Changing structures of summertime heatwaves over China during 1961–2017
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Abstract Despite the prevalence of artificial separation of daytime and nighttime hot extremes, they may actually co-occur or occur sequentially. Considering their potential lead-lag configuration, this study identified an entire heatwave period as consecutive days with either daytime or nighttime hot extremes and investigated the changes of the prevalence and sequence of daytime and nighttime hot extremes during heatwaves over China from 1961 to 2017. It was found that the majority (82%) of heatwaves were compound heatwaves that had both daytime and nighttime hot extremes exceeding the 90th percentile-based thresholds, while only 7% (11%) were purely daytime (nighttime) heatwaves that contained only daytime (nighttime) hot extremes. During the entire periods of compound heatwaves, daytime hot extremes usually occurred one day or a few days before nighttime hot extremes, which was in accordance with the daily variations in radiation and meteorological conditions, such as the increasing surface humidity and cloud cover, and decreasing solar radiation during the entire heatwave periods. From 1961 to 2017, compound heatwave numbers exhibited the sharpest increase with a statistically significant trend of 0.44 times decade −1 , in contrast to an insignificant trend of 0.00 times decade −1 for purely daytime heatwaves and a significant trend of 0.09 times decade −1 for purely nighttime heatwaves. Within the compound heatwave periods, hot nights were starting earlier and ending later, and numbers of concurrent daytime-nighttime hot extremes increased significantly at 0.20 days decade −1 . In particular, urban area were not only subject to increasingly more frequent and longer compound heatwaves, but also to more occurrences of concurrent daytime-nighttime hot extremes with more serious impact. This study provides instructions for researchers to customize and select appropriate heatwave indices.Abstract. This paper investigates the latest version 1.07 SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) tropical ozone from the 1.27 μm as well as from the 9.6 μm retrieval and temperature data with respect to day time variations in the upper mesosphere. The processes involved are compared to day time variations of the three-dimensional general circulation and chemistry model HAMMONIA (Hamburg Model of the Neutral and Ionized Atmosphere). The results show a good qualitative agreement for ozone. The amplitude of daytime variations is in both cases approximately 60% of the daytime mean. During equinox the daytime maximum ozone abundance is for both, the observations and the model, higher than during solstice, especially above 0.01 hPa (approx. 80 km). The influence of tidal signatures either directly in ozone or indirectly via a temperature response above 0.01 hPa can not be fully eliminated. Below 0.01 hPa (photo-)chemistry is the main driver for variations. We also use the HAMMONIA output of daytime variation patterns of several other different trace gas species, e.g., water vapor and atomic oxygen, to discuss the daytime pattern in ozone. In contrast to ozone, temperature data show little daytime variations between 65 and 90 km and their amplitudes are on the order of less than 1.5%. In addition, SABER and HAMMONIA temperatures show significant differences above 80 km.
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Trace gas
Microwave Limb Sounder
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Electron density irregularities on the dayside in the low-latitude
Low latitude
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Abstract. The diurnal variations in daytime airglow emission intensity measurements at three wavelengths OI 777.4 nm, OI 630.0 nm, and OI 557.7 nm made from a low-latitude location, Hyderabad (17.5° N, 78.4° E; 8.9° N MLAT) in India have been investigated. The intensity patterns showed both symmetric and asymmetric behaviour in their respective diurnal emission variability with respect to local noon. The asymmetric diurnal behaviour is not expected considering the photochemical nature of the production mechanisms. The reason for this observed asymmetric diurnal behaviour has been found to be predominantly the temporal variation in the equatorial electrodynamics. The plasma that is transported across latitudes due to the action of varying electric field strengths over the magnetic equator in the daytime contributes to the asymmetric diurnal behaviour in the neutral daytime airglow emissions. Independent magnetic and radio measurements support this finding. It is also noted that this asymmetric diurnal behaviour in the neutral emission intensities has a solar cycle dependence with a greater number of days during high solar activity period showing asymmetric diurnal behaviour compared to those during a low solar activity epoch. These intensity variations over a long timescale demonstrate that the daytime neutral optical emissions are extremely sensitive to the changes in the eastward electric field over low and equatorial latitudes.
