Physical controls on frost events in the central Andes of Peru using in situ observations and energy flux models

Saavedra, Miguel; Takahashi, K.

doi:10.1016/j.agrformet.2017.02.019

Cited by 17 publications

(20 citation statements)

References 33 publications

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“…It is clearly observed that the RSD spectrum is different for the three types of rainfall events. The general dependence of the form of the spectra and the spectral values with rainfall rate class is independent of time of day, as the for all the intervals the slope of the spectrum decreases with rainfall rate, but it can be noticed that the largest diameters are reached in the time interval (15)(16)(17)(18)(19)(20), corresponding to the time of maximum development of convection, where hailstorms occur in the valley [22,23,40]. In the morning and early afternoon (09-14 LST) also occur spectra with large raindrops in the high rainfall rate class, corresponding to early developing storms that can also produce hail in some cases.…”

Section: Raindrop Size Distributionmentioning

confidence: 99%

Diurnal Cycle of Raindrops Size Distribution in a Valley of the Peruvian Central Andes

et al. 2019

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In the Central Andes of Peru, convective and stratiform rainfall occurs, frequently associated with convective storms. The raindrop size distributions (RSD), measured by a Parsivel-2 optical disdrometer, were characterized by the variation of their normalized parameters. The RSD dataset includes measurements corresponding to 18 months between 2017 and 2019. As a result, it was found that the mass-weighted mean diameter Dm and the Nw parameter present respectively high and low values, in the interval of 15-20 LST (local standard time), wherein deeper and more active clouds appear. The events including convective rainfall contribute 67.5% of the accumulated total, wherein 92% corresponds to the 15-20 LST interval. It is concluded that the spectral variability of the RSD is strongly controlled by the cloudiness configuration field developing over the west (convection over highlands) and east (convection over Amazon) sides of the valley. In the afternoon, clouds develop and drift to the east, over the Andean valleys and towards the Amazon, intensified by local orographic circulation. The opposite happens at night, when the stratiform rainfall is dominant and it is controlled by clouds, located in the Inter-Andean valley, generated by the convection fields formed over the Amazon forest.Atmosphere 2020, 11, 38 2 of 21 (ZDR), differential phase shift (Φ DP ), cross-correlation coefficient (ρ hv ) and the specific differential phase (K DP ) [6].RSD variation in a specific case depends on the precipitation regime, climatological conditions, and geographical location [7,8]. Two main rain types can be defined as convective and stratiform, depending on the rain's spatial and temporal distribution and related to the cloud systems originating them, even if frequently the same cloud system produces both types of rain in different stages of its development and in different areas, in the case of complex and long living systems [9]. The relative weight of the different microphysical processes forming raindrops depends on the type of rainfall event. As convective rain originates in the updraft-downdraft circulation of convective clouds, a vigorous condensation-collision-coalescence process prevails in raindrop growth, producing high liquid water contents and relatively large drops, complemented with graupel and hail development by riming, which recycles in the vertical circulation, sometimes resulting in large raindrops in the rain shaft or hail on the ground [9,10]. In stratiform clouds, the vertical circulation is weaker, with slow and extended vertical ascent, favoring predominant steady drop growth by diffusion of water vapor into ice particles by the Bergeron-Findeisen process at temperatures below the melting point or vapor diffusion into droplets complemented by slow coalescence [9]. Meanwhile, the orographic component in the Andes is imposed as a forcing mechanism and the Andean clouds are deeper and more active than in neighboring areas as is the case for the transitional region between the Andes and the Amazon [11].Previo...

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Section: Raindrop Size Distributionmentioning

confidence: 99%

Diurnal Cycle of Raindrops Size Distribution in a Valley of the Peruvian Central Andes

et al. 2019

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“…The minimum mean temperatures have a strong seasonality, ranging from its lowest values in the dry season (June to August), with its lowest in July (0.5 • C), to its maximum values in the wet season (January to March) with an average value of 7 • C [31]. The lowest values of the minimum mean temperature are associated with cloudless conditions with large outgoing long-wave radiation, mainly during the dry season [19]. The seasonal pattern of the rainfall is due to low cloud cover and specific humidity, with minimum values in June and July at 07 LT, which also coincides with the time of the minimum temperatures (between 06 and 07 LT) in the same months.…”

Section: Site and Instrumentationmentioning

confidence: 99%

“…In the central Andes of Perú, on the Huancayo observatory, the thirty-three year-old climatology [19], shows a well-defined seasonal cycle of precipitation with a wet season from September to April (80% from December to March) and a dry season between May and August [20][21][22][23][24]. Further, the minimum temperature (T min ) was found to follow a seasonal pattern ranging from 7 • C in December-February to 0 • C in June-July.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, the maximum temperature (T max ) presents a low seasonal variability with maximum in February (18.5 • C) and October-November (21.0 • C). Also the physical controls on frost events in the Huancayo observatory was analyzed using in situ observations and energy flux models [19]. The results show low cloud cover, surface-specific humidity, and soil moisture are key factors that control the day-to-day variability of minimum temperature, which is more pronounced in the dry/cool season.…”

