While modern GPS receiver differential code bias estimation techniques have become highly refined, they still demonstrate unphysical behavior, namely, notable solar cycle variability. This study investigates the nature of these seasonal and solar cycle bias variabilities in the polar cap region using singleâstation bias estimation methods. It is shown that the minimization of standard deviation bias estimation technique is linearly dependent on the user's choice of shell height, where the sensitivity of this dependence varies significantly from 1 total electron content unit (1âTECUâ=â1016âelâmâ2) per 4000âkm in solar minimum winter to in excess of 1 TECU per 90âkm during solar maximum summer. Using an ionosonde, we find appreciable shell height variability resulting in bias variabilities of up to 2âTECU. Comparing northward face Resolute Incoherent Scatter Radar (RISRâN) measurements to a collocated GPS station, we find that RISRâderived GPS receiver biases vary seasonally but not with solar cycle. RMS differences between bias estimation methods and observation between 2009 and 2013 were found to range from 2.7âTECU to 3.4âTECU, depending on method. To account for the erroneous solar cycle variability of standard bias estimation approaches, we linearly fit these biases to sunspot number, removing the trend. RMS errors after sunspot detrending these biases are reduced to 1.91âTECU. Also, these ISRâderived and sunspotâdetrended biases are fit to ambient temperature, where a significant correlation is found. By using these temperatureâfitted biases we further reduce RMS errors to 1.66âTECU. These results can be taken as further evidence of temperatureâdependent dispersion in the GPS cabling and antenna hardware.