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Anomaly (physics)
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Diurnal temperature variation
Low latitude
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Abstract. The scope of this paper is to investigate the latest version 1.07 SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) tropical ozone from the 1.27 μm as well as from the 9.6 μm retrieval and temperature data with respect to daytime variations in the upper mesosphere. For a better understanding of the processes involved we compare these daytime variations to the output of the three-dimensional general circulation and chemistry model HAMMONIA (Hamburg Model of the Neutral and Ionized Atmosphere). The results show good agreement for ozone. The amplitude of daytime variations is in both cases approximately 60% of the daytime mean. During equinox the daytime maximum ozone abundance is for both, the observations and the model, higher than during solstice, especially above 80 km. We also use the HAMMONIA output of daytime variation patterns of several other different trace gas species, e.g., water vapor and atomic oxygen, to discuss the daytime pattern in ozone. In contrast to ozone, temperature data show little daytime variations between 65 and 90 km and their amplitudes are on the order of less than 1.5%. In addition, SABER and HAMMONIA temperatures show significant differences above 80 km.
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For midlatitude regions, routinely recorded ionograms have been used to investigate whether or not the occurrence levels of (1) daytime first‐hop distortions, (2) daytime second‐hop spread, and (3) nighttime spread F are influenced by 10.7‐cm solar‐flux changes, because of associated upper atmosphere neutral‐particle density (UA‐NPD) changes. Recordings for a 5‐year period (1979–1983) were used. It was found that generally speaking, occurrence levels of these parameters were lower for high solar‐flux values and higher for low solar‐flux values as variations occurred from day to day. These are the results expected if the UA‐NPD changes have an influence on the wave amplitudes of the medium‐scale traveling ionospheric disturbances (MS‐TIDs) thought to be responsible for the recording of these parameters. This association was particularly well defined for the occurrence of the daytime second‐hop spread. It is suggested that non linear effects of the atmospheric gravity waves (AGWs) responsible for the MS‐TIDs may be responsible for generating the daytime small‐scale structures, which experimental results indicate are the ionospheric structures responsible for the second‐hop spread. These structures may possibly be field aligned.
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Abstract We report the first observation of daytime tweek atmospherics based on measurements at Moshiri (44.37°N, 142.27°E) and Kagoshima (31.48°N, 130.72°E), Japan, during nonsolar eclipse days for 5 months in 1980–1994. The daytime tweeks were observed on geomagnetically quiet and stormy days. The daytime tweeks had clear frequency dispersion with an average duration of 12 ms, which was shorter than that in the nighttime (~50 ms). The average occurrences of the daytime tweeks at Moshiri and Kagoshima were 0.6 and 0.1 tweeks per minute during 10:00–15:00 LT, respectively. Daytime tweeks up to the second‐order mode were visible. There was no difference in the occurrence of each visible mode between storm time and magnetically quiet time. The daytime reflection heights were similar to those at night (85–100 km) but with greater variation. We evaluated the attenuation rate ( α n ) of tweeks by strictly taking the ionospheric reflection coefficient into account. For each frequency, α n was evaluated as a function of the electron density, electron density gradient, and ionospheric height. We found that α n had an inverse relationship with the electron density (or conductivity), electron density gradient, and ionospheric height. We suggest that the best conditions for daytime tweek observations are when the bottomside of the ionosphere is sharply defined and the ionospheric height is high.
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This study investigated the seasonal variations of daytime urban thermal environment (UTE) based on land surface temperature (LST) in Shenzhen of 2015. The spatial and temporal adaptive reflectance fusion model (STARFM) was used for retrieving seasonal daytime LST at high spatiotemporal resolution by combining MODIS and HJ-1B LST data. Next, the relationship between the land cover and daytime in each season was examined. Finally, daytime LST patterns were classified, and the effects of seasonal variations of high-grade daytime LSTs were analyzed with landscape metrics. The results showed that (1) the STARFM is capable of generating seasonal daytime LST data at high spatiotemporal resolution. (2) Daytime LSTs were generally higher in the western parts of Shenzhen in spring and summer. (3) Daytime LST in each land cover type showed an increasing trend form winter to summer and decreased from summer to autumn. The highest and lowest daytime LSTs in each season were observed in ISAs and water bodies. (4) Landscape metrics provided a quantitative method for describing seasonal variations in daytime LSTs, and it was found that seasons influenced the intensity and extent of daytime LSTs in Shenzhen. These findings may be helpful for urban planners developing regional urban strategies to improve daytime urban thermal comfort conditions.
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