Section: Introductionmentioning

confidence: 99%

“…Some important applications of these results lie in the local function that land-atmosphere interactions play in the rainfall process [26] and in the development of frost events [19] because the magnitude of the surface energy fluxes, the soil water content, and the effect of surface albedo on the dynamics of the PBL. Moreover, the seasonal and diurnal cycles of the boundary layer and of the energy budget components have been observed to have a critical influence on the climate system; however, these are not conveniently simulated by numerical regional or climate models [27,28].…”

Section: Introductionmentioning

confidence: 99%

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Seasonal and Diurnal Cycles of Surface Boundary Layer and Energy Balance in the Central Andes of Perú, Mantaro Valley

et al. 2019

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The present study presents a detailed analysis of the diurnal and monthly cycles the surface boundary layer and of surface energy balance in a sparse natural vegetation canopy on Huancayo observatory (12.04 ∘ S, 75.32 ∘ W, 3313 m ASL), which is located in the central Andes of Perú (Mantaro Valley) during an entire year (May 2018–April 2019). We used a set of meteorological sensors (temperature, relative humidity, wind) installed in a gradient tower 30 m high, a set of radiative sensors to measure all irradiance components, and a set of tensiometers and heat flux plate to measure soil moisture, soil temperatures and soil heat flux. To estimate turbulent energy fluxes (sensible and latent), two flux–gradient methods: the aerodynamic method and the Bowen-ratio energy-balance method were used. The ground heat flux at surface was estimated using a molecular heat transfer equation. The results show minimum mean monthly temperatures and more stable conditions were observed in June and July before sunrise, while maximum mean monthly temperatures in October and November and more unstable conditions in February and March. From May to August inverted water vapor profiles near the surface were observed (more intense in July) at night hours, which indicate a transfer of water vapor as dewfall on the surface. The patterns of wind direction indicate well-defined mountain–valley circulation from south-east to south-west especially in fall–winter months (April–August). The maximum mean monthly sensible heat fluxes were found in June and September while minimum in February and March. Maximum mean monthly latent heat fluxes were found in February and March while minimum in June and July. The surface albedo and the Bowen ratio indicate semi-arid conditions in wet summer months and extreme arid conditions in dry winter months. The comparisons between sensible heat flux ( Q H ) and latent heat flux ( Q E ), estimated by the two methods show a good agreement (R 2 above 0.8). The comparison between available energy and the sum of Q E and Q H fluxes shows a good level of agreement (R 2 = 0.86) with important imbalance contributions after sunrise and around noon, probably by advection processes generated by heterogeneities on the surface around the Huancayo observatory and intensified by the mountain–valley circulation.

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A combined view on precipitation and temperature climatology and trends in the southern Andes of Peru

Imfeld

Sedlmeier

Gubler

et al. 2020

Intl Journal of Climatology

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In the southern Peruvian Andes, communities are highly dependent on climatic conditions due to the mainly rain-fed agriculture and the importance of glaciers and snow melt as a freshwater resource. Longer-term trends and yearto-year variability of precipitation or temperature severely affect living conditions. This study evaluates seasonal precipitation and temperature climatologies and trends in the period 1965/66-2017/18 for the southern Peruvian Andes using quality-controlled and homogenized station data and new observational gridded data. In this region, precipitation exhibits a strong annual cycle with very dry winter months and most of the precipitation falling from spring to autumn. Spatially, a northeast-southwest gradient in austral spring is observed, related to an earlier start of the rainy season in the northeastern part of the study area. Seasonal variations of maximum temperature are weak with an annual maximum in austral spring, which is related to reduced cloud cover in austral spring compared to summer. On the contrary, minimum temperatures show larger seasonal variations, possibly enhanced through changes in longwave incoming radiation following the precipitation cycle. Precipitation trends since 1965 exhibit low spatial consistency except for austral summer, when in most of the study area increasing precipitation is observed, and in austral spring, when stations in the central-western region of the study area register decreasing precipitation. All seasonal and annual trends in maximum

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Physical controls on frost events in the central Andes of Peru using in situ observations and energy flux models

Cited by 17 publications

References 33 publications

Diurnal Cycle of Raindrops Size Distribution in a Valley of the Peruvian Central Andes

Diurnal Cycle of Raindrops Size Distribution in a Valley of the Peruvian Central Andes

Seasonal and Diurnal Cycles of Surface Boundary Layer and Energy Balance in the Central Andes of Perú, Mantaro Valley

A combined view on precipitation and temperature climatology and trends in the southern Andes of Peru

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