We investigate the generation of THz pulses when arrays of silver nanoparticles are irradiated by femtosecond laser pulses, providing the first reproducible experimental evidence in support of recent theoretical predictions of such an effect. We assess our results in the context of a model where photoelectrons are produced by plasmon-mediated multiphoton excitation, and THz radiation is generated via the acceleration of the ejected electrons by ponderomotive forces arising from the inhomogeneous plasmon field. By exploring the dependence of the THz emission on the femtosecond pulse intensity and as a function of metal nanoparticle morphology, and by comparing measurements to numerical modeling, we are able to verify the role of the particle plasmon mode in this process.

Mode Selective Enhanced Surveillance (Mode‐S EHS) reports are aircraft‐based observations that have value in numerical weather prediction (NWP). These reports contain the aircraft's state vector in terms of its speed, direction, altitude and Mach number. Using the state vector, meteorological observations of temperature and horizontal wind can be derived. However, Mode‐S EHS processing reduces the precision of the state vector from 16‐bit to 10‐bit binary representation. We use full precision data from research‐grade instruments, on board the UK's Facility for Atmospheric Airborne Measurements, to emulate Mode‐S EHS reports and to compare with derived observations. We aim to understand the observation errors due to the reduced precision of Mode‐S EHS reports. We derive error models to estimate these observation errors. The temperature error increases from 1.25 to 2.5 K between an altitude of 10 km and the surface due to its dependency on Mach number and also Mode‐S EHS precision. For the cases studied, the zonal wind error is around 0.50 m s−1 and the meridional wind error is 0.25 m s−1. The wind is also subject to systematic errors that are directionally dependent. We conclude that Mode‐S EHS‐derived horizontal winds are suitable for data assimilation in high‐resolution NWP. Temperature reports may be usable when aggregated from multiple aircraft. While these reduced precision, high‐frequency data provide useful, albeit noisy, observations, direct reports of the higher‐precision data would be preferable.

Aircraft are an important source of meteorological observations for both numerical weather models and aviation weather forecasting. There has been increasing interest in novel methods for gathering aircraft-based observations, especially mode-selective (Mode-S) enhanced surveillance (EHS)-derived data. This paper reports on the progress made in the United Kingdom at the Met Office on receiving and processing these data. Five receivers have been deployed, providing up to 5.7 million observations of horizontal wind and temperatures per day over the United Kingdom. The receivers are relatively low cost and deploying them at existing operational weather radar sites has been shown to be an ideal choice. Heading corrections are required to improve the quality of the wind observations. When corrected the Mode-S EHS wind data have similar observations-minus-background (o−b) statistics as Aircraft Meteorological Data Relay [AMDAR; using a Met Office version of the Unified Model over the United Kingdom (UKV)]. For the u wind component, the average per model run o−b root-mean-square value for the Mode-S EHS–derived data was 2.45 and 2.12 m s−1 for AMDAR. The AMDAR data are assimilated into the model.

We have become aware of several transcription errors in our equations. We would like to apologize for these and have described the corrections below. These were not represented in the modeling codes used, nor used for any conclusions drawn. There are six sign errors across three equations [(2a), (2b), and (5)]. Also, we have found four cases where the letter d has been replaced by the letter a across two equations [(4c) and (4d)]. These are reproduced below in both their erroneous and corrected forms:

Observations from aircraft are an important element of the global observing network. A promising new observation source, deriving wind and temperature measurements from air traffic management data, has previously been reported on by a small number of groups. This article further investigates the error characteristics by comparing a year's worth of in situ observed winds and temperatures from a commercial British Airways Boeing 747 (B747) with the derived Mode‐Selective (Mode‐S) Enhanced Surveillance (EHS) observations from the Met Office network of Mode‐S receivers. It is shown that, whilst the winds and high‐altitude temperatures are of good quality, they show error profiles with altitude that are different for ascent and descent. The data show that the situation of the aircraft is critical to understand the biases; this is dependent on the aircraft, operator and airport, making corrections infeasible. Further understanding is gained by an intercomparison flight with the UK Facility for Airborne Atmospheric Measurement (FAAM) BAe 146 aircraft. This showed a good comparison with Mode‐S EHS winds, with a RMS difference between the FAAM data and B747 Mode‐S EHS data of 1.5 and 0.9 m/s for the u and v components respectively. Comparing the FAAM data and B747 flight data recorder (FDR) provided RMS differences of 0.6 and 1.4 m/s respectively. This suggests that the data quality from Mode‐S EHS is similar to that which can be achieved from a commercial aircraft. The temperature RMS differences were found to be 1.6 and 0.5 K when the FAAM data were compared to the Mode‐S EHS data and FDR data from the B747 respectively, suggesting that the temperature Mode‐S EHS data are of an inferior quality.