An operational fog prediction system for Delhi using the 330 m Unified Model

Jayakumar, A.; Rajagopal, E. N.; Boutle, Ian; George, John P.; Mohandas, Saji; Webster, Stuart; Aditi, S.

doi:10.1002/asl.796

Cited by 30 publications

(37 citation statements)

References 26 publications

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“…Thus we do not employ any traditional parameterisation of activation commonly used in other models but instead simulate the actual supersaturation and growth of aerosol particles into droplets. Comparisons with a more detailed parcel model (Kokkola et al, 2008) demonstrate that this growth is solved with good accuracy for a range of air parcels and updraught velocities.…”

Section: Introductionmentioning

confidence: 88%

Aerosol–fog interaction and the transition to well-mixed radiation fog

et al. 2018

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Abstract. We analyse the development of a radiation fog event and its gradual transition from optically thin fog in a stable boundary layer to well-mixed optically thick fog. A comparison of observations and a detailed large-eddy simulation demonstrate that aerosol growth and activation is the key process in determining the onset of adiabatic fog. Weak turbulence and low supersaturations lead to the growth of aerosol particles which can significantly affect the visibility but do not significantly interact with the long-wave radiation, allowing the atmosphere to remain stable. Only when a substantial fraction of the aerosol activates into cloud droplets can the fog interact with the radiation, becoming optically thick and well mixed. Modifications to the parameterisation of cloud droplet numbers in fog, resulting in lower and more realistic concentrations, are shown to give significant improvements to an NWP model, which initially struggled to accurately simulate the transition. Finally, the consequences of this work for common aerosol activation parameterisations used in climate models are discussed, demonstrating that many schemes are reliant on an artificial minimum value when activating aerosol in fog, and adjustment of this minimum can significantly affect the sensitivity of the climate system to aerosol radiative forcing.

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Section: Introductionmentioning

confidence: 88%

Aerosol–fog interaction and the transition to well-mixed radiation fog

et al. 2018

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“…Orography is derived from the NASA Shuttle Radar Topographic Mission 90 m digital elevation map. Further details of the 1.5 km NCUM model are given in Jayakumar et al (2017). For comparison with the high-resolution simulation, temperature and wind data from the European Centre for Medium-range Weather Forecasts (ECMWF) reanalyses ERA-Interim (Dee et al, 2011) and new product ERA5 (Hersbach and Dee, 2016) at 925 hPa and 0600 UTC are employed.…”

Section: Model Datamentioning

confidence: 99%

A case‐study of land–atmosphere coupling during monsoon onset in northern India

Barton

Taylor

Parker

et al. 2019

Quart J Royal Meteoro Soc

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This article presents a land–atmosphere case‐study for a single day during monsoon onset, incorporating data from a research aircraft, satellite products and model outputs. The unique aircraft observations reveal temperature and humidity contrasts of up to 5 K and 4 g/kg in the planetary boundary layer induced by spatial variations in soil moisture. Both antecedent rain and irrigation were found to be drivers of this atmospheric variability. There is also evidence of soil moisture‐induced mesoscale circulations above some surfaces. This is the first time such responses have been observed in situ over India. Soil moisture‐driven temperature anomalies are larger than those found in previous observational studies in the African Sahel. Moreover, irrigation in the region is extensive, unlike in the Sahel, and has a similar atmospheric effect to antecedent rainfall. This implies that historical changes in irrigation practices are likely to have had an important influence on mesoscale processes within the Indian monsoon. We also examine evidence linking soil moisture and cloud formation. Above wetter soils we observed a suppression of shallow cloud, whilst the initiation of deep convection occurred mostly in areas affected by wet–dry soil moisture boundaries. To investigate the impact of soil moisture heterogeneity on large‐scale wind flow, three model depictions of the day are assessed: the European Centre for Medium‐Range Weather Forecasts ERA‐Interim and ERA5 reanalyses, and a high‐resolution (1.5 km) simulation generated using the Indian National Centre for Medium Range Weather Forecasting regional convection‐permitting Unified Model. We find evidence indicating surface flux uncertainties in the models lead to ∼3.5 hPa anomalies in the monsoon trough. This does affect the simulation of monsoon circulation and rainfall. Better representation of mesoscale land–atmosphere coupling is likely to improve the depiction of convection within weather and climate models over India.

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“…Clearly this choice is likely to be location and case specific, and require some adjustments for more polluted locations as discussed in Jayakumar et al (2017). A universal parametrization would require some link to aerosol.…”

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confidence: 99%

Aerosol-fog interaction and the transition to well-mixed radiation fog

Boutle¹,

Price²,

Kudzotsa³

et al. 2017

Preprint

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Abstract. We analyse the development of a radiation fog event and its gradual transition from optically thin fog in a stable boundary layer to well-mixed optically-thick fog. Comparison of observations and a detailed large-eddy simulation demonstrate that aerosol growth and activation is the key process in determining the onset of adiabatic fog. Weak turbulence and low supersaturations lead to the growth of aerosol particles which can significantly affect the visibility, but do not significantly interact with the long-wave radiation, allowing the atmosphere to remain stable. Only when a substantial fraction of the aerosol 5 become activated into cloud droplets can the fog interact with the radiation, becoming optically thick and well-mixed. Modifications to the parametrization of cloud droplet numbers in fog, resulting in lower and more realistic concentrations, are shown to give significant improvements to an NWP model, which initially struggled to accurately simulate the transition. Finally, consequences of this work for common aerosol activation parametrizations used in climate models are discussed, demonstrating that many schemes are reliant on an artificial minimum value when activating aerosol in fog, and adjustment of this minimum 10 can significantly affect the sensitivity of the climate system to aerosol radiative forcing.

show abstract

An operational fog prediction system for Delhi using the 330 m Unified Model

Cited by 30 publications

References 26 publications

Aerosol–fog interaction and the transition to well-mixed radiation fog

Aerosol–fog interaction and the transition to well-mixed radiation fog

A case‐study of land–atmosphere coupling during monsoon onset in northern India

Aerosol-fog interaction and the transition to well-mixed radiation fog

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