Surface Dew Point 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.

Analyzing uncertainty in probable maximum precipitation estimation with large ensemble climate simulation data

AbstractThis study aimed to evaluate probable maximum precipitation (PMP) estimated using surface dew points (SDP) or actual precipitable water obtained from upper‐air data (UAD) in the moisture‐maximization method with the help of sufficient extreme precipitation events using large‐scale climate ensemble simulation data (d4PDF). The deviations between the PMP variables estimated by the SDP and UAD approaches were analyzed for southern and northern areas of Japan to consider the regional characteristics of the deviations. We found that the deviations were high in northern areas where the SDPs are relatively low during precipitation events. The PMPs estimated using each approach were also compared to the extreme‐scale reference precipitation proposed in this study. The SDP approach overestimated the PMPs by over 20% compared to the reference precipitation in the northern region. However, the UAD approach showed very low average errors in all southern and northern areas. This tendency of the SDP approach was significantly related to the regional climatic characteristics of the SDP, which indicated that the SDP approach may estimate an uncertain PMP value depending on each regional climatic characteristic compared to the UAD approach. Regional climatic characteristics should be considered when using the SDP approach to estimate the PMP.

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.

A Significant Tornado in a Heterogeneous Environment During VORTEX-SE

On 1 March 2016, an EF2 tornado occurred near Birmingham, AL, and was examined as part of VORTEX-SE. The boundary-layer environment near the tornadic supercell was heterogeneous in space and unsteady in time, with what typically would be considered an excellent proximity sounding. In this case, however, the proximity sounding severely underestimated the CAPE. SPC mesoanalyses substantially underestimated the CAPE and wind shear as well. Tornadogenesis occurred near a weak, frontogenetical thermal boundary, where evaporation from antecedent light showers had also increased dewpoint values. A local maximum in surface dewpoint (and instability), and a local maximum in helicity both existed near the region of frontogenesis. As a QLCS moved into the region of higher CAPE air, part of it became supercellular. Tornadogenesis occurred near the local maximum in surface dewpoint.

Multiscale Analysis of the 1 June 2011 Northeast U.S. Severe Weather Outbreak and Associated Springfield, Massachusetts Tornado

On 1 June 2011, the 12th killer tornado in New England since 1950 tracked 63 km (39 mi) from Westfield to Charlton, MA resulting in 3 fatalities, 200 injuries, and EF3 damage. At least fourteen supercells produced six confirmed tornadoes and six hail reports ≥7 cm (≥2.75 in) in diameter across eastern New York and New England. This paper takes a multiscale look at meteorological factors contributing to this event. The synoptic pattern evolution closely resembles the composite mean shown by Banacos and Ekster (2010) for significant severe weather events in the northeast United States associated with an elevated mixed layer (EML). The presence of an EML and rich boundary-layer moisture (surface dewpoints 20-22oC) supported surface-based CAPE >4000 J kg-1 by early afternoon on 1 June. A strengthening prefrontal trough within the moist and unstable boundary layer, together with increasing low and deep-layer shear created an environment favorable for tornadic supercells. In particular, storms moved into an environment with increasing values of 0-1-km AGL bulk shear, increasing storm relative helicity, and lower lifted condensation level heights. Values of these parameters were largely consistent with significant-tornado occurrence in proximity studies. Tornadic signatures in WSR-88D and experimental CASA 3-cm dual-polarization radar data are described, in addition to a remarkable three-body scatter spike associated with lofted debris near peak apparent intensity of the EF3 tornado.

Long-Lived Tornadic Supercell over Colorado and Wyoming, 22 May 2008

On 22 May 2008, a slow-moving, meridional trough led to widespread severe weather across the Great Plains, Front Range Urban Corridor of Colorado and Laramie Mountains of Wyoming. The most damaging storm developed near the Denver International Airport and quickly became tornadic. A large tornado occurred with this storm that was responsible for EF3 damage in the town of Windsor, CO. After some weakening, the storm intensified and produced large hail and at least one tornado from the Wyoming-Colorado border northwestward to Laramie, WY. As the storm moved through differing elevations (4700 to 8700 ft (1430 to 2650 m), it also encountered markedly different meteorological environments, making this tornadic event particularly interesting and rare. In addition to the official Storm Data, this study will provide supplementary storm documentation based on accounts of local residents. The key synoptic and mesoscale features as well as shear and instability parameters are presented, with an emphasis on observational data.
 Additionally, in order for forecasters to gain an understanding of the high-elevation severe storm environment, a comparison is made with relatively low-elevation environments. The importance of assessing the contributing factors to equivalent potential temperature is demonstrated. Recommendations are made for forecasting severe weather at high-elevation locations. Analysis of equivalent potential temperature is critical when assessing surface data over high-elevation areas, rather than arbitrary judgment (i.e., “it’s too cold”) based on surface temperature and dewpoint.

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 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.

Analyzing Uncertainty in Probable Maximum Precipitation Estimation With Pseudoadiabatic Assumption

AbstractThis study aimed to evaluate a probable maximum precipitation (PMP) estimation approach using a moisture‐maximization method. This method enables the estimation of precipitable water (PW) using a surface dew point, under a pseudoadiabatic assumption. However, the deviation of the PW (as estimated using the surface dew point) from the actual observed PW mostly leads to an uncertain PMP estimation, as it is difficult to estimate the actual atmospheric moisture content in an air column using the surface dew point alone. In this study, to consider abundant atmospheric data spanning a long‐term period, we employed the reanalysis data from “Japanese 55‐year Reanalysis” (JRA‐55). The data showed good reliability for the surface dew point and PW. To quantify the deviation, we estimated the errors between the actual and estimated PW values for the moisture‐maximization method at 30 points across Japan. Here, the actual PW was extracted directly from JRA‐55, and the estimated PW was obtained using the surface dew point extracted from JRA‐55. We confirmed that the event PW was the largest source of error in the PMP estimation and that the magnitude of the errors was highly correlated with the surface dew point. We analyzed the vertical dew point profile for events with large estimation errors and confirmed that a low surface dew point showed a high deviation in the air column. Therefore, the use of PMP estimations with the moisture‐maximization method should be carefully considered in rainfall events with low surface dew points (e.g., lower than 18°C).

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.

CORRELATION ANALYSIS BETWEEN STORM EVENTS AND METEOROLOGICAL CONDITIONS

This study aims to determine the most dominant meteorological factors for extreme precipitation, such as probable maximum precipitation (PMP); this is important in determining the conditions that generate extreme events to understand their magnitude. This study analyzed historical heavy rainfall events and their corresponding meteorological factors. The factors considered in this study are precipitable water (PW), surface dew point (SDT), temperature, relative humidity (RH), convective available potential energy (CAPE), and vertical wind velocity (VVEL) in eight different regions in Japan. To collect sufficient data, we utilized reanalysis data from “Japanese 55-year Reanalysis” (JRA-55), and the relation between historical rainfall events and the selected factors was analyzed via the cumulative density function (CDF) exceeding 0.95. In southern Japan, the VVEL and PW were highly correlated factors for historical events. In northern Japan, PW was the highest correlated factor for the events. Conversely, temperature had the lowest extreme ratio in all areas. Based on this analysis, we can conclude that PMP estimation via PW is reasonable for these areas.

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.