, but did inhibit its growth. The implications for anti-soiling coatings are that it would be a difficult goal to eliminate condensation, and their performance will be influenced by dust composition and factors affecting condensation run-off such as RH and tilt angle. Variation in such parameters may partly explain inconsistent results from coating field trials reported so far.

Super-Clausius–Clapeyron Scaling of Extreme Hourly Convective Precipitation and Its Relation to Large-Scale Atmospheric Conditions

AbstractPresent-day precipitation–temperature scaling relations indicate that hourly precipitation extremes may have a response to warming exceeding the Clausius–Clapeyron (CC) relation; for the Netherlands the dependency on surface dewpoint temperature follows 2 times the CC relation (2CC). The authors’ hypothesis—as supported by a simple physical argument presented here—is that this 2CC behavior arises from the physics of convective clouds. To further investigate this, the large-scale atmospheric conditions accompanying summertime afternoon precipitation events are analyzed using surface observations combined with a regional reanalysis. Events are precipitation measurements clustered in time and space. The hourly peak intensities of these events again reveal a 2CC scaling with the surface dewpoint temperature. The temperature excess of moist updrafts initialized at the surface and the maximum cloud depth are clear functions of surface dewpoint, confirming the key role of surface humidity on convective activity. Almost no differences in relative humidity and the dry temperature lapse rate were found across the dewpoint temperature range, supporting the theory that 2CC scaling is mainly due to the response of convection to increases in near-surface humidity, while other atmospheric conditions remain similar. Additionally, hourly precipitation extremes are on average accompanied by substantial large-scale upward motions and therefore large-scale moisture convergence, which appears to accelerate with surface dewpoint. Consequently, most hourly extremes occur in precipitation events with considerable spatial extent. Importantly, this event size appears to increase rapidly at the highest dewpoint temperature range, suggesting potentially strong impacts of climatic warming.

Mold Issue in Details within the External Walled Structure

Article deals with the issue of mold in masonry structures. Attention was focused on the critical detail at expansion joint. Variants of solved detail are focused on the process of surface temperatures in the structure. This detail needs to be solved because of revitalization of the structure. Isotherms of the critical inner surface temperature and dew point temperature were used for the evaluation of the variants.

The Relative Roles of the Ocean and Atmosphere as Revealed by Buoy Air–Sea Observations in Hurricanes

Abstract Results from this multihurricane study suggest that the criticality of the oft-cited 26°C hurricane threshold linked to hurricane maintenance may be more closely associated with atmospheric thermodynamic conditions within the inner core than previously believed. In all cases, a positive sea–air contrast was observed within the storm inner core (i.e., surface ocean temperature greater than surface air temperature), despite the fact that 6% of the hurricanes exhibited sea surface temperatures (SSTs) less than the 26°C. For the storms sampled in this study, inner-core surface dewpoint temperatures never exceeded 26.5°C. This finding may provide an alternate explanation as to the criticality of the 26°C threshold since SSTs above 26°C would, in almost all instances, be associated with a positive enthalpy flux condition. Analyses from this study also illustrate that high wind SSTs fluctuate as a function of storm latitude, while inner-core near-surface dewpoint temperatures are much less sensitive to this parameter. As a result, and assuming all other factors to be equal, low-latitude hurricanes would, on average, be expected to experience surface moisture fluxes ~1/3 greater than storms located farther to the north. For systems sampled within the deep tropics, inner-core SST was found to fluctuate much less than surface dewpoint temperature, suggesting that the atmosphere, not the ocean, is more likely to influence the key thermodynamic parameter controlling surface moisture flux for this subset of hurricanes.

Estimation of leaf wetness duration for a short-grass surface

The measurement of leaf wetness duration (LWD) was investigated using subhourly dielectric, infrared surface temperature, dewpoint temperature, grass temperature and relative humidity (RH) measurements. Near real-time LWD data and information displays and alerts were made available timeously via a web-based system. LWD was estimated above a short-grass surface using five methods: dielectric leaf wetness sensors (LWS); a constant RH for which wetness events were registered for RH greater than 87%; RH between 70–87% if RH increased by more than 3% in 30 min; and two dewpoint depression-based methods for which surface-measured temperature, using an infrared thermometer (IRT), and grass temperature were compared with the dewpoint at either 0.1 or 2 m. The RH methods generally overestimated LWD compared to the other methods. There was reasonable agreement between IRT- and grass-temperature methods if rain days were excluded but these methods showed poor agreement with LWS measurements of LWD. Microclimatic and radiative conditions, during nocturnal condensing events, are reported. Automatic weather station data would have more value if grass temperature was included for determination of LWD by comparison of grass temperature with a measured dewpoint, with timeous alerts and web-based display of near real-time LWD data and graphics.